Measuring Techniques and Surface Properties Changed Adsorption

Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology New Series / Editor in Chief: W...

Author: K. Hermann | H. Ibach | K. Jacobi | M.A. Rocca | D. Sander | M.A. Van Hove | P.R. Watson | C. Wöll

65 downloads 905 Views 6MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form

DOWNLOAD PDF

Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology New Series / Editor in Chief: W. Martienssen

Group III: Condensed Matter Volume 42

Physics of Covered Solid Surfaces Subvolume A Adsorbed Layers on Surfaces Part 2 Measuring Techniques and Surface Properties Changed by Adsorption

Editor H.P. Bonzel Authors K. Hermann, H. Ibach, K. Jacobi, M.A. Rocca, D. Sander, M.A. Van Hove, P.R. Watson, Ch. Wöll

13

ISSN 1615-1925 (Condensed Matter) ISBN 3-540-41224-7 Springer-Verlag Berlin Heidelberg New York Library of Congress Cataloging in Publication Data Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, Neue Serie Editor in Chief: W. Martienssen Vol. III/42A2: Editor: H.P. Bonzel At head of title: Landolt-Börnstein. Added t.p.: Numerical data and functional relationships in science and technology. Tables chiefly in English. Intended to supersede the Physikalisch-chemische Tabellen by H. Landolt and R. Börnstein of which the 6th ed. began publication in 1950 under title: Zahlenwerte und Funktionen aus Physik, Chemie, Astronomie, Geophysik und Technik. Vols. published after v. 1 of group I have imprint: Berlin, New York, Springer-Verlag Includes bibliographies. 1. Physics--Tables. 2. Chemistry--Tables. 3. Engineering--Tables. I. Börnstein, R. (Richard), 1852-1913. II. Landolt, H. (Hans), 1831-1910. III. Physikalisch-chemische Tabellen. IV. Title: Numerical data and functional relationships in science and technology. QC61.23 502'.12 62-53136 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in other ways, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution act under German Copyright Law. Springer-Verlag Berlin Heidelberg New York a member of BertelsmannSpringer Science+Business Media GmbH © Springer-Verlag Berlin Heidelberg 2002 Printed in Germany The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product Liability: The data and other information in this handbook have been carefully extracted and evaluated by experts from the original literature. Furthermore, they have been checked for correctness by authors and the editorial staff before printing. Nevertheless, the publisher can give no guarantee for the correctness of the data and information provided. In any individual case of application, the respective user must check the correctness by consulting other relevant sources of information. Cover layout: Erich Kirchner, Heidelberg Typesetting: Authors and Redaktion Landolt-Börnstein, Darmstadt Printing: Computer to plate, Mercedes-Druck, Berlin Binding: Lüderitz & Bauer, Berlin SPIN: 10783464

63/3020 - 5 4 3 2 1 0 – Printed on acid-free paper

Preface Surface Science is understood as a relatively young scientific discipline, concerned with the physical and chemical properties of and phenomena on clean and covered solid surfaces, studied under a variety of conditions. The adsorption of atoms and molecules on solid surfaces is, for example, such a condition, connected with more or less drastic changes of all surface properties. An adsorption event is frequently observed in nature and found to be of technical importance in many industrial processes. For this reason, Surface Science is interdisciplinary by its very nature, and as such an important intermediary between fundamental and applied research. The beginning of Surface Science may be placed around the years 1900-1928, connected with seminal works by J.W. Gibbs, I. Langmuir, M. Knudsen, O. Stern, M. Volmer, C. Davisson and L. Germer, H.S. Taylor, J.E. Lennard-Jones, I.N. Stranski and others. In modern times, research activities in this field have literally exploded worldwide. Consequently, enormous progress can be recognized and it is no exaggeration, to note a high degree of maturity in this well-established scientific discipline. Tribute is being paid to this effect by the renowned Series of Landolt-Börnstein whose editor-in-chief Werner Martienssen, Frankfurt am Main, has initiated several volumes of collected scientific data in the field of Surface Science. Indeed, the point in time has arrived where all quantitative data, that have been generated over so many years, are worth being collected in tables and figures for critical review and reference purposes as well. The beginning has been made with Landolt-Börnstein volume 24, entitled Physics of Solid Surfaces. This volume, consisting of four subvolumes, appeared in 1993-96 and covers the properties of clean solid surfaces. The present volume 42 is devoted to Covered Solid Surfaces and, in particular, to Adsorbed Layers on Surfaces. It is as such a collection of data obtained for adsorbates on well-defined crystalline surfaces. "Well-defined" means surfaces of known crystallographic structure and chemical composition. These conditions can in most cases be realized by careful sample preparation in ultra-high vacuum. Work on the present volume started in late 1997 when I was first contacted by W. Martienssen. An initial outline of the volume was written in January of 1998. At this point I want to express my sincere gratitude to George Comsa, Bonn, and Gerhard Ertl, Berlin, for their support by making valuable suggestions, concerning both the outline and the choice of possible authors. In fact, the choices made at the time proved to be excellent ones, and the consulting of G. Comsa and G. Ertl turned out to be extremely helpful for the evolution of the present volume. It was almost clear at the beginning, that the amount of general information and quantitative data on Adsorbed Layers on Surfaces is enormous, too large to fit into a single volume. Hence, again several subvolumes had to be planned. Unfortunately, the chapters anticipated for each of the subvolumes did not arrive synchronously with the production schedule, such that the sequence of chapters actually printed in the subvolumes deviates from that in the general outline of the whole volume. We apologize for this inconvenience, but in the age of electronic information distribution this problem will be solved, once all volumes are available electronically. Search routines will guide the reader to the data of his desire. Until that time, the index of each subvolume will have to do. The present subvolume III/42A2 deals with Measuring Techniques and Surface Properties Changed by Adsorption. Finally and most importantly, I would like to extend my deep appreciation to all authors of this volume for their excellent contributions, and to the editing and production offices of Springer-Verlag for efficient cooperation and general support. Jülich, January 2002

The Editor

Editor H.P. Bonzel Forschungszentrum Jülich Institut für Grenzflächenforschung und Vakuumphysik (IGV) 52425 Jülich Germany

Authors K. Hermann Fritz-Haber-Institut der Max-Planck Gesellschaft (MPG) Abteilung Theorie D-14195 Berlin Germany 4.1 Surface structure on metals and semiconductors H. Ibach Institut für Grenzfläch enforschung und Vakuumphysik (IGV) Forschungszentrum Jülich D-52425 Jülich Germany 4.4 Surface free energy and surface stress K. Jacobi Fritz-Haber-Institut der Max-Planck Gesellschaft (MPG) D-14195 Berlin Germany 4.2 Electron work function of metals and semiconductors M.A. Rocca Centro di Fisica delle Superfici e Basse Temperature del CNR Istituto Nazionale di Fisica della Materia I-16146 Genova Italy 4.5 Surface phonon dispersion D. Sander Max-Planck Institut (MPI) für Strukturphysik D-06120 Halle Germany 4.4 Surface free energy and surface stress

M.A. Van Hove Lawrence Berkeley National Laboratory Materials Science 66 Berkeley, CA 94720 and Department of Physics University of California-Davis Davis, CA 95616 USA 4.1 Surface structure on metals and semiconductors P.R. Watson Department of Chemistry Oregon State University Corvallis, OR 97331 USA 4.1 Surface structure on metals and semiconductors Ch. Wö ll Lehrstuhl für Physikalische Chemie I Ruhr-Universität Bochum D-44801 Bochum Germany 2 Characterization of adsorbate overlayers: Measuring techniques

Landolt-Börnstein Editorial Office Gagernstr. 8, D-64283 Darmstadt, Germany fax: +49 (6151) 171760 e-mail: [email protected] Internet http://www.landolt-boernstein.com Helpdesk e-mail: [email protected]

Contents III/42 Physics of Covered Solid Surfaces A: Adsorbed Layers on Surfaces Part 2: Measuring Techniques and Surface Properties Changed by Adsorption 1

Introduction to physical and chemical properties of adlayer/substrate systems (H.P. BONZEL) ................................................... see subvolume III/42A1

2 2.1 2.1.1 2.1.2 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8 2.3 2.3.1 2.3.2 2.3.3 2.4 2.4.1 2.4.2 2.4.3 2.4.4 2.5 2.5.1 2.5.2 2.5.3 2.5.4 2.5.5 2.5.6 2.5.7 2.5.8 2.5.9 2.5.10 2.6 2.6.1 2.6.2 2.6.3 2.6.4 2.6.5 2.6.6 2.6.7

Characterization of adsorbate overlayers: measuring techniques (CH. WÖLL) .......... 2-1 Introduction .......................................................................... 2-1 Comparative information on techniques discussed in this chapter....................... 2-2 List of acronyms used in this chapter .................................................. 2-4 Direct methods ....................................................................... 2-4 Monitoring adsorption by calorimetry ................................................. 2-5 Quartz crystal microbalance .......................................................... 2-5 Chemiluminescence .................................................................. 2-5 Exoelectrons ......................................................................... 2-6 Adsorption-induced changes of surface stress ......................................... 2-6 Adsorption-induced changes in resistivity ............................................. 2-6 Reflectance ellipsometry ............................................................. 2-6 Change of work function ............................................................. 2-7 Techniques based on a mass spectrometer ............................................. 2-7 Determination of sticking coefficients using a molecular beam ......................... 2-7 Thermal Desorption Spectroscopy (TDS) ............................................. 2-8 Laser-induced Thermal Desorption (LITD) ............................................ 2-9 Techniques for a chemical analysis.................................................... 2-9 Secondary Ion Mass Spectroscopy (SIMS) ........................................... 2-10 Ion Scattering Spectroscopy (ISS) ................................................... 2-10 Auger Electron Spectroscopy (AES) ................................................. 2-10 X-ray Photoelectron Spectroscopy (XPS) ............................................ 2-11 Structural sensitive techniques ....................................................... 2-13 Low Energy Electron Diffraction (LEED) ............................................ 2-13 Diffuse Low Energy Electron Diffraction (DLEED) .................................. 2-14 Photoelectron Diffraction (PED) ..................................................... 2-15 Techniques employing X-ray standing waves (XSW) ................................. 2-16 Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) ................... 2-16 He-atom scattering (HAS) ........................................................... 2-18 Scattering of Rare Gases and Molecules .............................................. 2-19 X-ray Diffraction .................................................................... 2-19 Neutron Scattering .................................................................. 2-20 Ion Scattering Spectroscopy (ISS) ................................................... 2-20 Imaging techniques .................................................................. 2-21 Field Ion Microscopy (FIM) and Field Electron Microscopy (FEM) ................... 2-21 Transmission Electron Microscopy (TEM) ........................................... 2-22 Low Energy Electron Microscopy (LEEM) ........................................... 2-22 Photoemission Electron Microscopy (PEEM) ........................................ 2-22 Miscellaneous ....................................................................... 2-23 Scanning Tunneling Microscopy (STM) ............................................. 2-23 Atomic Force Microscopy (AFM) ................................................... 2-24

2.7 2.7.1 2.7.2 2.7.3 2.7.4 2.8 2.8.1 2.8.2 2.8.3 2.8.4 2.9 2.9.1 2.9.2 2.10 2.10.1 3 3.1 3.1.1 3.1.2 3.2 3.2.1 3.2.2 3.3 3.3.1 3.3.2 3.4 3.4.1 3.4.2 3.4.3 3.4.4 3.5 3.6 3.7 3.7.1 3.7.2 3.7.3 3.7.4 3.8 3.8.1 3.8.2 3.8.3 3.8.4 3.8.5 3.8.6

Vibrational spectroscopy of adsorbed particles ....................................... 2-25 Electron Energy Loss Spectroscopy (EELS) .......................................... 2-26 Infrared Reflection-absorption spectroscopy (IRAS) .................................. 2-26 Surface Enhanced Raman Spectroscopy (SERS) ...................................... 2-27 Inelastic scattering of He-atoms ...................................................... 2-27 Techniques probing the electronic structure .......................................... 2-28 Ultraviolet Photoelectron Spectroscopy (UPS) ....................................... 2-28 Inverse photoemission (IPE) ......................................................... 2-29 Near Edge X-ray Absorption Fine-Structure Spectroscopy (NEXAFS) ................ 2-30 Resonant X-ray Emission Spectroscopy (XES) ....................................... 2-31 Nonlinear optical techniques ......................................................... 2-32 Second Harmonic Generation (SHG)................................................. 2-32 Sum Frequency Generation (SFG) ................................................... 2-33 Bulk techniques ..................................................................... 2-33 Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) ............ 2-33 References .......................................................................... 2-35 Data: Adsorbate properties ....................................... see subvolume III/42A1 Adsorption of noble gases ........................................ see subvolume III/42A1 Noble gases on metals and semiconductors (P. ZEPPENFELD) ....... see subvolume III/42A1 Noble gases on graphite, lamellar halides, MgO and NaCl (M. BIENFAIT) .................................................... see subvolume III/42A1 Adsorption of alkali metals ....................................... see subvolume III/42A1 Alkali metals on metals (R.D. DIEHL, R. McGRATH) ............... see subvolume III/42A1 Alkali metals on semiconductors (E.G. MICHEL, R. MIRANDA) ..... see subvolume III/42A1 Adsorption of metals ............................................. see subvolume III/42A1 Metals on metals (H. BRUNE) ..................................... see subvolume III/42A1 Metals on semiconductors (V.G. LIFSHITS, K.OURA, A.A. SARANIN, A.V. ZOTOV) ............ see subvolume III/42A1 Non-metallic atomic adsorbates on metals and semiconductors .... see subvolume III/42A3 Chemisorbed hydrogen on metals and semiconductors (K. CHRISTMANN) ............................................... see subvolume III/42A3 C, N, O on metals and semiconductors (H. OVER) ................ see subvolume III/42A3 Halogens on metals and semiconductors (E.I. ALTMAN) .......... see subvolume III/42A1 P, S, As, Sb on metals and semiconductors (M. ENACHESCU, M. SALMERON) ................................. see subvolume III/42A3 Surface segregation of atomic species (non-metal on metal) (H.-J. GRABKE, CH. UEBING, H. VIEFHAUS) ....................... see subvolume III/42A3 Molecules on graphite, BN, MgO (except noble gases) (H. WIECHERT, J. SUZANNE) ...................................... see subvolume III/42A3 Molecular diatomic adsorbates on metals and semiconductors...... see subvolume III/42A3 CO and N2 on metals (A. FÖHLISCH, A. NILSSON, H.P. BONZEL) ... see subvolume III/42A3 NO, CN, O2 on metals (W.A. BROWN) ........................... see subvolume III/42A3 Diatomic molecules on alloys (B. E. NIEUWENHUYS) .............. see subvolume III/42A3 Diatomic molecules on semiconductors (K. HORN) ................ see subvolume III/42A3 Molecular polyatomic adsorbates on metals and semiconductors ... see subvolume III/42A3 H2O and OH on metals (G. PIRUG) ............................... see subvolume III/42A3 H2O and OH on semiconductors (W. JAEGERMANN, T. MAYER) ... see subvolume III/42A3 NH3 and PF3 on metals and semiconductors (E. HASSELBRINK) .... see subvolume III/42A3 CO2, NO2, SO2, OCS, N2O, O3 (B.E. KOEL) ...................... see subvolume III/42A3 Substituted hydrocarbons on metals (W.T. TYSOE, D.R. MULLINS) see subvolume III/42A3 Linear hydrocarbons and CH4 on metals and semiconductors (G. SOMORJAI, G. RUPPRECHTER) ................................. see subvolume III/42A3

3.8.7 3.8.8 3.8.9 3.8.10 3.8.11 3.9 3.10 3.11 3.12 4 4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.1.5 4.1.6 4.1.7 4.1.8 4.1.9 4.1.10 4.1.11 4.1.12 4.1.13 4.1.14 4.1.15 4.1.16 4.1.17 4.1.18 4.1.18 4.1.19 4.1.20 4.1.21

Cyclic hydrocarbons on metals and semiconductors (G. HELD, H.P. STEINRÜCK) ...................................... see subvolume III/42A3 Oxygenated hydrocarbons on metals and semiconductors (J. VOHS) . see subvolume III/42A3 Halogen-substituted hydrocarbons on metals and semiconductors (J. FIEBERG, J.W. WHITE) ........................................ see subvolume III/42A3 Polyatomic chain-like hydrocarbons on metals and semiconductors (M. GRUNZE) .................................................... see subvolume III/42A3 Large aromatic adsorbates on metals and semiconductors (M. SOKOLOWSKI, E. UMBACH) .................................. see subvolume III/42A3 Adsorption on oxides (H. KUHLENBECK, H.J. FREUND) ............ see subvolume III/42A3 Adsorption on alkali halides (J. HEIDBERG) ....................... see subvolume III/42A3 Surface diffusion on metals, semiconductors, and insulators (E.G. SEEBAUER, M.Y.L. JUNG) .................................. see subvolume III/42A1 Dynamics of activated adsorption (A.C. LUNTZ) .................. see subvolume III/42A3 Data: Adsorbate-induced changes of substrate properties ............................ 4.1-1 Surface structure on metals and semiconductors (M.A. VAN HOVE, K. HERMANN, P.R. WATSON) ................................... 4.1-1 Introduction................................................. 4.1-1 Relaxation vs. reconstruction ....................................................... 4.1-1 Notations and conventions .......................................................... 4.1-3 Organization of the tables .......................................................... 4.1-4 Organization of data for individual structures ........................................ 4.1-4 Adsorption on fcc(111) ............................................................. 4.1-6 Adsorption on hcp(0001) ........................................................... 4.1-6 Adsorption on bcc(110) ........................................................... 4.1-7 Adsorption on fcc (100) ............................................................ 4.1-7 Adsorption on bcc (100), pure or alloyed ............................................ 4.1-8 Adsorption on fcc (110) ............................................................ 4.1-8 Adsorption on hcp ( 10 1 0 ) ......................................................... 4.1-9 Adsorption on bcc (211) ............................................................ 4.1-9 Adsorption on bcc (111) ............................................................ 4.1-9 Adsorption on Si, Ge and C(111) ................................................... 4.1-9 Adsorption on Si and Ge(100) ..................................................... 4.1-10 Adsorption on diamond-like(311) .................................................. 4.1-10 Adsorption on zincblende(110) .................................................... 4.1-10 Adsorption on zincblende(110) .................................................... 4.1-10 Adsorption on zincblende(111) and (-1-1-1) ........................................ 4.1-11 Adsorption on zincblende(100) .................................................... 4.1-11 Adsorption on 6H-SiC(0001) ...................................................... 4.1-11 Acknowledgments ................................................................. 4.1-11 Tables ............................................................................ 4.1-12 Table 1. Techniques used for surface structure determination; listed by their acronyms ........ 4.1-12 Table 2. Structures of clean fcc(111) surfaces............................................ 4.1-14 Table 3. Adsorbate-induced structures on fcc(111) surfaces ............................... 4.1-15 Table 4. Structures of clean hcp(0001) surfaces ......................................... 4.1-31 Table 5. Adsorbate-induced structures on hcp(0001) surfaces. ............................. 4.1-31 Table 6. Structures of clean bcc(110) surfaces........................................... 4.1-43 Table 7. Adsorbate-induced structures on bcc(110) surfaces............................... 4.1-44 Table 8. Structures of clean fcc(100) surfaces ........................................... 4.1-45 Table 9. Adsorbate-induced structures on fcc(100) surfaces ............................... 4.1-47 Table 10. Structures of clean bcc(100) surfaces.......................................... 4.1-57

4.2 4.2.1 4.2.1.1 4.2.1.2 4.2.1.3 4.2.1.4 4.2.1.5 4.2.1.5.1 4.2.1.5.2 4.2.1.5.3 4.2.1.5.4 4.2.1.5.5 4.2.1.5.6 4.2.1.6 4.2.2 4.2.3 4.2.3.1 4.2.3.2 4.2.3.3 4.2.3.4 4.2.3.5 4.2.3.6 4.2.3.7

Table 11. Adsorbate-induced structures on bcc(100) surfaces.............................. 4.1-58 Table 12. Structures of clean alloyed bcc(100) surfaces ................................... 4.1-62 Table 13. Adsorbate-induced structures on alloyed bcc(100) surfaces....................... 4.1-63 Table 14. Structures of clean fcc(110) surfaces .......................................... 4.1-64 Table 15. Adsorbate-induced structures on fcc(110) surfaces .............................. 4.1-67 Table 16. Structures of clean hcp(10-10) surfaces........................................ 4.1-75 Table 17. Adsorbate-induced structures on hcp(10-10) surfaces............................ 4.1-76 Table 18. Structures of clean bcc(211) surfaces.......................................... 4.1-77 Table 19. Adsorbate-induced structures on bcc(211) surfaces.............................. 4.1-78 Table 20. Structures of clean bcc(111) surfaces.......................................... 4.1-79 Table 21. Adsorbate-induced structures on bcc(111) surfaces. ............................. 4.1-79 Table 22. Structures of clean Si; Ge and C(111) surfaces ................................. 4.1-80 Table 23. Adsorbate-induced structures on Si; Ge and C (111) surfaces ..................... 4.1-80 Table 24. Structures of clean Si and Ge (100) surfaces.................................... 4.1-86 Table 25. Adsorbate-induced structures on Si and Ge (100) surfaces........................ 4.1-87 Table 26. Structures of clean Si(311) surfaces ........................................... 4.1-91 Table 27. Adsorbate-induced structures on Si(311) surfaces ............................... 4.1-91 Table 28. Structures of clean zincblende(110) surfaces ................................... 4.1-92 Table 29. Adsorbate-induced structures on zincblende(110) surfaces ....................... 4.1-93 Table 30. Structures of clean zincblende(111) surfaces ................................... 4.1-95 Table 31. Adsorbate-induced structures on zincblende(111) surfaces ....................... 4.1-96 Table 32. Structures of clean zincblende(-1-1-1) surfaces ................................. 4.1-96 Table 33. Adsorbate-induced structures on zincblende(-1-1-1) surfaces ..................... 4.1-96 Table 34. Structures of clean zincblende(100) surfaces ................................... 4.1-97 Table 35. Adsorbate-induced structures on zincblende(100) surfaces ....................... 4.1-97 Table 36. Structures of clean 6H-SiC(0001) surfaces ..................................... 4.1-98 Table 37. Adsorbate-induced structures on 6H-SiC(0001) surfaces ......................... 4.1-98 Figures for 4.1 .................................................................... 4.1-99 References for 4.1 ................................................................ 4.1-109 Electron work function of metals and semiconductors (K. JAKOBI) ................... 4.2-1 Introduction ........................................................................ 4.2-1 List of abbreviations................................................................ 4.2-1 Definition of work function ......................................................... 4.2-1 Work function versus local potential ................................................ 4.2-2 Standardization of work-function change with coverage ............................. 4.2-3 Experimental methods .............................................................. 4.2-4 Thermionic emission (Therm) ..................................................... 4.2-4 Field electron emission (FEM) ..................................................... 4.2-4 Photoemission (PYS, ARUPS) ..................................................... 4.2-5 Secondary electron edge method (SE edge) ........................................ 4.2-6 Diode method (Diode) ............................................................. 4.2-6 Vibrating capacitor method (Kelvin) ............................................... 4.2-6 Data collection ..................................................................... 4.2-7 Rare gases ......................................................................... 4.2-7 Ne, Ar, Kr, Xe Atomically chemisorbed adsorbates ................................................ 4.2-13 Hydrogen, Deuterium ............................................................. 4.2-13 Carbon and C60.................................................................... 4.2-18 Nitrogen .......................................................................... 4.2-19 Oxygen ........................................................................... 4.2-20 Sulfur ............................................................................. 4.2-29 Selenium.......................................................................... 4.2-31 Tellurium ......................................................................... 4.2-31

4.2.3.8 4.2.3.9 4.2.3.10 4.2.4 4.2.4.1 4.2.4.2 4.2.4.3 4.2.4.4. 4.2.4.5 4.2.4.6 4.2.4.7 4.2.4.8 4.2.4.9 4.2.4.10 4.2.4.11 4.2.4.12 4.2.5

4.2.6

4.2.7

4.2.8

4.2.9 4.2.10 4.2.11 4.2.12 4.2.13 4.2.14 4.2.15

Chlorine .......................................................................... 4.2-32 Bromine .......................................................................... 4.2-34 Iodine ............................................................................ 4.2-35 Small molecules ................................................................... 4.2-35 H2 ................................................................................ 4.2-35 N2 ................................................................................ 4.2-36 O2 ................................................................................ 4.2-37 CO ............................................................................... 4.2-37 NO, N2O .......................................................................... 4.2-42 NH3, PH3, PF3, P(CH3)3, AsH3 ..................................................... 4.2-44 H2O, D2O ......................................................................... 4.2-46 H2S ............................................................................... 4.2-48 CO2, SO2, (CH3)2SO, (CH3)3PO3 ................................................... 4.2-48 C2N2, HCN ....................................................................... 4.2-49 CH3CN, HCOOH, HNCO ......................................................... 4.2-50 KOH, KCl, HCl, HBr ............................................................. 4.2-50 Nonpolar hydrocarbons............................................................ 4.2-51 Methane (CH4), Propane (C3H8), Ethylene (C2H4), Acetylene (C2H2), Propylene (CH3CH:CH2), Cyclopentane (C5H10), Pentadiene (C5H8), n-hexane (C6H14), Cyclohexane (C6H12), Cyclohexene (C6H10), 1,3-Cyclohexadiene (C6H8), Benzene (C6H6, C6D6), Toluene (C6H5-CH3), Ethylbenzene (C6H5C2H5), n-butylbenzene (C6H5C4H9), t-butylbenzen (C6H5C(CH3)3), m-xylene (C6H4(CH3)2), Biphenyle (C6H5C6H5), Naphtalene (C10H8), 2-Methylnaphtalene (C10H7CH3) Polar hydrocarbons ................................................................ 4.2-58 Methanol (CH3OH), Ethyleneoxide (C2H4O), Ethylenedioxide ((CH2)4O2), Acetone (C3H6O), Furan (C4H4O), Benzenethiol (C6H5SH), Pyridine (C6H5N), Aniline (C6H5NH2), Nitrobenzene (C6H5NO2), Cyanobenzene (C6H5CN) Halohydrocarbons ................................................................. 4.2-60 Chloro-methane (ClCH3), Chloro-ethane (ClC2H5), Di-chloro-methane (Cl2CH2), Tri-chloro-methane (Cl3CH), Tetra-chloro-methane (Cl4C), Bromo-methane (BrCH3), Di-bromo-methane (Br2CH2), Tetra-bromo-methane (Br4C), Iodo-methane (ICH3), Iodo-ethane (IC2H5), Chloro-tri-fluoro-methane (ClCF3), 1,2-di-chloro-ethane (ClCH2CH2Cl), 1,2-di-chloro-ethene (ClCH:CHCl), 1,2-chloro-bromo-ethane (ClCH2CH2Br), Iodo-benzene (IC6H5), Chloro-benzene (ClC6H5) Other hydrocarbons ............................................................... 4.2-62 Di-ethyl-zink ((C2H5)2Zn), glycine (α-amino acetic acid) (H2NCH2CO2H), Closo-1,2-di-carbado-decaborane (C2B10H12), TCNQ (Tetra-cyano-quino-dimethane) (C12N4H4) Alkali metals ...................................................................... 4.2-63 Li, Na, K, Rb, Cs Noble metals ...................................................................... 4.2-76 Cu, Ag, Au 3d transition metals................................................................ 4.2-83 Ti, V, Cr, Fe, Co, Ni 4d transition metals................................................................ 4.2-86 Zr, Nb, Mo, Rh, Pd 5d transition metals................................................................ 4.2-89 La, Hf, Ta, W, Re, Os, Ir, Pt Rare-earth metals.................................................................. 4.2-91 Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb Group IIa metals .................................................................. 4.2-93 Be, Sr, Ba

4.2.16 4.2.17 4.2.18 4.2.19

4.3 4.4 4.4.1 4.4.2 4.4.2.1 4.4.2.2 4.4.2.3 4.4.2.4 4.4.2.5 4.4.3 4.4.3.1 4.4.3.2 4.4.3.3 4.4.4 4.4.5 4.4.5.1 4.4.5.2 4.4.5.3 4.4.5.4 4.4.5.5 4.4.5.6 4.4.6 4.4.7 4.4.7.1 4.4.7.2 4.4.7.3 4.4.7.3.1 4.4.7.4 4.4.7.5 4.4.7.6 4.4.7.7 4.4.7.8 4.4.7.9 4.4.7.10 4.4.7.11 4.4.8 4.4.9 4.4.9.1 4.4.9.2 4.4.9.3

Group IIIa metals ................................................................. 4.2-95 Al, Ga, Group IVa elements ............................................................... 4.2-96 C, Si, Ge, Sn, Pb Group Va elements ................................................................ 4.2-98 N, P, As, Sb, Bi Other elements .................................................................... 4.2-99 Hg, U Figures for 4.2 ................................................................... 4.2-100 References for 4.2 ................................................................ 4.2-118 Electron binding energy of metals and semiconductors (R. DENECKE, N. MARTENSSON, A. NILSSON) ..................... see subvolume III/42A3 Surface free energy and surface stress (D. SANDER, H. IBACH) ....................... 4.4 -1 Introduction ........................................................................ 4.4 -1 Experimental determination of surface free energy................................... 4.4 -2 Cleavage experiments .............................................................. 4.4 -3 Pendant drop and drop weight method .............................................. 4.4 -4 Zero creep experiments ............................................................. 4.4 -5 Orientation dependence of the surface free energy ................................... 4.4 -6 Empirical relation between surface free energy and other quantities .................. 4.4 -8 Experimental determination of the absolute value of the surface stress ................ 4.4 -8 Lattice parameter of small particles ................................................. 4.4 -8 Surface phonons as indicator of surface stress ....................................... 4.4 -9 Absolute surface stress from the bending of thin crystal plates ....................... 4.4 -9 Experimental determination of changes of surface stress due to adsorption .......... 4.4 -10 Calculations of surface free energy and surface stress ............................... 4.4 -13 Inert gas crystals .................................................................. 4.4 -14 Ionic crystals ...................................................................... 4.4 -14 III-V compounds .................................................................. 4.4 -15 Group IV materials ................................................................ 4.4 -15 Metals ............................................................................ 4.4 -16 Calculated adsorbate-induced surface stress ........................................ 4.4 -16 Data .............................................................................. 4.4 -18 Clean surfaces .................................................................... 4.4 -19 Surface free energy from cleavage experiments ..................................... 4.4 -19 Surface free energy of metals near the melting point ................................ 4.4 -19 Temperature dependence of the surface free energy................................. 4.4 -21 Temperature dependence of the anisotropy of the surface free energy ............... 4.4 -22 Calculated surface free energy and surface stress for inert gas crystals ............... 4.4 -22 Calculated surface free energies and surface stress for alkali halides ................. 4.4 -23 Calculated surface free energy and surface stress of III-V compounds ............... 4.4 -23 Calculated surface free energy and surface stress for Si and Ge ..................... 4.4 -24 Calculated adsorbate-induced changes of stress on semiconductor surfaces .......... 4.4 -25 Calculated surface free energies of metals .......................................... 4.4 -26 Calculated surface stress ........................................................... 4.4 -32 Calculated adsorbate induced surface stress on Pt(111) ............................ 4.4 -34 Adsorbate-induced changes of surface free energy .................................. 4.4 -34 Adsorbate-induced changes of surface stress ....................................... 4.4 -36 Gas adsorption .................................................................... 4.4 -36 Alkali metal deposition ............................................................ 4.4 -40 Semiconductor and metal deposition ............................................... 4.4 -40 References for 4.4 ................................................................. 4.4 -44

4.5 4.5.1 4.5.1.1 4.5.1.2 4.5.1.3 4.5.1.4 4.5.1.4.1 4.5.1.4.2 4.5.1.5 4.5.1.6 4.5.2 4.5.2.1 4.5.2.2 4.5.2.3 4.5.2.4 4.5.2.5

4.6

Surface phonon dispersion (M.A. ROCCA) ........................................... 4.5-1 Introduction ........................................................................ 4.5-1 Background and general layout ..................................................... 4.5-1 Symmetry considerations, energy and momentum conservation and relevant selection rules in inelastic scattering ........................................ 4.5-3 Folding of the surface Brillouin zone by symmetry reduction, mode mixing, phonon crossing and opening of energy gaps ........................................ 4.5-3 Phonon anomalies .................................................................. 4.5-4 Effect of mass loading, modification of force constants and surface stress ............ 4.5-4 Kohn anomaly ..................................................................... 4.5-5 Dispersion of adsorbate induced modes ............................................. 4.5-6 Theoretical models ................................................................. 4.5-7 Data collection ..................................................................... 4.5-7 Correspondence of units ............................................................ 4.5-9 Metal surfaces ..................................................................... 4.5-9 Ag, Al, Cu, Mo, Ni, Pb, Pt, Rh, Ru, W Elemental semiconductors and insulators ........................................... 4.5-20 C, Ge, Si Compound semiconductors ........................................................ 4.5-22 GaAs, GaP, InAs, InP Oxides and Salts .................................................................. 4.5-23 MgO, NaCl Acknowledgements................................................................ 4.5-24 Figures for 4.5 .................................................................... 4.5-25 References for 5.4 ................................................................. 4.5-68 Surface optical properties (N. ESSER, W. RICHTER) ................ see subvolume III/42A3

2 Measuring techniques CH. WÖLL

2.1 Introduction Whereas the observation of molecular adsorption on a solid surface can be monitored by the naked eye (corrosion of e.g. iron surfaces, formation of patina on copper,...), more detailed investigations require the availability of rather sophisticated equipment. The diffraction of electrons represents the first method of its kind to portray the structure of single crystalline solid surfaces [27DAVa; 27DAVb]. Even in the first studies the adsorption of gases on the specimen has been noted and found to cause „anomalous“ beams [27DAVb], very likely the first observation of an ordered molecular adlayer on a solid substrate. Today electron diffraction prevails as the standard technique to characterize adsorbate covered surfaces of wellordered solids. As a result of the comparatively simple technical requirements this technique enjoys widespread distribution and tremendous success in the determination of structures and relaxation-effects on clean surfaces as well as in the investigation of adsorbate overlayers. The immense body of knowledge present today about the application of this technique is the source not only for ongoing research in surface science but also for the development of related techniques, e.g. the different versions of photoelectron diffraction. The diffraction of electrons is complemented by the oldest technique for structure determination of bulk matter, the diffraction of X-rays. Due to the very small (typ. 1015 part/cm2) scattering cross section of a monolayer this technique is not suitable for the determination of adsorbate structures on solid substrate surfaces in a straightforward fashion, which also holds true for neutron scattering, another standard technique in bulk structure determination. Despite the tremendous success of electrons in surface science studies other probe particles also generate diffraction patterns from surfaces. The application of neutral atoms and molecules with thermal energies for surface diffraction studies [30EST] had been preceded by electron scattering by only a few years. Although this method has been applied in numerous investigations, it has not developed into a widespread technique, mostly because of the considerable experimental efforts required to generate and detect molecular (and atomic) beams. Atoms at higher than thermal energies exhibit de Broglie wavelengths significantly smaller than the lattice-spacing of solids and can therefore not be used for diffraction studies. By going to even higher energies, however, the wavelength becomes so small that the motion of the particles can be treated classically. Subsequently, the scattering of low, medium and high energy ions has been used together with a classical trajectory analysis in a large number of works to investigate the structure of surfaces, clean and adsorbate-covered. In the following the different probe techniques suitable for structural analysis of adsorbed layers on surfaces will be briefly discussed. We will begin with the conceptually most simple and direct methods, which are principally also suited for designing sensor devices. We will proceed with slightly more complicated yet still straightforward techniques based on a mass spectrometer and then continue with diffraction and other structural sensitive techniques which make full use of the advanced technology available today. Subsequently, methods sensitive to adsorbate vibration and electronic structure will be presented. Together with a brief description of the respective technique, the major limitations will be briefly mentioned. The description of the rather large set of measuring techniques starts with a list of acronyms for the different methods and a table, which classifies the techniques according to a number of different criteria. The table should be used, however, only as a rough guide, a more detailed discussion of the respective merits and limitations will be provided in the related paragraphs.

Landolt -Börnst ein New Series III/42A2

2-2

2 Measuring techniques

[Ref. p. 2-35

2.1.1 Comparative information on techniques discussed in this chapter For the list of acronyms used in this chapter, see page 2-4 Elemental Chemical state LEED HREELS HAS SEM,TEM ISS TPD SIMS SHG SFG XPS AES UPS NEXAFS XES STM

(+) + + + + (no H) + (no H) + (no H) + (no H) -

+ (+) (+) + (+) (+) (+) ++ ++ (+)

AFM IRAS EXAFS LITD PED XSW XRD SERS IPE FIM FEM Φ, ∆Φ

(+) + (+) (+) (+)

+ (+) (+) (+) (+) (+)

-

-

Binding energy (1) ind. ind. ind. ind. +

ind.

ind.

Structural order, coh.length + + + +

Geometric structure (ordered) + (+) + + (+) (+) (+) (+) XPD (+) (+) (+) (+) +

+ -

-

+ -

+ (+) + + + + (+) -

-

-

(+) -

(ind.) ind.

Resol. [Å] 0.01

orient. 0.01 vert 0.2 hor orient. 0.01 0.01 0.01 0.01

Geometric structure (disordered) (+) (+) (+) + (+) XPD (+) (+) (+) (+) (+) + (+) + -

Resol. [Å] 0.05

orient.

orient.

(+)

Lando lt -Bö rnst ein New Series III/42A2

Ref. p. 2-35]


Phase Electronic Intertransitions structure pretation (valence) (2) LEED + + HREELS ++ HAS + + SEM,TEM (+) ISS (+) TPD + SIMS + SHG (+) SFG XPS (+) + AES UPS ++ + NEXAFS (+) + XES ++ + STM (+) (+) + AFM IRAS EXAFS LITD PED XSW XRD SERS IPE FIM FEM Φ, ∆Φ

(+)

(+)

(+)

Vibrations

Diffusion

++ + (FIR) (3) + (+) + (+) (+) (+)

2-3

Destructive

Synchrotron required

yes yes yes yes yes -

+

+ ++ + (+) + + + + +

++ + -

+ -

yes varies varies

-

-

-

-

-

yes yes

yes

yes helpful

-

(1) Basically all methods can be used to roughly determine the binding energy by determining the temperature where the molecule is desorbed from the surface.“ind“ is entered when the method is frequently applied for this purpose. (2) Many techniques require significant theoretical and computational effort to obtain the desired information. In this column ++ indicates that this effort is small, whereas – indicates that significant effort is required. (3) Mainly applied to vibrations in the Far-Infrared regime (< 200 cm-1 or < 25 meV)


2-4


[Ref. p. 2-35

2.1.2 List of acronyms used in this chapter AES AFM DLEED EXAFS HAS HREELS IPE IRAS ISS LEED LEEM LEIS LITD MEIS NEXAFS PEEM PED QCM QMS RBS SEM SERS SFG SHG SIMS STM TEM TDS TPD UPS XANES XES XPS XRD XSW Φ

Auger Electron Spectroscopy Atomic Force Spectroscopy Diffuse Low Energy Electron Diffraction Extended X-ray Absorption Fine Structure He-Atom Scattering High-Resolution Electron Energy-Loss Spectroscopy Inverse Photoemission Infrared Reflection Absorption Spectroscopy Ion Scattering Spectroscopy Low Energy Electron Diffraction Low Energy Electron Microscopy Low Energy Ion Scattering Laser-Induced Thermal Desorption Medium Energy Ion Scattering Near Edge X-ray Absorption Fine Structure Photoelectron Electron Microscopy Photoelectron Diffraction Quartz Crystal Microbalance Quadrupole Mass Spectrometer Rutherford Backscattering Scanning Electron Microscopy Surface Enhanced Raman Spectroscopy Sum Frequency Generation Second Harmonic Generation Secondary Ion Mass Spectrometry Scanning Tunneling Microscopy Transmission Electron Microscopy Thermal Desorption Spectroscopy Temperature Programmed Desorption Ultraviolet Photoelectron Spectroscopy X-ray Absorption Near Edge Structure, see NEXAFS X-ray Electron Spectroscopy X-ray Photoelectron Spectroscopy X-ray Diffraction X-ray Standing Wave Work Function

2.2 Direct methods The adsorption of a molecule on a surface, as schematically illustrated in Fig. 1, leads to changes of a number of different quantities and properties. The main problem in surface science is that these changes are restricted to the top substrate layer and are thus very small in relation to any changes of the bulk. As a result, rather complicated surface sensitive techniques have been developed in the past decades to gain information on the adsorption process and the nature of the substrate-adsorbate complex. Very often these Lando lt -Bö rnst ein New Series III/42A2

Ref. p. 2-35]


2-5

methods are rather indirect, and a significant computational effort is required to obtain e.g. precise information on adsorbate geometries from the experimental data. There are, however, a few general methods where the required information can be obtained in a rather direct way. Correspondingly, these techniques are in principle suited for applications as sensors. In the following we will briefly list the most important of these conceptually very simple methods before proceeding with the methods which have been designed for surface studies.

Fig. 1. Adsorption of a molecule on a solid substrate. In the case shown in the figure the process is called associative, since the molecule is not dissociated upon adsorption.

2.2.1 Monitoring adsorption by calorimetry One of the most direct ways to follow an adsorption process and to quantitatively determine the excess energy is by detection of the corresponding rise in substrate temperature. Although substrates with thicknesses in the mm range have heat capacities which are far too large, the preparation of very thin films makes such measurements possible. In the case of polycrystalline films evaporated onto thin glass substrates direct measurements of heats of adsorption have been reported for a number of different adsorbate/substrate combinations [78WED]. For single crystalline films, however, the task is considerably more difficult, since the growth of very thin films with high structural quality poses a huge experimental challenge. These problems, however, have in recent years been overcome and it was possible to apply the method e.g. to the case of oxygen on Ni(100), where temperature rises originating from the adsorption of amounts as small as 0.01 monolayers could be detected [91BOR]. Although this method is very elegant, the severe technological limitations restrict its application to but a few cases. Recently, a novel approach has been demonstrated for detecting the small temperature changes accompanying the adsorption of gases on metal surfaces. In a pioneering investigation the heat evolution in the adsorption and subsequent reaction of O2 and H2 to form water on a thin Pt-layer evaporated on a SFM bimetallic cantilever has been studied [94GIM].

2.2.2 Quartz crystal microbalance Another physical quantity which can in principle be used to detect adsorption is the corresponding increase in weight. The detection of such mass-changes via a precise measurement of the resonance frequency of a quartz crystal is a standard technique to monitor the deposition of metal films. The method is, however, only rarely applied to the investigation of adsorbates because of experimental problems and the difficulty to grow well-defined films on quartz substrates. Recently, however, a quartz crystal microbalance (QCM) has been used to monitor the adsorption of noble gases and simple hydrocarbons on surfaces of Ag-films [90KRI; 96DAL].

2.2.3 Chemiluminescence In principle the adsorption process can be viewed as a chemical reaction and several phenomena accompanying reactions in the gas-phase or the liquid also occur for surface reactions. One of these is Lando lt -Bö rnst ein New Series III/42A2

2-6


[Ref. p. 2-35

chemiluminescence, where electronically excited product molecules decay to their ground state by emission of photons. Of course this process requires that the adsorption energy is sufficiently large and that non-radiative processes do not come into play. Due to the fairly small number of surface reaction sites considerable experimental effort is required for detection. Nevertheless, chemiluminescence accompanying adsorption has been observed in a few cases, e.g. for the adsorption of chlorine on Ksurfaces [85AND].

2.2.4 Exoelectrons A very convenient way to follow adsorption is the detection of electrons generated during the adsorption process. Since the reaction with the surface must be sufficiently energetic for the emitted electrons being able to overcome the substrate work-function, the phenomenon has been observed only in a few cases, e.g. during the oxidation of Cs- and Na-surfaces [94GRO],[92BOE].

2.2.5 Adsorption-induced changes of surface stress The creation of a surface can give rise to significant mechanical stress, which can be related to the difference in chemical environment for surface atoms and bulk atoms. Generally, adsorption of particles is expected to change this stress. Since the absolute forces related to this phenomenon are rather small, significant experimental effort is required to detect the adsorption-induced changes in surface stress. Such measurements are, however, feasible and results have been reported for polycrystalline films evaporated onto specially designed cantilevers [86ABE]. Recently, it has been possible to extend these measurements to single crystalline substrates, including the oxidation of silicon [91SAN] and molecular adsorbates on Ni(100) [94GRO].

2.2.6 Adsorption-induced changes in resistivity One of the oldest and experimentally most straightforward ways to detect adsorption on metals – even for weak adsorbate-substrate interaction as in the case of N2-molecules adsorbed on Cu - is the measurement of the conductivity of thin metal films [72WIS; 87WIS]. Attaining a detailed understanding of the basic microscopic mechanism causing this effect has been hampered by the fact that the thin films used for these experiments generally exhibit rather poor structural quality. Recently, it has been shown theoretically, that the change in dc-resistivity upon molecular adsorption is related to the reduction of electron-hole lifetime in the top layers of the substrate through excitations of frustrated translations of the adsorbed molecules [91PER; 94PER].

2.2.7 Reflectance ellipsometry Adsorption of atomic or molecular species affects the electronic structure of the substrate and, as a consequence, the reflectivity (or color) of the surface. Although these changes are typically very small, independent measurements of the reflectivity for differently polarized light (s vs. p) and the phase delay between the two polarizations allow to monitor e.g. the adsorption of noble gas adlayers on graphite with submonolayer sensitivity [93YOU]. Recently, it has been demonstrated that the method can be combined with an optical microscope to image in-situ the patterns formed in surface reactions using visible light [95ROT; 96HAA].


Ref. p. 2-35]


2-7

2.2.8 Change of work function In case of conducting samples adsorption events are typically accompanied by a change of the workfunction, Φ, i.e. the minimum energy required to remove an electron from the probe. The microscopic origin of this behavior is related to the formation of a dipole-adlayer, which is particularly strong if the molecule carries a significant dipole moment (e.g. in the case of the cyclic ether trioxane, C3H6O3, [94HOF]). But also in case of physisorbed noble gas atoms, e.g. Xe, noticeable changes in workfunction, ∆Φ, can be observed [87JAC]. A variety of methods has been used to detect these changes, some of which are conceptually rather simple and can be used also for sensor applications (e.g. vibrating capacitor method). Several methods for detecting work function changes are based on equipment primarily used for other methods (e.g. UPS). Since work-function changes are rather important for both monitoring the adsorption of adparticles and the understanding of adsorption–induced changes in electronic structure, chapter 4.2 is devoted to this topic.

2.3 Techniques based on a mass spectrometer 2.3.1 Determination of sticking coefficients using a molecular beam

molecular beam

F1 F2 open open

F2 to QMS sample

to pump

Pressure

flag F1

Time

Fig. 2. Schematics for determining the sticking coefficient using the King and Wells method [72KIN]. The diagram on the right hand shows the mass spectrometer (QMS) signal after first opening flag F1 and then flag F2.

An important question concerning a particular adsorbate/substrate combination is whether for a given substrate temperature the particle or molecule sticks to the surface, and what the sticking probability amounts to. The conceptionally most simple method to answer this questions is the so-called King and Wells method [72KIN] as illustrated in Fig. 2. A molecular beam containing either the pure substance or a mixture with an inert (e.g. He, Ar) carrier gas impinges on the substrate and the pressure in the recipient is measured using either a mass-insensitive pressure gauge (e.g. an ionization gauge) or a mass spectrometer. The experiment starts by determining the pressure inside the chamber containing the clean substrate with the molecular beam of the corresponding particle (e.g. CO) blocked by a flag (F2) with a chemically inert surface. After opening the flag the pressure drops due to adsorption on the sample surface. The pressure is recorded until saturation sets in. If the particle or molecule sticks to the surface with unity sticking coefficient, the pressure inside the chamber will initially drop to zero, since all incident particles are trapped by adsorption to the surface. If the number of free surface sites is reduced, particles are scattered back into the vacuum chamber, giving rise to an increase of the pressure. Measurements of this kind give rise to detailed information of the absolute value of the sticking coefficient and its dependence on coverage, defects and coadsorbates. Although the method requires substantial technical effort, preparation


2-8


[Ref. p. 2-35

of a well collimated molecular beam, it can be used to measure sticking probabilities on virtually all types of substrates. Structural order is not a prerequisite, and the method can be applied to metals and semiconductors as well as to insulators. For very small (500 eV) the scattering of the photoelectron by the neighboring atoms is dominated by forward scattering, i.e. the scattered intensity is peaked in the direction of neighboring atoms (see Fig. 7). As a result, information on the local environment of a photo-ionized atom can be studied by experimentally determining the angular distribution of emitted photoelectrons [88FAD]. In a typical application the presence of perpendicular and tilted CO-molecules on clean and potassium-modified Ni(110) could be demonstrated by experimentally determining the angular distribution of the C1s photoelectrons [89WES]. For smaller photoelectron energies (< 300 eV), the forward scattering mechanism is no longer dominant and interference effects lead to a distribution of intensity over a much larger angular regime. As a result, data analysis is not as straightforward and requires significant theoretical support. However, if experimental photoelectron angular distributions are recorded for a series of different photon incident energies (so-called "scan energy photoelectron diffraction"), the theoretical analysis of the experimental spectra yields very detailed information on the position of the adsorbate atoms. It is of particular interest that in addition to the atomic positions, information on the type of atoms is also contained in the experimental data. Furthermore, this chemical sensitivity makes it possible to separately determine the positions of atoms of the same type, which are equivalent for the free molecule but become chemically distinct when adsorbed on a surface [99WEI]. Although the theoretical analysis of the experimental data is rather complex, recently a direct method has been proposed, which allows for a direct extraction of geometrical data from the experimental results [93SCHb]. The application of photoelectron diffraction has the same limitations as LEED, i.e. charging for insulating substrates requires additional effort. Note, that long-range order is not necessary for applying this method.


2-16


[Ref. p. 2-35

2.5.4 Techniques employing X-ray Standing Waves (XSW) The availability of synchrotron sources of second and third generation have made possible the application of X-ray based techniques commonly used for bulk investigations for surface studies which were not feasible previously because of intensity problems. With regard to the determination of structural parameters on single crystalline substrates novel approaches employing X-ray standing waves (XSW) [93ZEG] are particularly interesting. In this technique the wavelength of the incident X-rays is chosen such that the superposition of the incident beam and one particular Bragg spot generate a standing wave at the surface. Atoms positioned in the node of this standing wave will absorb little or no radiation, while those placed at the corresponding maxima will show enhanced absorption. By slightly tuning the wavelength of the incident radiation the position of nodes and maxima shifts slightly, and a corresponding analysis of the photoabsorption cross section of the given atoms provides detailed information on the positions. By additionally employing a triangulation scheme the method can be used to precisely determine the absolute position of adatoms relative to the substrate atoms. With regard to practical aspects the most popular variant is the so-called normal-incidence XSW method, where the incident beam is normal to the corresponding Bragg planes [93ZEG]. Recently, the method has been combined with an energy-resolved detection of the corresponding photoelectrons, which makes it possible to determine the geometric position of one type of atom in different chemical environments separately. For example in the case of PF3 adsorbed on Ni(111) this so called chemical-shift normal incidence X-ray standing wave (CS-NIXSW) technique makes it possible to determine the position of three different P-species independently [99JAC].

2.5.5 Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) In XPS the kinetic energy of photoelectrons emitted after excitation by photons with a fixed energy is determined, whereas in EXAFS (extended X-ray absorption fine structure) the photoabsorption cross section is measured as a function of X-ray photon energy. In contrast to NEXAFS (see below) in EXAFS the absorption is measured in a fairly large interval of electron energies (typ. several 100 eV). As schematically depicted in Fig. 8, an X-ray photon is absorbed by exciting an electron into a continuum state. This electron travelling away from the core-excited atom is scattered by the neighboring atoms as discussed in connection with X-ray photoelectron diffraction (XPD). Depending on the kinetic energy of the electron, which is given by the difference between the photon energy hν, the core-level binding energy Eb and the inner potential V of the electrons inside the probe, constructive or destructive interference will occur at the position of the core-excited atom. As a result the X-ray absorption cross section is modulated, it increases when the constructive interference dominates for the emitted photoelectron, and decreases when destructive interference takes place. As a result, the exact shape of the X-ray absorption edge depends on the geometric surrounding of the core-excited atom, and e.g. the distributions of distances to nearest neighbors can be determined by a procedure which essentially consists of a Fourier-transformation [95ARV; 96BAB]. The outgoing wave will in general be non-spherical. If, for example, the initial state is a p-type orbital, the orientation of the p-lobes will depend on the direction of the incident light. By varying the angle of incidence of the exciting X-rays the backscattering amplitude from neighbors in different directions can be changed, thus increasing the amount of information which can be extracted from the EXAFS-data. As an example, interatomic distances and molecular orientation could be determined for formate (HCOO–) on Cu(110) [85PUS].


Ref. p. 2-35]


2-17

Fig. 8. In EXAFS, the absorption of X-ray radiation is determined as a function of photon energy. The photoelectrons generated in the photoabsorption process at an adsorbate-atom are backscattered from substrate atoms and lead to modulation of the absorption cross section through interference phenomena. In the center figure the lines of equal phase of the backscattered radiation go through the excited atom (see top) resulting in constructive interference, whereas in the bottom figure the photoelectron kinetic energy is slightly different, resulting in destructive interference at the position of the excited atom.

Although the EXAFS-method requires a tunable source for X-rays, which is most conveniently realized by a synchrotron, it has significant advantages because of the rather straightforward data analysis. If X-ray absorption is determined directly, e.g. in transmission using an X-ray sensitive detector, the method is not intrinsically surface sensitive. In fact, bulk EXAFS has found widespread application in the determination of interatomic distances in (disordered) bulk samples, in particular for compounds containing transition metals. Surface sensitivity is achieved by measuring X-ray absorption indirectly via detection of secondary electrons. This variant is frequently called SEXAFS (surface EXAFS). Note also that this method does not require single-crystalline substrates.


2-18


[Ref. p. 2-35

2.5.6 He-Atom Scattering (HAS) Helium atom scattering (HAS) Octane / Cu(111) [112]

Relative intensity

1

20

0

-4

-2

0

2

4

K [Å-1]

Fig. 9. Left: He-atoms with thermal energies (10-60 meV) from a molecular beam source are scattered off the very top surface charge density (left), whereas electrons penetrate several layers. As a result, He-atom scattering, HAS, offers a unique surface sensitivity. Right: Due to the very low incident energy He-atoms are particularly well suited for the investigation of delicate adsorbate layers. The angular distribution has been recorded for ordered monolayers of octane (C8H18) on Cu(111).

In order to obtain well-resolved diffraction peaks from ordered adsorbate overlayers, the wavelength of the scattered particle is required to lie in the regime of 1-10 Å. Therefore, only slow and light atoms are well suited for this application, of which helium, the lightest readily available neutral atom, finds widespread use. A particular advantage of 4He atoms is the fact that an adiabatic expansion of He through a small (typ. 10-20 µm) nozzle results in the formation of a supersonic beam with a very narrow energy distribution (values of less than 2% of the initial spread can be reached [77TOE]), so that diffraction studies can be carried out without any monochromator. Inspection of a typical interaction potential between a surface and a He atom demonstrates dramatic differences in the interaction between a surface and noble gas atom on the one hand and electrons on the other. The steep repulsive branch of the gas-surface potential prohibits any penetration of the He-atoms into the substrate and limits the interaction to the first layer only. Electrons, on the other hand, penetrate several layers, see Fig. 9. This fundamental difference results in a tremendous enhancement of the surface sensitivity and makes it possible to detect single atomic and molecular adsorbates. In contrast to LEED, however, the cross section depends very sensitively on the electronic structure of the adsorbate surface complex. In many cases it is found that the cross-section of a molecular adsorbate like CO is significantly larger than the corresponding gas-phase value [88YIN]. The elastic diffuse scattering signal caused by the presence of adsorbed atoms and molecules or step edges could also be detected directly and was used to infer on size and location of such surface defects [87LAH; 92WOE]. The pronounced surface sensitivity of He-atom scattering can be exploited to directly determine whether adsorbates preferentially adsorb at defect sites by monitoring the He-atom reflectivity in the course of an adsorption experiment as a function of surface coverage [00BEC]. The high surface sensitivity of He-atom scattering is best demonstrated by the straightforward detection of hydrogen-atom overlayers. This has first been reported for the case of H-overlayers on Ni(110) [83RIE]. In this case the unit-cell of the adsorbate is several times larger than that of the substrate. The corresponding additional diffraction peaks are clearly visible in He-atom scattering [83RIE], but give rise to only weak electron diffraction (LEED) spots. The detection of such superspots is no problem for modern state-of-the–art LEED instruments, whereas for the straightforward detection of (1x1) H-atom overlayers on metal substrates the scattering of He-atoms is still the method of choice [95WIT]. Recently, it has been demonstrated that He-beams can be focussed to below 1 µm using Fresnel zone plates [99DOA] thus opening the route to spatially resolved studies and investigations of small particles. An advantage in connection with the investigation of molecular adlayers is the fact that light atoms with de-Broglie wavelengths in the 0.1 nm regime have incident energies which are so small that Lando lt -Bö rnst ein New Series III/42A2

Ref. p. 2-35]


2-19

scattering of thermal-energy He-atoms is strictly non-destructive. The method can thus be applied to characterize the surface geometry of the outer, CH3-terminated surface of self-assembled monolayers of alkanethiols [91CAM], which is difficult to study with other methods due to the small cross-section of Cand H-atoms for electrons and X-rays. The most striking advantage of using He-atoms as opposed to electrons is the fact that neutral atoms are not sensitive to electric or magnetic fields. As a result insulating substrates can be investigated in a straightforward fashion [99BRA].

2.5.7 Scattering of rare gases and molecules The use of noble gases other than He in atom-surface scattering suffers from the fact that the corresponding molecular beams are significantly inferior to He beams with regard to monochromaticity and intensity. In addition for noble gas atoms heavier than He the scattering process becomes dominated by multiphonon-excitations, thus reducing the flux in the elastic diffraction channels. Only in a few cases have other noble gas atoms been used in diffraction studies (Ne [94RIE], Ar [89SCH]). The scattering of molecules to obtain structural information on surfaces is generally hampered by the fact that the angular distributions obtained by scattering of molecules from a surface are to a large extent governed by rotational excitations. As a result, only in a few cases have molecules been used for structural characterizations of adlayers. Note, however, that recently it could be demonstrated that diffraction of hydrogen molecules in different rotationally excited states can provide interesting information about details of the charge distribution on compound surfaces [98BER]. Molecular beam techniques are a rather convenient way to obtain direct information on the atomsurface resp. molecule surface potentials by monitoring selective adsorption processes, which can be either mediated by diffraction [80HOI] or by rotational excitation [83YU].

2.5.8 X-ray diffraction Despite the fact that X-ray scattering constitutes the standard technique for bulk structure determination, quantitative studies at surfaces have so far only been carried out for selected systems. This results from the small cross section of single atoms for X-rays. Very bright X-ray sources like synchrotrons in connection with glancing incident angles can, however, be used to overcome these limitations and the required surface-sensitivity can be achieved. As a consequence, X-ray diffraction, or XRD, has in recent years become a very attractive method for obtaining detailed structural information on ordered molecular adsorbates, even in the case of larger molecules (n-alkane thiolates [93FEN]). Since X-ray induced damage is a general phenomenon observed for many adsorbate systems, the applicability of the technique to a given system has to be carefully examined in particular for molecular adlayers. Note, that in the case of metallic substrates the damage is typically not generated by the incident X-ray photons but is caused by the secondary electrons resulting from the absorption of X-rays in the substrate and the subsequent decay of core-excitations by primary and secondary Auger transitions. Only very recently it has become possible to also use laboratory sources for unraveling the structure of organic overlayers on metal surfaces. For example the ordering and the adsorption-induced intramolecular distortions have been determined in adlayers of end-capped quarterthiophene [99MEYa] and 2-thiouracil [99MEYb] on Ag(111).


2-20


[Ref. p. 2-35

2.5.9 Neutron Scattering Similar to the case of X-ray scattering the application of neutron scattering in surface science is severely hampered by the small scattering cross section of a surface adlayer. Nevertheless, neutron scattering is an important technique in association with the characterization of molecular adlayers of very different composition on graphite substrates. The successful application to this special surface is due to the availability of a particular type of graphite powder, grafoil, which consists of flat sheets of graphite particles oriented such that a large fraction (∼30%) of the surface-planes are coplanar. Diffraction studies have been carried out for a large number of adlayers ranging from adsorbed atoms (Ar, [77TAU]) and diatomics to larger molecules (hexane, C6H14, [92HAN]). Apart from graphite, the only other substrate for which neutron studies on adlayers supported by a single crystalline surface have been reported is MgO [91LAR; 98LAR].

2.5.10 Ion Scattering Spectroscopy (ISS) A major disadvantage of all diffraction techniques is the fact that a straightforward, direct determination of the geometric structure of an adlayer solely from the diffraction peak intensities is not possible. As a result, information on the structure in real space can only be obtained by various types of fitting procedures. In this context the scattering of particles with high energies and correspondingly small deBroglie wave-lengths offers the possibility to directly infer on real-space structures by, e.g. channeling and blocking. (See Fig. 10) The energy regime between 100 eV and 10 keV is commonly called low energy ion scattering (LEIS). In this regime the energy is sufficiently high to describe the interaction with solid substrates in terms of classical physics. The ions incident on the adsorbate-covered surface follow classical trajectories, and after one or more collisions the backscattered particle is detected. The determination of the surface composition from the energy-loss of the ion has been described in paragraph 3.4.2 on Ion Scattering Spectroscopy (ISS). For a fixed incident direction of the ions the analysis of the angular distribution of the backscattered ions allows for a precise determination of atomic positions. Generally, a direct determination of the structure from the angular distributions of the backscattered particles is not feasible. With the aid of computer programs, however, it is possible to simulate the angular distributions of the scattered ions by analysing the classical trajectories of a large number of ions scattered off a substrate with an assumed geometry [93NIE]. After comparing the theoretical results with those obtained experimentally the assumed geometry can be adjusted so as to minimize the deviation between experiment and simulation. In case of hydrogen atom overlayers on Ru(001), the analysis of the ions scattered from the H-atoms revealed that the H-atoms are adsorbed on threefold sites of the Ru-substrate, 1 Å above the plane of the surface atoms [93NIE]. Fig. 10. In ion scattering spectroscopy, ISS, charged atoms are accelerated towards a substrate. When the ions impinge on the surface, the atoms in the first layer generate a shadow cone which, depending an the precise geometry, can make atoms in deeper layers invisible. Whereas all atoms of the first substrate layer are visible for the scattering geometry depicted on the right, some substrate atoms are located in the shadowing cone for the scattering geometry shown on the left.


Ref. p. 2-35]


2-21

Of course, the interaction of the high-energy ions with the substrate also causes damage due to sputtering. This is generally an unwanted effect in investigations of overlayers on solid substrates. Fortunately, the detection efficiency for ions is rather large, thus in most cases the total fluency can be reduced to below 10-3 ions per surface atom, a value for which the ion-induced damage can be safely neglected. The sputtering can, however, be employed to study depth profiles, e.g. to investigate whether dosing a substrate with another compound leads to excessive subsurface diffusion [93NIE]. When increasing the ion energies further, the scattering cross sections become smaller, resulting in a deeper penetration of the particles into the substrate. As a result, medium energy ion scattering (MEIS) and Rutherford back scattering (RBS) are less surface sensitive (and thus less well-suited for the investigation of adsorbate overlayers) but are the methods of choice when either information on deeper layers or a very high precision of the atomic positions is needed [93NIE]. From an experimental point of view the analysis of ions with higher energies has the disadvantage of requiring more expensive equipment (accelerator, energy analyzer). When applying the method to semiconductors and insulators, the appearance of charging phenomena can strongly affect the neutralization probabilities in the scattering process and thus significantly complicate a quantitative analysis [79Joi].

2.6 Imaging techniques 2.6.1 Field Ion Microscopy (FIM) and Field Electron Microscopy (FEM)

FEM

FIM

e-

- +

+

EVac EF

e-

-

Fig. 11. In field electron microscopy, or FEM, the negative voltage applied to a metal tip (left) is increased to the point where the electrons can tunnel from the tip into the vacuum (bottom left). In field ion microscopy, or FIM, the voltage is reversed and leads to the field-induced ionization of rare gas atoms trapped at the tip surface (right). Atomic resolution can readily be achieved with FIM.

In field electron microscopy (FEM) electrons are extracted from a metallic substrate by applying a very strong electric field, the emission pattern is recorded using a fluorescence screen. In order to reach the required field strengths (~ 100eV/nm) very sharp metal tips are employed, the fabrication of which poses a formidable task. Although the first real-space images of molecules adsorbed on metal surfaces have been obtained using field electron microscopy for a phthalocyanine molecule adsorbed on a tungsten surface Landolt -Börnst ein New Series III/42A2

2-22


[Ref. p. 2-35

[50MUE], the method has not found widespread application for direct imaging of molecular adsorbates, mainly due to technical difficulties in preparing the sharp metal tips. However, it has been demonstrated that the FEM-method is capable of monitoring adsorbate motion or diffusion on a substrate via fluctuations in the electron emission. In fact, the method has become one of the most important tools for measuring the diffusion coefficient of adsorbates on metal surfaces [90GOM]. In one experiment the temporal variation of the emitted electrons has been studied on the picosecond time-scale, thus allowing the observation of the motion of a single adsorbed atom [93HEI]. Recently the method has been extended to study fluctuations in the course of a surface chemical reaction in adsorbed molecular adlayers on a Pt-substrate [99SUC]. In field ion microscopy (FIM), basically the same setup is used as in FEM (see Fig. 11), but with a reversed polarity (positive tip) of the applied voltage. Imaging is carried out by introducing an appropriate gas (e.g. He, Ne) into the chamber. When the gas atoms come close to the metal tip they experience an electric field of increasing strength, which can be made strong enough to cause field ionization. The positive ions are then accelerated in the radially symmetric field and generate an image of the field desorption tip with atomic resolution. Although the method cannot be applied to image adsorbates directly, it has been the basis for one of the first methods used for chemical surface analysis, the atom probe [68MUE]. More recently an improved version of the method, pulsed field desorption mass spectrometry (PFDMS), has been applied to identify adsorbate products [89KRU] as well as to study surface reactions and to determine kinetic parameters, e.g. in the case of CO and NO on Rh-crystals [97KRU].

2.6.2 Transmission Electron Microscopy (TEM) So far investigations of the geometric structure of adsorbate overlayers by transmission electron microscopy have only been possible using the transmission and diffraction of very high energy electrons (several 100 keV). The method has been successfully applied for structure determination of metallic overlayers on semiconductor substrates (e.g. In/Si(111)[97COL], Ge/Si(111)[96LEG], (Au + Cu)/Si(111) [91HOM]). For molecular and organic adsorbates the applicability of the method is limited because of the rather low threshold for radiation induced damage (dissociation). For large molecules, e.g. proteins, however, the adlayer can be coated with thin metal overlayers which can then be imaged with electron microscopy [91AMR].

2.6.3 Low Energy Electron Microscopy (LEEM) The use of electrons with low energy (< 200 eV) to obtain structural information on adlayers by either direct imaging or rastering is limited by the fact that the performance of electron optical elements at such low energies is rather poor. Bauer and coworkers, however, have developed a special type of electron microscope, where the electrons are first accelerated to high kinetic energies, focussed, and subsequently decelerated to low energies before they impinge on the surface [98BAU]. After the interaction they are again accelerated to high energies and focussed on a channel plate using standard high-voltage electron optics. Although the lateral resolution is limited to about 100 Å, steps of monatomic height are clearly visible in the micrographs. Numerous works have been carried out for adsorbate overlayers [99LEEM], including the motion of reaction fronts on single crystalline surfaces.

2.6.4 Photoemission Electron Microscopy (PEEM) In conventional electron microscopy the imaged electrons are generated by reflection, diffraction or transmission of the primary electrons directed from an external source towards the specimen. In contrast, photoemission electron microscopy employs an external photon source to generate electrons internally by Lando lt -Bö rnst ein New Series III/42A2

Ref. p. 2-35]


2-23

photoemission. By combining an ultraviolet lamp, generating photons with an energy slightly less than the work-function of the substrate, with a conventional electron optical system, images of adsorbate-covered regions on a surface can be obtained by employing the adsorbate-induced lowering of the work-function: photoelectrons are emitted only on patches covered with an adsorbate, thus allowing for real-time studies of changes in the shape of the patterns, e.g. resulting from diffusion (see e.g. the case of K on Pd(111) [98SNA]) or reaction fronts running across a substrate surface, e.g. in the case of CO oxidation on Pd(100) [97ASA]. The imaging-contrast described above is based on the difference in work-function and thus is not intrinsically element-specific. When a photon source in the soft X-ray regime is available, however, maps showing the distribution of a specific element on the surface can be generated by first recording images for photon energies slightly above and below a characteristic absorption edge of the particular element and then computing the difference of the two maps. If the electron optics additionally are augmented by an energy-filter and the experiments are carried out using the high brilliance of a third-generation synchrotron, a large variety of new imaging techniques becomes available [98WIC], which is too expansive to be covered here in detail.

2.6.5 Miscellaneous Many of the optical techniques, e.g. SHG, can be converted into a microscopical technique by simply focussing the incident beam. For example in the case of SHG (see chapter on SHG) a resolution of 5 µm has been achieved in a study on the diffusion of Sb on Ge(111) [92SCH].

Piezo-tube

2.6.6 Scanning Tunneling Microscopy (STM)

Preamplifier

Adjustment of tunneling gap

Tunneling voltage

Computer and display

Fig. 12. In scanning tunneling microscopy, STM, the distance between a metal tip and a conductive substrate with a small potential difference (typ. 0.1 eV – 2 eV) is reduced until quantum mechanical tunneling leads to the flow of a small current. When the tip is scanned across the surface a feedback electronic readjusts the distance so as to keep the current constant. The corresponding feedback signal can then be used to generate a topographical image of the substrate.

Among the different microscopical techniques applied for the investigation of adsorbate layers, scanning tunneling microscopy has so far found the most widespread application, mostly due to its fairly straightforward implementation [93WIE]. In this technique the distance between a sharp metal tip and a substrate is decreased until quantum-mechanical tunneling generates small currents even for small (< 2V) voltages across the gap. When the tip is moved along the surface (see Fig. 12), this current will change due to variations of the gap between tip and surface. With the help of a feedback system the gap can be readjusted and the corresponding feedback signal is used to create an image of the surface. In case of clean metal surfaces these images contain mostly topographical information, and adsorbed particles can be imaged in a straightforward fashion provided that the motion of the particle along the surface is substantially slower than the scanning of the tip. Generally, lowering the temperature will decrease the diffusivity of adparticles and at cryogenic temperatures even noble gas atoms can be stably imaged [90EIG]. It has been demonstrated that the STM-tip can also be used as a tool to displace and move Landolt -Börnst ein New Series III/42A2

2-24


[Ref. p. 2-35

adsorbed particles in a controlled fashion (Xe atoms [90EIG], O2-molecules [97BRI], CO-molecules [97BAR]). The STM-tip has also been successfully used to assemble nanostructures, which in turn can be used for further experiments [93CRO], [96CRO]. In case of adsorbates it becomes important that the STM-images, when recorded in the so-called constant current mode, actually correspond to lines of constant electron density at the substrate Fermi level. As a result, atomic and molecular adsorbates which locally decrease the density of states at the Fermi level create depressions in the STM micrographs rather than protrusions as might be expected naively. In principle the STM can also be used to derive information on the electronic structure of the surface by measuring the current through the tip as a function of the applied voltage (so-called I(V)-curves). The method thus also offers the possibility to directly determine the local density of electronic states, both above and below the Fermi edge. By evaluation of the second derivative of the I(V)-curves it has very recently also become possible to measure molecular vibrations of adsorbed molecules. In the case of acetylene (C2H2) adsorbed on Cu(001) the C-H-stretch mode at 358 meV could be clearly identified [98STI]. Frequently, images recorded by STM are also used to determine information on surface crystallography, in particular lattice constants of two-dimensional periodic structures. In principle STM can be calibrated against the lattice-constant of the substrate under investigation; however, the imaging process can significantly distort the adsorbate overlayer. In the case of molecular overlayers on graphite systematic errors as large as 10% have been reported [93DAI]. Today STM is becoming a standard technique in the structural characterization of conducting surfaces (metals, semi-conductors). For insulators the situation is hampered by the lack of conductivity, but materials like TiO2 have successfully been imaged at higher temperatures [99BEN]. A major drawback of STM is the lack of chemical sensitivity. Despite significant effort and several promising developments a routine procedure is not yet in sight to reliably determine the type of atom imaged with the STM. The technique is not limited to ultrahigh vacuum and studies at ambient pressure and in the liquid phase are carried out routinely.

2.6.7 Atomic Force Microscopy (AFM)

Laser

Detector A B C

Height h ~ (A+B) - (C+D)

Lateral-Force F ~ (A+C) - (B+D)

Cantilever motion of sample

F

h

D x-, y-, zScanner

x

x

Fig. 13. In scanning force microscopy, SFM, or atomic force microscopy, AFM, the force between a sharp tip and a substrate is determined by measuring the deflection of a flexible cantilever. Scanning the tip across the substrates then yields the morphology of the substrate. Several imaging modes are possible with modern instruments, including the detection of the lateral force (on the right).


Ref. p. 2-35]


2-25

In scanning force microscopy, or SFM (also known as atomic force microscopy, AFM), a sharp tip at the end of a cantilever is approached towards a substrate while monitoring the force between tip and substrate. Using specially designed cantilevers the sensitivity can be increased to a point where the attraction (originating from van der Waals forces) between tip and substrate can be detected. Depending on the particular requirements, the distance can be reduced further up to the point where the short-range repulsive (instead of the long range attractive) forces dominate. Using a feedback system in a similar fashion as in STM (see above) the tip is scanned across the surface while keeping the force between tip and surface constant by readjusting the distance between tip and surface. Compared to STM the technique has the advantage that electrical conductivity of the substrate is not required. With regard to the characterization of adsorbed layers, however, atomic force microscopy, is not quite as powerful as STM, since the resolution is somewhat limited. The resolution of single adsorbed molecules has been reported in few cases, e.g. for alkanethiolate adlayers adsorbed on Au-substrates [92ALV]. Very recently highresolution images have also been obtained for the case of Xe-adlayers grown on a graphite substrate [99ALL]. A striking advantage of AFM in comparison to STM and other surface science techniques is the fact that AFM can be used for virtually all types of solid materials (including insulators) under ambient conditions and for substrates immersed in liquids in a rather straightforward fashion. As a result, AFM is becoming a standard technique for the structural characterization of materials [92BRU]. Despite significant efforts in connection with a chemical functionalization of the scanning tip, a major limitation of AFM is the lack of chemical sensitivity.

2.7 Vibrational spectroscopy of adsorbed particles A11

A12

O

O

O

O

C

C

C

C

Ni

Ni

Ni

Ni

E 4

E 3

Fig. 14. An adsorbed molecule shows characteristic vibrational frequencies which provide important information on the adsorption site and on the chemical interaction with the substrate. Whereas the internal vibrations like the internal stretch ν1 of the CO-molecule shown in the top can be compared to the corresponding values in the gas-phase, the socalled external vibrations, ν2–ν4, exist only in for the adsorbate.

With regard to the identification of adsorbed molecular species, vibrational spectroscopy plays a key role. For determining the stoichiometry of a molecule other methods are better suited (e.g. XPS), but the chemical state of an adsorbed molecule can be best identified by vibrational spectroscopy. This is in part due to the fact that a vast amount of data exists for bulk compounds. For example the comparison of C–O stretch frequencies in metal-organic compounds like nickeltetracarbonyl, Ni(CO)4, with corresponding data for the surface species allows important conclusions to be drawn about the nature of the molecular adsorbate. In many cases the number of modes observed in vibrational spectroscopy provides direct information on the symmetry of the adsorption site. It has been found that in many cases the frequency of internal stretching modes shows a correlation with the adsorption site. For example the internal vibration Lando lt -Bö rnst ein New Series III/42A2

2-26


[Ref. p. 2-35

has been demonstrated to significantly vary between the gas phase, for an on-step species e.g. on a Pt(111)-surface and for a bridge-species on the same surface. However, this correlation should be applied with great care since recently a number of exceptions from a simple correlation between vibrational frequency and adsorption site has been reported (CO/Pd(110) [93WAN], CO/Ni(111) [93SCHb], NO/Pt(111)+NO/Ni(111) [93MAT], NO/Ni(111) [93MAP], N2/Ni(110) [96BER]).

2.7.1 Electron Energy Loss Spectroscopy (EELS) In connection with the determination of the vibrational excitations of clean and adsorbate-covered surfaces the technique which has had the greatest impact is electron energy loss spectroscopy (EELS). Electrons with energies of typically between 2 and 400 eV are first monochromatized, then scattered off a surface and finally detected using an energy analyzer. During the interaction with the sample, energy can be transferred to the sample in the form of elementary excitations (electronic transitions, substrate phonons, adsorbate vibrations). In addition to the energy of the respective excitation the polarization of the particular vibrational mode and the momentum (in case of ordered structures) can be determined by recording energy loss spectra at scattering angles different from the specular. With regard to vibrational spectroscopy the technique is mostly applied to the energy range between 10 and 400 meV, but studies at lower energies have also been reported. Measurements at larger energy transfers probe electronic excitations (intramolecular, inter- and intraband transitions), from which detailed information on the electronic structure of the surface can be derived. For electron energy loss spectroscopy, two scattering regimes with different scattering geometries can be identified. If electrons are detected in the specular or near specular direction (to within a few degrees), the so-called dipole scattering regime, the excitation of vibrations is governed by a dipole mechanism. In close analogy to IR-spectroscopy (see below), in this regime only vibrations with transition dipole moments orientated perpendicular to the surface can be observed. For example in case of hydrogen adlayers adsorbed on W(001) only the totally symmetric modes, where the H-atom is displaced normal to the surface, can be observed [87WOO]. For scattering angles significantly away from the specular direction the intensity for the dipole mechanism typically drops by several orders of magnitude and excitations dominated by another mechanism, impulsive scattering [82IBA], can be detected. In this regime also vibrations with non-perpendicular orientations of the transition dipole moment to the surface become visible in the experimental spectra. An example is H/W(001), for which impulsive scattering reveals those modes where the H-atom vibrates parallel to the surface [87WOO]. Measurements in this impulsive regime are also very important for the detection of surface vibration (phonon) dispersion curves, which carry information on the interaction between adsorbed particles [91WOE]. The method can be directly applied to metal and semiconductor substrates; however, in the case of insulators charging problems can make measurements very difficult. Nevertheless, it has been possible to overcome this limitation in many cases and high-quality EEL-spectra have been obtained, e.g. for hydrogen adlayers on diamond C(111) [94AND].

2.7.2 Infrared Reflection-Absorption Spectroscopy (IRAS) The standard technique for probing the vibrational excitation spectrum of molecular materials in the bulk is infrared absorption spectroscopy. Photons in the infrared regime (400 – 4000 cm-1) can be absorbed by excitation of vibrations with appropriate frequencies. Since photons in the IR-regime are not intrinsically surface sensitive, the application of the technique for problems related to surface science is hampered by the small absorbance of an adsorbed monolayer. For a saturated monolayer of CO molecules, a rather favorable case, the extinction has been found to vary between 1.7 x 10-3 for CO on Pt(111) [92HOL] and 1.4 x 10-2 for CO on Cu(111)[88RAV]. In addition, on metal surfaces electric fields are rather effectively screened. At the surface of a metal, this screening is very strong parallel to, but less effective normal to the surface. This effect is the basis of the so-called IR surface selection rule, which states that in


Ref. p. 2-35]


2-27

IR-spectroscopy only vibrations exhibiting transition dipole moments orientated normal to the surface can be detected. An important application of this technique is the determination of orientation (e.g. tilt-angle of molecular axis) in ultrathin organic layers on metal and semiconductor substrates, e.g. organothiols adsorbed on Au or organosilanes adsorbed on Si. This method works by comparing spectra recorded at grazing incidence for the monolayer (typically the spectra are recorded in ambient) to the corresponding bulk data [92PAR]. Compared to electron energy loss spectroscopy (EELS), the technique offers a significantly higher resolution (refined apparatuses can reach values of 0.005 cm-1 and better). Experimental halfwidths as low as 0.025 cm-1 have been reported for physisorbed monolayers, e.g. CO-adlayers on NaCl(001) [96HEI]. Since, however, the experimental setup for recording IR-spectra of adsorbed monolayers on substrates mounted in an UHV-apparatus is somewhat more complicated, EELS is the more versatile technique. On the other hand, IR-spectroscopy can be applied to insulators in a straightforward way and can be used outside vacuum if the problems related to the absorption by the ambient gas can be overcome. Very recently synchrotrons have been used as a source for infrared radiation. Despite the significant experimental effort, this approach extends investigations towards the far-infrared [90HIR]. A particular exciting result is the fact that by monitoring the reflectivity of an adsorbate covered metal surface vibrational modes can be seen which are invisible in conventional IR-spectroscopy due to the „surface selection rule“ (see above)[94HIR]. In addition the radiation coming from single electron bunches in the storage ring can be employed for time-resolved studies down to the nanosecond-regime [99LOB].

2.7.3 Surface Enhanced Raman Spectroscopy (SERS) In Raman spectroscopy an intense light beam (typically from a laser source) illuminates the sample, and the amount of inelastically scattered light is determined as a function of wavelength. From the resulting spectra the vibrational frequencies of adsorbed species can be determined and used to identify the adsorbates, similar to the case of IR-spectroscopy. Note, that the selection rules for Raman spectroscopy and IR-spectroscopy are different. For application to adsorbate adlayers normal Raman spectroscopy lacks sensitivity, although recently the method could be applied to detect vibrations on clean and adsorbate covered semiconductor surfaces (e.g. Sb and Bi adsorbed on GaAs(110) [98HAI]). For significantly curved („rough“) metal surfaces in certain cases a huge amplification of the signal is observed and forms the basis for a technique which has been dubbed surface enhanced Raman spectroscopy (SERS) [85MOS]. The strong amplification is assigned to a coupling between the light and surface plasmons of the curved metal surface and has made possible a number of studies in ultrahigh vacuum as well as on the liquid/solid interface [99HAI].

2.7.4 Inelastic scattering of He-atoms In addition to obtaining structural information about adsorbate overlayers on a surface, He-atom scattering is also suited to obtain information on adsorbate vibrations. By using a time-of-flight technique the amount of energy exchanged with the surface can be determined and used to infer on the vibrational excitation spectrum of a surface. The technique has mostly been applied to study thermal energy (< 25 meV) external vibrations. These are particular normal modes of the adsorbed particle, where the whole molecule performs periodic motions relative to the surface. These modes, which were first seen for CO adsorbed on Pt(111) [86LAH], carry important information on the potential energy surface, which governs the motion of a particle along a surface [96HOF]. For larger molecules, also internal vibrations like the so-called xylophone-mode in n-octane are located in the thermal energy regime and can be detected with He-atom scattering [97WIT]. The energy resolution of He-atom scattering is sufficiently high (< 0.1 meV or < 0.8 cm–1) to determine the vibrational lifetime via an analysis of the profile of the corresponding


2-28


[Ref. p. 2-35

loss-peaks and thus to draw important conclusions on the damping-mechanism of molecular motion relative to a surface [98WIT], an issue directly related to wearless sliding friction [99PER]. Important information on interaction of adsorbates with the substrate can also be obtained by comparing the surface phonon dispersion curves before and after the adsorption. In the case of hydrogen adsorption the effects are small for most cases (e.g. H on Pt(111)[89BOR]), in some cases rather striking differences are seen( H on W(110), [92HUL]). Although for an adsorbate the interaction between adsorbate and substrate is of primary interest, also the interaction between the adsorbates is of importance for a detailed understanding of e.g. two-dimensional phase transitions. Information on the interaction between adjacent adparticles can be derived from analyzing the corresponding phonon dispersions curves for the frustrated translations. For example in case of CO-adlayers for most metals only weak adparticle-adparticle interactions are found [97BRA]. The method is sufficiently sensitive to check whether e.g. Xe-Xe interactions in a physisorbed monolayer on Cu-surfaces differ from those seen in the gas-phase [97GRA]. The ultimate resolution available today with a state-of-the-art He-atom scattering apparatus is better than 100 µeV and allows to study diffusion of adsorbates on surfaces by analyzing the energetic width of the quasi-elastic scattering peak [88FRE]. The method has been applied to quite different systems, e.g. H/Pt(111) [99GRA] and Xe/Pt(111)[99ELL]. Since the probe particles used in He-atom scattering carry no charge, the method can be applied to all kinds of substrates. Limitations apply to the maximum energy which can be detected with this technique. So far the detection of vibrations above 30 meV has been limited to only very few cases.

2.8 Techniques probing the electronic structure To understand the nature of the interaction between an adsorbate and a substrate it is of paramount interest to gather precise information on the adsorption induced changes in electronic structure of both, the adparticle and the substrate. Since very often this type of information is also the key for understanding the theoretical aspects of adsorption phenomena a variety of techniques has been used, depending on the particular kind of information desired.

2.8.1 Ultraviolet Photoelectron Spectroscopy (UPS)

Continuum

eh fixed

Count rate

Electron energy

to electron energy analyzer

Fig. 15. In ultraviolet photoelectron spectroscopy, or UPS, photons in the UV-regime (10-100 eV) generate photoelectrons. From the electron kinetic energy as determined by an energy analyzer the positions of occupied electronic states can be determined.

In the case of ultraviolet photoelectron spectroscopy, photons in the energy range of up to 100 eV are used for the primary excitation process. As a result, information on core-level binding energies cannot be obtained and the type of elements present on a surface cannot easily be determined. The photoelectrons emitted from the sample upon absorption of an UV-photon originate from more weakly bound electronic


Ref. p. 2-35]


2-29

states, and the photoelectron spectra thus provide direct information of the valence levels, see Fig. 15. In particular for adsorbates such data allow for important conclusions on the adparticle-substrate and the adparticle-adparticle interaction. The method also makes a more reliable identification of an adsorbed molecule possible. As an example the distinction of adsorbed C2H4 and C2H6 (which is very difficult with XPS, see above) causes no problem in this case, since the occupied π-orbital of C2H4 (which is absent in C2H6) can easily be seen with UPS. In many cases the comparison of UV-spectra of adsorbed molecular species with the corresponding data for the gas phase provides precise information about the changes of the molecular electronic structure upon adsorption of the molecule. Depending on the symmetry of the adsorbate, the technique can also be used to infer on the orientation of the adsorbed molecule by using polarized photons and by employing the dipole selection rules. As an example, the UPS-technique has been employed to decide whether a linear (unbrachned), saturated hydrocarbon (n-alkane) is adsorbed with its C-C-C-plane normal or parallel to the substrate [97WEC]. In the case of ordered adlayers, the dispersion of adsorbate-induced valence states can be determined with UPS by restricting the angular acceptance of the energy analyzer. From data obtained by this so-called angular resolved ultraviolet photoelectron spectroscopy (ARUPS) method the electronic bandstructure can be determined, from which in turn important information on the adsorbate-adsorbate interaction can be extracted [92WEI]. The technique can also be used to determine the work-function Φ and the adsorption-induced workfunction changes ∆Φ by analyzing the position of the secondary electron cut-off at low binding energies in the UPS data [94HOF]. The application of the technique and the interpretation of the experimental results is not as straightforward as in the case of XPS (see above). As in the other variants of photoelectron spectroscopy the application is difficult for insulating substrates. UPS is still the standard method for obtaining information on the electronic structure in the valence regime (binding energies < 30 eV), although – at least in cases of metal substrates – small changes in the molecular electronic structure are observed by the superimposed electronic structure of the substrate.

2.8.2 Inverse Photoemission (IPE)

Photon energy

e-

Fig. 16. In inverse photoemission, or IPE, an incident electron is temporarily trapped in an unoccupied molecular orbital typically several eV above the Fermi edge, from where it can decay to an low-lying empty orbital (at the Fermi edge) by photon emission.

Count rate

In principle this technique is a reversed version of ultraviolet photoelectron spectroscopy, or UPS. The Bremsstrahlung emitted when low energy electrons are decelerated and absorbed in a sample is analyzed using a monochromator. The resulting emission spectra (see Fig. 16) contain structures, from which the position and dispersion of the unoccupied electronic levels at a surface can be determined by computing the difference between the incident electron energy and the energy of the emitted photons. The technique thus provides information complementary to UPS, where the occupied states are probed. The application of the method to adsorbates is not straightforward since the resulting photon emission intensities are very low and the obtainable resolution is rather limited. Despite these experimental problems, it has been possible to determine the position and dispersion of unoccupied electronic states for a number of different


2-30


[Ref. p. 2-35

adsorbate systems, including molecular adlayers, e.g. carbon monoxide chemisorbed on Ni(110) [89MEM]. The method can in a straightforward fashion applied only to conducting (metal) substrates.

Continuum

h variable Absorption

Photon enenergy h

2.8.3 Near Edge X-ray Absorption Fine-Structure Spectroscopy (NEXAFS)

Fig. 17. In NEXAFS-spectroscopy a core electron is excited into an unoccupied molecular orbital by absorption of a X-ray photon. The absorption spectrum (right) shows sharp maxima when the photon energy matches the corresponding difference of the electronic orbitals.

One major problem concerning the evaluation of the electronic structure of an adsorbate is the fact that with the standard technique, ultraviolet photoelectron spectroscopy, or UPS, only the total sum of all electronic states is observed. There is no way, a priori, to determine whether the electronic states giving rise to a particular feature in the UP-spectra are localized mainly at the adsorbate (i.e. backdonation from a metallic substrate as in the case of CO adsorbed on transition metal surfaces), or in the substrate (e.g. donation from an adsorbed particle into the substrate) or whether it is due to states best described by a hybridisation between molecular and adsorbate states. In particular for transition metals with their d-bands located close to the Fermi edge the UPS-data are typically dominated by emission from these d-states, and subtle changes are virtually impossible to detect. A typical example for such an interaction is the case of saturated hydrocarbons, where the changes in electronic structure accompanying the so-called CH-stretch „soft modes“ seen in EELS [78DEM] and IR-spectroscopy [93RAV; 95HOS] could not be seen with UPS [98WIT]. Another technique, X-ray absorption spectroscopy, however, has been successfully employed to image these states. Here the application of X-ray absorption spectroscopy in the vicinity of the K-edges of low-Z elements (most important: C, N, O) offers significant advantages, since by the excitation process only elements of one type (e.g. the carbon atoms) are addressed. In X-ray photoelectron spectroscopy (XPS) (see above) the experimental information is obtained by analyzing the kinetic energy of the photoelectrons generated by the absorption of photons of fixed energy. In X-ray absorption spectroscopy the absorption of X-ray photons is measured as a function of photon energy. Accordingly, the technique requires a tunable X-ray source and can only be carried out at an electron synchrotron. The principle of this soft X-ray absorption spectroscopy (the commonly used acronym is NEXAFS, for near edge X-ray absorption fine structure spectroscopy) is schematically depicted in Fig. 17. For photon energies above the ionization threshold the core-electron is excited into a continuum state corresponding to a free electron with a positive kinetic energy. If the photon energy lies below the ionization threshold, absorption is only possible if the photon energy matches the difference in energy between the initial state (typically a core level, e.g. C1s, N1s, O1s) and an unoccupied molecular orbital. In that case the excitation process does not lead to an ionized, but rather to a quasibound state. In contrast to EXAFS (see above), here only the near edge regime (intervals of 50 eV) is investigated. The NEXAFS-technique is mainly used for deriving two different types of information. First, the spectroscopical data are useful in determining the electronic structure of an adsorbate. In the case of acetylene (C2H2), for example, adsorption on a Cu-surface leads to a splitting of the two π-levels, which are degenerated in the gas-phase. The technique can thus be used to obtain information about the electronic structure and is complementary to ultraviolet photoelectron spectroscopy (UPS) in the sense that unoccupied states are observed. The main advantage over UPS stems from the fact that in NEXAFS Lando lt -Bö rnst ein New Series III/42A2

Ref. p. 2-35]


2-31

the matrix elements governing the excitation process are large only for final states with significant contributions from atomic orbitals localized at the core-excited atom. As an example, in the case of hydrocarbons adsorbed on transition metal surfaces, pure metal states are not observed, which considerably simplifies the analysis of the experimental results [99WEI]. A second important application of this technique is the determination of molecular orientation within an adsorbed overlayer. Since the X-rays generated in the electron synchrotron by deflecting electrons with energies in the 1 GeV range are polarized with the E-vector orientated parallel to the plane of the synchrotron, the X-ray absorption dichroism can be conveniently measured by recording absorption spectra for normal and grazing incidence, respectively. From measurements at different angles of incidence one can thus obtain the orientation of the transition dipole moment with respect to the surface normal, from which in turn the orientation of the molecule can be derived. For many adsorbates the adsorption process is accompanied by molecular distortions, e.g. an aplanar, out-of-plane bend of the C-H-bonds in benzene adsorbed on transition metal surfaces [95MAI]. In the case of hydrocarbons, such distortions are difficult to detect with photoelectron diffraction or X-ray diffraction, because the scattering cross-section of the H-atoms for electrons and X-ray photons is very small. NEXAFS, on the other hand, is sensitive to the accompanying changes in symmetry of the molecular orbitals and can thus be used to determine these distortions in a semiquantitative fashion. Using this method it could also be demonstrated that ethylene, C2H4, adsorbs on a Cu(001)-surface in an essentially undistorted, planar adsorption geometry, whereas acetylene, C2H2, on the same surface shows a significant tilt of the C-H-bonds away from the C-C-bond [98FUH]. NEXAFS can be applied to a large number of adsorbate/substrate combinations. If the absorption is detected via the secondary electron yield, highly insulating substrates represent a problem. The situation is, however, considerably better than in conventional photoelectron spectroscopy, since small (several eV) shifts in the kinetic energy of the secondary electrons do not affect the positions of resonances in the spectra. Charging problems are eliminated by employing the X-ray fluorescence to monitor the absorption (Fluorescence Yield Near Edge Structure or FYNES) instead of the secondary electrons.

Kontinuum Continuum

h’

h fixed h fest Intensity Intensität

h’ Photonenenergie Fluorescent Photon enenergy h’

2.8.4 Resonant X-ray Emission Spectroscopy (XES)

Fig. 18. In X-ray emission spectroscopy, or XES, the energy distribution of the X-ray photons emitted after the primary absorption process is determined using a second monochromator.

Although NEXAFS-spectroscopy has obvious advantages over the standard technique to determine electronic structure, namely UPS, the interpretation and theoretical analysis of the data suffers to some extent from the fact that the final state of the excitation process is characterized by the presence of a corehole. The presence of such a core-hole can be described by increasing the atomic number Z by 1 (so called equivalent cores approximation), and as a result the binding energies of the electronic states are significantly lowered. Although the theoretical analysis of this situation can be handled by explicitly considering the presence of the core-hole, it is not the true ground state which this spectroscopy probes. Only recently has this problem been overcome by establishing a much more sophisticated variant of this technique, namely resonant X-ray emission spectroscopy, XES. Landolt -Börnst ein New Series III/42A2

2-32


[Ref. p. 2-35

In X-ray emission spectroscopy, it is the X-ray radiation emitted when a second electron undergoes a transition to the core-hole generated in the primary X-ray absorption process, that is detected with an energy dispersive analyzer, see Fig. 18. Principally, this process is the same as that used in electron microscopes for the EDX (energy dispersive X-ray detection) technique where core-holes excited by the high-energy (typ. 10 keV up to several 100 keV) electrons give rise to X-ray fluorescence, which is measured by energy-dispersive semiconductor detectors with a resolution of typically 100 eV. With this kind of resolution it is only possible to determine the different elements present in a sample. When the resolution is increased to beyond 1 eV by using a X-ray monochromator, additional information on the electronic structure of the sample can be obtained. If furthermore soft X-ray photons are used for the excitation process, the technique can be applied to investigate final states which are basically the same as probed with UP-spectroscopy. The striking advantage over UPS, however, is the fact that only final states with electron densities around a given element are imaged, e.g. in the case of saturated hydrocarbons on a transition metal surface pure metal states are invisible. Although this technique has so far been applied to a few systems only, it is expected that with the availability of third generation synchrotron sources the technique will find a more widespread application.

2.9 Nonlinear optical techniques 2.9.1 Second Harmonic Generation (SHG)

SHG

SFG

Fig. 19. The two nonlinear techniques SHG and SFG employ laser radiation which is so intense that interaction with matter leads to the combination of two photons of the same frequency (SHG, left) or of two photons of different energy (SFG, right).

When the intensity of electromagnetic radiation becomes very intense, in addition to linear effects (electronic and vibrational excitations, Raman scattering, etc.) nonlinear effects become important. This can be described formally by adding higher terms to the Taylor expansion of the polarizability tensor. Experimentally, the second quadratic polarizability term becoming nonzero results in the generation of photons with twice the incident energy, see Fig. 19. In bulk crystals exhibiting inversion symmetry, the second term has to be zero, but for non-centrosymmetric crystals like e.g. β-barium borate (β-BaB2O4) the effect becomes so strong that it can be used for frequency doubling. The relevance of second harmonic generation, or SHG, for the investigation of adsorbate layers becomes apparent when one considers that the mere presence of the surface considerably lowers the symmetry and, in particular, implies the loss of inversion symmetry, even if present in the bulk of the material. As a result, the surface of any substrate can in principle give rise to a SHG-signal. After the sensitivity of SHG to adsorbed layers in the monolayer and submonolayer regime had been demonstrated for a number of systems [89SHE; 94COR], this method has in recent years received considerable attention. Note, however, that this method is useful only for materials with bulk inversion symmetry, since the surface signal is otherwise dominated by that from the bulk. The striking advantage of this method as compared to other methods employed in surface science is the fact that it does not require ultrahigh vacuum. Basically, the only requirement is that there are no other Lando lt -Bö rnst ein New Series III/42A2

Ref. p. 2-35]


2-33

sources for the SHG-signal. Since this condition is generally fulfilled by solids with inversion symmetry, by normal liquids (but not by liquid crystals), and by gases, adsorption phenomena at surfaces can be studied for a large variety of systems. Although this spectroscopic technique is not inherently structure sensitive, the symmetry of both, solid substrate and adsorbate overlayer can be mapped by using polarized light. One of the first SHG-experiments carried out in connection with adsorbates on solid substrates in an ultrahigh-vacuum environment were measurements on the diffusion of CO-molecules adsorbed on a Ni(110)-surface [91XU]. In this experiment, first a pattern of regularly spaced stripes of adsorbed CO-molecules is generated using a laser beam. By detecting the SHG-signal diffracted from this grating the temporal decay of the pattern could be monitored and analyzed in terms of a diffusion constant. By orienting the diffraction pattern with regard to the substrate, anisotropies in the diffusion coefficient could also be studied [91XU]. In later work the technique has been used to follow adsorption/desorption phenomena at the solid-gas interface for pressures up to 1 atm. Investigations have also successfully been performed at the solid/liquid interface, e.g. the adsorption of organothiols from an ethanolic solution on a solid Au-substrate could be followed in real time [99DAN].

2.9.2 Sum Frequency Generation (SFG) The technique of sum frequency generation, or SFG, is related to the SHG technique discussed above. In contrast to SHG, where the incident laser beam consists of photons of one wavelength only, in SFG two different types of photons with frequencies ν1 and ν2 are used. At sufficiently high intensity this will not only generate photons with twice the energy of the incident photons, 2⋅ν1 and 2⋅ν2, but the nonlinear effects will in addition lead to the emission of photons with an frequency equal to the sum of the different frequencies, ν1 + ν2. By using one wavelength in the visible part of the spectrum and a second, tunable laser in the IRregime, the intensity of the SFG signal can be determined as a function of IR-wavelength. Also in this case the sensitivity to adlayers in the submonolayer coverage regime has been demonstrated [95BAI] [89SHE]. By a symmetry analysis it can be demonstrated that molecular vibrations which are both IR- and Ramanactive can be seen. The current large interest in this method results from the fact that vibrational spectra of adsorbed species which provide information complementary to IR can be recorded under non-vacuum conditions. As an example, very recently the technique has been used to investigate molecular orientations and conformations in confined systems in the context of tribological phenomena [00EIS]. In addition it should be noted that the method can be used to study very fast processes with a time resolution down to the pico/femto second regime. In the past the complexity of the equipment necessary to carry out SFG experiments has limited the number of studies but recent advances in laser technology have strongly reduced the effort (and the expenses) needed to set up an experiment.

2.10 Bulk techniques 2.10.1 Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) Today the characterization of bulk (solid and liquid) chemical compounds, in particular in the absence of crystalline order is dominated by nuclear magnetic resonance (NMR) spectroscopy. Sophisticated spectrometers operating at frequencies of 850 MHz and above can be used to determine the structure and to trace the dynamics of single atoms even in large biological molecules. The application to molecules adsorbed on surfaces, however, is limited by the rather low sensitivity of the technique. So Landolt -Börnst ein New Series III/42A2

2-34


[Ref. p. 2-35

far, studies on surface phenomena on single crystal surfaces with standard NMR (i.e. for nuclear spins in C or H atoms) have not been successfully carried out. It was possible, however, to apply standard NMR-techniques to investigate the dynamics of a lithium isotope, 8Li, adsorbed e.g. on a Ru(0001)surface [96EBI]. A different situation emerges if materials with a very high specific surface are used (compare to neutron spectroscopy). A particular important example are zeolithes [94BEL], where 1H and 13C NMR has been directly used to study the adsorption of CO [92BRU] and benzene [92LIU]. Also powders have been successfully investigated, e.g. reactions of different organic molecules on charcoal [95WAG]. Recently, experiments have been carried out by employing a novel scheme for detecting the NMR resonance. By using a highly sensitive cantilever from an atomic force microscope, it has been possible to increase the sensitivity of the method to a point where the detection of individual nuclear spins - and thus the application to surface phenomena - comes into sight [92RUG; 94RUG]. There is another technique based on the detection of spin resonance phenomena, where instead of the nuclear spin that of an unpaired electron is detected. Although this technique is much more limited than NMR since only molecules (and atoms) with unpaired electrons can be investigated, the technique is several orders of magnitude more sensitive than NMR and, at first sight, appears to be better suited for surface applications than NMR. Unfortunately, however, it has turned out that the application of electron spin resonance, or ESR, to surface problems is severely hampered by the fact that the unpaired electron couples strongly to metallic substrates. As a result, ESR-measurements on adsorbed molecules are virtually impossible [85FAR; 87ZOM]. Substrates with lower electron density and with a significant bandgap, however, provide a better basis and recently ESR has successfully been used to study the molecular motion of NO2 on sapphire (Al2O3)-substrates [95SCH].



2-35

References for 2 27DAVa 27DAVb 30EST 50MUE 68MUE 72KIN 72WIS 74DAV 76FUG 76SCO 77TAU 77TOE 78DEM 78WAG 78WED 79JOI

80HOI 81HER 82FUG 82IBA 83YU

83RIE 84HEI 84UMB

Davisson, C. J., Germer, L. H.: The scattering of electrons by a single crystal of Nickel.: Nature (London) 119 (1927) 558. Davisson, C. J., Germer, L. H.: Diffraction of Electrons by a Crystal of Nickel: Phys. Rev. 30 (1927) 705. Estermann, I., Stern, O.: Beugung von Molekularstrahlen: Z. Phys. 61 (1930) 95. Müller, E. W.: Die Sichtbarmachung einzelner Atome und Moleküle im Feldelektronenmikroskop: Z. Naturforsch. 5a (1950) 473. Müller, E. W., Panitz, J. A., McLane, S. M.: The atom-probe field ion microscope: Rev. Sci. Instrum. 39 (1968) 83. King, D. A., Wells, M. G.: Molecular beam investigation of adsorption kinetics on bulk metal targets: nitrogen on tungsten: Surf. Sci. 29 (1972) 454. Wissmann, P.: The effect of gas adsorption on the conductivity of thin metal films: Thin Solid Films 13 (1972) 189. Davis, D. W., Shirley, D. A.: The prediction of core-level binding-energy shifts from CNDO molecular orbitals: J. Electron. Spectrosc. Relat. Phenom. 3 (1974) 137. Fuggle, J. C., Umbach, E., Menzel, D.: X-ray excited Auger spectra (XAES) from chemisorbed species: Solid State Commun. 20 (1976) 89. Scofield, J. H.: Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV: J. Electron. Spectrosc. Relat. Phenom. 8 (1976) 129. Taub, H., Carneiro, K., Kjems, J. K., Pasell, L., McTague, J. P.: Neutron scattering study of 36Ar monolayer films adsorbed on graphite: Phys. Rev. B 16 (1977) 4551. Toennies, J. P., Winkelmann, K.: Theoretical studies of highly expanded free jets: Influence of quantum effects and a realistic intermolecular potential: J. Chem. Phys. 66 (1977) 3965. Demuth, J., Ibach, H., Lehwald, S.: CH vibration softening and the dehydrogenation of hydrocarbon molecules on Ni(111) and Pt (111).: Phys Rev Lett 40 (1978) 1044. Wagner, C., Riggs, W., Davis, L., Moulder, J., Muilenberg, G.: Handbook of X-Ray Photoelectron Spectroscopy: Perkin Elmer Corporation. Wedler, G.:(1978) The role of adsorption calorimetry in the study of surface phenomena: J. Thermal Analysis 14 (1978) 15. Joite, S., Hoinkes, H., Kaarmann, H., Wilsch, H.: SIMS on ZnO surfaces: the influence of space charge accumulation layers on secondary ion yields and measurement of true hydrogen concentration.: Surf. Sci. 84 (1979) 462. Hoinkes, H.: The physical interaction potential of gas atoms with single-crystal surfaces, determined from gas-surface diffraction experiments.: Rev. Mod. Phys. 52 (1980) 933. Hermann, K., Bagus, P. S.: Core level shake up structures of N2 adsorbed on nickel surfaces: cluster models: Solid State Communications 38 (1981) 1257. Fuggle, J. C., Umbach, E., Kakoschke, R., Menzel, D.: High-resolution Auger spectra of adsorbates: J. Electron. Spectrosc. Relat. Phenom. 26 (1982) 111. Ibach, H., Mills, D. L.: Electron energy loss spectroscopy and surface vibrations: New York: Academic Press. Yu, C., Whaley. K. B., Hogg, C.S.,, Sibener, S.J.,:(1983) Selective adsorption resonances in the scattering of n-H2, p-H2, n-D2, and o-D2 from Ag(111): Phys. Rev. Lett. 51 (1982) 2210. Rieder, K. H.: Low-coverage Ordered Phases of Hydrogen on Ni(110): Phys. Rev. B 27 (1983) 7799. Heilmann, P., Lang, E., Heinz, K., Müller, K.: Determination of Surface Structure by LEED: Marcus, P. M., Jona, F. (eds.), New York: Plenum, 1984. Umbach, E., Hussain, Z.:(1984) Angle-dependent changes of Auger line shapes from adsorbed molecules: Phys. Rev. Lett. 52 (1984) 457.

Lando lt -Bö rnst ein New Ser ies III/42 A2

2-36

85AND 85BEN 85FAR 85MOS 85PUS

86ABE

86LAH 86SCH 87JAC 87LAH

87WIS 87WOO

87ZOM 88FAD 88FRE 88HEI 88ILL

88RAV

88YIN

89BOR

89KRU 89LUN

2 Measuring techniques Andersson, D., Kasemo, B., Wallden, L.: Surface chemiluminescence in the Ksolid+Cl2 gas reaction: Surf. Sci. 152-153 (1985) 576. Benninghoven, A.: Static SIMS applications-from silicon single crystal oxidation to DNA sequencing.: J. Vac. Sci. Technol. A 3 (1985) 451. Farle, M., Zomack, M., Baberschke, K.: ESR of adsorbates on single crystal metal surfaces under UHV conditions: Surf. Sci. 160 (1985) 205. Moskovits, M.: Surface-enhanced spectroscopy: Rev. Mod. Phys. 57 (1985) 783. Puschmann, A., Haase, J., Crapper, M. D., Rieley, C. E., Woodruff, D. P.: Structure determination of the formate intermediate on Cu(110) by use of X-ray-absorption finestructure measurements: Phys. Rev. Lett. 54 (1985) 2250. Abermann, R., Koch, R.: In situ study of thin film growth by internal stress measurement under ultrahigh vacuum conditions: silver and copper under the influence of oxygen.: Thin Solid Films 142 (1986) 65. Lahee, A. M., Toennies, J. P., Wöll, C.: Low energy adsorbate vibrational modes observed with inelastic helium atom scattering: CO on Pt(111): Surf. Sci. 177 (1986) 371. Scheithauer, U., Meyer, G., Henzler, M.: A new LEED instrument for quantitative spot profile analysis: Surf. Sci. 178 (1986) 441. Jacobi, K.: Work-function changes and photoemission final-state relaxation of Ne, Ar, Kr, Xe, H2 and N2 on gallium.: Surf. Sci. 192 (1987) 499. Lahee, A. M., Manson, J. R., Toennies, J. P., Wöll, C.: Helium Atom Differential Cross Sections for Scattering from Single adsorbed CO Molecules on a Pt(111) Surface: J. Chem. Phys. 86 (1987) 7194. Wissmann, P. (ed.): Thin metal films and Gas Chemisorption: Amsterdam: Elsevier. Woods, J. P., Kulkarni, A. D., Erskine, J. L., Wette, F.:(1987) Vibrational properties of beta1-H and beta1-D on W(001): electron-energy-loss measurements and lattice-dynamic calculations: Phys. Rev. B 36 (1987) 5848. Zomack, M., Baberschke, K.: Submonolayers of paramagnetic NO2 adsorbed on argon and xenon films: Phys. Rev. Lett. 36 (1987) 5756. Fadley, C. S.: . Core-Level Spectroscopy in Condensed Systems: Kanamor, J., Kotani, A. (eds.), Berlin: Springer, 1988. Frenken, J. M. W., Toennies, J. P., Wöll, Ch.:(1988) Self-Diffusion at a Melting Surface Observed by He Scattering: Phys. Rev. Lett. 60 (1988) 1727. Heinz, K.: Diffuse low-energy electron diffraction: Prog. Surf. Sci. 27 (1988) 239. Illing, G., Heskett, D., Plummer, E. W., Freund, H.-J., Somers, J., Lindner, T., Bradshaw, A. M., Buskotte, U., Neumann, M., Starke, U., Heinz, K., Andres, P. L. d., Saldin, D., Pendry, J. B.: Adsorption and reaction of CO2 on Ni(110): X-ray photoemission, near-edge X-ray absorption fine-structure and diffuse LEED studies: Surf. Sci. 206 (1988) 1. Raval, R., Parker, S. F., Pemble, M. E., Hollins, P., Pritchard, J., Chesters, M. A.: ETRAIRS, EELS, and LEED studies of the adsorption of carbon monoxide on Cu(111): Surf. Sci. 203 (1988) 353. Yinnon, A. T., Kosloff, R., Gerber, R. B., Poelsema, B., Comsa, G.: Cross sections for He scattering from surface imperfections: vacancies and CO adsorbates on Pt (111): J. Chem. Phys. 88 (1988) 3722. Bortolani, V., Franchini, A., Santoro, G., Toennies, J. P., Wöll, C., Zhang, G.: Surface phonons on the Pt(111) surface: a comparison of He-scattering experiments with latticedynamical calculations: Phys. Rev. B 40 (1989) 3524. Kruse, N., Abend, G., Block, J. H.: Observation of Rh-subcarbonyls on stepped Rh surfaces during catalytic reactions: J. Chem. Phys. 91 (1) (1989) 577-83 Luntz, A. C., Grimblot, J., Fowler, D. E.: Sequential precursors in dissociative chemisorption: O2 on Pt(111): Phys. Rev. B 39 (1989) 12903.

Lando lt -Börnst ein New Ser ies III/42A2

2 Measuring techniques 89MEM

89SCH 89SHE 89WES

90BRA 90EIG 90GOM 90HIR

90KRI 90POR

91AMR

91BOR 91CAM

91HOM 91LAR 91NIL 91PER 91SAN 91WOE 91XU 92ALV

92BOE 92BRU

2-37

Memmel, N., Rangelov, G., Bertel, E., Dose, V., Kometer, K., Rosch, N.: Carbon monoxide chemisorption on a nickel surface: an investigation of unoccupied bands: Phys. Rev. Lett. 63 (1989) 1884. Schweizer, E. K., Rettner, C. T.: Quantum effects in the scattering of argon from 2HW(100): Phys. Rev. Lett. 62 (1989) 3085. Shen, Y. R.: Surface properties probed by second-harmonic and sum-frequency generation: Nature (London) 337 (1989) 519. Wesner, D. A., Coenen, F. P., Bonzel, H. P.: X-ray photoelectron diffraction study of perpendicular and tilted CO on clean and potassium-modified Ni(100): Phys. Rev. B 39 (1989) 10770. Brand, J. L., Arena, M. V., Deckert, A. A., George, S. M.: Surface diffusion of n-alkanes on Ru(001): J. Chem. Phys. 92 (1990) 5136. Eigler, D. M., Schweizer, E. K.: Positioning single atoms with a scanning tunnelling microscope: Nature (London) 344 (1990) 524. Gomer, R.: Diffusion of adsorbates on metal surfaces: Rep. Prog. Phys. 53 (1990) 917. Hirschmugl, C. J., Williams, G., Hoffmann, F., Chabal, Y.: Adsorbate-substrate resonant interactions observed for CO on Cu(100) in the far infrared.: Phys. Rev. Lett. 65 (1990) 480. Krim, J., Watts, E., Digel, J.: Slippage of simple liquid films adsorbed on silver and gold substrates: J. Vac. Sci. Technol. A 8 (1990) 3417. Porwol, T., Illing, G., Freund, H.-J., Kuhlenbeck, H., Neumann, M., Bernstorff, S., Braun, W., Niessen, W. v., Liegener, C. M.: Autoionization versus photoionization of molecular adsorbates: CO2 physisorbed on Ni(100): Phys. Rev. B 41 (1990) 10510. Amrein, M., Wang, Z., Guckenberger, R.: Comparative study of a regular protein layer by scanning tunneling microscopy and transmission electron microscopy: J Vac Sci Technol B 9 (1991) 1276. Borroni-Bird, C. E., Al-Sarraf, N., Andersson, S., King, D. A.: Single crystal adsorption microcalorimetry: Chem. Phys. Lett. 183 (1991) 516. Camillone, N., Chidsey, C. E. D., Liu, G., Putvinski, T. M., Scoles, G.: Surface structure and thermal motion of n-alkane thiols self-assembled on Au(111) studied by low energy helium diffraction: J. Chem. Phys. 94 (1991) 8493. Homma, I., Tanishiro, Y., Yagi, K.: REM and TEM studies of 2D Au-Cu alloy adsorbates on a Si(111) surface: Surf. Sci. 242 (1991) 81. Larese, J. Z., Hastings, J. M.: Rotational tunneling of methane on MgO surfaces: a neutron scattering study: J. Chem. Phys. 95 (1991) 6997. Nilsson, A., Martensson, N.: Core-level shake-up spectra from ordered C, N and O overlayers on Ni (100): Chem. Phys. Lett. 182 (1991) 147. Persson, B. N. J.: Surface resistivity and vibrational damping in adsorbed layers: Phys. Rev. B 44 (1991) 3277. Sander, D., Ibach, H.: Experimental determination of adsorbate-induced surface stress: oxygen on Si(111) and Si(100): Phys. Rev. B 43 (1991) 4263. Wöll, C.: Phonons on surfaces: The importance of structure and adsorbates: Appl. Phys. A 53 (1991) 377. Xu-Dong, X., Zhu, X., Daum, W., Shen, Y.: Anisotropic surface diffusion of CO on Ni(110): Phys. Rev. Lett. 66 (1991) 2352. Alves, C. A., Smith, E. L., Porter, M.D.: Atomic scale imaging of alkanethiolate monolayers at gold surfaces with atomic force microscopy: J. Am. Chem. Soc. 114 (1992) 1222. Böttcher, A., Grobecker, R., Gerber, T., Morgante, A., Ertl, G.: Exoelectron emission during the oxidation of Na films: Surf. Sci. 280 (1992) 170. Brundle, C. R., C.A. Evans, J., Wilson, S., Eds.: Encyclopedia of Materials Characterization: Boston: Butterworth-Heinemann, 1992.


2-38 92BRU 92HAN 92HOL 92HUL 92LIU

92PAR

92RUG 92SCH 92WEI

92WOE

93CRO 93DAI

93DHA

93FEN 93HEI

93MAC

93MAP

93MAT

93NIE 93RAV

2 Measuring techniques Brunner, E., Pfeifer, H., Wutscherk, T., Zscherpel, D.: 13C NMR Investigation on the Adsorption of Carbon Monoxide in H-ZSM-5: Z. Phys. Chem. 178 (1992) 173. Hansen, F. Y., Taub, H.: Melting mechanism in monolayers of flexible rod-shaped molecules: Phys. Rev. Lett. 69 (1992) 652. Hollins, P.: The influence of surface defects on the infrared spectra of adsorbed species: Surf. Sci. Rep. 16 (1992) 51. Hulpke, E., Ludecke, J.: Hydrogen-induced phonon anomaly on the W(110) surface: Phys. Rev. Lett. 68 (1992) 2846. Liu, S.-B., Ma, L.-J., Lin, M. W., Wu, J.-F., Chen, T.-L.: NMR Investigation of the Distribution of Benzene in NaX adn NaY Zeolites: Influence of Cation Location and Adsorbate Concentration: J. Phys. Chem. 96 (1992) 8129. Parikh, A. N., Allara, D. L.: Quantitative determination of molecular structure im multilayered thin films of biaxial and lower symmetry from photon spectroscopies. I. Reflection infrared vibrational spectroscopy: J. Chem. Phys. 96 (1992) 927. Rugar, D., Yannoni, C. S., Sidles, J. A.: Mechanical detection of magnetic resonance: Nature (London) 360 (1992) 563. Schultz, K. A., Seebauer, E. G.: Surface diffusion of Sb on Ge(111) monitored quantitatively with optical second harmonic microscope: J. Chem. Phys. 97 (1992) 6958. Weinelt, M., Huber, W., Zebisch, P., Steinrück, H.-P., Reichert, B., Birkenheuer, U., Rosch, N.: Ethylene adsorbed on Ni(110): an experimental and theoretical determination of the two-dimensional band structure: Phys. Rev. B 46 (1992) 1675. Wöll, C., Lahee, A. M.: Investigation of surface imperfections by diffuse scattering of Heatoms. Helium Atom scattering from surfaces: Hulpke, E.:(ed.), Springer Series in Surf Sci, Heidelberg: Springer Verlag, 1992. Crommie, M. F., Lutz, C. P., Eigler, D. M.:(1993) Confinement of electrons to quantum corrals on a metal surface: Science 262 (1992) 218. Dai, P., Wang, S.-K., Taub, H., Buckley, J. E., Ehrlich, S. N., Larese, J. Z., Binnig, G., Smith, D. P. E.: X-ray-diffraction and scanning-tunneling-microscopy studies of a liquidcrystal film adsorbed on single-crystal graphite: Phys. Rev. B 47 (1993) 7401. Dhanak, V. R., Baraldi, A., Comelli, G., Paolucci, G., Kiskinova, M., Rosei, R.: CO adsorption on unreconstructed and reconstructed Rh(100) surfaces: LEED and XPS studies: Surf. Sci. 295 (1993) 287. Fenter, P., Eisenberger, P., Liang, K. S.: Chain-length dependence of the structures and phases of CH3CH2 n-1SH self-assembled on Au(111): Phys. Rev. Lett. 70 (1993) 2447. Heinzelmann, H., Watanabe, F., McClelland, G. M.: Observing the Motion of a Single Adsorbed Atom with Picosecond and Subnanometer Resolution: Phys. Rev. Lett. 70 (1993) 3611. Maciejewski, P., Hofer, U., Wurth, W., Umbach, E.: Determination of adsorbate orientation by means of angle-resolved Auger fine structure: CO on Ni(110): J. Electron. Spectrosc. Relat. Phenom. 62 (1993) 1. Mapledoram, L., Wander, A., King, D.: Breakdown of adsorbate site assignment from vibrational frequencies. NO on Ni(111) revisited by tensor LEED: Chem. Phys. Lett. 208 (1993) 409. Materer, N., Barbieri, N., Gardin, D., Starke, U., Batteas, J. K., Van Hove, M. A., Somorjai, G. A.: Dynamical LEED analyses of the Pt(111)-p(2x2)-NO and the Ni(111)-c(4x2)-2NO structures: substrate relaxation and unexpected hollow-site adsorption.: Phys. Rev. B 48 (1993) 2859. Niehus, H., Heiland, W., Taglauer, E.: Low-energy ion scattering at surfaces: Surf. Sci. Rep. 17 (1993) 213. Raval, R., Parker, S. F., Chester, M. A.: C-H...M interactions and orientational changes of cyclohexane on Cu(111): a RAIRS, EELS and LEED study: Surf. Sci. 289 (1993) 227.


2 Measuring techniques 93SCHb

93SCHb

93WAN

93WIE

93YOU 93ZEG 94AND

94BEL 94COR 94GIM 94GRO

94GRO 94HIR 94HOF 94PER 94POR

94RIE 94RUG 95ARV 95BAI 95HOS

95MAI

2-39

Schindler, K. M., Hofmann, P., Fritzsche, V., Bao, S., Kulkarni, S., Bradshaw, A. M.: Experimental demonstrations of direct adsorbate site identification using photoelectron diffraction: Phys. Rev. Lett. 71 (1993) 2054. Schindler, K.-M., Hofmann, P., Weiss, K.-U., Dippel, R., Gardner, P., Fritzsche, V., Bradshaw, A., Woodruff, D., Davila, M., Asensio, M., Conesa, J., Gonzalez-Elipe, A.: Is the frequency of the internal mode of an adsorbed diatomic molecule a reliable guide to its local adsorption site?: J. Electron. Spectrosc. Relat. Phenom. 64-65 (1993) 75. Wander, A., Hu, P., King, D.: Ambiguities in adsorbate site assignment from vibrational frequencies. A TLEED structural study of (2x1)CO-Pd(110): Chem. Phys. Lett. 201 (1993) 393. Wiesendanger, R., Guntherodt, H.-J. (eds.): Scanning Tunneling Microscopy I-III : Theory of STM and Related Scanning Probe Methods: Springer Series in Surface Science, Heidelberg: Springer, 1993. Young, H., Meng, X., Hess, G.:(1993) Multilayer adsorption of xenon, krypton, and argon on graphite: an ellipsometric study: Phys. Rev. B 48 (1993) 14556. Zegenhagen, J.: Surface structure determination with X-ray standing waves: Surf. Sci. Rep. 18 (1993) 199. Ando, T., Aizawa, T., Yamamoto, K., Kamo, M., Sato, Y.: The chemisorption of hydrogen on diamond surfaces studied by high resolution electron energy-loss spectroscopy: Diamond Relat. Mater. 3 (1994) 975. Bell, A. T., Pines, A., Eds.: NMR Techniques in Catalysis: New York, Marcel Dekker. Corn, R. M., Higgins, D. A.: Optical second harmonic generation as a probe of surface chemistry: Chem. Rev. 94 (1994) 107. Gimzewski, J. K., Gerber, C., Meyer, E., Schlittler, R. R.: Observation of a chemical reaction using a micromechanical sensor: Chem. Phys. Lett. 217 (1994) 589. Grobecker, R., Shi, H., Bludau, H., Hertel, T., Greber, T., Bottcher, A., Jacobi, K., Ertl, G.: Emission of exoelectrons during oxidation of Cs via thermal activation of a metastable O-2 surface species.: Phys. Rev. Lett. 72 (1994) 578. Grossmann, A., Erley, W., Ibach, H.: Adsorbate-induced surface stress: CO on Ni(100) and Ni(111): Surf. Sci. 313 (1994) 209. Hirschmugl, C. J., Williams, G. P., Persson, B. N. J., Volokitin, A. I.: Adsorbate vibrational dynamics in the anomalous skin effect frequency region.: Surf. Sci. 317 (1994) L1141. Hofmann, M., Wegner, H., Glenz, A., Wöll, C., Grunze, M.: The adsorption of the cyclic ether trioxane on Cu(111): J. Vac. Sci. Technol. A 12 (1994) 2063. Persson, B. N. J., Volokitin, A. I.: Infrared reflection-absorption spectroscopy of dipoleforbidden adsorbate vibrations: Surf. Sci. 310 (1994) 314. Porwol, T., Domotor, G., Hemmerich, I., Klinkmann, J., Freund, H.-J., Liegener, C. M.: Angular-resolved autoionization study of CO on Ni(110): experiment and theory: Phys. Rev. B 49 (1994) 10557. Rieder, K. H.: Surface structural research with atom beam diffraction: helium versus neon: Surf. Rev. Lett. 1 (1994) 51. Rugar, D., Zuger, O., Hoen, S., Yannoni, C. S., Vieth, H.-M., Kendrick, R. D.: Force detection of nuclear magnetic resonance: Science 264 (1994) 1560. Arvanitis, D., Baberschke, K.: Adsorbate-substrate bonding and dynamics as determined by SEXAFS: J. Electron. Spectrosc. Relat. Phenom. 75 (1995) 149. Bain, C. D.: Sum frequency vibrational spectrocopy at the solid/liquid interface: J. Chem. Soc. Faraday Trans. 91 (1995) 1281. Hostetler, M. J., Manner, W.L., Nuzzo, R. G., Girolami, G. S.: Two-dimensional melting transitions of rod-like molecules analyzed by reflection-absorption infrared spectroscopy: J. Phys. Chem. 99 (1995) 15269. Mainka, C., Bagus, P. S., Schertel, A., Strunskus, T., Grunze, M., Wöll, C.: Linear dichroism in X-ray absorption spectroscopy of strongly chemisorbed planar molecules: role of adsorption induced rehybridisations: Surf. Sci. 341 (1995) 1055.


2-40 95ROT

95SCH

95STE 95WAG 95WIT 95WIT 96BAB 96BAR

96BER

96CRO 96DAL 96EBI

96HAA 96HEI

96HOF 96LEG 96STA 96WES

97ASA

97BAR 97BRA

97BRI

2 Measuring techniques Rotermund, H. H., Haas, G., Franz, R. U., Tromp, R. M., Ertl, G.: Imaging pattern: formation in surface reactions from ultrahigh vacuum up to atmospheric pressures: Science 270 (1995) 608. Schlienz, H., Beckendorf, M., Katter, U. J., Risse, T., Freund, H.-J.: Electron spin resonance investigations of the molecular motion of NO2 on Al2O3/(111) under ultrahigh vacuum conditions: Phys. Rev. Lett. 74 (1995) 761. Stellwag, C., Held, G., Menzel, D.: The geometry of ordered benzene layers on Ru(001): Surf. Sci. 325 (1995) L379. Wagner, G. W., MacIver, B. K., Yang, Y.-C.: Magic Angle Spinning NMR Study of Adsorbate Reactions on Activated Charcoal: Langmuir 11 (1995) 1439. Witte, G., Toennies, J. P., Wöll, C.: Comparison of surface phonon dispersion for the clean and hydrogen covered Rh(111) surface: Surf. Sci. 323 (1995) 228. Witte, G., Wöll, C.: External vibrations of hydrocarbons on Cu(100): J. Chem. Phys. 103 (1995) 5860. Baberschke, K., Wende, H., Srivastava, P., Chauvistre, R.: New opportunities in the soft Xray absorption to characterize the adsorbate bonding: J. Phys. IV France 7 (1996) 469. Baraldi, A., Comelli, G., Lizzit, S., Cocco, D., Paolucci, G., Rosei, R.: Temperature programmed X-ray photoelectron spectroscopy: a new technique for the study of surface kinetics: Surf. Sci. 367 (1996) L67. Bertino, M., Steinhögel, W., Range, H., Hofmann, F., Witte, G., Hulpke, E., Wöll, C.: The low energy thermal excitation spectrum of nitrogen molecules adsorbed on Ni(110): Implications for molecular adsorption sites: Appl. Phys. A 62 (1996) 95. Crommie, M. F., Lutz, C. P., Eigler, D. M., Heller, E. J.: Quantum interference in 2D atomic-scale structures: Surf. Sci. 361/362 (1996) 864. Daly, C., Krim, J.: Sliding friction of solid xenon monolayers and bilayers on Ag(111).: Phys. Rev. Lett. 76 (1996) 803. Ebinger, H. E., Jänsch, H. J., Polenz, C., Polivka, B., Preyss, W., Saier, V., Veith, R., Fick, D.: NMR observation of Diffusion Barriers for Lithium Adsorbed on Ru(0001): Phys. Rev. Lett. 76 (1996) 656. Haas, G., Franz, R., Rotermund, H., Tromp, R., Ertl, G.: Imaging surface reactions with light: Surf. Sci. 352-354 (1996) 1003. Heidberg, J., Grunwald, M., Hustedt, M., Traeger, F.: High-resolution PIRSS using a tunable diode laser: the multiplet of the collective Nu2 bending vibration of the p(2x1) monolayer CO2 adsorbed on NaCl(001): Surf. Sci. 368 (1996) 126. Hofmann, F., Toennies, J. P.: High-resolution helium atom time-of-flight spectroscopy of low-frequency vibrations of adsorbates: Chem. Rev. 96 (1996) 1307. LeGoues, F. K., Hammar, M., Reuter, M. C., Tromp, R. M.: In situ TEM study of the growth of Ge on Si(111): Surf. Sci. 349 (1996) 249. Starke, U., Pendry, J. B., Heinz, K.: Diffuse low-energy electron diffraction: Prog. Surf. Sci. 52 (1996) 53. Westre, E. D., Brown, D. E., Kutzner, J., George, S. M.: Surface diffusion of carbon monoxide and potassium coadsorbed on Ru(001): confirmation of a 1:1 CO:K trapping interaction.: J. Chem. Phys. 104 (1996) 7313. Asakura, K., Lauterbach, J., Rotermund, H., Ertl, G.: Spatio-temporal pattern formation during catalytic CO oxidation on a Pt(100) surface modified with submonolayers of Au: Surf. Sci. 374 (1997) 125. Bartels, L., Meyer, G., Rieder, K.-H.: Basic steps involved in the lateral manipulation of single CO molecules and rows of CO molecules: Chem. Phys. Lett. 273 (1997) 371. Braun, J., Kostov, K. L., Witte, G., Wöll, C.: CO overlayers on Ru(0001) studied by Helium Atom Scattering: Structure, dynamics, and the influence of coadsorbed H and O: J. Chem. Phys. 106 (1997) 8262. Briner, B. G., Doering, M., Rust, H.-P., Bradshaw, A. M.: Mobility and trapping of molecules during oxygen adsorption on Cu(110): Phys. Rev. Lett. 78 (1997) 1516. Lando lt -Börnst ein New Ser ies III/42A2

2 Measuring techniques 97COL 97DOL

97GRA

97KRE 97KRU 97SCH

97WEC

97WIT 98BAU 98BER

98FOE

98FUH

98HAI 98LAR 98SNA

98STI 98UMB 98WIC

98WIT

99ALL

2-41

Collazo-Davila, C., Marks, L. D., Nishii, K., Tanishiro, Y.: Atomic Structure of the In on Si(111)(4x1) surface: Surf. Rev. Lett. 4 (1997) 65. Doll, R., Gerken, C. A., Van Hove, M. A,, Somorjai, G. A.: Structure of disordered ethylene adsorbed on Pt(111) analyzed by diffuse LEED: asymmetrical di-sigma bonding favored.: Surf. Sci. 374 (1997) 151. Graham, A. P., Bertino, M. F., Hofmann, F., Toennies, J. P., Wöll, C.: Experimental determination of a longitudinal phonon dispersion curve in a quasi-two-dimensional system.: J. Chem. Phys. 106 (1997) 6194. Kreuzer, H. J., Payne, S. H., Grunze, M., Wöll, C.: Adsorption and Desorption of N2 on Ni(110): Entropy vs. Energy: Z. Phys. Chem. 202 (1997) 273. Kruse, N., Voss, C.: Surface Reactions and Adsorbate-Induced Reconstruction: CO and NO on Rh Crystals: Z. Phys. Chem. 202 (1997) 213. Schaich, T., Braun, J., Toennies, J. P., Buck, M., Wöll, C.: Structural changes accompanying the hydrogen desorption from the diamond C(111) H(1x1)-surface revisited by helium atom scattering: Surf. Sci. 385 (1997) L958. Weckesser, J., Fuhrmann, D., Weiss, K., Wöll, C., Richardson, N. V.: Photoemission from long chain alkanes adsorbed on a metal surface and the electronic structure of transpolyethylene CnHan: Surf. Rev. Lett. 4 (1997) 209. Witte, G., Fuhrmann, D., Wöll, C.: Low-Energy Molecular Vibrations investigated by Inelastic Scattering of He Atoms: Chem. Phys. Lett. 265 (1997) 347. Bauer, E.: LEEM basics: Surf. Rev. Lett. 5 (1998) 1275. Bertino, M. F., Glebov, A. L., Toennies, J. P., Träger, F., Pijper, E., Kroes, G. J., Mowrey, R. C.: Observation of large differences in the diffraction of normal- and para-H2 from LiF(001).: Phys. Rev. Lett. 81 (1998) 5608. Föhlisch, A., Wassdahl, N., Hasselstrom, J., Karis, O., Menzel, D., Martensson, N., Nilsson, A.: Beyond the chemical shift: vibrationally resolved core-level photoelectron spectra of adsorbed CO: Phys. Rev. Lett. 81 (1998) 1730. Fuhrmann, D., Wacker, D., Weiss, K., Hermann, K., Witko, M., Wöll, C.: The adsorption of small hydrocarbons on Cu(111): A combined He-atom scattering and x-ray absorption study for Ethane, Ethylene and Acetylene: J. Chem. Phys. 108 (1998) 2651. Haier, P., Santos, P., Esser, N., Richter, W.: Interaction between Sb and Bi adsorbates on the GaAs(110) surface.: Surf. Sci. 399 (1998) 264. Larese, J. Z.: Neutron scattering studies of the structure and dynamics of methane absorbed on MgO(100) surfaces: Physica B 248 (1998) 297. Snabl, M., Ondrejcek, M., Chab, V., Chvoj, Z., Stenzel, W., Conrad, H., Bradshaw, A. M.: Surface diffusion of K on Pd(111): coverage dependence of the diffusion coefficient determined with the Boltzmann-Matano method.: J. Chem. Phys. 108 (1998) 4212. Stipe, B. C., Rezaei, M. A., Ho, W.: Single-molecule vibrational spectroscopy and microscopy.: Science 280 (1998) 1732. Umbach, E., Glockler, K., Sokolowski, M.:(1998) Surface "architecture" with large organic molecules: interface order and epitaxy: Surf. Sci. 402-404 (1998) 20. Wichtendahl, R., Fink, R., Kuhlenbeck, H., Preikszas, D., Rose, H., Spehr, R., Hartel, P., Engel, W., Schlögl, R., Freund, H.-J., Bradshaw, A. M., Lilienkamp, G., Bauer, E., Schmidt, T., Benner, G., Umbach, E.: SMART: an aberration-corrected XPEEM/LEEM with energy filter: Surf. Rev. Lett. 5 (1998) 1249. Witte, G., Weiss, K., Jakob, P., Braun, J., Kostov, K. L., Wöll, C.: Damping of molecular motion on a solid substrate: evidence for electron-hole pair creation: Phys. Rev. Lett. 80 (1998) 121. Allers, W., Schwarz, A., Schwarz, U. D., Wiesendanger, R.: Dynamic scanning force microscopy at low temperatures on a noble-gas crystal: atomic resolution on the xenon (111) surface: Europhys. Lett. 48 (1999) 276.


2-42 99BEN

99BRA

99DAN 99DOA

99ELL 99GRA

99HAI

99JAC

99KRE 99LOB

99MEYa 99MEYb

99LEEM 99PER 99SUC

99WEI 00BEC

00EIS

2 Measuring techniques Bennet, R. A., Stone, P., Price, N. J., Bowker, M.: Two (1x1) reconstructions of TiO2(110): surface rearrangement and reactivity studied using elevated temperature scanning tunneling microscopy: Phys. Rev. Lett. 82 (1999) 3831. Braun, J., Toennies, J. P., Wöll, C.: Local layer-by-layer growth of Ni on hydrogen terminated diamond C(111): A combined helium atom scattering and XPS study: Phys. Rev. B 60 (1999) 11707. Dannenberger, O., Buck, M., Grunze, M.: Self-Assembly of n-Alkanethiols: A Kinetic Study by Second Harmonic Generation: J. Phys. Chem. B 103 (1999) 2202. Doak, R. B., Grisenti, R. E., Rehbein, S., Schmahl, G., Toennies, J. P., Wöll, C.: Towards Realization of an Atomic deBroglie Microscope: Helium Atom Focusing using Fresnel Zone Plates: Phys. Rev. Lett. 83 (1999) 4229. Ellis, J., Graham, A. P., Toennies, J. P.: Quasielastic helium atom scattering from a twodimensional gas of Xe atoms on Pt(111): Phys. Rev. Lett. 82 (1999) 5072. Graham, A. P., Menzel, A., Toennies, J. P.: Quasielastic helium atom scattering measurements of microscopic diffusional dynamics of H and D on the Pt(111) surface: J. Chem. Phys. 111 (1999) 1676. Hai, L., Weaver, M. J.: Surface-enhanced Raman scattering as a versatile vibrational probe of transition-metal interfaces: thiocyanate coordination modes on platinum-group versus coinage-metal electrodes: Langmuir 15 (1999) 8743. Jackson, G. J., Ludecke, J., Woodruff, D. P., Chan, A. S. Y., Singh, N. K., McCombie, J., Jones, R. G., Cowie, B. C. C., Formoso, V.: Chemical-shift X-ray standing wave studies: coadsorption site determination of PFx fragments on Ni(111): Surf. Sci. 441 (1999) 515. Kreuzer, H. J., Payne, S. H., Drozdowski, A., Menzel, D.: Theory of dissociative and nondissociative adsorption and desorption: J. Chem. Phys. 110 (1999) 6982. Lobo, R., LaVeigne, J., Reitze, D. H., Tanner, D. B., Carr, G. L.: Performance of new infrared beamline U12IR at the National Synchrotron Light Source: Rev. Sci. Instrum. 70 (1999) 2899. Meyerheim, H. L., Gloege, T., Maltor, H.: Surface X-ray diffraction on large organic molecules: thiouracil on Ag(111): Surf. Sci. 442 (1999) L1029. Meyerheim, H. L., Gloege, T., Maltor, H., Sokolowski, M., Umbach, E., Bäuerle, P.: Bond stretching and distortion in large organic molecules on Ag(111) determined by surface xray diffraction: Surf. Rev. Lett. 6 (1999) 883. See papers in: Surf. Rev. Lett., Vol. 5, Nr. 6, (1999). Persson, B. N. J., Tosatti, E., Fuhrmann, D., Witte, G., Wöll, C.: Low-frequency adsorbate vibrational relaxation and sliding friction: Phys. Rev. B 59 (1999) 11777. Suchorski, Y., Beben, J., James, E. W., Evans, J. W., Imbihl, R.: Fluctuation-induced transitions in a bistable surface reaction : catalytic CO oxidation on a Pt field emitter tip: Phys. Rev. Lett. 82 (1999) 1907. Weiss, K., Weckesser, J., Wöll, C.: An X-ray absorption study of saturated hydrocarbons physisorbed on metal surfaces: Theochem. 458 (1999) 143. Becker, T., Boas, C., Burghaus, U., Wöll, C.: Adsorption probability of CO on a metaloxide: The case of oxygen-terminated ZnO and the influence of defects: Phys. Rev. B 61 (2000) 4538. Eisert, F., Gurka, M., Legant, A., Buck, M., Grunze, M.: Detection of molecular alignment in confined films: Science 287 (2000) 468.


4 Data: Adsorbate-induced changes of substrate properties

4.1 Surface structure on metals and semiconductors M. A. VAN HOVE, K. HERMANN, P. R. WATSON

4.1.1 Introduction The structure of surfaces at the atomic scale is basic to the understanding of many surface and interface properties. The effect of adsorbates on surface structure is particularly important because adsorbatecovered surfaces are technologically far more relevant than the clean substrate surfaces. Adsorbatecovered surfaces are also very relevant to the vast class of interfaces between two solids or between a solid and a fluid (liquid or gas). This chapter lists the experimentally determined effects of adsorption on the substrate surface structure, focusing on those cases where detailed and rather complete structures have been determined. This implies single-crystal surfaces with mostly well-ordered adsorbates. Much of the information is derived from the atomic coordinates and other information contained in the Surface Structure Database (SSD), Version 3 [99W], and is complemented with more recent results from the literature. The data were obtained with a variety of surface techniques, which are listed with their acronyms in Table 1. The emphasis is on the atomic-scale structure as defined by atomic positions, relaxations and reconstructions, structural models and bonding configurations. Included are both atomic and molecular adsorbates. The data for atomic adsorbates far outnumber those for molecular adsorbates, but the effects are rather similar, which is interesting in its own right; the tables in this chapter therefore show them side by side for direct comparison. Adatom positions are included in the tables so that the adsorbate-induced effects can be directly related to the adatom. However, for adsorbed molecules only the positions of the atoms that bond to the substrate are listed in the tables, since they have the most direct influence on the substrate. More complete structural details can be found in the Surface Structure Database [99W]. The tables in this chapter are limited to adsorption on metal and semiconductor substrates for the simple reason that virtually no detailed information is available from experiment about adsorbate-induced structural effects on other substrate materials, including ionic crystals and many other compounds.

4.1.2 Relaxation vs. reconstruction Central to adsorbate-induced changes in a substrate are the two concepts of relaxation and reconstruction, which collectively may be called restructuring. The terms relaxation and reconstruction need to be defined here, since various interpretations are used in the literature, especially for reconstruction. By relaxation of a substrate surface we mean small atomic displacements from ideal or clean-substrate positions. The displacements shall be small compared to near-neighbor distances, such that no rebonding (bond breaking or new bond formation) takes place within the substrate. Such relaxation may induce the formation of a two-dimensional superlattice if the displacements modify the initial substrate surface symmetry. This is especially common in adsorption, since the adsorbate itself often creates a superlattice,

Lando lt -Bö rnst ein New Ser ies III/42A2

4.1-2

4.1 Surface structure on metals and semiconductors

[Ref. p 4.1-109

particularly at fractional coverages less than one. For example, a ¼-monolayer of atomic adsorbate could be arranged in a (2x2) superlattice, doubling the substrate periodicity in two surface directions; each adatom can induce relatively small local relaxations in the substrate and within the superlattice unit cell: these relaxations, especially layer bucklings and lateral displacements, often break the clean-substrate periodicity while conforming to the superlattice periodicity. Relaxations must be referenced to another structure, for which the obvious choices are the ideal bulklike positions or the already relaxed clean-substrate positions. Since the clean-substrate positions are not uniquely known (each analysis gives somewhat different results), we use as an unambiguous reference for relaxations the ideal bulk-like positions obtained by a mathematical termination of the bulk lattice. However, we also include in this chapter, for direct comparison with the adsorbate-induced relaxations, tables of the published structural results determined for relaxed clean surfaces. Adsorbate-induced relaxations occur in many varieties. Of general interest are interlayer spacing changes: since clean surfaces exhibit spacing changes relative to the ideal bulk lattice, it is useful to consider the further changes due to adsorbates. For instance, on metals the clean-surface spacing relaxations are often reversed by adsorption: while the clean surface usually (but not always) exhibits a contraction of the topmost interlayer spacing, an expansion is often observed after adsorption. Also interesting is layer buckling (also called rumpling), whereby a coplanar atomic layer loses its coplanarity because an adsorbate pulls or pushes some substrate atoms out of the plane relative to other atoms. Another effect is lateral relaxation, in which adsorbates shift substrate atoms parallel to the surface; a frequent case is a radial relaxation of substrate atoms away from or toward the adsorbate site. Another case of lateral relaxation is the collective rotation of substrate atoms around the adsorbate site; this displacement is often called clock rotation. One could also look at all these relaxations in terms of adsorbate-induced changes in bond lengths, which are the chemically more important quantities; however, surface scientists have thought mostly in terms of displacement components perpendicular and parallel to the surface, and we shall do so here as well. By reconstruction of a substrate surface we mean large atomic displacements that cause rebonding (bond breaking and/or new bond formation) within the substrate. Frequently, but not always, such a reconstruction changes the two-dimensional lattice of the surface, creating or modifying or removing a superlattice. Reconstructions are of course usually accompanied by additional small relaxations. Reconstruction is a relative term: here reconstruction is understood with respect to the ideal bulklattice termination, rather than with respect to the actual clean surface. Of particular interest in adsorption are several cases: the induction of a new reconstruction, when none was present on the clean surface; the removal of a clean-surface reconstruction (sometimes inelegantly called un-reconstruction or de-reconstruction); and the change from one reconstruction to another (which could be called rereconstruction). Many types of reconstruction exist at surfaces. One class of reconstruction, common on certain clean metal surfaces, is that of missing or added atoms (e.g. missing or added rows); the remaining atoms still occupy bulk-like positions, usually with small local relaxations from those bulk-like positions. Microfacetting is a frequent outcome of this type of reconstruction. Adsorption often removes such reconstructions, but can also induce them, or stabilize them. Another class consists in forming or removing a more closely-packed surface layes, such as a quasi-hexagonally close-packed layer on top of square-lattice substrate, as happens with some metal surfaces. Dimerization and similar types of rebonding (e.g. π-chain formation) are commonly found on semiconductors, and these reconstructions are frequently removed by adsorption, but can also be stabilized by adsorption. Stacking faults occasionally are also seen on these materials. Absorption of adatoms into subsurface sites occurs for a variety of materials and can lead to interstitial or substitutional absorption within the substrate, in which case the remaining substrate atoms have near-bulk-like positions; absorption can also lead to other forms of compound formation, that may not respect the substrate lattice, but rather tend toward the lattice of the bulk compound. As with many definitions, there exist borderline cases where our definitions of relaxation vs. reconstruction are debatable. For example, large bond rotations with substantial atomic displacements but without rebonding occur in surfaces such as clean GaAs(110): we classify these as not reconstructed (relative to the ideal bulk termination, which is also nearly regenerated by certain adsorbates), although many authors prefer to call these reconstructed. In the case of clean W(100)-c(2x2), the displacements Lando lt -Börnst ein New Ser ies III/42 A2

Ref. p. 4.1-109]


4.1-3

from the ideal bulk positions are relatively small and could be called relaxations, but these may be sufficient to cause new bond formation between W atoms, and we label this situation therefore as reconstruction (this case has also been called displacive reconstruction in the literature). We treat relaxations and reconstructions very differently in the tables of this chapter. With relaxations, it is of primary interest to compare the quantitative magnitude and direction of the small displacements, including in particular changes in interlayer spacings, such as expansions and contractions. By contrast, with reconstructions it is of primary importance to know the qualitative type of reconstruction, rather than the detailed atomic positions; and the type of reconstruction is more easily understood when described in words than in numbers. Thus, our tables will in general list relaxations numerically, but reconstructions will be explained textually, although some important structural quantities will often be listed as well in the latter case. If more details are desired, it is suggested to consult the Surface Structure Database [99W].

4.1.3 Notations and conventions The individual structures listed in the tables are named using standard notations, particularly for superlattices: we use Wood, “rect” (rectangular) or occasionally matrix notations for the superlattices, which are defined in many books and reviews [86V, 99W]; they appear in the exact form used in the Surface Structure Database [99W]. Adsorption sites are also labeled in a conventional way, e.g. fcc-hollow site for adsorption at an fcclattice-continuation site above an fcc(111) surface. Figures are provided to clarify the more common adsorption sites and local adsorption geometries. For an adatom, the adsorption site coincides with the atomic position, or its projection into the substrate: we may call this the adsorption axis. But with an admolecule this needs clarification. For a molecule with a rotation axis perpendicular to the surface, the adsorption site coincides with the molecular rotation axis, which we may again call adsorption axis. Thus, for CO standing perpendicular to the surface at a high-symmetry position, the C-O axis uniquely defines the site, and the C atom (which normally bonds to the surface) is located at that site; for ring-like benzene lying flat on the surface with its main symmetry axis perpendicular to the surface, the empty center of the molecular ring typically lies at a high-symmetry location and thereby defines the adsorption site, while the 6 carbon and 6 hydrogen atoms are all removed from that site at lower-symmetry positions. For low-symmetry adsorption, ad hoc descriptions are given in each individual case, and in these situations the adsorbate-induced relaxations often become quite complicated (asymmetrical) and are not listed in detail: it is suggested to consult the Surface Structure Database [99W] for further information. Relaxations are labeled in the tables as illustrated schematically in Figs. 1 and 2, which define our generic labeling scheme applicable to all metallic substrates. The principle is to look from the adsorption site or axis outward, in any given layer. Consider the four coplanar and symmetrical light-grey substrate atoms depicted in Fig. 1, which looks down onto a particular atomic layer: these symmetry-equivalent atoms form a shell numbered s, at a radial distance rls from the (projected) adsorbate site (more precisely, this shell is cylindrical around the adsorbate site axis, which is very often an axis of rotational symmetry). If the local rotational symmetry is maintained, adsorption can cause these four atoms to be displaced radially by the common distance ∆rls from the (projected) adsorbate site and rotated tangentially by a common angle αls around that site. Figure 2 shows a side view of several substrate layers, each of which is shown as a gray slab of non-zero thickness, since it may be buckled: each possibly buckled layer originates in one non-buckled layer of the ideally-terminated bulk lattice. The dashed line is the adsorption axis, i.e. the projection of the adsorbate site down to each substrate layer. In a given layer, the first shell of atoms around that projected adsorbate site is numbered i = 1, with possible radial displacement by ∆r1 and possible tangential rotation by α1. The z-coordinate (perpendicular to the surface) of these nearest atoms numbered i = 1 defines the reference plane for this given layer (shown as a heavy line in Fig. 2): by definition, it thus has buckling amplitude b1 ≡ 0. The atoms of the second, third and farther shells have radial displacements ∆r2, ∆r3, etc., and tangential rotations α2, α3, etc. They also can have buckling amplitudes b2, b3, etc. relative to


4.1-4


[Ref. p 4.1-109

the reference plane of that layer. The radial displacements and bucklings are expressed in percent relative to the values and interlayer spacings in the bulk.

4.1.4 Organization of the tables The tables are arranged so that similar structures are close together for easiest comparison. The coarsest subdivision is thus between metal substrates (see Sects. 4.1.6-4.1.14) and semiconductor substrates (see Sects. 4.1.15-4.1.18). Within the metals, the tables progress generally from the surfaces with highest symmetry and closest packing to those with lowest symmetry and least packing of the ideal termination. The order is thus: fcc(111), hcp(0001), bcc(110), fcc(100), bcc(100), fcc(110), hcp(10-10), bcc(211), bcc(111). Within the semiconductors, the same principles apply, starting with elemental substrates before turning to compound substrates: diamond(111), diamond(100), diamond(311), zincblende(110), zincblende(111), zincblende(1-1-1), zincblende(100), and 6H-SiC(0001). For a given crystal face, a first table gives the clean-surface relaxations of the interlayer spacings, or the type of clean-surface reconstruction (all relative to the ideally terminated bulk). Then, a table gives the adsorbate-induced relaxations or reconstruction type. Within this table, the structures are grouped by two-dimensional superlattice, starting with the smallest and highest-symmetry unit cells and progressing to the largest and lowest-symmetry unit cells (this includes disordered adlayers where available). For a given unit cell, the structures are listed alphabetically by substrate material and then by adsorbate element(s). A particular structure with several adsorbates per unit cell will appear several times in the table if the adsorbates occupy inequivalent sites. This is because the tables focus on one type of adsorption site at a time, for the most direct comparison, so that different adsorption sites coexisting in a single structure are found listed in different parts of the tables.

4.1.5 Organization of data for individual structures In the tables, when relaxations are listed, each (possibly buckled) layer is given one row, starting with the top substrate layer (numbered 1 in Fig. 2). The absence of structural data for deeper layers in second or subsequent rows means that they were not determined. All distances and angles are given in Ångström and degrees, respectively. Multiple data in a data field correspond to successive shells of atoms in a particular layer, as defined above and in Figs. 1 and 2. Let us explain this with two examples extracted from Tables 3 and 9, respectively (omitting a few obvious columns): surface

clean adsrec. ind rec. no Pd(111)+(3x3)- no C6H6+2CO: C6H6 site surface

Ni(100)+ p4g(2x2)-2C

clean adsrec. ind rec. no no

∆dl,l+1 [%]

bls [%]

∆rls [%]

2.6 ± 2.2

0.0 ± 2.2, 2.2 ± 2.2

0, 0.8 ± 7.0 0, 0

∆dl,l+1 [%]

bls [%]

∆rls [%]

3.9 ± 4.5 4.4 ± 4.0

0 3.2 ± 3.9 0, 8.5 ± 4.5 0, 0

αls [°]

αls [°]

d01 [Å]

∆r0 [Å]

2.16 ± 0.05 0

d01 [Å]

∆r0 [Å]

± 14.3 ± 2.6 0.12 ± 0.04 0, 0

Lando lt -Börnst ein New Ser ies III/42 A2

Ref. p. 4.1-109]


4.1-5

The first of these two structures, Pd(111)+(3x3)-C6H6+2CO, contains 3 adsorbates in each unit cell, all of which are adsorbed at fcc-hollow sites. In the entry shown above only the structure around the benzene site is described (the structure around the CO adsorption sites is listed as a separate entry in the same Table 3). The center of the benzene molecule, which defines the adsorption site or axis, lies over an fcc-hollow site (indicated by the heading of Table 3). The height of the C atoms of the benzene, above the first ring of Pd atoms around the fcc-hollow site in the top metal layer, is given as d01 = 2.16 ± 0.05 Å. The second shell of Pd atoms around that site in the top metal layer is buckled into the substrate by b1b = 2.2 ± 2.2 %, relative to the first shell, for which (by definition) b1a = 0.0 (± 2.2) %, while its shell radius is (perhaps) expanded by ∆r1b = 0.8 ± 7.0 % relative to bulk positions. No rotations αls are noted, and no information about the second metal layer l = 2 is given, other than its spacing of ∆d12 = 2.6 ± 2.2 Å, measured relative to the first shell of Pd atoms in the first Pd layer; the second Pd layer is thus, in this example, assumed to be internally unrelaxed, i.e. not to be buckled, expanded laterally or rotated. The second structure, Ni(100)+p4g(2x2)-2C, contains two (equivalent) C adatoms in each (2x2) unit cell, related by p4g symmetry (i.e. glide-plane symmetry, as well as 4-fold rotation and mirror planes). The “no” entries indicate that neither the clean Ni(100)-(1x1) nor the C-covered substrate are reconstructed (in the sense that no Ni-Ni bonds are made or broken relative to the ideally-terminated substrate); admittedly, this is debatable for the C-covered surface, since the Ni-Ni distances within the first Ni layer do change appreciably. The heading of Table 9, from which this entry was extracted, specifies adsorption at a clock-rotated hollow site; the absence of a non-zero entry for lateral adsorbate shifts ∆r0 confirms that the C atoms are indeed at the high-symmetry hollow sites. The height of the C adatoms over the plane of the nearest Ni atoms is listed as d01 = 0.12 ± 0.04 Å, indicating nearly coplanar adsorption. If there were other Ni atoms in that first layer at a different height, i.e. buckled, the corresponding C-Ni spacing would be included in the same data field, e.g. as an additional 0.22 ± 0.04 Å to indicate that the next shell of Ni atoms would be deeper in the surface, buckled inward, by 0.22 - 0.12 = 0.10 Å; however, this particular structure has no buckling in the top Ni layer (it is not allowed by symmetry), as also indicated by the absence of an entry b1b in the buckling column. The data imply that the first shell of four Ni atoms is probably expanded radially by ∆r1a = 3.2 ± 3.9 % and most likely rotated by α1a = ± 14.3 ± 2.6 °, relative to the ideally-terminated Ni lattice; the initial ± before the rotation angle specifies that both clockwise and counter-clockwise rotations occur within the unit cell. The spacing change (relative to the bulk value) between the first and second Ni layers is given as ∆d1,2 = 3.9 ± 4.5 %, indicating a probable expansion; note that this spacing is measured between the planes of those Ni atoms which are closest to the (projected) adsorption site in each layer, i.e. between first Ni shells in each layer, as shown in the general case in Fig. 2. In the second row of data for this structure, which describes the second Ni layer, we find that a buckling by b2b = 8.5 ± 4.5 % occurs between the first shell of Ni atoms closest to the (projected) adsorption site (in this case the Ni atom directly below the adsorption site, for which by definition b2a = 0 %) and the next shell of second-nearest Ni atoms: the positive value indicates that the second Ni shell in this layer lies deeper below the surface than the first shell. Furthermore, the spacing between the second and third layers is shown to also probably be expanded, by ∆d2,3 = 4.4 ± 4.0 %. We illustrate next an entry for semiconductors, from Table 23, which contains some numerical data: surface Si(111)+ (√3x √3)R30°-In

clean rec. yes

ads-ind d01 [Å] ∆d12 [Å] ω [°] rec. no 1.85 ± 0.05 -15 ± 3

description [description]

This entry indicates that the adsorbate (In) has removed the clean-surface reconstruction. The adatom is located at a height d01 = 1.85 ± 0.05 Å above the first shell of outermost Si atoms. The adsorption occurs in a T4 site (as stated higher in the table and in the description included in this entry). And the spacing


4.1-6


[Ref. p 4.1-109

between Si atoms in the outermost bilayer is contracted by ∆d12 = -15 ± 3 % relative to the bulk value. (The rotation angle ω is not relevant to this structure.)

4.1.6 Adsorption on fcc(111) The clean fcc(111) and hcp(0001) surfaces are the most compact and dense possible, with hexagonal atomic arrangements. They have the least tendency to reconstruct and relax interlayer spacings. Only Au(111) among them is known to reconstruct (to an even denser hexagonal outer layer with smaller lattice constant). Table 2 for the clean fcc(111) surfaces shows that the topmost interlayer spacing can be either expanded (Ag, Al, Pd, Pt), or undecided (Cu, Ni), or contracted (Rh), based on experiment. There does exist a general trend toward contraction of the topmost interlayer spacing in many metal surfaces, but it is only systematically verified for less-close-packed surfaces, such as fcc(110). The deeper interlayer spacings in clean fcc(111) surfaces are less well characterized at this time: their relaxations can be assumed to be smaller than the uncertainty of the analysis. Table 3 lists the adsorbate-induced changes on fcc(111). Reconstructions are relatively rare, and occur mostly with adsorbed metal atoms (especially alkali atoms) in the form of substitutional adsorption. Phosphorus and sulfur also can produce reconstructions in some cases, of a more complex type, but also tending toward compound formation; the structure of this ultra-thin compound layer need not be simply related to any known bulk compound structure. Considering the non-reconstructed cases, one finds a general trend toward expansion of the local topmost substrate interlayer spacing, relative to the clean surface. But there is one major exception to this trend: electropositive adsorbates (especially the alkali atoms) generally produce a contraction of this spacing. A similar contrasting trend is seen in the buckling induced within the top substrate layer: with electronegative adsorbates, the trend is toward positive buckling, i.e. substrate atoms farther from the adsorbate site tend to be deeper in the surface; the reverse is seen for electropositive adsorbates (again for alkali atoms especially). Radial relaxations around the adsorbate site are mostly within the error bars and probably small or negligible in most cases; the few more decisive results are insufficient in number to establish a clear trend. This applies even more so to the few tangential rotations that may have been observed. Buckling in the second substrate layer shows a tendency to be the reverse of that in the first substrate layer, particularly for the (2x2) structures with adsorption in fcc-hollow sites.

4.1.7 Adsorption on hcp(0001) The surface structure of ideal hcp(0001) is very similar to that of fcc(111), the difference occuring in the stacking sequence of the third and deeper metal layers. No hcp(0001) surface is known to reconstruct when clean. Table 4 shows clean-surface relaxations for hcp(0001). As with fcc(111), the topmost interlayer spacing can be expanded (Be, Mg), undecided (Co), or contracted (Gd, Ru, Sc). Compared to the fcc(111) surfaces, it seems at present that even fewer hcp(0001) surface reconstruct upon adsorption, cf. Table 5, at least among those studied. Trends in adsorbate-induced relaxations on hcp(0001) are less clear than on fcc(111), cf. Table 5. Perhaps the effects seen on fcc(111) do not carry over to hcp(0001), or the effects on hcp(0001) are more sensitive to details of the atomic arrangements within the various unit cells. A more exhaustive analysis and comparison of the results on a single metal, Ru(0001) [97M1], also suggests that structural trends may be difficult to extract for this one metal, and thus even more so for the class of hcp(0001) surfaces.


Ref. p. 4.1-109]


4.1-7

4.1.8 Adsorption on bcc(110) The ideal bcc(110) surface presents a distorted hexagonal lattice of slightly lower intrinsic atomic density than fcc(111) or hcp(0001). No clean reconstructions of these surfaces are reported, cf. Table 6. There is a tendency toward a contraction of the outermost interlayer spacing for K, Mo and W, without clear deviation from the bulk value for the other studied metals. Adsorption does not cause reconstruction on bcc(110), cf. Table 7. (There have been reports of a possible H-induced lateral shift of the top metal layer; but later studies could not confirm these results.) Adatoms appear to favor the "center" site (which is the continuation site of the bcc lattice), even though it is only two-fold coordinated. Adjacent to this site is a three-fold coordinated hollow site which is preferred by hydrogen, while in one structure, Mo(110)+(2x2)-S, the adatom appears to settle midway between those two sites. The adsorbate does not seem to induce a systematic expansion of the outermost metal-metal interlayer spacing on bcc(110); this is somewhat surprising in view of the results on other surfaces, but perhaps the statistics in this small group of results are not sufficient to reach a firm conclusion.

4.1.9 Adsorption on fcc (100) The ideal bulk-like fcc(100) surface, cf. Table 8, is atomically less dense and more "open" than the hexagonal fcc(111) and hcp(0001) surfaces, or the bcc(110) surface. Also it is more asymmetrical between vacuum and bulk than the hexagonal surfaces, in the sense that a surface atom has 0 nearest neighbors on the vacuum side and 4 on the bulk side, compared with 0 and 3 for the hexagonal surfaces; in addition the surface atoms in fcc(100) have only 4 nearest neighbors in the surface plane, as opposed to 6 in the hexagonal surfaces, so that the surface atoms in fcc(100) are relatively more affected by the outof-plane asymmetry. As a result one finds a slightly stronger tendency to both reconstruction and relaxation on the square-lattice fcc(100) surface. Reconstruction of the clean surface occurs for Ir, Pt and Au(100), as on fcc(111): in each case the top layer contracts and rearranges to form a quasi-hexagonal layer more similar to the fcc(111) surface (but with slightly different lattice constants, yielding different superlattices). The relaxations of interlayer spacings on fcc(100) surfaces are more biased toward a contraction of the top spacing. This spacing still appears to expand slightly for a few metals (Al, Pd), while no clear relaxation is seen on others (Ag, Ni, Rh); several metals now show a contraction (Al, Pb, Pd). There is also a tendency toward an oscillatory relaxation of the deeper interlayer spacings: alternating contractions and expansions with decaying amplitudes. Table 9 lists the adsorbate-induced changes on fcc(100). Adsorbates induce reconstructions of fcc(100) perhaps more frequently than for the hexagonal surfaces, but the statistics are poor, and the choice of metals studied probably not random. However, the adsorbates that cause reconstructions tend to be the same as on the hexagonal surfaces: primarily alkali adatoms, some other metal adatoms that form a one-layer alloy with the substrate, and oxygen. While sulfur induces reconstructions on fcc(111) and fcc(110), none is evident on fcc(100). On the other hand, adsorbates can also remove a clean-surface reconstruction (few such cases are listed in Table 9, but examples are known qualitatively by the change in their LEED patterns). Atomic adsorption occurs predominantly at or near four-fold coordinated hollow sites of fcc(100); the smaller adsorbates (H, C, N) penetrate relatively deeply into that hollow and partly bond to the second metal layer. Interlayer spacings are changed by adsorption in similar ways as on the hexagonal surfaces. Many adsorbates (primarily the electronegative ones) cause an expansion of the outermost interlayer spacing, while others (primarily the electropositive ones) yield contractions. The magnitude of the effect seems to be comparable to the case on the hexagonal surfaces. Also, there are similar examples of buckling, especially in the second metal layer. Notable is the very clear case of "clock reconstruction" observed for C and N adsorbed on Ni(100).


4.1-8


[Ref. p 4.1-109

4.1.10 Adsorption on bcc (100), pure or alloyed The bcc(100) surface is in turn less dense and more open than the fcc(100) surface. In fact, the surface atoms do not bond together on bcc(100); instead, the 4 nearest neighbors of a surface atom are all in the second metal layer, causing very strong asymmetry between vacuum and bulk. One thus finds an even stronger tendency toward reconstruction and relaxation on this surface, especially when clean. Table 10 shows that 2 of the 5 bcc(100) metals listed reconstruct when clean (Mo, W). The non-reconstructed clean metal surfaces exhibit quite strong contractions of the outermost interlayer spacing, and a probable expansion of the next deeper spacing. Adsorbates, cf. Table 11, tend to compensate or even overcompensate for the missing half-crystal: this is already apparent on the closer-packed surfaces, but becomes much clearer with the more open surfaces like bcc(100) and fcc(110) (see Sect. 4.1.11 for the latter). The reconstructions tend to be removed or replaced by other reconstructions, while the relaxation of the outermost interlayer spacing often turns from a large contraction to a sizable expansion. Adsorption of adatoms occurs primarily within the large hollows of this surface, with frequent bonding to the second metal layer and a large induced buckling of that second metal layer. Alloys with a bcc(100)-like lattice include MoRe with variable composition, listed in Tables 12 and 13. The clean surfaces behave like clean, unreconstructed bcc(100) surfaces [note that clean Mo(100) reconstructs, while pure Re has an hcp lattice], as shown by the interlayer spacings listed in Table 12. Oxygen adsorption causes a missing-row reconstruction, while H and C induce spacing changes (and C can also penetrate interstitially).

4.1.11 Adsorption on fcc (110) The tendency noted above toward more reconstructions and relaxations on more "open" surfaces is again very evident for the fcc(110) surface. There is once more a large asymmetry for surface atoms between the vacuum side and the bulk: each surface atom has 0 nearest neighbors in the vacuum and 5 toward the bulk, one of which is directly below the surface atom, and the latter only has 2 nearest neighbors in the surface plane. Clean Ir, Pt and Au(110) all reconstruct, cf. Table 14, as for the (111) and (100) surfaces. But the (110) surface reconstructs into missing-row structures that expose narrow facets of hexagonal symmetry. While no other fcc(110) surfaces are known to spontaneously reconstruct when clean, the ease with which trace amounts of adsorbates can reconstruct several of these surfaces suggests that they are energetically close to reconstructing. Relaxations of interlayer spacings on the clean unreconstructed (and reconstructed) fcc(110) surfaces show a clear pattern of oscillatory contractions and expansions as one penetrates from one layer to the next. Adsorbates can induce the removal or change of a reconstruction on fcc(110) surfaces, cf. Table 15. The resulting reconstruction which has been studied most is that of oxygen on Cu, Ag and Ni(110), and N on Rh(110): it consists of one-dimensional chains like -Cu-O-Cu-O-, where the Cu atoms can be most easily viewed as adatoms on a bulk-like (but relaxed) Cu(110) surface. Another interesting type of induced reconstruction is a simple 1:1 metallic alloy in the top layer, obtained by substitution of half the surface atoms. A number of more complex reconstructions are also known, produced primarily with N, O, S and P, as well as some other metallic adatoms. Adsorbate-induced relaxation changes on unreconstructed fcc(110) surfaces are similar in magnitude to the bcc(100) case. The larger adsorbates, S and metals, tend to occupy the higher-symmetry hollow site at the center of the rectangle formed by 4 surface atoms, maximizing the number of nearest neighbors, and in particular bonding directly to the second metal layer, thereby inducing a large buckling there. Smaller adatoms, like H and O, favor 3-fold coordinated bonding sites on the flanks of those hollows (also bonding to atoms of both the first and second substrate layers); this lowers the symmetry and induces more complex relaxations in the substrate, such as asymmetrical lateral relaxations.


Ref. p. 4.1-109]


4.1-9

4.1.12 Adsorption on hcp (10 1 0 ) The ideal hcp ( 10 1 0 ) surface shows strong similarities with fcc (110): it also consists of ridges and troughs of close-packed atomic chains. However, the bulk structure allows two inequivalent terminations, with shallow and deep troughs, respectively. In all cases, it is the shallow-trough termination that is observed. The studied cases, cf. Table 16, exhibit no reconstructions when clean, but clear contractions and expansions of the top two interlayer spacings, respectively; the effect is largest in Be, for which an oscillatory trend in the spacing relaxations is apparent down to the 4th interlayer spacing. Rather few adsorbate-induced structures on hcp ( 10 1 0 ) have been studied in detail, cf. Table 17. They show no reconstructions, but a tendency to reduction or even reversal of the interlayer spacing changes. An exception appears to be presented by hydrogen on Re and Ru(10-10), where the outermost interlayer spacing remains close to the clean-surface value, while the next interlayer spacing is contracted.

4.1.13 Adsorption on bcc (211) The ideal bcc(211) surface shows strong similarities to the fcc(110) surface, with ridges and troughs of close-packed chains of atoms, but the troughs are wider and shallower; also the ridges are displaced longitudinally to give a lower symmetry than fcc(110) has. No reconstruction of the clean surface is evident, cf. Table 18, and relaxations of the interlayer spacings are similar to the case of fcc(110). The bcc(211) surfaces appear to be prone to reconstruction due to adsorption, cf. Table 19, with missing-row structures of different kinds being induced by H and O on Fe(211). Oxygen on W(211) seems to reduce the clean-surface spacing relaxations, although these were not optimized in the one study of this system.

4.1.14 Adsorption on bcc (111) Only one study is reported on the detailed adsorbate-induced structure of bcc (111). The clean surfaces of Fe and Mo(111) are not reconstructed. The ideal bcc (111) surface is very open, exposing 1st, 2nd and 3rd layer substrate atoms; it exhibits large interlayer spacing relaxations that are oscillatory, but the oscillation is not simply antiphase from layer to layer, cf. Table 20. Hydrogen on Mo(111) at a coverage of 3 monolayers, cf. Table 21, fills each of the large hollows with 3 adatoms that are located off-center on lateral, inclined bridge sites. The outermost Mo-Mo interlayer spacing is barely affected, while the second interlayer spacing is brought back toward the bulk value from a large contraction in the clean case.

4.1.15 Adsorption on Si, Ge and C(111) The clean surfaces of the diamond(111) type are well known to reconstruct in a variety of complex ways, cf. Table 22. For instance, for clean Si(111) the well-known (7x7) structure is the stable form, while the metastable (1x1), (2x1), (5x5) and (9x9) structures have also frequently been reported. However, only the (1x1), (7x7) and (2x1) structures have been determined in detail (but the other (nxn) structures are expected to be straightforward generalizations of the (7x7) structure). Such reconstructions of the clean surface strongly improve the bonding between surface atoms from a very unfavorable bulk-like arrangement. It is then not surprising that adatoms will as a rule perturb this situation fundamentally, and thus generate completely different surface structures. Table 23 lists adsorbate-induced structures on Si, Ge and C(111). Hydrogen affects C(111) and presumably Si and Ge(111) in the simplest manner: removal of the reconstruction by capping the dangling bonds of the ideal bulk-like termination, with some residual interlayer spacing relaxations that


4.1-10


[Ref. p 4.1-109

reflect the difference between a monolayer of H and the missing half-crystal of the bulk. The same appears to happen with some other adatoms, in particular halide adatoms, and molecules. In these instances, the bulk is terminated in a complete bilayer, which offers bonds perpendicular to the surface that can be capped well by monovalent adsorbates. The bulk diamond lattice can also be terminated between the layers of this bilayer, leaving three times as many dangling bonds to satisfy: this can be accomplished by adding a trivalent adsorbate like As, Sb or Bi, which then forms a layer that substitutes for the outermost half of the more stable Si bilayer. A similar feature is part of the so-called honeycomb-chained-trimer (HCT) reconstruction due to several metal adsorbates. Here a lateral relaxation in the lower half of the bilayer leads to trimerization of those Si or Ge atoms. A related type of structure, called conjugate honeycomb-chained-trimer (CHCT) model, occurs for other metal adsorbates: here it is the metal adatoms that trimerize instead of the substrate atoms; we thus classify this as not reconstructed, since the Si-Si bonding topology is bulk-like. As Table 23 shows, a number of other reconstructions have been identified, many of which are quite complex.

4.1.16 Adsorption on Si and Ge(100) Compared to their (111) surface, the (100) surface of diamond lattices are simpler: the main clean form of these surfaces is the tilted-dimer (2x1) or c(4x2) reconstruction, determined on both Si and Ge, cf. Table 24. The c(4x2) phase is regarded as the more stable form, in which alternate dimers tilt in opposite directions. When heated, the tilting of the dimers becomes random and then on average forms a (2x1) lattice with disordered tilts. Several adsorbates, cf. Table 25, remove the tilted-dimer reconstruction, by simply capping dangling bonds of the ideal bulk-like termination. This can occur with H, Co and S. At lower coverages, adatoms (or larger molecular species) can maintain the dimer by capping its own dangling bonds, but the tilt is removed, resulting in a symmetric dimer. Metallic adsorbates generally also maintain the dimer, while symmetrizing it, after adsorption in a variety of configurations above and between the dimers: the adsorption occurs in so-called bridge, top, valley, cave or pedestal sites, depending on the metal. In yet other cases, as with Sb, the adsorbate itself forms dimers above the bulk-like substrate. Or the adsorbate forms dimers above substrate dimers, as with Al and Ga. And, not surprisingly, more complex reconstructions can occur on this type of surface as well.

4.1.17 Adsorption on diamond-like(311) The clean surface of Ge(311) has a complex reconstruction, cf. Table 26. While the corresponding structure of Si(311) is not well-established, adsorption of either H or Pb on Si(311) produces a very different reonstruction than seen on Ge(311), cf. Table 27.

4.1.18 Adsorption on zincblende(110) The clean (110) surfaces of zincblende compounds exhibit large relaxations (without superlattice), sometimes called reconstruction, cf. Table 28. There is no bond breaking or making relative to the ideal bulk termination, but mainly bond rotations with small bond length changes. In particular, the surface exposes zigzag rows of atoms, which are coplanar (untilted) in the ideal surface, and are tilted in the actual clean surface by angles around 25-30° from the surface plane. Most adsorbates which have been deposited on zincblende(110) surfaces largely remove the cleansurface relaxations, in particular canceling or even slightly reversing the clean-surface tilting, cf. Table 29. These atoms cap the dangling bonds of the ideal surface, in some cases (Sb, Bi) forming an additional layer of zigzag atoms, thus mimicking a continuation of the bulk lattice. Aluminum, on the other hand, substitutes for Ga in the outermost layers, penetrating to deeper substitutional sites in proportion to the amount of adsorbate present, while maintaining the clean-surface tilting.


Ref. p. 4.1-109]


4.1-11

4.1.19 Adsorption on zincblende(111) and (-1-1-1) The clean (111) and (-1-1-1) surfaces of zincblende reconstruct, cf. Tables 30 and 32: in the (111) case a missing-atom (2x2) structure appears for GaAs, with extensive relaxations around the empty site; the clean (-1-1-1) structure is rather more complex, with a large (3x3) supercell and additional disorder. Adsorbates, however, can totally remove these complex clean-surface reconstructions, and restore a bulk-like termination, cf. Tables 31 and 33. Sulfur and oxygen can bond at top sites on a full-bilayerterminated substrate, capping the dangling bonds, while the interlayer spacings in the substrate can relax. Or S can substitute for the outer half of the external bilayer.

4.1.20 Adsorption on zincblende(100) Clean zincblende(100) reconstructs in various arrangements of dimers, forming different superlattices like (2x1), (4x2) and c(8x2), cf. Table 34. The one documented case of adsorbate structure, cf. Table 35, has S adatoms removing the reconstruction of clean GaAs(100) and adsorbing at bridge sites.

4.1.21 Adsorption on 6H-SiC(0001) Clean 4H-SiC(0001) has a bulk-like surface termination with a (1x1) unit cell and small relaxations of the interlayer spacings, cf. Table 36. The adsorption of H, O and OH saturates the dangling bonds at top sites of the ideal termination in a full SiC bilayer and changes the interlayer spacings by amounts smaller than 0.1Å, cf. Table 37.

Acknowledgments This work was supported in part by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. It relied heavily on the Surface Structure Database supported by the Standard Reference Data Program of the National Institute of Standards and Technology of the U.S. Department of Commerce, with newer results supplied by individual authors.


Table 1. Techniques used for surface structure determination; listed by their acronyms

ALICISS ARAES

Alkali ICISS Angular Resolved Auger Electron Spectroscopy

ARPES ARUPS ARXPS ARXPD ARPEFS At. diffr. ATLEED At. scatt.

Angular Resolved Photoelectron Spectroscopy Angular Resolved Ultraviolet Photoelectron Spectroscopy Angular Resolved X-ray Photoelectron Spectroscopy Angular Resolved X-ray Photoelectron Diffraction Angular Resolved Photoelectron Fine Structure Atom Diffraction Automated Tensor LEED Atom Scattering

CAICISS CMTA

Coaxial Impact-Collision Ion Scattering Spectroscopy Constant-Momentum Transfer Averaging

DLEED

Diffuse LEED

EAPFS EELFS EELS ESDIAD EXAFS EXELFS EXFAS

Electron Appearance Potential Fine Structure Electron Energy Loss Fine Structure Electron Energy Loss Spectroscopy Electron Stimulated Desorption Ion Angular Distribution Extended X-ray Absorption Fine Structure Extended Electron Energy Loss Fine Structure Extended Fine Auger Structure

Fluorescence XRD FYNES

Fluorescence X-ray Diffraction Fluorescence-Yield Near-Edge Structure

GIXD GIXS

Grazing-Incidence X-ray Diffraction Grazing-Incidence X-ray Scattering

He diffr. HEIS HREELS

Helium Diffraction High-Energy Ion Spectroscopy High-Resolution Electron Energy Loss Spectroscopy

ICISS ISS

Impact Collision Ion Scattering Spectroscopy Ion Scattering Spectroscopy

KLEED

Kinematic Low-Energy Electron Diffraction



LEIS LEED LEPD

Low-Energy Ion Spectroscopy Low-Energy Electron Diffraction Low-Energy Positron Diffraction

MEED MEIS MEIS-SB

Medium-Energy Electron Diffraction Medium-Energy Ion Spectroscopy MEIS with Shadowing and Blocking

Neutr. diffr. NEXAFS NPD

Neutron Diffraction Near-Edge X-ray Absorption Fine Structure Normal Photoelectron Diffraction

OPD

Off-normal Photoelectron Diffraction

PED PES PEXAFS PLEED

Photoelectron Diffraction Photoelectron Spectroscopy Photoemission Extended X-ray Absorption Fine Structure (Spin-) Polarized LEED

QDLEED QKLEED

Quasi-Dynamic Low-Energy Electron Diffraction Quasikinematical Low-Energy Electron Diffraction

RBS RHEED

Rutherford Backscattering Reflection High-Energy Electron Diffraction

SEELFS SEXAFS SIMS SPLEED

Surface Electron Energy Loss Fine Structure Surface Extended X-ray Absorption Fine Structure Secondary Ion Mass Spectroscopy Spin-Polarized LEED

TEAS TED TOF-SARS

Thermal Energy Atomic Scattering Transmission Electron Diffraction Time-of-Flight Scattering and Recoiling Spectroscopy

XAFS XANES XAS XPD XPS XRD XSW

X-ray Absorption Fine Structure X-ray Absorption Near-Edge Structure X-ray Absorption Spectroscopy X-ray Photoelectron Diffraction X-ray Photoelectron Spectroscopy X-ray Diffraction X-ray Standing Wave


4.1-13

4.1-14 Table 2. Structures of clean fcc(111) surfaces. Surface

∆d12 [%] 10 ± 2

∆d23 [%] 5.5 ± 2

∆d34 [%] 0±6

∆d45 [%] 0

∆d56 [%] 0

Ref.

Description

94S6

unreconstructed surface; exhibiting strong temperaturedependent interlayer spacings above 600K: top spacing grows from contraction of -2.5±0.5% below 600K to +10±2% at 1150K (wrt to bulk value); 2nd spacing grows from +0.6% to +5.5%; 3rd spacing shows smaller effect bulk termination with expanded top spacing bulk termination with expanded top spacing multilayer relaxation: expansion of the 1st and 2nd interlayer spacings unreconstructed surface with expanded top interlayer spacing bulk termination with expanded top interlayer spacing unreconstructed relaxed surface relaxed bulk termination relaxed bulk termination: possible slight expansion of top interlayer spacing unreconstructed surface with possible slight contraction of top interlayer spacing unreconstructed clean surface with negligible contraction of top interlayer spacing unreconstructed surface with expanded top interlayer spacing unrelaxed bulk termination bulk termination with top spacing contraction unreconstructed surface with multilayer relaxations unrelaxed bulk termination slight relaxation of top two interlayer spacings slight relaxation of top two interlayer spacings bulk termination with expanded top spacing

Ag(111)

Tech- Clean dbulk nique rec. [Å] MEIS no 2.36

Al(111) Al(111) Al(111)

LEED no LEED no LEED no

2.338 2.22 ± 1.3 2.329 0.91 ± 0.5 2.338 1.7 ± 0.3

0 0 0.5 ± 0.7

0 0 0

0 0 0

0 0 0

80J 82N1 90N

Al(111)

LEED no

2.338 1.3 ± 0.9

0

0

0

0

94S5

Al(111) Al(111) Cu(111) Cu(111)

no no no no

2.338 2.329 2.09 2.09

3.08 ± 2.1 1.33 ± 0.4 -0.67 ± 1 0.75 ± 1

0 0.04 ± 0.4 0 0

0 0 0 0

0 0 0 0

0 0 0 0

83M1 94B8 84L 95B1

Cu(111)

LEED LEED LEED VLEED XPD

no

2.09

-1.44 ± 1

0

0

0

0

97H1

Ni(111)

LEED no

2.035 -0.25 ± 1

0

0

0

0

93K1

Ni(111)

XPD

no

2.03

2.96

0

0

0

0

97H1

Ni(111) Ni(111) Pd(111) Pd(111) Pd(111) Pd(111) Pt(111)

HEIS LEED LEED HEIS LEED LEED LEED

no no no no no no no

2.033 2.03 2.246 2.25 2.27 2.246 2.265

0±1 -1.23 ± 1.2 2.41 ± 0.9 0 ± 4.4 0.88 ± 1.3 1.34 ± 1.3 1.1 ± 4.4

0 0 0.63 ± 0.9 0 -1.76 ± 1.3 -1.34 ± 1.3 0

0 0 0.63 ± 1.8 0 -1.76 ± 1.8 2.23 ± 1.3 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0

81N1 75D 94G4 83K 94B4 87O 79A

4.1-15 Surface

Clean dbulk ∆d12 [Å] rec. [%] no 2.265 0.49 ± 0.9

∆d23 [%] 0

∆d34 [%] 0

∆d45 [%] 0

∆d56 [%] 0

Ref.

Description

81F

bulk termination with expanded top spacing unreconstructed relaxed bulk termination unreconstructed clean surface with slight first layer expansion unreconstructed surface with relaxed top two interlayer spacings; 0.5±0.4% contracted in-plane lattice parameter for all layers (incl. bulk) bulk termination with top spacing expansion unrelaxed bulk termination unreconstructed termination with relaxation of top two interlayer spacings unreconstructed relaxed bulk termination unrelaxed bulk termination slightly relaxed bulk termination

Pt(111) Pt(111)

Technique SPLEED LEED LEED

no no

2.26 1.33 ± 0.4 2.265 1.1 ± 1.3

0.44 ± 1.3 0.22

-1.33 ± 1.8 0 0 0

0 0

94B5 95M1

Pt(111)

LEED no

2.254 1.38 ± 0.6

-0.4 ± 0.7

0.22 ± 0.9

0

0

97G1

Pt(111) Pt(111) Rh(111)

MEIS no LEED no LEED no

2.268 1.41 ± 0.9 0 2.265 0 ± 2.2 0 2.196 -2.86 ± 1.4 0.16 ± 1.4

0 0 0

0 0 0

0 0 0

79V1 85H1 93W1

Rh(111) Rh(111) Rh(111)

LEED no LEED no LEED no

2.188 -1.28 ± 0.9 -1.28 ± 1.8 0.09 ± 2.3 2.192 0 ± 4.6 0 0 2.19 -1.37 ± 0.9 0 0

0 0 0

0 0 0

94B5 84V 80H

Pt(111)

Table 3. Adsorbate-induced structures on fcc(111) surfaces. Surface

Tech- Clean Adsnique rec. ind rec.

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

adsorption at fcc-hollow sites (see Fig. 3) Ni(111)+ (√3x√3) R30°-Cl Ni(111)+ (√3x√3) R30°-O

AR- no PEFS

no

4.7 ± 0.0003 0

0

0

1.837 ± 0.0008 0

91W3

atomic adsorption in fcc-hollow site with contraction between the 1st and 2nd Ni layers

HEIS no

no

-4.2 ± 1.5

0

0

1.2

81N2

atomic adsorption (in undetermined hollow sites; fcc assumed here); expanded top Ni-Ni interlayer spacing

0

0

4.1-16 Tech- Clean Adsnique rec. ind rec. LEED no no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

0 ± 1.0

0

0

0

1.08 ± 0.02

0

91M2

SEno XAFS

no

0

0

0

0

1.16 ± 0.10

0

92H1

O adsorbed in fcc-hollow site; substrate has expanded 1st interlayer spacing; no lateral shifts or buckling oxygen adsorbed in fcc-hollow sites; no buckling in 1st Ni layer

LEED no

no

0.8 ± 2.0

0

0

0

1.59 ± 0.05

0

96W

LEED no

no

-3.9 ± 3.0

0

0

0

2.22 ± 0.06

0

93B2

LEED no

no

1.5 ± 0.9

0

2.5 ± 3.0

0

2.70 ± 0.03

0

94G4

LEED no

no

6.2 ± 2.2

0

0

0

1.29 ± 0.05

0

87O

LEED no

no

0.7 ± 1.3

0

0.6 ± 2.5

0

1.55 ± 0.03

0

97Y

atomic adsorption in fcc-hollow site; buckling in top two layers of substrate

LEED no

no

-0.9 ± 0.8 1.2 ± 1.3

-3.8 ± 1.7 1.3 ± 0.8

0 0

0 0

3.01 ± 0.04

0

97K1

Ag(111)+ (2x2)-K

LEED no

no

-0.9 ± 0.8 -0.1 ± 0.8

-4.2 ± 1.3 1.3 ± 0.8

0 0

0 0

1.52 ± 0.02

0

96L1

Ag(111)+ (2x2)-Rb

LEED no

no

-0.9 ± 0.8 -0.5 ± 0.8

-4.2 ± 0.1 1.3 ± 0.1

0 0

0 0

2.84 ± 0.03

0

96L1

atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 2 substrate layers atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 2 substrate layers atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 2 substrate layers

Surface

Ni(111)+ (√3x√3) R30°-O Ni(111)+ (√3x√3) R30°-O Rh(111)+ (√3x√3) R30°-S Rh(111)+ (√3x√3) R30°-I Pd(111)+ (√3x√3) R30°-S Pd(111)+ (√3x√3) R30°-CO Pt(111)+ (√3x√3) R30°-S Ag(111)+ (2x2)-Cs

atomic adsorption on unreconstructed substrate: S adsorbs on fcc-hollow site; substrate relaxations negligible atomic adsorption in three fold fcc-hollow site on unreconstructed; relaxed Rh substrate atomic S in fcc-hollow site on unreconstructed; relaxed substrate; oscillitory expansion of top 4 Pd-Pd interlayer spacings molecular upright adsorption (C down) in fcchollow sites

4.1-17 Surface

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-2.3 ± 1.9 -2.5 ± 2.5

0 0.2 ± 2.6

-0.2 ± 5.0 -0.1 ± 6.7

0 0

2.07 ± 0.06

0

95M4

no

0.3 ± 1.5

2.0 ± 3.9

0

0

0.97 ± 0.08

0

93H1

no

5.7 ± 4.9

-1.5 ± 5.0; 0.0 ± 5.0

0

0

1.28 ± 0.05

0

95D1

complex reconstruction with overlayer and substitution: two Li adatoms located on fcc and hcp-hollow sites and one Li atom substituting for a Cu atom in each cell atomic adsorption with equal occupation of fcc and hcp-hollow sites; forming honeycomb-like lattice; buckling in 1st Ni layer: expansion of 2nd Ni-Ni interlayer spacing K atoms occupy atop sites; CO molecules perpendicular to surface; occupying fcc and hcphollow sites

no

1.7 ± 1.5

5.9 ± 1.5

5.0 ± 4.0

2.35

1.09 ± 0.03

0

90V3

Tech- Clean Adsnique rec. ind rec. LEED no no

Cu(111)+ (2x2)-3Li: 1 Li fcchollow site Ni(111)+ LEED no (2x2)-2H: 1 H at fcchollow site PED no Ni(111)+ (2x2)K+2CO: 1 CO at fcchollow site Ni(111)+ LEED no (2x2)-O

Ni(111)+ (2x2)-O

SEno XAFS

no

4.4 ± 4.9

8.3 ± 4.9

0

0

1.16 ± 0.10

0

92H1

Ni(111)+ (2x2)-O

LEED no

no

5.7 ± 1.0 0.8 ± 1.0

4.5 ± 1.0 -2.0 ± 1.0

0 0

0 0

1.11 ± 0.02

0

94S2

Ni(111)+ (2x2)-O Ni(111)+ (2x2)-S

PED

no

no

8.5 ± 5.0

4.9 ± 10.0

0

0

1.08 ± 0.10

0

96D1

LEED no

no

2.7 ± 1.5 2.2 ± 1.5

0 0

2.0 ± 2.0 0

0 0

1.5 ± 0.03

0

89W

oxygen adsorbed in fcc-hollow sites; buckling and lateral shifts in 1st Ni layer: 3 Ni next to O are lifted and rotated/outwards shifted; 1st Ni-Ni interlayer spacing contracts; deeper layers are bulk like oxygen adsorbed in fcc-hollow sites; buckling in 1st Ni layer S in fcc-hollow site on unreconstructed relaxed substrate: buckling in the first and second Ni layers; no evidence for rotation of hollow site atomic O overlayer in fcc-hollow sites on unreconstructed; slightly buckled substrate overlayer in 3-fold-hollow fcc sites; expansions of top 2 Ni-Ni interlayer spacings; lateral radial expansion of 3-fold site

4.1-18 Surface

Pt(111)+ (2x2)-C2H3


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-1.6 ± 4.4 -1.1 ± 4.4

-4.9 ± 4.4 -3.5 ± 4.4

-7.0 ± 5.5 0.2 ± 5.5

0 0

1.19 ± 0.10; 1.30 ± 0.10

0

93S4

ethylidyne species (CCH3=C2H3) formed from ethylene (C2H4) with upright C-C axis: lower C in fcc-hollow site; upper C forms methyl group (LEED data not sensitive to H positions); buckling in top 2 Pt layers densely packed molecular adsorption with 1 CO on top site; 1 CO on hcp-hollow site and 1 CO on fcchollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer densely packed molecular adsorption with 1 NO on top site; 1 NO on hcp-hollow site and 1 NO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer atomic adsorption on unreconstructed relaxed substrate; adatom at fcc-hollow site coadsorption of atomic oxygen and molecular CO on relaxed substrate O on fcc-hollow site; CO on top site

Rh(111)+ LEED no (2x2)-3CO: 1CO at fcchollow site

no

3.1 ± 1.8 -0.1 ± 2.7

0.0 ± 1.8 3.7 ± 1.8

0.0 ± 7.0 -0.4 ± 7.0

0 0

1.47 ± 0.04

0

97G3

Rh(111)+ LEED no (2x2)-3NO: 1NO at fcchollow site

no

4.0 ± 1.8 -1.4 ± 2.7

0.0 ± 1.8 2.6 ± 1.8

0.0 ± 7.0 0.0 ± 7.0

0 0

1.30 ± 0.04

0

98Z

Rh(111)+ (2x2)-O Rh(111)+ (2x2)(O+1CO): O site Rh(111)+ (2x2)(O+2CO): O site Pt(111)+ (2x2)-C2H3

LEED no

no

4.8 ± 2.0

2.3 ± 2.3

0

0

1.24 ± 0.06

0

97S2

LEED no

no

5.3 ± 1.4

-1.8 ± 1.4

3.9 ± 3.8

0

1.28 ± 0.04

0

97S2

LEED no

no

4.4 ± 1.8

0.0 ± 2.3

1.3 ± 3.8

0

1.31 ± 0.09

0

97S2

coadsorption of atomic oxygen and molecular CO on unreconstructed; relaxed substrate; oxygen in fcc-hollow site; CO in top site and hcp-hollow site

LEED no

no

3.3 ± 1.3 -1.0 ± 4.4

4.9 ± 2.2 -3.5 ± 4.0

-6.0 ± 5.0 0.0 ± 5.0

0 0

1.49 ± 0.10

0

93S4

ethylidyne species (CCH3=C2H3) formed from ethylene (C2H4) with upright C-C axis: lower C in fcc-hollow site; upper C forms methyl group (LEED data not sensitive to H positions); buckling in top 2 Pt layers

4.1-19 Surface

Pt(111)+ (2x2)-O

Pt(111)+ (2x2)-NO Pt(111)+ (2x2)-S Ag(111)+ (3x3)-Cs


LEED no

no

LEED no

no

LEED no

no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

2.4 ± 1.3 -1.1 ± 1.3

3.1 ± 0.9 -0.9 ± 0.9

1.7 ± 2.0 0.1 ± 3.0

0 0

1.19 ± 0.02

0

95M1

2.4 ± 0.9 0 0.3 ± 2.2 3.5 ± 1.8 2.1 ± 0.8

3.1 ± 2.6 -0.9 ± 0.9 3.5 ± 1.8 3.5 ± 1.8 -4.2 ± 1.3; -4.7 ± 1.3 -1.7 ± 1.3; -2.5 ± 1.3 0; -1.3 ± 2.0; -1.7 ± 2.0 -3.4 ± 1.3; -3.8 ± 1.3 -1.7 ± 1.3; -2.5 ± 1.3 0; -1.3 ± 2.0; -1.7 ± 2.0

2.4 ± 1.2 -5.7 ± 1.2 1.9 ± 2.5 0.0 ± 3.8 0; 0 0; 0 0; 0; 0 0; 0 0; 0 0; 0; 0

0 0 0 0 0; 0 0; 0 0; 0; 0 0; 0 0; 0 0; 0; 0

1.26 ± 0.06

0

94M2

1.54 ± 0.03

0

97Y

3.02 ± 0.03

0

97K1

atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling and lateral relaxation in the first 2 Pt layers; slight expansion and contraction of first two Pt-Pt interlayer spacings; resp. molecular adsorption perpendicular to surface in fcc 3-fold hollow sites on relaxed substrate atomic S adsorption on fcc-hollow sites; buckling in first layer of substrate atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 3 substrate layers

2.72 ± 0.03

0

97K1

1.2 ± 1.3 0.0 ± 1.7

Ag(111)+ (3x3)-K

LEED no

no

2.0 ± 1.3 1.6 ± 2.0 -0.5 ± 3.8

atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 3 substrate layers

4.1-20 Surface

Ag(111)+ (3x3)-Rb


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

2.4 ± 0.8

-3.8 ± 1.3; -4.2 ± 1.3 -1.7 ± 1.3; -2.5 ± 1.3 0; -1.7 ± 1.3; -0.8 ± 1.3

0; 0 0; 0 0; 0; 0

0; 0 0; 0 0; 0; 0

2.84 ± 0.03

0

97K1

atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 3 substrate layers

molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over fcc-hollow sites; both with relaxed bonds (H ignored); 1st substrate layer relaxed; topmost PdPd interlayer spacing expanded to 2.32Å (average) from bulk value of 2.25Å molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over fcc-hollow sites; both with relaxed bonds (H ignored); 1st substrate layer relaxed; topmost PdPd interlayer spacing expanded to 2.32Å (average) from bulk value of 2.25Å atomic overlayer with O adsorbed in fcc-hollow sites; possibly off-center toward top sites; top 2 substrate layers relaxed; both buckled atomic adsorption on unreconstructed relaxed substrate; adatom at fcc-hollow site molecular adsorption; C-O axis perpendicular to surface; CO occupy equally (0.25 ML each) fcc and hcp-hollow sites O atom sites not determined explicitly molecular adsorption in mixed fcc/hcp sites; CO tilted and bent away from nearest CO; buckled first and second Ni layers

1.2 ± 1.3 -0.5 ± 1.7

Pd(111)+ LEED no (3x3)-C6H6+ 2CO: 2CO sites

no

0.4 ± 2.2

0.0 ± 2.2; -2.2 ± 2.2

0; 3.2 ± 7.0

0; 0

1.22 ± 0.05; 1.31 ± 0.05

0

94B4

Pd(111)+ LEED no (3x3)-C6H6+ 2CO: C6H6 site

no

2.6 ± 2.2

0.0 ± 2.2; 2.2 ± 2.2

0; 0.8 ± 7.0

0; 0

2.16 ± 0.05

0

94B4

Rh(111)+ (2x1)-O

LEED no

no

-0.8 ± 0.1

-3.2 ± 0.05

0

0

1.18 ± 0.05

0

96C1

Rh(111)+ LEED no (2x1)-O PED no Ni(111)+ c(4x2)-2CO: 1CO at fcchollow site Ni(111)+ LEED no c(4x2)-2CO: 1CO at fcchollow site

no

3.9 ± 2.0

1.8 ± 2.0

0

0

1.23 ± 0.04

0

97S2

no

3.2 ± 7.4

0

0

0

1.29 ± 0.07

0

94D1

no

6.1 ± 4.9

5.9 ± 4.9; 4.9 ± 4.9

complex

0; 0

1.25 ± 0.10; 1.37 ± 0.10

0

94M1

4.1-21 Surface


Ni(111)+ c(4x2)-2NO: 1NO at fcchollow site Rh(111)+ LEED no c(4x2)-2S: 1 S at fcchollow site Rh(111)+ (disordered)-I

LEED no

no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

4.6 ± 2.0

7.3 ± 2.0; 0.0 ± 2.0

complex

0; 0

1.17 ± 0.04; 1.32 ± 0.04

0

94M2

molecular NO perp. to surface; in both fcc and hcp 3-fold hollow sites; relaxations in first 2 substrate layers

-2

-10.0; 0.2 -1.0; 0.5

complex

0; 0 0; 0

1.72; 1.49; 1.72

0

96W

atomic adsorption on unreconstructed substrate: equal occupation of fcc-hollow and hcp-hollow sites; S lateral shifts in both sites towards one of the nearby Rh atoms; to make S-S distances more equal; 1st Rh layer buckled atomic adsorption in three fold fcc-hollow site on unreconstructed; relaxed Rh substrate

-0.1 no

-3.9 ± 3.0

complex

0

0

0

2.22 ± 0.06

0

93B2

0.0 ± 2.0 0; 0.0 ± 2.0 0.0 ± 2.0 0; 0.0 ± 2.0 0.0 ± 2.0 0; 0.0 ± 2.0 0.0 ± 2.0

0 0; 0 0 0; 0 0 0; 0 0

3.10 ± 0.03

0

97K1

2.84 ± 0.03

0

96L1

2.97 ± 0.03

0

96L1

2.90 ± 0.03

0

96S1

0.0 ± 2.0

0

2.80 ± 0.03

0

96S1

adsorption at hcp-hollow sites (see Fig. 4) Ag(111)+ (√3x√3) R30°-Cs Ag(111)+ (√3x√3) R30°-K Ag(111)+ (√3x√3) R30°-Rb Rh(111)+ (√3x√3) R30°-Cs Rh(111)+ (√3x√3) R30°-K

LEED no

no

-0.1 ± 1.4 -0.5 ± 1.4

LEED no

no

-0.5 ± 0.8 0.0 ± 0.8

LEED no

no

-0.5 ± 0.8 0.0 ± 0.8

LEED no

no

-0.2 ± 1.4

0 0; 0.4 ± 1.4 0 0; 0.9 ± 0.8 0 0; 0.9 ± 0.8 0

LEED no

no

-1.1 ± 1.4

0

atomic overlayer in hcp-hollow sites on unreconstructed substrate; with buckling in the second substrate layer atomic overlayer in hcp-hollow sites on unreconstructed substrate; with buckling in the second substrate layer atomic overlayer in hcp-hollow sites on unreconstructed substrate; with buckling in the second substrate layer atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-0.2 ± 1.4

0

0.0 ± 2.0

0

2.84 ± 0.03

0

96S1

atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site

LEED no

no

1.0 ± 0.8

0

0

0

2.71 ± 0.02

0

98M4

atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site

LEED no

no

-2.1 ± 1.9 -2.7 ± 2.5

0 0; -0.2 ± 2.6

0.2 ± 5.0 0; 0

0 0; 0

2.15 ± 0.06

0

95M4

LEED no

no

1.8 ± 1.5

2.0 ± 3.9

0

0

0.97 ± 0.08

0

93H1

PED

no

no

5.7 ± 4.9

-1.5 ± 5.0; 0.0 ± 5.0

0; 0

0; 0

1.28 ± 0.05

0

95D1

complex reconstruction with overlayer and substitution: two Li adatoms located on fcc and hcp-hollow sites and one Li atom substituting for a Cu atom in each cell atomic adsorption with equal occupation of fcc and hcp-hollow sites; forming honeycomb-like lattice; buckling in 1st Ni layer: H-coordinated Ni atoms raised; expansion of 2nd Ni-Ni interlayer spacing K atoms occupy atop sites; CO molecules perpendicular to surface; occupying fcc and hcphollow sites

LEED no

no

-0.3 ± 1.0

-3.1 ± 0.9

0

0

2.68 ± 0.03

0

98M4

LEED no

no

4.6 ± 4.6 1.0 ± 4.6

3.6 ± 4.6 0; 0.0 ± 4.6

0.4 ± 6.1 0; 0.0 ± 0.2

0 0; 0

1.20 ± 0.10; 1.28 ± 0.10

0

94B5

Rh(111)+ LEED no (2x2)-3CO: 1CO at hcphollow site

no

6.7 ± 1.8 -3.8 ± 2.7

0.0 ± 1.8 0; -3.6 ± 1.8

-0.4 ± 6.1 0; 0.0 ± 0.2

0 0; 0

1.47 ± 0.07; 1.47 ± 0.07

0

97G3

Rh(111)+ (2x2)-K

no

-1.6 ± 1.4

-1.8 ± 1.4

0.0 ± 2.0

0

2.78 ± 0.03

0

96S1

Surface

Rh(111)+ (√3x√3) R30°-Rb Pt(111)+ (√3x√3) R30°-K Cu(111)+ (2x2)-3Li: 1 Li at hcphollow site Ni(111)+ (2x2)-2H: 1 H at hcphollow site Ni(111)+ (2x2)K+2CO: 1 CO at hcphollow site Pt(111)+ (2x2)-K Rh(111)+ (2x2)-C2H3

LEED no

atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site ethylidyne species (CCH3 = C2H3) formed from ethylene (C2H4) with upright C-C axis: lower C in hcp-hollow site; upper C forms methyl group; buckling in top 2 Rh layers densely packed molecular adsorption with 1 CO on top site; 1 CO on hcp-hollow site and 1 CO on fcchollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site

4.1-23 Surface

Rh(111)+ (2x2)-3NO: 1NO at hcphollow site Rh(111)+ (3x3)-C6H6+ 2CO: 2CO sites Rh(111)+ (3x3)-C6H6+ 2CO: C6H6 site Ni(111)+ c(4x2)-2CO: 1CO at hcphollow site Ni(111)+ c(4x2)-2CO: 1CO at hcphollow site


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

7.2 ± 1.8 -1.5 ± 2.7

0.0 ± 1.8 0; -2.7 ± 1.8

0.0 ± 6.1 0; 0.0 ± 0.2

0 0; 0

1.29 ± 0.07

0

98Z

densely packed molecular adsorption with 1 NO on top site; 1 NO on hcp-hollow site and 1 NO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over hcp-hollow sites; both with relaxed C-C bonds (H ignored); 1st substrate layer relaxed molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over hcp-hollow sites; both with relaxed C-C bonds (H ignored); 1st substrate layer relaxed molecular adsorption; C-O axis perpendicular to surface; CO occupy equally (0.25 ML each) fcc and hcp-hollow sites O atom sites not determined explicitly molecular adsorption in mixed fcc/hcp sites; CO tilted and bent away from nearest CO; buckled first and second Ni layers

LEED no

no

-1.1 ± 3.2

-0.9 ± 3.2; -0.9 ± 3.2

-0.7 ± 6.1; -2.1 ± 6.1

0; 0

1.36 ± 0.10; 1.39 ± 0.10

0

94B4

LEED no

no

-1.1 ± 3.2

0.9 ± 2.2; 0.9 ± 3.2

0; -3.9 ± 6.1

0; 0

2.07 ± 0.04

0

94B4

PED

no

no

3.2 ± 7.4

0

0

0

1.30 ± 0.07

0

94D1

LEED no

no

6.1 ± 4.9

-4.9 ± 4.9; -5.9 ± 4.9 0; -3.9 ± 4.9; -1.5 ± 4.9

complex

0; 0 0; 0; 0

1.37 ± 0.10; 1.27 ± 0.10; 1.25 ± 0.10

0

94M1

-4.6 ± 4.9

complex

4.1-24 Surface

Ni(111)+ c(4x2)-2NO: 1NO at hcphollow site

Rh(111)+ c(4x2)-2S: 1 S at hcphollow site


LEED no

no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-1.2 ± 2.0

-7.4 ± 2.0; 0.0 ± 2.0

complex

0; 0

1.32 ± 0.04; 1.17 ± 0.04; 1.32 ± 0.04

0

94M2

molecular NO perp. to surface; in both fcc and hcp 3-fold hollow sites; relaxations in first 2 substrate layers

-0.7 ± 2.0

0; -1.5 ± 2.0; -2.5 ± 2.0

complex

0; 0; 0

-1.9

-10.3; -0.2 0; -0.3; -1.5 -3.9 ± 3.4; -6.9 ± 3.4

complex

0; 0 0; 0; 0 0; ± 1.6; ± 2.5

1.72; 1.49; 1.72

0

96W

1.93 ± 0.05; 2.01 ± 0.05; 2.01 ± 0.05

0

96H2

atomic adsorption on unreconstructed substrate: equal occupation of fcc-hollow and hcp-hollow sites; S lateral shifts in both sites towards one of the nearby Rh atoms; to make S-S distances more equal; 1st Rh layer buckled molecular C6H6 centered on hcp sites on unreconstructed substrate; C-C bonds parallel to [110] direction; slight ring expansion; no significant buckling of benzene; strong buckling of top Ni layer molecular C6H6 centered on hcp sites on unreconstructed substrate; C-C bonds parallel to [110] direction; slight ring expansion; no significant buckling of benzene; strong buckling of top Ni layer

-0.4

complex

Ni(111)+ ( LEED no √7x√7) R19°-C6H6: high C

no

2.5 ± 3.0

0; 0.8 ± 5.8

Ni(111)+ LEED no (√7x√7) R19°-C6H6: low C

no

2.5 ± 3.0

-3.9 ± 3.4; -6.9 ± 3.4

0; 0.8 ± 5.8

0; 1.97 ± 0.05; ± 1.6; 2.05 ± 0.05; ± 2.5 2.05 ± 0.05

0

96H2

-5.5 ± 2.1

0; -10.7 ± 1.7

0; 0

0; 0

0

94S5

adsorption at top sites (see Fig. 5) Al(111)+ (√3x√3) R30°-K (90K)

LEED no

no

3.23 ± 0.05

atomic K in top site on unreconstructed but relaxed substrate: Al directly below K depressed into bulk; Al in next layer laterally displaced by small shift; perpendicular relaxation between top two Al layers


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-5.8 ± 0.9

0, -11.4 ± 0.9

0; 0

0; 0

3.36 ± 0.03

0

94N2

adatoms in top sites of unreconstructed relaxed substrate: downward buckling of Al directly below Rb in top Al layer

LEED no

no

8.1 ± 2.3

97G3

no

1.7 ± 4.6 -8.6 ± 2.9

0; 0 0 0; 0

0

no

0; 0 0.0 ± 7.3 0; 0

1.20 ± 0.05

PED

0; 3.6 ± 2.7 0 0; -0.5 ± 4.4

2.87 ± 0.04

0

94D2

Ni(111)+ (2x2)-K

AR- no PEFS

no

-6.4 ± 2.0

0

0

0

3.02 ± 0.01

0

93H5

Ni(111)+ (2x2)-K

LEED no

no

-4.2 ± 1.5

0; -5.9 ± 1.0

0; 0

0; 0

2.82 ± 0.04

0

93K1

PED no Ni(111)+ (2x2)K+2CO: 1 K at top site Rh(111)+ LEED no (2x2)-3CO: 1 CO at top site

no

6.2 ± 4.9

0; 0.5 ± 5.0

0; 0

0; 0

3.02 ± 0.05

0

95D1

molecular adsorption at top sites: CO upright; C down on relaxed substrate; top substrate layer slightly buckled K atoms occupy atop sites; outer Ni layer spacing contracted but no significant buckling; K has large vibrational amplitude parallel to surface atomic adsorption on top sites; with contraction of first Ni interlayer spacing; negligible lateral relaxations and buckling atomic adsorption on top sites; with buckling of the first two Ni layer and small horizontal relaxation of the top Ni layer (within error bars) K atoms occupy atop sites; CO molecules perpendicular to surface; occupying fcc and hcphollow sites

no

3.1 ± 1.8

0; 0.0 ± 1.8 3.6 ± 1.8

0; 0.0 ± 0.2 -0.6 ± 7.0

0; 0 0

1.83 ± 0.07

0

97G3

Rh(111)+ LEED no (2x2)-Cs Rh(111)+ LEED no (2x2)-3NO: 1 NO at top site

no

-1.6 ± 1.5

0; 0 0; 0 0

0

96S1

4.5 ± 1.8

0; 0 0; 0.0 ± 0.2 0.0 ± 6.1

2.96 ± 0.03

no

0; -1.8 ± 1.4 0; 0.0 ± 1.8 2.7 ± 1.8

1.76 ± 0.07

0

98Z

Surface

Al(111)+ (√3x√3) R30°-Rb (100K) Rh(111)+ (√3x√3) R30°-CO Ni(111)+ (2x2)-K

-0.2 ± 2.7

1.2 ± 2.7

densely packed molecular adsorption with 1 CO on top site; 1 CO on hcp-hollow site and 1 CO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer atomic adsorption on unreconstructed unrelaxed substrate; adatom at top site densely packed molecular adsorption with 1 NO on top site; 1 NO on hcp-hollow site and 1 NO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer

4.1-26 Surface


Rh(111)+ (2x2)(O+1CO): CO at top site Rh(111)+ LEED no (2x2)(O+2CO): 1 CO at top site

no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

5.3 ± 1.4

0; 1.8 ± 1.4

0; 0.0 ± 0.1

0; 0

1.83 ± 0.05; 1.87 ± 0.05

0

97S2

coadsorption of atomic oxygen and molecular CO on relaxed substrate O on fcc-hollow site; CO on top site

4.4 ± 2.3

0; 0.0 ± 2.2

0; 0.0 ± 0.1

0; 0

1.86 ± 0.05; 1.86 ± 0.05

0

97S2

coadsorption of atomic oxygen and molecular CO on unreconstructed; relaxed substrate; oxygen in fcc-hollow site; CO in top site and hcp-hollow site

distorted molecular adsorption on relaxed; unreconstructed substrate: C-N axis near parallel to surface with N near fcc 3-fold hollow site and N near bridge site; C-C-N bond angle is 123±15° (vs. 180° for free molecule; making methyl (CH3) group of acetonitrile points away from surface; molecular adsorption; C-C axis (almost) parallel to surface: molecule in aligned-bridge site with C atoms almost directly above top layer Ni atoms; C-C bond extended ~0.27Å relative to gas phase molecule

molecular adsorption with adatoms at low-symmetry sites Ni(111)+ (2x2)CH3CN

LEED no

no

94G1

Ni(111)+ (disordered)C2H4

PED

no

94B2

no

adsorption at substitutional site in top substrate layer (see Fig. 6) Ag(111)+ (√3x√3) R30°-Sb

CA- no ICISS

yes

0

0

0

0

0

0

97N2

atomic Sb adsorbate substitutional in outermost layer site

4.1-27 Surface

Al(111)+ (√3x√3) R30°-K (300K) Al(111)+ (√3x√3) R30°-Li Al(111)+ (√3x√3) R30°-Na Al(111)+ (√3x√3) R30°-Na Al(111)+ (√3x√3) R30°-Na Al(111)+ (√3x√3) R30°-Na+O Al(111)+ (√3x√3) R30°-Rb (300K) Al(111)+ (√3x√3) R30°-Rb (300K) Cu(111)+ (√3x√3) R30°-Sn

Tech- Clean Adsnique rec. ind rec. LEED no yes

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-1.9 ± 1.0

0

0

0

2.16 ± 0.03

0

94S5

LEED no

yes

-1.7 ± 0.9 -0.8 ± 0.9

0 0

0 0

0 0

0.41 ± 0.1

0

96N

atomic K in quasi-substitutional sites formed by ejection of 1/3 of top-layer Al; perpendicular relaxation between top two Al layers; no lateral relaxations adatoms in substitutional sites in top Al layer

SEno XAFS

yes

-0.0 ± 1.3

0

0

0

1.67 ± 0.03

0

91S1

Na in a sixfold substitutional site

XSW no

yes

0

0

0

0

1.20 ± 0.2

0

92K1

Na atom in substitutional sites in top Al layer

LEED no

yes

-2.5 ± 1.1

0

0

0

1.47 ± 0.02

0

94B8

atomic adsorption in substitutional sites; replacing one third of atoms in top Al layer

XSW no

yes

0

0

0

0

1.20 ± 0.08

0

95S2

LEED no

yes

-2.7 ± 0.9

0

0

0

2.41 ± 0.02

0

94N2

Na atom in substitutional sites of reconstructed substrate; O atop Na atoms; substrate atom positions assumed bulk-like adatoms in substitutional sites in top Al layer

XSW no

yes

0

0

0

0

2.39 ± 0.10

0

94S4

Rb adatoms in substitutional sites on reconstructed substrate; substrate atom positions assumed bulklike

LEIS no

yes

0

0

0

0

0.39 ± 0.10

0

92O3

substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards

4.1-28 Surface

Pt(111)+ (√3x√3) R30°-Sn Pt(111)+ (√3x√3) R30°-Sn Pt(111)+ (√3x√3) R30°-Sn Rh(111)+ (√3x√3) R30°-Sn Cu(111)+ (2x2)-3Li: 1 Li in subst. site Pt(111)+ (2x2)-Sn Pt(111)+ (2x2)-Sn

Tech- Clean Adsnique rec. ind rec. AL- no yes ICISS

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

0

0

0

0

0.22 ± 0.05

0

91O3

atomic substitutional adsorption in fcc-hollow site; approximating Pt3Sn(111) termination substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards atomic substitutional adsorption in fcc-hollow site; approximating Rh3Sn (111) termination

LEIS no

yes

0

0

0

0

0.22 ± 0.10

0

92O3

LEED no

yes

-0.2 ± 2.2 2.9 ± 4.4

0 0

0 0

0

0.23 ± 0.05

0

93A

AL- no ICISS XPD

yes

0.0 ± 2.3

0

0.29 ± 0.05

0

97L1

LEED no

yes

-2.3 ± 1.9 -2.5 ± 2.5

0 0.2 ± 2.6

0 0

0 0

0.60 ± 0.06

0

95M4

AL- no ICISS LEED no

yes

0

0

0

0

0.22 ± 0.05

0

91O3

yes

-0.2 ± 2.2 2.0 ± 4.4

0 0

0 0

0 0

0.30 ± 0.05

0

93A

yes

0

0

0

0

1.20 ± 0.2

0

92K1

Na atom in substitutional sites in top Al layer

97N2

atomic 1/4 ML Sb (2x2) overlayer adsorbed in hcp-hollow sites on mixed (√3x√3)R30° Ag+Sb layer containing 1/3 ML Sb

Al(111)+ XSW no (disordered)-Na

complex reconstruction with overlayer and substitution: two Li adatoms located on fcc and hcp-hollow sites and one Li atom substituting for a Cu atom in each cell atomic substitutional adsorption in fcc-hollow site; approximating Pt3Sn(111) termination substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards

adsorption at substitutional site in top substrate layer and as overlayer Ag(111)+ (2√3x2√3) R30° -7Sb

CA- no ICISS

yes

4.1-29 Surface

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

yes

94B1

ordered mixed alloy in top two layers: relaxation of top two interlayer spacings

surface alloy structure: Na-Al-Na 'sandwich' on a reconstructed Al layer with a (2x2) vacancy structure; lower Na in substitutional site in Al vacancy; upper Na in fcc sites; sandwich Al in hcp sites surface alloy structure: Na-Al-Na 'sandwich' on a reconstructed Al layer with a (2x2) vacancy structure; lower Na in substitutional site in Al vacancy; upper Na in fcc sites; sandwich Al in hcp sites composite double-layer surface alloy: 1 Na atom substituting for a surface Al atom; 1 Na atom in a fcc-hollow adsorption site; 1 Al atom in a hcphollow adsorption site ternary surface alloy: K-Al-Na 'sandwich' on a reconstructed Al layer with a (2x2) vacancy structure; Na in substitutional site in Al vacancy; K in fcc sites above 2nd-layer Al; sandwich Al in hcp sites


adsorption at substitutional site in top two substrate layers Au(111)+ (√3x√3) R30°-4Pd

LEED yes

complex reconstruction Al(111)+ (2x2)-2Na

LEED no

yes

95B5

Al(111)+ (2x2)-2Na

SEno XAFS

yes

95B5

Al(111)+ (2x2)-2Na

XPD

no

yes

95F1

Al(111)+ LEED no (2x2)-Na+K

yes

96C2

4.1-30 Surface

Rh(111)+ (√7x√7) R19°-3P

Tech- Clean Adsnique rec. ind rec. LEED no yes

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

97L2

reconstruction with packed Rh pentagons and triangles; 3 symm.-equivalent P atoms per unit cell in 8-fold coordinated sites; these form a dense; relatively coplanar layer (buckled 0.17Å); 2nd and 3rd layers are pure Rh; buckled 0.06Å and 0.08Å resp.; vs bulk reconstructed mixed top layer of stoichiometry CuS commensurate with substrate; Cu atoms in this CuS layer are coplanar; 2/3 of S lie ~0.56Å below this Cu layer in hollow sites relative to bulklike substrate; other 1/3 S lie about coplanar with top Cu; over top site of substr. complex reconstruction forming Cu4S units (1 per unit cell); each having a S atom adsorbed in the fourfold site on top of a Cu tetramer; additional S atoms are present at a level just below the Cu4 plane; the positions of these atoms relative to the bulk are undetermined complex reconstruction forming Cu4S units (2 per unit cell); each having a S atom adsorbed in the fourfold site on top of a Cu tetramer; additional S atoms are present at a level just below the Cu4 plane; the positions of these atoms relative to the bulk are undetermined S overlayer on 'clock-reconstructed' pseudo-(100) Ni outer layer such that S atoms have two different layer spacings; one from a 'dropped' layer at regular fault-lines in the reconstruction; note: outer layer Ni x,y coordinates are indicative only; as is exact substrate registry

Cu(111)+ (√7x√7) R19°-3S

XSW no SEXAFS

yes

90P2

Cu(111)+ (√7x√7) R19°-3S

XRD no

yes

97F2

Cu(111)+ XRD no (4,1/-1,4)-6S

yes

97F2

Ni(111)+ (5√3x2) rect-8S

yes

96L4

XSW no

4.1-31 Table 4. Structures of clean hcp(0001) surfaces. ∆d12 [%] 5.1 ± 0.4

∆d23 [%] -0.2 ± 0.5

∆d34 [%] 0.2 ± 0.5

∆d45 [%] 0

∆d56 [%] 0

Ref.

Description

Be(0001)

Tech- Clean dbulk nique rec. [Å] LEED no 1.79

92D

Co(0001) Gd(0001) Gd(0001) Mg(0001) Ru(0001) Sc(0001)

LEED LEED LEED LEED LEED LEED

0.0 ± 2.4 -1.4 ± 1.0 -1.4 ± 0.5 2.7 ± 0.3 -1.8 ± 0.9 -1.9 ± 0.8

0 2.1 ± 1.0 1.0 ± 0.5 0.8 ± 4.0 0 0

0 0 0 -0.4 ± 0.5 0 0

0 0 0 0 0 0

0 0 0 0 0 0

78L 92Q2 95G3 93S3 83M3 82T2

Tb(0001) Ti(0001)

LEED no LEED no

2.847 -5.3 ± 1.1 2.34 -2.1 ± 2.1

1.4 ± 1.1 0

0 0

0 0

0 0

91Q 76S1

Zn(0001) Zr(0001)

LEED no LEED no

2.44 2.57

0 0

0 0

0 0

0 0

75U 79M

bulk termination with large expansion of top interlayer spacing bulk hcp termination multilayer relaxation unreconstructed with multilayer relaxation bulk termination with top spacing expansion bulk termination with top spacing contraction bulk-like termination with contraction of top interlayer spacing multilayer relaxation bulk-like termination with contraction of top interlayer spacing bulk termination with top spacing contraction bulk hcp termination with top spacing contraction

Surface

no no no no no no

2.05 2.89 2.89 2.592 2.14 2.64

-2.0 ± 2.0 -1.7 ± 1.9

Table 5. Adsorbate-induced structures on hcp(0001) surfaces. Surface


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

atomic adsorption in fcc-hollow sites; with slight contraction of topmost Ru-Ru interlayer spacing two O layers are present in the structure; one forms an overlayer in which the O bonds to 3fold hollow sites on the Zr surface; the other layer has the O atoms in tetrahedral hole sites between the first two Zr layers

adsorption at fcc-hollow sites (see Fig. 7) Ru(0001)+ (1x1)-H Zr(0001)+ (1x1)-2O: 1 O at fcchollow sites

LEED no

no

-1.8 ± 1.4

0

0

0

1.10 ± 0.06

0

87L2

LEED no

yes

33.7 ± 1.9

0

0

0

0.89 ± 0.05

0

97W

4.1-32 Surface

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

1.4 ± 1.9

8.9 ± 1.9

0

0

1.52 ± 0.03; 1.71 ± 0.03

0

95O2

Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp and fcc sites

no

-1.0 ± 1.4

0

0

0

2.90 ± 0.04

0

92G

no

-1.4 ± 1.4

0

0

0

2.50 ± 0.04

0

94H3

no

-0.5 ± 0.7 -0.5 ± 1.0

-8.8 ± 0.7 2.3 ± 1.0

-0.7 ± 2.8 3.0 ± 2.3 0.6 ± 3.5 0.8 ± 3.0

1.42 ± 0.05; 1.23 ± 0.05

0

97S4

no

0.9 ± 2.3

-5.6 ± 1.4

-5.1 ± 4.5 0

1.39 ± 0.07; 1.27 ± 0.07

0

99S1

atomic adsorption in fcc-hollow site on nearly unrelaxed substrate atomic adsorption in fcc-hollow site on nearly unrelaxed substrate intact molecular adsorption in top; hcp and fcc sites; upright orientation with the N end down; significant different site-specific inner NO bondlengths: NO(top)=1.13; NO(hcp/fcc)=1.24/1.22Å; significant buckling in top metal layer O in hcp-hollow site; NO in top and fcc-hollow sites

no

-0.5 ± 1.4

-3.3 ± 1.4

0.0 ± 4.5

-6.1 ± 3.0 1.39 ± 0.07; 1.26 ± 0.07

0

99S1

O in fcc and hcp-hollow sites; NO in top site

no

9.3 ± 0.9

4.2 ± 0.9

-5.2 ± 5.0 0

0

94N1

O atoms adsorbed in hcp and fcc sites; forming honeycomb pattern; CO molecules adsorbed upright in top sites; relaxations in topmost Ru layer in both lateral and perpendicular directions


Ru(0001)+ (2x2)Cs+2CO: 1 CO at fcchollow site Ru(0001)+ LEED no (2x2)-K Ru(0001)+ LEED no (2x2)-Na Ru(0001)+ LEED no (2x2)-3NO: 1 NO at fcchollow site

Ru(0001)+ LEED no (2x2)O+2NO: 1 NO at fcchollow site Ru(0001)+ LEED no (2x2)2O+NO: 1 O at fcc-hollow site Ru(0001)+ LEED no (2x2)2O+CO: 1 O at fcc-hollow site

1.42 ± 0.08; 1.51 ± 0.08


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

-1.9 ± 2.3

-2.8 ± 1.9

0

0

3.04 ± 0.05; 2.98 ± 0.05

0

94H2

LEED no

no

1.8 ± 2.8

0.9 ± 2.8

complex

0

1.32 ± 0.2; 1.34 ± 0.2

0

92H2

Ru(0001)+ LEED no c(4x2)-2S: 1 S near fcchollow site

no

-4.7 ± 0.9

-7.9 ± 0.9; -0.9 ± 0.9 0.5 ± 0.9

complex

1.79 ± 0.02; 1.60 ± 0.02; 1.77 ± 0.02

0

94S3

complex

0; 0 0

atomic adsorption in 3-fold coordinated fcc site on unreconstructed substrate; anisotropic thermal distribution of Rb; large parallel root mean square displacement = 0.37Å adsorption roughly on threefold fcc sites; buckling and pairing reconstruction of the first metal layer; slight expansion of the first metal interlayer spacing S close to hcp and fcc-hollow sites shifted away from symmetric positions; buckling and lateral shifts of rows in the first substrate layer; buckling in the second substrate layer

Surface

Ru(0001)+ (2x2)-Rb

Ru(0001)+ (2x1)-H

-1.5 ± 0.9

adsorption at hcp-hollow sites (see Fig. 8) Ru(0001)+ (1x1)-O Ru(0001)+ (√3x√3) R30°-Cs

LEED no

no

3.7

0

0

0

1.25

0

96S2

LEED no

no

-1.9 ± 1.9 -0.9 ± 3.3

0

0

0

3.15 ± 0.03

0

92O1

Ru(0001)+ LEED no (√3x√3) R30°-Cs+O: Cs site Ru(0001)+ LEED no (√3x√3) R30°-Cs+O: O site

no

-2.8 ± 1.0

0

0

0

3.04 ± 0.03

0

92O2

no

-2.8 ± 1.0

0

0

0

1.52 ± 0.07

0

92O2

atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site; atomic adsorption in hcp-hollow sites of unreconstructed substrate; relaxations in top 2 Ru-Ru interlayer spacings; no detectable lateral relaxations adsorption of Cs and O in hcp-hollow sites; change of O-Ru bond length due to coadsorption of Cs adsorption of Cs and O in hcp-hollow sites; change of O-Ru bond length due to coadsorption of Cs

4.1-34 Surface

Ru(0001)+ (√3x√3) R30°-K Ru(0001)+ (√3x√3) R30°-Li Ru(0001)+ (√3x√3) R30°-N Ru(0001)+ (√3x√3) R30°-Na Ru(0001)+ (√3x√3) R30°-Rb


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

-1.9 ± 2.3

0

0

0

2.94 ± 0.04

0

92G

atomic adsorption in hcp-hollow site on nearly unrelaxed substrate

0 0; 0 1.3 ± 2.8

0 0; 0 0

2.25 ± 0.05

0

95G2

1.10 ± 0.06

0

97S3

atomic adsorption in 3-fold hcp-hollow site on unreconstructed substrate; buckling in 2nd substrate layer atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site

LEED no

no

-2.4 ± 2.3 1.3 ± 2.3

LEED no

no

-0.9 ± 2.3

0 0; 2.3 ± 1.9 0

LEED no

no

-0.9 ± 2.3

0

0

0

2.51 ± 0.05

0

94H3

atomic adsorption in hcp-hollow site on nearly unrelaxed substrate

LEED no

no

-0.9 ± 2.3

0

0

0

3.03 ± 0.05

0

94H2

LEED no

no

-1.0 ± 0.9

0

0

0

1.67 ± 0.02

0

94J2

LEED no

no

-4.5 ± 3.6 4.6 ± 3.1

2.2 ± 3.1 0; 2.8 ± 3.6

1.4 ± 4.4 0; 0

0 0; 0

1.68 ± 0.04; 1.73 ± 0.07

0

94B3

Ru(0001)+ LEED no (2x2)Cs+CO: CO at hcp-hollow site

no

1.4 ± 1.9

8.4 ± 1.9

0

0

1.47 ± 0.04; 1.65 ± 0.04

0

95O2

atomic adsorption in 3-fold coordinated hcphollow site on unreconstructed substrate; anisotropic thermal distribution of Rb; large parallel root mean square displacement = 0.37Å S in hcp-hollow sites on unreconstructed; relaxed substrate: no lateral shifts or buckling in the substrate adatoms in 3-fold hcp-hollow sites; contracted average first and second substrate interlayer spacings of 2.16 and 2.18Å; resp.; compared to 2.23Å for the bulk Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp sites between Cs atoms

Ru(0001)+ (√3x√3) R30°-S Re(0001)+ (2x2)-S

4.1-35 Surface

Ru(0001)+ (2x2)Cs+2CO: 1 CO at hcphollow site Ru(0001)+ LEED no (2x2)-N Ru(0001)+ LEED no (2x2)-3NO: 1NO at hcphollow site

Ru(0001)+ (2x2)-O

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

1.4 ± 1.9

8.9 ± 1.9

0

0

1.52 ± 0.03; 1.71 ± 0.03

0

95O2

Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp and fcc-sites

no

-1.0 ± 2.3

3.3 ± 2.3

0

0

0

97S3

no

1.8 ± 0.7

-8.8 ± 0.7

0

97S4

-2.8 ± 1.0

0; -2.3 ± 1.0

1.05 ± 0.05; 1.12 ± 0.05 1.0 ± 2.8 -3.0 ± 2.3 1.31 ± 0.05; 1.12 ± 0.05 0; 0; -0.8 ± 3.5 0.8 ± 3.0

-2.3 ± 1.4 3.7 ± 1.4

3.3 ± 1.4 0; 3.7 ± 1.4

5.4 ± 6.4 0; 0

0

89L5

atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site intact molecular adsorption in top; hcp and fcc sites; upright orientation with the N end down; significant different site-specific inner NO bond lengths: NO(top)=1.13; NO(hcp/fcc)=1.24/1.22Å; significant buckling in top metal layer atomic adsorption in hcp-hollow sites; slight contraction of first Ru-Ru interlayer spacing while second spacing essentially bulk-like; buckling of first and second Ru layers O atoms adsorbed in hcp sites; CO molecules adsorbed in top sites; tilted by 12.6°; relaxations of topmost Ru layer in both lateral and vertical directions CO tilt could be either vibrational or static O atoms adsorbed in hcp and fcc sites; forming honeycomb pattern; CO molecules adsorbed upright in top sites; relaxations in topmost Ru layer in both lateral and perpendicular directions


LEED no

no

0 0; 0

1.18 ± 0.03; 1.25 ± 0.03

Ru(0001)+ LEED no (2x2)-O+CO: O at hcphollow site

no

Ru(0001)+ LEED no (2x2)2O+CO: 1 O at hcp-hollow site Ru(0001)+ LEED no (2x2)(O+N2): O at hcp-hollow site

no

-3.3 ± 0.9

4.2 ± 0.9

5.2 ± 5.0

0

1.23 ± 0.08; 1.32 ± 0.08

0

94N1

no

-2.8 ± 2.8

3.3 ± 2.8

6.4 ± 2.8

0

1.25 ± 0.06; 1.32 ± 0.06

0

95O1

95N

coadsorption of atomic oxygen and molecular dinitrogen on unreconstructed; relaxed substrate; oxygen in hcp-hollow site; N2 on top site; perpendicular to surface

4.1-36 ∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

0.9 ± 1.9

-6.5 ± 1.4

6.4 ± 4.3

0

1.19 ± 0.05; 1.05 ± 0.05

0

99S1

O and NO in hcp-hollow sites

3.4 ± 2.3

-5.6 ± 1.4

5.1 ± 4.5

0

1.21 ± 0.07; 1.09 ± 0.07

0

99S1

O in hcp-hollow site; NO in top and fcc-hollow sites

4.6 ± 1.4

-3.3 ± 1.4

0.0 ± 4.5

6.1 ± 3.0

1.20 ± 0.07; 1.07 ± 0.07

0

99S1


no

0.2 ± 0.9 -1.6 ± 0.9

94J2

2.4 ± 0.9 -0.5 ± 0.9

0 0; 0 0 0; 0

0

no

4.5 ± 3.7 0; 0.0 ± 0.4 complex complex

1.61 ± 0.02; 1.64 ± 0.02

LEED no

1.4 ± 0.9 0; -1.4 ± 0.9 3.3 ± 0.9 0; -1.4 ± 0.9

1.20 ± 0.02; 1.27 ± 0.02

0

89P2

Ru(0001)+ LEED no (2x1)-O+NO: O at hcphollow site Ru(0001)+ LEED no (2x1)-O+NO: NO at hcphollow site

no

3.7 ± 1.9 -2.8 ± 1.4

0.0 ± 0.9 0; 0.0 ± 0.9

0 0

0 0; 0

1.26 ± 0.05; 1.26 ± 0.05

0

99S1

S in hcp-hollow sites on unreconstructed; relaxed substrate: buckling in the first and second Ru layers; lateral shifts in the first Ru layer atomic adsorption in hcp-hollow sites; top 2 Ru layers buckled; bulk-like first and second Ru-Ru interlayer spacings (measured wrt center of mass of the layers) O and NO in hcp-hollow sites

no

3.7 ± 1.9 -2.8 ± 1.4

0.0 ± 0.9 0; 0.0 ± 0.9

0 0; 0

0 0; 0

1.32 ± 0.04; 1.32 ± 0.04

0

99S1

O and NO in hcp-hollow sites

Surface


Ru(0001)+ (2x2)-O+NO: O at hcphollow site Ru(0001)+ LEED no (2x2)O+2NO: O at hcp-hollow site Ru(0001)+ LEED (2x2)2O+NO: 1 O at hcp-hollow site Ru(0001)+ LEED no (2x2)-S Ru(0001)+ (2x1)-O

no

4.1-37 Surface


Ru(0001)+ c(4x2)-2S: 1 S near hcphollow site Ru(0001)+ LEED no (√7x√7) R19°-C6H6

Ru(0001)+ (3x3)C6H6+2NO: C6H6 at hcphollow site Ru(0001)+ (3x3)C6H6+2NO: 1 NO at one hcp-hollow site Ru(0001)+ (3x3)C6H6+2NO: 1 NO at other hcp-hollow site Ru(0001)+ (3x3)C6H6+2O: C6H6 at hcphollow site

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

-3.3 ± 0.9

-7.9 ± 0.9; 0.9 ± 0.9 0; -0.5 ± 0.9 0.5 ± 2.3; 1.4 ± 2.3

complex

1.73 ± 0.02; 1.56 ± 0.02; 1.75 ± 0.02

0

94S3

0; 4.5 ± 9.0

0; 0 0; 0 0; 0.0 ± 5.0

2.15 ± 0.04; 2.07 ± 0.04

0

95S4

S close to hcp and fcc-hollow sites shifted away from symmetric positions; buckling and lateral shifts of rows in the first substrate layer; buckling in the second substrate layer intact molecular adsorption in hcp sites; with C3v(σ_v) orientation; i.e. C atoms near top and bridge sites; no significant buckling in top metal layer; very strong contraction of first two metal interlayer spacings; H ignored intact molecular C6D6 and NO adsorption in hcp sites; benzene essentially in C3(σ_d) orientation; i.e. C atoms in equal positions; no significant buckling in top metal layer; H ignored;

-2.0 ± 0.9

complex

no

-4.2 ± 2.3

LEED no

no

-4.8 ± 2.3

-0.8 ± 2.3; 0.4 ± 2.3

0; 0.0 ± 3.3

0; 2.18 ± 0.05; -4.6 ± 3.6 2.20 ± 0.05

0

97S5

LEED no

no

-5.1 ± 2.3

0.0 ± 2.3; -0.9 ± 2.3

0; 0.0 ± 3.3

0; 0.0 ± 3.6

1.33 ± 0.05; 1.33 ± 0.05; 1.31 ± 0.05

0

97S5

intact molecular C6D6 and NO adsorption in hcp sites; benzene essentially in C3(σ_d) orientation; i.e. C atoms in equal positions; no significant buckling in top metal layer; H ignored;

LEED no

no

-4.0 ± 2.3

0.9 ± 2.3; 0.0 ± 2.3

0; 2.0 ± 3.3

0; 1.30 ± 0.05; -1.6 ± 3.6 1.32 ± 0.05; 1.32 ± 0.05

0

97S5

intact molecular C6D6 and NO adsorption in hcp sites; benzene essentially in C3(σ_d) orientation; i.e. C atoms in equal positions; no significant buckling in top metal layer; H ignored;

LEED no

no

-4.5 ± 1.4

-1.9 ± 1.4; -1.0 ± 1.4

0; 0.6 ± 3.3

0; 0.0 ± 2.6

0

97S5

intact molecular C6D6 and atomic O adsorption in hcp sites; benzene essentially in C3(σ_v) orientation; i.e. C atoms near top and bridge sites; no significant buckling in top metal layer; clock rot. possible in top Ru layer; H ignored;

2.21 ± 0.03; 2.17 ± 0.03

4.1-38 Surface

Ru(0001)+ (3x3)C6H6+2O: 1 O at one hcp-hollow site Ru(0001)+ (3x3)C6H6+2O: 1 O at other hcp-hollow site

αls [°]


∆dl,l+1 [%]

bls [%]

∆rls [%]

d01 [Å]

∆r0 Ref. [Å]

Description

-3.5 ± 1.4

0.9 ± 1.4; -0.9 ± 1.4

0; 0; -2.0 ± 4.4 3.2 ± 3.6

1.38 ± 0.03; 1.40 ± 0.03; 1.36 ± 0.03

0

97S5


LEED no

-2.6 ± 1.4

1.0 ± 1.4; 2.0 ± 1.4

0; 0; 1.33 ± 0.03; -1.1 ± 4.4 -2.6 ± 3.6 1.35 ± 0.03; 1.37 ± 0.03

0

97S5


no

0.4 ± 1.8

0; 1.6 ± 1.4

0; 0

0; 0

1.10 ± 0.05

0

93O2

no

-4.2 ± 0.9

0; 0.5 ± 0.9; -2.8 ± 0.9

0; 0; 0

0; 0; 0

2.23 ± 0.02

0

94H1

molecular adsorption in top site on unreconstructed substrate; with buckling in top substrate layer intact molecular adsorption in two different top sites (bilayer) on unreconstructed relaxed substrate: significant buckling in top metal layer; contraction of first two metal interlayer spacings

no

-1.4 ± 0.9

0; 3.2 ± 0.9; 2.8 ± 0.9

0; 0; 0

0; 0; 0

2.08 ± 0.02

0

94H1

intact molecular adsorption in two different top sites (bilayer) on unreconstructed relaxed substrate: significant buckling in top metal layer; contraction of first two metal interlayer spacings

0

0

0

0

2.00 ± 0.05

0

94B7

molecular adsorption in on-top site with molecular axis perpendicular to unreconstructed substrate

no

adsorption at top sites (see Fig. 9) Ru(0001)+ LEED no (√3x√3) R30°-CO Ru(0001)+ LEED no (√3x√3) R30°-2H2O: 1 H2O at high top site Ru(0001)+ LEED no (√3x√3) R30°-2H2O: 1 H2O at low top site Ru(0001)+ LEED (√3x√3) R30°-N2


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

-2.8

0

0

0

3.54 ± 0.06

0

97N1

LEED no

no

0.0 ± 2.3

0; -4.7 ± 1.9

0; 0

0; 0

3.25 ± 0.08; 3.15 ± 0.08

0

92O1

Ru(0001)+ LEED no (2x2)Cs+CO: Cs at top site Ru(0001)+ LEED no (2x2)Cs+2CO: Cs at top site Ru(0001)+ LEED no (2x2)-3NO: 1NO at top site

no

-7.0 ± 1.9

0; -8.4 ± 1.9

0; 0

0; 0

3.12 ± 0.04; 2.94 ± 0.04

0

95O2

atomic overlayer in on-top sites on unreconstructed substrate; with buckling and lateral relaxation in the first metal layers atomic adsorption in top sites of unreconstructed substrate; relaxations in top 2 Ru-Ru interlayer spacings; buckling in top Ru layer; no detectable lateral relaxations Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp sites between Cs atoms

no

-7.5 ± 1.9

0; -8.8 ± 1.9

0; 0

0; 0

3.13 ± 0.04; 2.94 ± 0.04

0

95O2

Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp and fcc sites

no

8.3 ± 0.7

0; 8.4 ± 0.7; 0

0

97S4

2.3 ± 1.0

2.3 ± 1.0

0; 0; 1.72 ± 0.05; -2.9 ± 2.8; ± 3.0 1.90 ± 0.05 3.4 ± 2.8 ± 2.3; 0 -0.6 ± 3.5 -0.8 ± 3.0

intact molecular adsorption in top; hcp and fcc sites; upright orientation with the N end down; significant different site-specific inner NO bondlengths: NO(top)=1.13; NO(hcp/fcc)=1.24/1.22Å; significant buckling in top metal layer O atoms adsorbed in hcp sites; CO molecules adsorbed in top sites; tilted by 12.6°; relaxations of topmost Ru layer in both lateral and vertical directions CO tilt could be either vibrational or static O atoms adsorbed in hcp and fcc sites; forming honeycomb pattern; CO molecules adsorbed upright in top sites; relaxations in topmost Ru layer in both lateral and perpendicular directions

Surface

Ru(0001)+ (√3x√3) R30°-Xe Ru(0001)+ (2x2)-Cs

Ru(0001)+ LEED no (2x2)-O+CO: CO at top site

no

Ru(0001)+ LEED no (2x2)2O+CO: CO at top site

no

95N

-3.3 ± 0.9

0; -4.2 ± 0.9

0; 0.5 ± 0.5

0; 0

1.98 ± 0.08; 1.89 ± 0.08

0

94N1

4.1-40 Surface

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

-6.1 ± 2.8

0; -3.3 ± 2.8

0; 0.1 ± 2.8

0; 0

1.93 ± 0.06; 1.86 ± 0.06

0

95O1

no

4.2 ± 1.9

0; 6.5 ± 1.4

0; 0.0 ± 0.4

0; 0

1.75 ± 0.04; 1.89 ± 0.04

0

99S1

coadsorption of atomic oxygen and molecular dinitrogen on unreconstructed; relaxed substrate; oxygen in hcp-hollow site; N2 on top site; perpendicular to surface O and NO in hcp-hollow sites

no

5.1 ± 1.4

0; 3.3 ± 1.4

complex

0; 0

1.76 ± 0.07; 1.89 ± 0.07

0

99S1


no

5.6 ± 2.3

0; 5.6 ± 1.4

0; ± 0.5 ± 0.5

complex

1.74 ± 0.06; 1.86 ± 0.06

0

99S1

O in hcp-hollow site; NO in top and fcc-hollow sites

95S3

1 S atom in fcc site; 3 S atoms close to hcp sites; shifted away from symmetric positions; buckling in the first substrate layer correlated with the number of coordinated S atoms; nearly identical bond lengths for all S-Ru bonds

76S2

atomic interstitial in octahedral sites between first and second Ti layers; slight expansion of Ti-Ti spacing; forms trilayer of TiN compound exposing (111) face


Ru(0001)+ (2x2)(O+N2): N2 at top site Ru(0001)+ LEED no (2x2)-O+NO: O at top site Ru(0001)+ LEED no (2x2)2O+NO: NO at top site Ru(0001)+ LEED no (2x2)O+2NO: 1 NO at top site

adsorption at both fcc-hollow and near-hcp sites Ru(0001)+ (√7x√7) R19°-4S

LEED no

no

adsorption at octahedral interstitial sites within 1st substrate spacing (see Fig. 10) Ti(0001)+ (1x1)-N

LEED no

no

4.3 ± 2.1

0

0

0

-1.22 ± 0.05; 1.22 ± 0.05

0

4.1-41 Surface

Zr(0001)+ (1x1)-C Zr(0001)+ (1x1)-N


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å]

Description

0.4 ± 1.9

0

0

0

-1.33 ± 0.10; 1.33 ± 0.10

0

88W1

LEED no

-0.8 ± 0.9

0

0

0

-1.30 ± 0.05; 1.30 ± 0.05

0

87W4

atomic adsorption in octahedral interstitial sites between 1st and 2nd Zr layers; inducing slight expansion between these Zr layers atomic adsorption in octahedral interstitial sites between 1st and 2nd Zr layers; inducing slight contraction between these Zr layers

0

-1.22 ± 0.05; 2.22 ± 0.05

0

97W

two O layers are present in the structure; one forms an overlayer in which the O bonds to 3fold hollow sites on the Zr surface; the other layer has the O atoms in tetrahedral hole sites between the first two Zr layers

95W1

interstitial O in octahedral sites: 0.25ML O between 1st & 2nd Zr layers; 0.25ML between 2nd & 3rd Zr layers; these two (2x2) O arrays are displaced laterally from one another by a unit translational vector of the substrate; lowering the overall symmetry

94B3

sulfur adatoms; adsorbed near 3-fold hcp-hollow sites; form expanded hexamers crowning one 3Re-atom hump per unit cell; alternating S-S distances in the ring are 3.32Å and 2.95Å; average first substrate interlayer spacing is 2.21Å

no

adsorption at tetrahedral sites within 1st substrate spacing (see Fig. 11) Zr(0001)+ LEED no (1x1)-2O: 1 O interstitial

no

33.7 ± 1.9

0

0

adsorption at octahedral interstitial sites within 1st and 2nd substrate spacings Zr(0001)+ (2x2)-2O

LEED no

yes

adsorption at low-symmetry or mixed sites Re(0001)+ (2√3x2√3) R30°-6S

LEED no

no

4.1-42 Surface

Ru(0001)+ (3x3)-4Kr

Ru(0001)+ (2x2)-3O


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 Ref. [Å] 97N1

LEED no

no

98K

Ru(0001)+ LEED no (2x2)-3O Ru(0001)+ LEED no (2x2)-Cs+3O

no

98G2

no

98K

Description

multi-site atomic overlayer on unrecon-structed substrate; with buckling and lateral relaxation in the first metal layers: I Kr per cell in hcp or fcchollow site; 3 Kr per cell in lower-symmetry sites; see comments O atoms occupy 3/4 of hcp-hollow sites; sitting slightly off-hollow; 1st substrate layer is buckled: Ru atoms bonded to 3 O atoms are depressed inward relative to those bonded to 2 O atoms by 0.02 ± 0.03 Å; 2nd substrate layer is also buckled: Ru atoms below adatom vacancy are raised by 0.08 ± 0.03 Å over the others same as above; but buckling in 1st Ru layer is reversed to -0.03 ± 0.02 Å similar to Ru(0001)+(2x2)-3O: Cs occupies O vacancy sites; reversing the buckling in the 1st Ru layer; and reducing the average spacing between 1st and 2nd Ru layers 0.05 ± 0.03 Å compared to the O-only case

adsorption at interstitial sites near vacancy sites Be(0001)+ (√3x√3) R30°-3H

LEED no

yes

99P

1/3 of top-layer Be atoms are missing and each is replaced by 3 H atoms in bridge sites around the vacancy; 1st and 2nd Be-Be spacings are expanded by 0.6 ± 1.1 and 1.65 ± 1.3 %; resp.

4.1-43 Surface


∆dl,l+1 [%]

αls [°]

∆rls [%]

bls [%]

d01 [Å]

∆r0 Ref. [Å]

Description

adsorption at interstitial sites in lattice reconstructed to fcc Zr(0001)+ (2x2)-O

LEED no

yes

85H2

O atoms in octahedral holes within fcc reconstructed Zr; with layer stacking AcBaCb... (O atoms in lower case); O atoms form (2x2) 0.25ML interstitial layers

Table 6. Structures of clean bcc(110) surfaces. ∆d23 [%] 0

∆d34 [%] 0

∆d45 [%] 0

∆d56 [%] 0

Ref.

Description

Fe(110)

Tech- Clean dbulk ∆d12 nique rec. [Å] [%] LEED no 2.029 0.5 ± 2.0

80S

K(110)

LEED no

3.72

0

0

0

0

92I

Mo(110) Mo(110)

LEED no LEED no

2.227 -1.7 ± 1.8 2.224 -4.0 ± 0.6

0 0.2 ± 0.8

0 0

0 0

0 0

81M 97A3

Nb(110)

HEIS no

2.338 0.0 ± 4.3

0

0

0

0

90W3

V(110) W(110) W(110) W(110)

LEED LEED HEIS ARXPD LEED

no no no no

2.141 2.23 2.23 2.238

-0.5 ± 0.5 0.0 ± 4.5 0.0 ± 1.8 1.0 ± 2.2

0 0 0.0 ± 1.8 0

0 0 0 0

0 0 0 0

0 0 0 0

81A 76V1 87S2 93K2

no

2.236 -3.1 ± 0.6

0.0 ± 0.9

0.0 ± 1.0

0

0

97A1

bulk termination with possible slight expansion of topmost interlayer spacing lateral shear displacement of 0.23Å between top 2 surface layers; preserving the 2-dimensional periodicity bulk termination with contracted top layer spacing bulk-like terminated surface with moderate inward relaxation of top layer bulk terminated structure with no detectable relaxations slightly contracted bulk termination unrelaxed bulk termination bulk-like termination unreconstructed surface with small expansion of top interlayer expansion possible bulk-like terminated surface with small inward relaxation of the top layer

Surface

W(110)

-0.7 ± 0.3

4.1-44 Table 7. Adsorbate-induced structures on bcc(110) surfaces. Surface

Tech- Clean adsnique rec. ind rec.

∆dl,l+1 [%]

bls [%]

∆rls αls [%] [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

bcc Cr(110) film grown epitaxially on Cu(100); film is about 11Å thick; Cr(110) is overlain with 0.7±0.2 monolayer of pseudomorphic bcc Cu (with 0.3ML vacancies); in-plane lattice constant fit to 2.44±0.07Å atomic Fe adsorption in center sites (extending substrate lattice) on unreconstructed substrate atomic S at center site; top substrate layer laterally relaxed atomic overlayer near distorted center hollow site; i.e. bridging two nearest neighbors but shifted 0.04Å perp. to bridge toward 3-fold coordinated hollow site; substantial relaxations up to 0.3Å in top 2 substrate layers

adsorption at center sites (see Fig. 12) Cr(110)+ LEED no (1x1)-0.7MLCu

no

4.7 ± 0.0003

0

0

0

1.837 ± 0.0008

0

94J1

W(110)+ (1x1)-Fe Fe(110)+ (2x2)-S Mo(110)+ (2x2)-S

no

no

1.9 ± 2.2

0

0

0

2.07 ± 0.05 0

97T2

LEED no

no

81S1

LEED no

no

94T

XPD

adsorption at 3-fold coordinated sites (see Fig. 13) Mo(110)+ (1x1)-H

LEED no

no

-2.0 ± 0.4

0

0

0

1.10 ± 0.30

0.14 ± 0.48

97A3

W(110)+ (1x1)-H

LEED no

no

-1.7 ± 0.5

0

0

0

1.20 ± 0.30

0.19 ± 0.36

97A1

H adsorbed close to quasi threefold coordinated site; Mo surface exhibits moderate contraction of first interlayer distance; deeper layer distances are bulk-like H adsorbed in quasi-threefold coordinated site; W surface undergoes no reconstruction upon H adsorption; only small contraction of first interlayer spacing

4.1-45 Surface

Fe(110)+ (2x2)-2H

Mo(110)+ (2x2)-2H

Tech- Clean adsnique rec. ind rec. LEED no no

LEED no

no

∆dl,l+1 [%]

bls [%]

0.0 ± 2.0

-2.0 ± 1.2

1.0 ± 2.9

-1.0 ± 0.8

-3.5 ± 0.7 -0.2 ± 0.7

Fe(110)+ (2x1)-H Fe(110)+ (3x1)-2H

∆rls αls [%] [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

atomic adsorption in threefold-coordinated sites with displacement towards twofoldcoordinated bridge sites; forming distorted honeycomb-like lattice; substrate relaxation of c(2x2) type: buckling in 1st and 2nd Fe layers H forms a honeycomb like adlayer occupying positions close to threefold coordinated hollow sites; adsorbate induces moderate buckling of two topmost Mo layers; contraction of first interlayer distance atomic adsorption in 3-fold coordinated hollow sites atomic adsorption in 3-fold coordinated hollow sites; two H per unit cell

0; 0 0; 0

0; 0 0; 0

1.09 ± 0.20

0.18 ± 0.33

93H1

0.9 ± 0.4; 2.7 ± 0.4 -1.4 ± 0.7; -1.4 ± 0.7

0; 0 0; 0

0; 0 0; 0

1.02 ± 0.20

0.23 ± 0.20

97A2

LEED

-1.0 ± 2.5

0

0

0

0.90 ± 0.10

0.25

85M2

LEED

-1.0 ± 2.5

0

0

0

1.00 ± 0.05

0.25

85M2

Table 8. Structures of clean fcc(100) surfaces. Surface

Tech- Clean nique rec. LEED no LEED no MEED no LEED no LEED no LEED no

Ag(100) Al(100) Al(100) Al(100) Au(100) Au(100)(1x1) Au(100)- XRD yes (incommen surate 'hex') Co(100)

LEED no

dbulk [Å] 2.043 2.025 2.022 2.025 2.04 2.04

∆d12 [%] 0.0 ± 4.9 0.0 ± 1.5 1.5 ± 4.9 2.6 ± 0.2 0.0 ± 4.9 -1.5 ± 2.0

∆d23 [%] 0.0 ± 1.5 0 0 0.0 ± 0.3 0 -2.0 ± 2.0

∆d34 [%] 0 0 0 -0.5 ± 0.4 0 0

∆d45 [%] 0 0 0 0 0 0

∆d56 [%] 0 0 0 0 0 0

2.04

1.77

Ref.

Description

91L 76V2 83M2 95B3 82L 94W5

no multilayer relaxation unrelaxed bulk termination bulk termination with possible slight top contraction unreconstructed surface with multilayer relaxations metastable unreconstructed surface impurity-stabilized unreconstructed surface; with possible contraction of top two interlayer spacings incommensurate hexagonal top layer; with 20% expanded spacing to 2nd layer (due to variable registries); top 4 layers are found corrugated by 14; 7; 3; 1 % (defined as maximum thickness of layer) bulk termination with top spacing contraction

91O1

-4.0 ± 2.8

0

0

0

0

78M

4.1-46 Surface Cu(100) Cu(100) Cu(100) Cu(100) Cu(100) Ir(100)(1x1) Ir(100)(5x1) Ir(100)(5x1) Ni(100) Ni(100) Ni(100) Ni(100) Ni(100) Ni(100) Pb(100) Pd(100) Pd(100) Pd(100) Pt(100)(1x1) Rh(100) Rh(100) Rh(100)

Technique LEED LEED SPLEED MEIS LEED LEED

Clean rec. no no no

dbulk [Å] 1.805 1.81 1.805

∆d12 [%] -1.1 ± 2.8 -1.7 ± 1.1 -1.2 ± 1.1

∆d23 [%] 1.7 ± 2.8 1.1 ± 1.1 0.9 ± 1.1

∆d34 [%] 1.5 ± 2.8 0 0

∆d45 [%] 0 0 0

∆d56 [%] 0 0 0

no no yes

1.807 -2.4 ± 0.8 1.807 -0.4 ± 5.5 1.92 -3.6 ± 0.5

1.0 ± 1.0 -0.4 ± 5.5 0

0 0 0

0 0 0

0 0

Ref.

Description

83D1 86A 87L1

bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with multilayer relaxations

91J 93M3 83H

multilayer relaxation relaxed bulk termination unreconstructed metastable surface with top spacing contraction quasi-hexagonal commensurate buckled top-layer reconstruction with 'two-bridges' registry quasi-hexagonal commensurate buckled top-layer reconstruction with 'two-bridges' registry bulk termination with slight top spacing expansion bulk termination with top spacing contraction contraction of top interlayer spacing relaxed; unreconstructed surface relaxed; unreconstructed surface unreconstructed relaxed substrate multilayer relaxation essentially unrelaxed bulk termination multilayer relaxation multilayer relaxation unreconstructed metastable structure with slight top spacing expansion unrelaxed bulk termination bulk termination with possible slight top interlayer expansion bulk termination with slight top interlayer contraction

LEED yes

1.92

81V

LEED yes

1.92

83L

LEED MEIS LEED LEED SIMS LEED LEED LEED LEED LEED HEIS

1.76 1.76 1.762 1.762 1.762 1.762 2.463 1.945 1.945 1.945 1.96

no no no no no no no no no no no

1.1 ± 1.1 -8.9 ± 0.5 -1.1 ± 1.0 -1.3 ± 1.0 -4.7 ± 3.4 0.5 ± 0.6 -8.0 ± 1.2 0.3 ± 2.6 3.1 ± 1.5 4.9 ± 1.5 0.2 ± 2.6

0 0 0 0 -1.3 ± 9.1 -0.1 ± 0.6 3.1 ± 1.2 0 -1.0 ± 1.5 0.3 ± 0.5 0

0 0 0 0 0 0 -3.0 ± 1.2 0 0 -0.8 ± 1.0 0

0 0 0 0 0 0 -2.0 ± 4.0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

75D 83F 89O 94L2 94X 94N3 90L1 80B 90Q 96B 81D

LEED no LEED no

1.9 0.5 ± 1.1 1.902 0.5 ± 1.0

0 0.0 ± 1.5

0 0

0 0

0 0

80H 88O

LEED no

1.902 -1.2 ± 1.6

0.0 ± 1.6

0

0

0

93B3

4.1-47 Table 9. Adsorbate-induced structures on fcc(100) surfaces. Surface

Technique

Clean Adsrec. ind rec.

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

adsorption at hollow sites (see Fig. 14) Pd(100)+ Transm. no (1x1)-H (D) Channe ling Pt(100)+ LEED yes (1x1)-Cu

no

0

0

0

0

0.30 ± 0.05

0

88B

atomic adsorption in 4-fold hollow site

no

2.0 ± 5.1

0

0

0

1.79 ± 0.10

0

94A

Al(100)+ c(2x2)-Na (100K) Cu(100)+ c(2x2)-Bi Cu(100)+ c(2x2)-Cl Cu(100)+ c(2x2)-Cl

LEED no

no

0.35 ± 0.50

0

0

0

2.57 ± 0.01

0

95B3

GIXD no

no

-5.5

0

0

0

2.18 ± 0.08

0

97M2

XSW

no

no

3.9 ± 2.2

0

0

0

1.53 ± 0.04

0

89P1

ARPEFS

no

no

11.3 ± 1.2 0.5 ± 1.5

91W4

no

2.4 ± 1.7

0 0; 0 0

0

LEED no

0 0; 0 0

1.60 ± 0.005

Cu(100)+ c(2x2)-Cl Cu(100)+ c(2x2)-Li Cu(100)+ c(2x2)-N

0 0; 2.3 ± 0.7 0

1.60 ± 0.03

0

83J

LEED no

no

-0.4 ± 2.2

0

0

0

1.96 ± 0.08

0

93M3

partial pseudomorphic monolayer covering about 50% of unreconstructed substrate; probably in islands with 1ML; best fit with mix of 50% bare Pt(100)-(1x1) atomic Na in hollow site on unreconstructed and essentially unrelaxed substrate atomic adsorption on unreconstructed substrate; adatom at fcc-hollow site atomic adsorption in hollow site with expanded top Cu-Cu interlayer spacing atomic adsorption in hollow site; with multilayer relaxation and 2nd Cu layer buckling atomic adsorption in hollow site of unreconstructed substrate Li atoms in fourfold hollow sites

SEno XAFS

no

4.4 ± 2.8 0

93L2

7.9 ± 2.8

0 0; 0 0

0

no

0 0; 0 0

0.40 ± 0.05

LEED no

0 0; -5.5 ± 2.8 0

0.00 ± 0.05

0

87Z

Cu(100)+ c(2x2)-N

atomic overlayer in 4-fold hollow sites; outward expansion of first Cu layer; possible corrugation of second Cu layer atomic overlayer coplanar with top Cu layer in 4-fold hollow sites

4.1-48 Surface

Cu(100)+ c(2x2)-N

Technique

Clean Adsrec. ind rec. LEED no no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

7.4 0

0 0; 0 0

0 0; 0 0

0.06

0

89Z

1.60 ± 0.02

0

90Y

N almost coplanar with 1st Cu layer; buckling in 2nd Cu layer (Cu below N pushed down atomic adsorption at a 4-fold hollow site top Ni layer relaxes outward

SEno XAFS XSW SEno XAFS

no

11.3 ± 2.8

0 0; -5.0 0

no

2.3

0

0

0

1.55

0

97T1

Ni(100)+ c(2x2)-Li

LEED no

no

-0.3 0.4

97J1

no

no

-1.7 ± 1.7 1.7 ± 1.7

0.84 ± 0.70

0

98D2

LEED no

no

-0.7 ± 0.6 -0.1 ± 0.6

0 0; 0 0 0; 0 0 0; 0 0 0

0

XRD

0 0; 0 0 0; 0 0 0; 0 0 0

1.92

Ni(100)+ c(2x2)-N+ (disord.)-K Ni(100)+ c(2x2)-Na

0 0; 1.5 0 0; 3.4 ± 1.7 0 0; 0 0 0

2.38 ± 0.04

0

94N3

atomic adsorption in 4-fold hollow sites of unreconstructed relaxed substrate; negligible buckling in 2nd Ni layer

0.86 ± 0.10

0

83F

atomic adsorption in 4-fold hollow sites

0 0; -2.0 ± 1.1 0 0; -11.3 ± 5.7 0

0 0; 0 0 0; 0 0

0 0; 0 0 0; 0 0

0.77 ± 0.02

0

89O

0.85 ± 0.10

0

94X

1.31 ± 0.03

0

86B

oxygen adsorbed in hollow site; buckling in 2nd Ni layer; top Ni-Ni interlayer spacing expanded overlayer in hollow sites on relaxed; unreconstructed substrate; 2nd Ni layer buckled atomic adsorption in hollow sites

Ni(100)+ c(2x2)-Cl Ni(100)+ c(2x2)-Cl

-0.9 ± 1.1 5.1 ± 5.7

Ni(100)+ c(2x2)-O Ni(100)+ c(2x2)-O

MEIS no

no

LEED no

no

6.7 ± 1.1 -1.2 ± 1.1

Ni(100)+ c(2x2)-O

SIMS

no

no

12.3 ± 3.4 -14.3 ± 9.1

Ni(100)+ c(2x2)-S

ARPEFS

no

no

4.0 ± 1.7

atomic overlayer in 4-fold hollow sites on unreconstructed substrate; with lateral relaxations in the first 2 metal layers atomic adsorption on unreconstructed relaxed substrate; adatom at fourfold hollow site K removes clock-reconstruction of Ni(100)+pmg(2x2)-2N

4.1-49 Surface

Ni(100)+ c(2x2)-S

Technique


Ni(100)+ c(2x2)-S Pd(100)+ c(2x2)-K

XPD

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

1.9 ± 1.7 -1.5 ± 1.7

0 0; -0.6 ± 1.7 0

0 0; 0 0

0 0; 0 0

1.30 ± 0.02

0

90S2

1.38 ± 0.10

0

92S1

0 0; 0 0

0 0; 0 0

2.54 ± 0.02

0

96B

sulfur in hollow site; expansion of top NiNi interlayer spacing; contraction of 2nd Ni-Ni spacing; second Ni layer buckled atomic atomic adsorption in 4-fold hollow sites; with expansion of top Ni-Ni spacing atomic adsorption in 4-fold hollow site; possible slight buckling in 2nd Pd layer

1.24 ± 0.02

0

96K1

adsorption of S on fourfold hollow sites; multilayer substrate relaxations 4-fold site; lateral expansion of top Cu layer S in 4-fold hollow; site laterally expanded; no vertical buckling in 2nd Cu layer 4-fold hollow site for S; lateral expansion of site; buckling in 2nd layer (atom below S pushed down)

no

no

5.7 ± 5.7

LEED no

no

0.2 ± 3.0 2.1 ± 1.0

Pd(100)+ c(2x2)-S

LEED no

no

2.6 ± 0.8

0 0; 2.1 ± 1.0 0

Cu(100)+ (2x2)-S Cu(100)+ (2x2)-S Cu(100)+ (2x2)-S

XRD

no

no

0

0

1.6 ± 0.7

0

1.19 ± 0.10

0

90V2

MEIS no

no

0

0

1.6 ± 0.7

0

1.30 ± 0.02

0

90J2

LEED no

no

2.7 ± 2.8 1.6 ± 2.8

90Z2

no

no

1.8 0

1.28 ± 0.03

0

92S2

Ni(100)+ (2x2)-O

LEED no

no

4.7 ± 1.1 -3.2 ± 1.1

0.80 ± 0.05

0

90O1

Ni(100)+ (2x2)-O

SIMS

no

8.4 ± 6.8 -3.2 ± 1.1

0 0; 0; 0 0 0; 0; 0 0 0; 0; 0 0 0; 0; 0

0

ARPEFS

0 0; 0; 0 2.2 0; 0; 0 0 0; 0; 0 0 0; 0; 0

1.28 ± 0.03

Cu(100)+ (2x2)-S

0 0; -4.0 ± 2.8; -4.0 ± 2.8 0 0; -0.6; -1.8 0 0; -2.3 ± 1.1; -5.7 ± 1.1 0 0; -14.8 ± 6.8; -14.8 ± 6.8

0.85 ± 0.10

0

94X

no

atomic adsorption in 4-fold hollow sites with lateral relaxation of the first Cu layer and vertical buckling of the second Cu layer oxygen in hollow site; expansion of top Ni-Ni interlayer spacing; second Ni layer buckling overlayer in hollow sites on relaxed; unreconstructed substrate; 2nd Ni layer buckled

4.1-50 Surface

Ni(100)+ (2x2)-S

Technique


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

2.7 ± 2.8 -2.4 ± 2.8

0 0; -4.0 ± 2.8; -4.0 ± 2.8

0 0; 0; 0

0 0; 0; 0

1.25 ± 0.03

0

90O2

sulfur in hollow site; 1st Ni-Ni interlayer spacing expanded; second Ni layer buckling

Pd(100)+ (2x2)-O

LEED no

no

6.7 ± 1.0 -3.1 ± 0.8

0 0; -2.6 ± 0.8; -6.2 ± 0.8

0.0 ± 2.0 0; 0; 0

0 0; 0; 0

0.83 ± 0.02

0

96K1

adsorption of O on fourfold hollow sites; multilayer substrate relaxations; no lateral relaxations of substrate atoms; significant buckling allowed by symmetry

Pd(100)+ (2x2)-S

LEED no

no

6.3 ± 0.8 -1.6 ± 0.8

96K1

adsorption of S on fourfold hollow sites; multilayer substrate relaxations; no lateral relaxations of substrate atoms; significant buckling allowed by symmetry

no

-0.6 ± 2.1

0 0; 0; 0 0

0

LEED no

0.0 ± 2.0 0; 0; 0 0

1.13 ± 0.02

Rh(100)+ (2x2)-O Ni(100)+ c(4x2)-K

0 0; -3.1 ± 0.8; -4.2 ± 0.8 0

0.95 ± 0.04

0

88O

LEED no

no

-4.3 ± 2.3 4.3 ± 4.3

93F3

-0.6 ± 2.1

0 0; 0 0

0

no

0 0; 0 0

2.68 ± 0.05

Rh(100)+ LEED no c(4x2)-Cs XRD no Cu(100)+ (disordered)K 0.18ML

0 0; 4.3 ± 4.3 0

2.87 ± 0.06

0

89v2

hollow site adsorption with slight top RhRh interlayer contraction atomic adsorption in hollow sites; buckling of 2nd Ni layer; lateral shift in 1st Ni layer 4-fold symmetric hollow site adsorption

no

0.7 ± 1.0

0

0

0

2.10 ± 0.40

0

93M1

LEED no Ni(100)+ (disordered)K 1/4ML

no

-2.6 ± 2.3 2.6 ± 2.6

0 0; 2.6 ± 2.6

0 0; 0

0 0; 0

2.66 ± 0.03

0

93W5

disordered fourfold hollow adsorption of atomic K; with little vertical relaxation of top two interlayer spacings and no lateral displacements disordered atomic adsorption at K coverages of 0.04,0.08; 0.14,0.17,0.22 and 0.25: K in hollow sites; adsorption height: 2.72,2.735,2.675,2.675,2.675 and 2.66Å; resp.; buckling of 2nd Ni layer: Ni atom directly below K moves up by 0.075,0.06,0.075,0.060,0.060,0.045Å; resp.

4.1-51 Surface

Technique


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

0

0

0.80 ± 0.03

0.1

83D2

atomic adsorption 0.1Å laterally away from 4-fold hollow site towards bridge site atomic adsorption in quasi fourfold hollow sites; S atoms shifted towards bridge sites; relaxation of the first 2 Rh layers and slight buckling of 2nd Rh layer atomic adsorption in quasi fourfold hollow sites; S atoms shifted towards bridge sites; relaxation of the first 2 Rh layers and buckling of 2nd Rh layer; lateral shift of atoms in 1st Rh layer

adsorption at off-hollow sites Ni(100)+ c(2x2)-O Rh(100)+ c(2x2)-S

LEED no

no

2.3

LEED no

no

2.3

-0.5

0

0

1.3

0.27

93L4

Rh(100)+ (2x2)-S

LEED no

no

1.8 -0.7

0 0.0; 3.2

-3.6 0

0 0

1.35

0.27

93L4

LEED no Ni(100)+ (disordered)O

no

-5.2 ± 2.8 4.0 ± 2.8

0 4.0 ± 2.8

0 0

0 0

0.86 ± 0.03

0.45 ± 0.10 91S2

Ni(100)+ LEED no (disordered)-S

no

-1.3

0

0

0

1.2

0.6

2.7 ± 1.7

0

0

0

2.01 ± 0.03 93Z

91S2

disordered hollow site adsorption in off center position (pseudobridge); 2nd layer buckled; sideshift of Ni atoms close to O of up to 0.15Å possible; local minimum for 4-fold-site with 1st layer buckling disordered hollow site adsorption in off center position (pseudobridge); 2nd layer buckled; side shift of Ni atoms close to O of up to 0.15Å possible; local minimum for 4-fold-site with 1st layer buckling

admolecules at top sites (see Fig. 15) Ni(100)+ AR- no (disordered)- PEFS NH3

no

0

molecular NH3 adsorbed at top site on relaxed substrate; H ignored

4.1-52 Surface

Technique


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

atomic adsorption (3Pb per supercell) at and near hollow sites; forming 3-Pb-wide strips (domains) of c(2x2) structure with compressed domain boundaries; no buckling in Pb layer or relaxations in substrate detected atomic adsorption on unreconstructed substrate; antiphase boundary structure of c(2x2) domains; all Li atoms occupy hollow sites domain-wall overlayer structure; inducing relaxations in substrate

adsorption at hollow and other sites Cu(100)+ c(5√2x√2) R45°-3Pb

LEED no

no

86H

Ni(100)+ c(5√2x√2) R45°-3Li

LEED no

no

97J2

Cu(100)+ c(9√2x√2) R45°-5Bi Cu(100)+ c(8x2)-7Mn

XRD no

no

98M1

LEED no

no

94G2

commensurate quasi-hexagonal Mn overlayer: one Mn per cell over hollow site of unreconstructed substrate; Mn layer strongly buckled (0.53Å); and slightly relaxed laterally; top Cu layer slightly buckled (0.04Å)

91G

carbon adsorbed in fcc-hollow site; clockwise rotation of top Ni layer atoms around hollow (shift in directions by 0.45Å); buckling of 2nd Ni layer (Ni directly below C moves up)

adsorption at clock-rotated hollow site Ni(100)+ LEED no p4g(2x2)-2C

no

3.9 ± 4.5

0

3.2 ± 3.9

4.4 ± 4.0

0; 8.5 ± 4.5

0; 0

± 14.3 0.12 ± 0.04 ± 2.6 0; 0

0

4.1-53 Clean Adsrec. ind rec. no no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

-2.8 ± 5.7

0

4.8 ± 7.9

no

no

-2.8 ± 5.7

0

Ni(100)+ XRD no p4g(2x2)-2N

no

3.4 ± 4.0

0

Surface

Technique

Ni(100)+ PED p4g(2x2)-2C Ni(100)+ PED p4g(2x2)-2N

∆r0 [Å]

Ref.

Description

± 17.4 0.10 ± 0.10 ± 7.1

0

91K

4.8 ± 7.9

± 17.4 0.10 ± 0.10 ± 7.1

0

91K

2.9 ± 0.1

± 15.0 0.03 ± 0.13 ± 0.5

0

99D

carbon adsorbed in hollow site; clock rotation of 4 Ni neighbors by 0.55Å; expansion of top Ni-Ni interlayer spacing N adsorbed in hollow site; clock rotation of 4 Ni neighbors by 0.55Å; top Ni-Ni interlayer expansion N adsorbed in hollow site; clock rotation of 4 Ni neighbors by 0.30Å; top Ni-Ni interlayer expansion

d01 [Å]

adsorption at substitutional sites in top substrate layer (see Fig. 16) Cu(100)+ c(2x2)-Au Cu(100)+ c(2x2)-Mn Cu(100)+ c(2x2)-Mn

LEED no

yes

4.0 ± 2.8

0

0

0

0.10 ± 0.05

0

87W2

LEED no

yes

-0.9 ± 1.7

0

0

0

0.30 ± 0.02

0

93W7

PED

no

yes

-9.7 ± 4.4

0

0

0

0.40 ± 0.04

0

96T1

Cu(100)+ c(2x2)-Pd Ni(100)+ c(2x2)-Mn

LEED no

yes

0.0 ± 1.7

0

0

0

0.02 ± 0.03

0

88W2

LEED no

yes

0.0 ± 1.7

0

0

0

0.25 ± 0.02

0

93W7

Ni(100)+ c(2x2)-Sn Pd(100)+ c(2x2)-Mn Al(100)+ c(2x2)-Na (300K)

LEIS no

yes

0

0

0

0

0.44 ± 0.05

0

94L1

LEED no

yes

-15.4 ± 2.6

0

0

0

0.20 ± 0.05

0

90T2

SEno XAFS

yes

2.9 ± 5.5

0

0

0

0.61 ± 0.10

0

92A

substitutional adsorption; forming buckled monolayer of mixed alloy ordered mixed Mn-Cu top layer with Mn buckled outwards 2-dimensional surface alloy of Mn and Cu; Mn replaces every other Cu atom in outermost layer; Mn buckled outwards substitutional adsorption; forming buckled monolayer of mixed alloy ordered mixed Mn-Ni top layer with Mn buckled outwards by 0.25Å; small relaxations of top 3 interlayer spacings ordered surface alloy with Sn buckled above Ni mixed top layer; with Mn buckled outward mixed top Al/Na layer: Na on top sites of next Al layer; top-layer Al atoms between Na atoms; buckled outward

4.1-54 Surface

Cu(100)+ (disordered)Bi 0.3ML

Technique

Clean Adsrec. ind rec. GIXD no yes

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

2.9 ± 5.5

0

0

0

0.61 ± 0.10

0

97M2

adatom at substitutional site; in random configuration

93B4

single (1x1) Fe layer under single Au layer; acting as surfactant

missing row reconstruction with O incorporated at kink sites at nearly same height as 1st Cu layer O in 4-fold coordinated site with 1 Cu neighbor missing; missing Cu row in (1,1) direction; lateral shift of top Cu atoms adjacent to rows (pairing; 0.3Å) and lifting up (0.01Å); buckling in 2nd Cu layer (0.1Å); Cu below O is lifted missing-row reconstruction; with O in 4fold coordinated sites with 1 Cu neighbor missing; SEXAFS results consistent with earlier LEED results on lateral and perpendicular relaxations in top Cu layer (Cu expands into missing rows)

adsorption at substitutional sites in 2nd substrate layer Au(100)+ (1x1)-Fe+ (1x1)-Au

LEED yes

yes

adsorption at hollow sites of missing-row substrate Cu(100)+ (2√2x√2) R45°-2O Cu(100)+ (2√2x√2) R45°-2O

PED

no

yes

90A

LEED no

yes

90Z1

Cu(100)+ (2√2x√2) R45°-2O

SEno XAFS

yes

93L1

4.1-55 Surface

Technique


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

92A

mixed top Al/Na layer: Na on top sites of next Al layer; top-layer Al atoms between Na atoms; buckled outward by 1.41Å

every other [110] row in top Ag layer missing; with 1st Ag-Ag interlayer spacing reduced by -3.6 ± 2.4 %; K substitute for missing Cu; but 1.17 ± 0.05 Å above remaining top-layer Cu atoms; in 2nd Ag layer a lateral displacement of Ag by 0.04 ± 0.003 Å toward K sites is seen missing row type reconstruction; Li positions unknown

adsorption at substitutional sites of laterally shifted top substrate layer Al(100)+ c(2x2)-Na (300K)

SEno XAFS

yes

adsorption in troughs of missing-row reconstruction Ag(100)XRD no (2x1)+ (disordered)K

yes

98M3

Cu(100)LEED no (2x1)+ (disordered)Li

yes

93M2

adsorption in substitutional and near-hollow overlayer sites Cu(100)+ (3x3)-5Li

LEED no

yes

95M3

complex reconstruction with overlayer and substitution: small pyramids of 4 Cu atoms capped by single Li atoms; the pyramids being separated and joined by pairs of substitutional Li atoms

4.1-56 Surface

Cu(100)+ (4x4)-10Li

Technique

Clean Adsrec. ind rec. LEED no yes

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

95M5

complex reconstruction with overlayer and substitution: 4 Li adatoms forming a square cluster located on top of islands of 9 Cu atoms; which islands are separated and joined by rows of substituting Li atoms four Li adatoms forming a square cluster located on top of islands of nine Cu atoms; the islands are separated and joined by rows of substituting Li atoms 9 Li adatoms forming a square cluster located on top of islands of 16 Cu atoms; the islands are separated and joined by rows of substituting Li atoms

Ni(100)+ (4x4)-10Li

LEED no

yes

97J1

Ni(100)+ (5x5)-17Li

LEED no

yes

97J1

complex reconstruction Al(100)+ (√5x√5) R27°-Yb

XPD; no LEED

yes

97F1

Pd(100)+ (√5x√5) R27°-4O

LEED no

yes

94V2

formation of mixed Yb-Al top layer by substitutional adsorption of Yb; residual first-layer Al atoms are strongly displaced from equilibrium position; also expansion of first interlayer spacing atomic adsorption: PdO oxide monolayer with Pd atoms placed on 3 different adsorption sites: 1 Pd sits on top; 2 Pd on bridge; 1 Pd on hollow sites per unit cell; significant expansion in interlayer spacing and rumpling in the oxide layer

4.1-57 Surface

Cu(100)+ c(4x4)-3Pb

Technique

Clean Adsrec. ind rec. LEED no yes

Pd(100)+ LEED no p4g(2x2)-2Al

∆dl,l+1 [%]

αls [°]

∆rls [%]

bls [%]

d01 [Å]

∆r0 [Å]

yes

Ref.

Description

96G2

Pb chains in [1,-1,0] direction; replacing every other Cu row; 3 Pb per unit cell: 1 Pb substitutional in hollow site; 2 Pb in intermediate asymmetrical sites; remaining Cu between Pb chains relaxed; small corrugation in first pure substrate layer top layer is 100% Pd; 2nd layer is 50% Pd and 50% Al; 3rd layer and beneath is 100% Pd at ideal fcc positions; clockreconstruction in top layer; buckling in 2nd layer (Pd outward)

97O1

Table 10. Structures of clean bcc(100) surfaces. Surface Fe(100) Fe(100) Fe(100) Mo(100)(disordered) Mo(100)(disordered) Mo(100)(disordered) Ta(100) Ta(100)

Technique LEED LEED MEIS LEED

Clean rec. no no no yes

dbulk [Å] 1.433 1.433 1.433 1.574

∆d12 [%] -1.6 ± 2.8 -4.9 ± 2.1 -4.5 ± 2.8 -11.7 ± 6.4

∆d23 [%] 0 4.9 ± 2.1 3.5 ± 2.8 0

∆d34 [%] 0 0 0 0

∆d45 [%] 0 0 0 0

∆d56 [%] 0 0 0 0

Ref.

Description

77L1 87W1 89H2 75I2

bulk termination with contraction of top layer spacing bulk termination with multilayer relaxation bulk termination with multilayer relaxation bulk termination with contraction of top interlayer spacing

LEED yes

1.574 -9.5 ± 1.9

-1.0 ± 1.9

0

0

0

80C

bulk termination with multilayer relaxation

LEED yes

1.575 -5.4 ± 1.3

1.6 ± 1.3

0.3 ± 1.3

0

0

75I2

bulk termination with contraction of top interlayer spacing

LEED no PED no

1.65 -0.9 ± 1.8 1.2 ± 1.8 1.649 -10.0 ± 5.0 0

0 0

0 0

0 0

82T1 89B1

bulk termination with multilayer relaxation contraction of first interlayer spacing

4.1-58 Surface V(100) W(100)(disordered) W(100)(disordered) W(100)(disordered) W(100)(disordered) W(100)c(2x2) W(100)c(2x2) W(100)c(2x2) W(100)c(2x2)

dbulk [Å] 1.514 1.58

∆d12 [%] -6.9 ± 0.7 -6.3 ± 6.3

∆d23 [%] 1.1 ± 0.7 0

∆d34 [%] 0 0

∆d45 [%] 0 0

∆d56 [%] 0 0

Ref.

Description

82J 76V1

bulk termination with 2-layer relaxation bulk termination with top layer spacing contraction

LEED yes

1.58

-7.6 ± 1.9

0

0

0

0

80M1

bulk termination with top layer spacing contraction

LEED yes

1.58

-6.3

1.9

0

0

0

88P2

multilayer relaxation

LEED yes

1.58

-9.2 ± 6.3

0

0

0

0

88P1

LEED yes

1.58

-3.2 ± 3.2

0

0

0

0

78B

disordered version of W(100)-c(2x2) reconstruction; with top-layer W atoms randomly displaced laterally by 0.16Å in 4 equivalent [011] directions zig-zag displacive reconstruction of top layer

XRD yes

1.58

-3.8 ± 10.1 0

0

0

0

88A

LEED yes

1.58

-7.0 ± 1.9

1.3 ± 1.9

0

0

0

89L1

LEED yes

1.583 -6.2 ± 1.6

0

0

0

0

92S3

Technique LEED LEED

Clean rec. no yes

zig-zag chain reconstruction with lateral relaxations in 1st and 2nd layers reconstructed zigzag; reconstruction with lateral displacements zig-zag chain relaxation with lateral displacements in 1st layer

Table 11. Adsorbate-induced structures on bcc(100) surfaces. Surface


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

28 -3.0

0 0

0 0

0 0

0.16

0

92J

atomic adsorption in 4-fold hollow sites; with large expansion of top Cr-Cr spacing

adsorption at hollow sites (see Fig. 17) Cr(100)+ (1x1)-N

LEED no

no

4.1-59 Tech- Clean Adsnique rec. ind rec. MEIS no no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

11.2 ± 2.8 0.7 ± 2.8

0 0

0 0

0 0

0.38 ± 0.04

0

89H2

Fe(100)+ (1x1)-O Fe(100)+ (1x1)-O Mo(100)+ (1x1)-Si Cr(100)+ c(2x2)-N

LEED no

no

7.7 ± 7.0

0

0

0

0.48 ± 0.10

0

77L2

LEED no

no

0 0 0

0 0 0

0

87J

no

0 0 0

0.45 ± 0.04

LEED yes

8.2 ± 2.8 2.7 ± 2.8 0.0 ± 6.4

1.16 ± 0.10

0

75I1

LEED no

no

11.6 ± 2.8 -6.4 ± 2.8

0 0, -9.0 ± 2.8

0 0, 0

0 0, 0

0.36 ± 0.04

0

98S2

Cr(100)+ c(2x2)-S

AR- no PEFS

no

0 0 0 0 0

88T1

no

0 0 0 0 0

0

LEED no

0 0 0 0 0

1.17 ± 0.02

Fe(100)+ c(2x2)-C+O (chemically disordered) Fe(100)+ c(2x2)-N Fe(100)+ c(2x2)-P Fe(100)+ c(2x2)-S Fe(100)+ c(2x2)-S

-9.0 ± 1.4 2.1 ± 2.1 -1.4 ± 2.1 -2.1 ± 4.9 0.0 ± 7.0

atomic adsorption in 4-fold hollow sites (assumed); with expansion of top 2 Fe-Fe spacings\ atomic adsorption deep in 4-fold hollow sites atomic adsorption in 4-fold hollow sites; with expansion of top 2 Fe-Fe spacings\ atomic adsorption in 4-fold hollow sites on unrelaxed substrate atomic overlayer in bcc-hollow sites on unreconstructed substrate; expansion and (slight) contraction of top 2 substrate interlayer spacings; resp.; with buckling in the second metal layer atomic adsorption in hollow sites with top Cr-Cr spacing relaxation (no detectable layer buckling)

0.48 ± 0.10

0

78J

LEED no

no

7.7 ± 3.5

0

0

0

0.27 ± 0.05

0

82I

XPD

no

no

0

0

0

0

1.02

0

97H2

LEED no

no

0

0

0

0

1.05 ± 0.05

0

77L3

AR- no PEFS

no

-2.1 ± 1.4

0

0

0

1.10 ± 0.02

0

88Z

Surface

Fe(100)+ (1x1)-O

decomposed CO as atomic C and O randomly positioned in hollow sites of a c(2x2) lattice; LEED shows c(2x2) (C and O indistinguishable) atomic adsorption in 4-fold hollows atomic adsorption in hollow sites on unreconstructed unrelaxed substrate atomic adsorption in hollow sites atomic adsorption in hollow sites with multilayer relaxation (no detectable layer buckling)

4.1-60 Tech- Clean Adsnique rec. ind rec. LEED yes no

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-6.7 ± 3.2 7.9 ± 2.5

0 -9.5 ± 2.5

0 0

0 0

0.47 ± 0.03

0

95J

Mo(100)+ c(2x2)-S

LEED yes

no

-1.6 ± 3.8

0

0

0

1.03 ± 0.10

0

95J

atomic adsorption in hollow site; with buckling in 2nd Mo layer; with shortest CMo bond to 2nd Mo layer atomic adsorption in hollow site; with buckling in 2nd Mo layer

W(100)+ c(2x2)-N

LEED yes

no

-2.9 ± 3.8 8.7 ± 3.8 -9.0 ± 3.8

-3.1 ± 3.8 0 -17.1 ± 3.8

0 0 0

0 0 0

0.41 ± 0.05

0

95B4

W(100)+ c(2x2)-S

LEIS yes

no

-0.5 ± 2.5

0

0

0

1.02 ± 0.02

0

94O2

Mo(100)+ (3√2x√2) R45°-2S Mo(100)+ c(4x2)-3S

LEED yes

no

95J

LEED yes

no

95J

W(100)+ Dyes (disordered)- LEED O

no

Surface

Mo(100)+ c(2x2)-C

0.0 ± 6.3

0

-9.6 ± 5.0

0

0.59 ± 0.10

0

86R

-1.3 ± 12.7

0

0

0

1.17 ± 0.04

0

85P

atomic adsorption in four fold hollow sites; second W layer buckled (outward under adsorbate) atomic overlayer on undistorted four-fold hollow site; top W-W spacing relaxed to near bulk value atomic adsorption in quasi hollow site; with buckling and lateral relaxation in the first 2 Mo layers atomic adsorption: 1 S in hollow and 2 S in quasi hollow sites (at different heights) per unit cell; buckling in 2nd Mo layer; lateral relaxations in the first two Mo layers atomic adsorption in hollow sites with lateral W relaxations towards O position

adsorption at bridge sites (see Fig. 18) W(100)+ (1x1)-2H

LEED yes

no

atomic adsorption in bridge sites of both azimuthal orientations (2H per unit cell)

4.1-61 Surface


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

85T

atomic O adsorption under bridge in top Ta layer and above bridge in second Ta layer (4-fold coordinated interstitial site); top Ta layer buckled

89M3

missing-row reconstruction of substrate oxygen is disordered in 2nd layer top sites

92S3

adsorption site of H not determined; dimer reconstruction with lateral displacements in 1st layer; contraction of 1st interlayer spacing by 4.5%

interstitial adsorption between two topmost substrate layers (see Fig. 19) Ta(100)+ (3x1)-O

LEED yes

no

adsorption on missing-row reconstructed substrate W(100)LEIS yes (2x1)+ (disordered)O

yes

dimerization in top substrate layer W(100)+ c(2x2)-H

LEED yes

yes

4.1-62 Table 12. Structures of clean alloyed bcc(100) surfaces. Surface

Tech- Clean dbulk ∆d12 ∆d23 nique rec. [%] [%] [Å] LEED no 1.564 -11.9 ± 0.6 5.1 ± 0.9

∆d34 [%] -3.7 ± 0.8

∆d45 [%] 3.9 ± 1.1

∆d56 [%] -2.5 ± 1.3

Ref.

Description

96H1

unreconstructed; relaxed surface: strong oscillatory relaxation of interlayer spacings; top layer is pure Mo; oscillatory segregation in deeper layers

1.567 -11.5 ± 0.6 4.7 ± 0.7

-3.3 ± 0.8

3.2 ± 0.8

-2.1 ± 1.0

97K2

deep multilayer relaxation; layer dependent stoichiometry: c1(Mo)=100%±15%; c2(Mo)=72%±13%; c3(Mo)=90%±13%; c4(Mo)=88%±16%

1.57

-3.0 ± 1.0

2.3 ± 1.0

-1.8 ± 1.1

97K2

deep multilayer relaxation; layer dependent stoichiometry: c1(Mo)=91%±13%; c2(Mo)=85%±16%; c3(Mo)=89%±14%; c4(Mo)=98%±20%

Mo75Re25 (100)-(1x1) (chem. disordered alloy) Mo85Re15 LEED no (100)-(1x1) (chem. disordered alloy) Mo95Re05 LEED no (100)-(1x1) (chem. disordered alloy)

-11.1 ± 0.8 4.4 ± 0.9

4.1-63 Table 13. Adsorbate-induced structures on alloyed bcc(100) surfaces. Surface

Tech- Clean adsnique rec. ind rec.

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

no

96H1

no

96K2

unreconstructed; relaxed substrate: H in all bridge sites; oscillating concentration profile of clean surface remains due to low adsorption temperature; cleansurface relaxation of first two interlayer spacings is lifted; relaxation of deeper interlayer spacing remains occupation of hollow sites by C atoms; 1st interlayer spacing similar to MoC(100); c1(Mo)=76%±23%; c2(Mo)=66%±22%; c3(Mo)=82%±20%

no

96H1

unreconstructed; relaxed substrate: C resides both deep in hollow sites of top layer and interstitially in octahedral sites below top layer atoms; C causes expansion of top two interlayer spacings; oscillatory layer relaxation below these layers; Mo segregation in top two layers

94O1

missing row reconstruction of substrate with O adsorbed on top of second layer substrate atoms; substrate: disordered alloy with surface segregation: 1st metal layer Mo concentration >= 0.96; Re depletion in 2nd and enrichment in 3rd metal layers; resp.

adsorption on unreconstructed bcc(100)-like substrate Mo75Re25(100) LEED no + (1x1)-2H (chem. disordered alloy) Mo75Re25(100) LEED no + (1x1)-C (chem. disordered alloy) Mo75Re25(100) LEED no + (1x1)-2C (chem. disordered alloy)

adsorption on reconstructed bcc(100)-like substrate Mo75Re25(100) LEIS no -(2x1)+ (2x1)2O (chem. disordered alloy)

yes

4.1-64 Surface

Tech- Clean adsnique rec. ind rec. yes Mo75Re25(100) LEED no -(2x1)+ (2x1)2O (chem. disordered alloy)

∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

∆r0 [Å]

d01 [Å]

Ref.

Description

95H1

missing row reconstruction; 3-fold coordinated O on sides of remaining rows; Mo segregation toward Ocoordinated sites; expansion of first interlayer distance by 7.7%

Table 14. Structures of clean fcc(110) surfaces. Surface Ag(110) Ag(110) Ag(110) Ag(110) Ag(110) Al(110) Al(110) Al(110) Al(110) Au(110)(1x2) Au(110)(1x2) Au(110)(1x2) Au(110)(1x2) Cu(110) Cu(110)

∆d12 [%] -6.6 ± 1.5 -7.6 ± 2.8 -9.5 ± 2.1 -7.4 ± 2.0 1.0 ± 1.5 -10.0 ± 7.0

Technique LEED HEIS MEIS LEED ICISS LEED

Clean rec. no no no no no no

dbulk [Å] 1.445 1.44 1.446 1.445 1.445 1.428

LEED LEED LEED LEED

no no no yes

1.43 -9.1 ± 7.0 1.425 -8.5 ± 0.8 1.43 -8.4 ± 1.0 1.44

∆d23 [%] 0 4.2 ± 2.8 6.0 ± 2.8 0.6 ± 2.0 -4.0 ± 2.0 0

∆d34 [%] 0 0 0 -2.4 ± 2.0 0 0

∆d45 [%] 0 0 0 -0.4 ± 2.0 0 0

∆d56 [%] 0 0 0 0 0 0

0 5.2 ± 1.1 5.6 ± 1.1

0 0 2.3 ± 1.3

0 0 1.8 ± 1.5

0 0 0

Ref.

Description

82N2 84K 87H2 89L4 92B1 72L

bulk termination with top spacing contraction bulk termination with multilayer relaxation relaxations in top two interlayer spacings multilayer relaxations multilayer relaxations bulk termination; with suggested 10% relaxation of top interlayer spacing relaxed bulk termination bulk termination with multilayer relaxation bulk termination with multilayer relaxation missing-row reconstruction with multilayer relaxation; 2nd row pairing and 3rd row buckling missing-row reconstruction with relaxation of top layer spacing missing-row reconstruction with multilayer relaxation; including 3rd-layer buckling missing-row reconstruction; with multilayer relaxations down to 4th layer bulk termination with multilayer relaxations bulk termination with multilayer relaxations

77G 84A 84N 85M1

LEIS yes

1.44

86M

MEIS yes

1.44

86C2

XRD yes

1.443

90V1

HEIS no LEED no

1.278 -5.3 ± 1.6 1.278 -8.4 ± 0.6

3.3 ± 1.6 2.3 ± 0.8

0 0

0 0

0 0

83S 83A

4.1-65 Surface Cu(110) Cu(110) Cu(110) Cu(110) Cu(110) Cu(110)

Technique LEED MEIS ICISS LEED LEIS XRD

Clean rec. no no no no no no

dbulk [Å] 1.276 1.278 1.28 1.278 1.278 1.278

∆d12 [%] -9.2 ± 3.9 -7.5 ± 1.6 -10.2 ± 7.8 -9.4 ± 1.6 -3.1 ± 3.1 -7.8 ± 0.5

∆d23 [%] 2.3 ± 3.9 2.5 ± 1.6 0 4.9 ± 1.6 0 1.8 ± 0.5

∆d34 [%] 0 0 0 0 0 0

∆d45 [%] 0 0 0 0 0 0

∆d56 [%] 0 0 0 0 0 0

Ref.

Description

83D1 86C3 86Y2 87B 89V1 93H2

Ir(110)(1x2)

LEED yes

1.359

86C1

Ir(110)(1x3) Ir(110)(1x3) Ni(110) Ni(110) Ni(110) Ni(110) Ni(110) Ni(110) Ni(110) Pb(110) Pb(110) Pb(110) Pd(110) Pd(110)(1x2) Pd(110) Pd(110) Pt(110)(1x2)

TOF- yes SARS LEIS yes

1.358

90S1

1.357

92H3

bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with top layer contractions bulk termination with multilayer relaxations contraction of the 1st interlayer spacing unreconstructed surface with relaxations of top 2 interlayer spacings missing-row reconstruction with multilayer relaxations; row-pairing in second layer and buckling in third layer missing-row reconstruction exposing (111) facets; with relaxations in first 2 layers missing-row reconstruction with multilayer relaxations

MEIS LEED HEIS LEED LEED MEIS LEED MEIS LEED LEED LEED LEED

1.245 1.245 1.245 1.245 1.245 1.246 1.245 1.75 1.74 1.75 1.37 1.37

no no no no no no no no no no no no

LEED no LEED no MEIS yes

-4.0 ± 0.8 -8.4 ± 0.8 -4.1 ± 0.8 -9.8 ± 1.6 -8.6 ± 0.5 -9.0 ± 1.0 -8.4 ± 1.6 -15.8 ± 2.3 -16.4 ± 1.7 -19.4 ± 2.9 -5.8 ± 2.9 -5.1 ± 2.2

1.37 -5.1 ± 1.5 1.376 -1.0 ± 1.5 1.39

0 3.1 ± 1.0 0 3.8 ± 1.6 3.1 ± 0.6 3.5 ± 1.4 3.6 ± 1.6 0 3.5 ± 5.7 4.6 ± 4.6 0.7 ± 2.2 0

0 0 0 0 -0.4 ± 0.7 0 1.2 ± 1.6 0 -4.4 ± 1.7 -6.9 ± 2.9 0 0

0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0

79V2 84G1 84T3 85X1 85A 86Y1 87R1 86F2 89L3 90B 85B1 85B1

bulk termination with top spacing contraction bulk termination with multilayer relaxations bulk termination with top spacing contraction bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with top spacing contraction multilayer relaxation down to 3rd interlayer spacing multilayer relaxation down to 3rd interlayer spacing bulk termination with multilayer relaxation alkali-impurity stabilized missing-row reconstruction

2.9 ± 1.5 5.2 ± 1.5

0 0

0 0

0 0

87S1 93W3 88F1

relaxations in top two interlayer spacings unreconstructed surface with multilayer relaxations missing-row reconstruction with multilayer relaxation; including 3rd-layer buckling

4.1-66 Surface Pt(110)(1x2)

Tech- Clean dbulk nique rec. [Å] LEED yes 1.39

∆d12 [%]

∆d23 [%]

∆d34 [%]

∆d45 [%]

∆d56 [%]

Ref.

Description

88F2

missing-row reconstruction with multilayer relaxation; including 2nd- and 4th-layer pairing; and 3rd- and 5thlayer buckling missing-row reconstruction with multilayer relaxation; including 2nd- and 4th-layer pairing and 3rd-layer buckling missing-row reconstruction; with multilayer relaxations down to 4th layer missing-row reconstruction; with top spacing contraction missing-row reconstruction; with multilayer relaxations down to 3rd layer missing-row reconstruction; multilayer relaxation

Pt(110)(1x2)

LEED yes

1.387

88S

Pt(110)(1x2) Pt(110)(1x2) Pt(110)(1x2) Pt(110)(1x2) Pt(110)(1x3)

XRD yes

1.387

90V1

PED

yes

1.387

91H2

TOF- yes SARS RHEE yes D LEED yes

1.387

91M1

1.387

92K2

1.39

88F2

Pt(110)(1x3) Pt(110)(1x3)

XRD yes

1.387

93R

TOF- yes SARS

1.387

91M1

Rh(110) Rh(110)

LEED no LEED no

1.34 -0.8 ± 1.5 1.345 -6.9 ± 1.0

0 1.9 ± 1.0

0 0

0 0

0 0

80H 87N

Rh(110) Rh(110)(1x2)

LEED no LEED yes

1.345 -6.7 ± 1.5 1.345

2.2 ± 2.2

0

0

0

94B6 93C3

(1x3) reconstruction; probably impurity-stabilized; missing-row reconstruction with multilayer relaxation; including 2nd-layer pairing; and 3rd- and 4th-layer buckling missing-row reconstruction with multilayer relaxation 2-missing-rows reconstruction; leaving partial low 2nd-layer ridge within 3-wide trough; this structure is thought to be impurity-stabilized relaxed bulk termination unreconstructed surface with relaxations of top two interlayer spacings unreconstructed substrate with multilayer relaxation missing-row reconstruction with multilayer relaxation; metastable reconstruction after desorption of O from Rh(110)-p2mg(2x2)-2O

4.1-67 Table 15. Adsorbate-induced structures on fcc(110) surfaces. Surface

Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec.

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

pseudomorphic Fe monolayer; Fe-Cu and Cu(1)-Cu(2) interlayer spacings are (within error bar) equal to Cu-Cu bulk interlayer spacing Pt filling troughs of unreconstructed; relaxed substrate; extending bulk Pd fcc structure atomic adsorption in hollow (center) site

adsorption at center sites of unreconstructed substrate (see Fig. 20) Cu(110)+ (1x1)-Fe

LEED no

no

-0.6 ± 2.0

0

0

0

1.25 ± 0.03

0

89M1

Pd(110)+ (1x1)-Pt Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S

LEED no

no

6.1 ± 2.2

0

0

0

1.22 ± 0.03

0

93W4

LEED no

no

10.2 ± 1.6

0

0

0

0.84 ± 0.03

0

85B2

ICISS no

no

5.0 ± 3.2

0

0

0

0.89 ± 0.05

0

86F1

AR- no PEFS

no

10.4 ± 1.6 0

87R2

no

12.5 ± 3.2

0 0; 0 0

0

SEno XAFS MEIS no

0 0; 0 0

0.82 ± 0.02

Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S

0 0; 10.4 ± 1.6 0

0.83 ± 0.04

0

87W3

no

5.2 ± 3.2

0

0

0

0.87 ± 0.03

0

79v2

SEno XAFS

no

14.0 ± 2.4

0

0

0

0.77 ± 0.02

0

94Y

Rh(110)+ c(2x2)-S

LEED no

no

7.5 -3.8

0 0; -8.3

0 0; 0

0 0; 0

0.82

0

94W4

atomic adsorption in bulk continuation site (center of rectangle) atomic adsorption in bulk continuation site (center of rectangle) with buckling in 2nd Ni layer atomic adsorption in bulk continuation site (center of rectangle) atomic adsorption in hollow (center) site atomic overlayer in hollow sites of unreconstructed substrate; with expansion of top Ni-Ni spacing atomic adsorption on relaxed; unreconstructed substrate: S on the center hollow site; 2nd layer Rh buckled

4.1-68 Surface


bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

adsorption at 3-fold coordinated sites of unreconstructed substrate (see Fig. 21) Rh(110)+ (1x1)-2H

LEED no

no

-1.3 ± 3.7

0

0

0

0.78 ± 0.05

0.92 ± 0.05 91H1

atomic adsorption of hydrogen in 3-fold hollows on either side of Rh ridges; reducing clean-surface relaxation

Ni(110)+ (2x1)-2H

LEED no

no

-4.4 ± 1.6 5.2 ± 1.6

0 0

0 0

0 0

0.41 ± 0.10

0.66

Pd(110)+ (2x1)-2H

LEED no

no

-2.2 ± 1.5 2.9 ± 1.5

0 0

0 0

0 0

0.60 ± 0.10

0.46 ± 0.30 87S1

Rh(110)+ (2x1)-2O

LEED no

no

1.1 ± 4.5 2.6 ± 5.2

0 0

0 0

0 0

0.60 ± 0.05

0.58 ± 0.10 93G1

Rh(110)+ (2x1)-2O

LEED no

no

-1.1 ± 3.0 2.6 ± 5.2

0 0; 0

0 0; ± 0.05; ± 0.07

0 0; 0

0.60 ± 0.04

0.77 ± 0.10 95B2

atomic adsorption in fcc 3-fold hollows on (111) facets of unreconstructed substrate with multilayer relaxations perp. to surface atomic adsorption over outermost 3-fold coord. hollow sites over (111) facets of bulklike substrate with interlayer spacing relaxations atomic O (2 per (2x1) unit cell) in asymmetrical 3-fold coordinated sites; forming zigzag chains within troughs of slightly relaxed substrate O in fcc 3-fold hollow site on facets of unreconstructed substrate; with multilayer relaxation; incl. lateral relaxation in 2nd Rh layer

Rh(110)+ (1x2)-H

LEED no

no

-2.5 ± 2.0

3.0 ± 0.7

0.007 ± 0.03

0

0.80 ± 0.10

1.04 ± 0.10 89P3

87R1

atomic adsorption in nearly 3-fold sites on (111) facets on side of troughs (with long HRh distance to 2nd-Rh-layer atoms); top-Rhrows to which H is bonded are buckled out and laterally shifted towards H ('shiftbuckling')

4.1-69 Surface

Rh(110)+ (1x2)-3H

Rh(110)+ (1x3)-H

Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. LEED no no -1.6 ± 1.0

LEED no

no

-4.1 ± 1.5 1.1 ± 1.5

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

2.2 ± 1.5

0

0

0.71 ± 0.10; 1.00 ± 0.10; 1.15 ± 0.10

0.55 ± 0.20; 89M2 1.22 ± 0.20; 1.66 ± 0.20

2.2 ± 1.5 0

0.04 ± 0.03 0 0 0

0.51 ± 0.10

0.70 ± 0.20 89L2

Ref.

Description

atomic adsorption of hydrogen with top layer relaxation (slight buckling of doubly occupied Rh atoms); all H in 3 inequivalent quasi-3-fold sites in sides of troughs of unreconstructed substrate atomic adsorption of H in 3-fold sites on side of troughs; slight buckling of top layer

adsorption at outermost 3-fold sites and bottom long-bridge sites in trough (see Fig. 21 and 22) LEED no Rh(110)+ c(4x2)-N+2O: O at 3-fold sites

no

0.7 ± 3.7

0

0

0

0.57 ± 0.04

-0.57 ± 0.10 95G1

LEED no Rh(110)+ c(4x2)-N+2O: N at longbridge site

no

0.7 ± 3.7

0

0

0

-1.23 ± 0.05

0

95G1

0

1.37 ± 0.05

0

78C

substrate reconstruction with missing rows parallel to ridges; atomic adsorption in outermost 3-fold coordinated fcc-hollow sites on the flanks of the ridges; N in long-bridge sites at bottom of troughs; buckling in 3rd substrate layer substrate reconstruction with missing rows parallel to ridges; atomic adsorption in outermost 3-fold coordinated fcc-hollow sites on the flanks of the ridges; N in long-bridge sites at bottom of troughs; buckling in 3rd substrate layer

adsorption at short-bridge sites of unreconstructed substrate (see Fig. 23) Ir(110)+ c(2x2)-O

LEED yes

no

-2.2 ± 5.1

0

0

atomic adsorption in short-bridge site on unreconstructed substrate with top Ir-Ir layer spacing contraction

4.1-70 Surface


bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

95W2

atomic adsorption on relaxed; unreconstructed substrate: 1 S at center,1 S at long-bridge; 2 S at off-center sites; off-center site S shift by 0.39Å from center; 1st-layer Rh atoms forming the long-bridge site are buckled outward by 0.20Å and laterally shift by 0.27Å to open up the site

CO occupies atop sites on unreconstructed substrate; small buckling of top Cu layer molecular CO adsorption near bridge site of unreconstructed; perhaps slightly relaxed; substrate; with C-O axis tilted 19° from surface normal CO molecules tilted in alternate directions along the short bridge rows; 20° tilt of whole molecule CO near bridge site adsorption on ridges of unreconstructed substrate; C-O axis tilted 24° from surface normal in zigzag fashion; multilayer relaxation in substrate CH3COO (acetate) adsorption; with both O down; O are approx. atop so molecule bridges 2 Cu atoms; C-C axis and molecular plane perp. to surface; H atom sites in methyl group not determined

adsorption at multiple sites Rh(110)+ (3x2)-4S

LEED no

no

admolecules near top or short-bridge sites over ridges of unreconstructed substrate (see Figs. 23 and 24) Cu(110)+ (2x1)-CO Ni(110)+ (2x1)-2CO

PED

no

no

-11.0 ± 4.7

AR- no PEFS

no

Ni(110)+ (2x1)-2CO

LEED no

Rh(110)+ (2x1)-2CO

LEED no

Cu(110)+ PED (disordered)CH3COO

no

0; 0 0

0; 0 0

1.87 ± 0.02

0

95H3

1.9 ± 1.6

0; -11.0 ± 4.7 0

1.43 ± 0.02

0

93H4

no

0.0 ± 4.0

0

0

0

1.29 ± 0.06

0

94Z

no

1.9 ± 3.7

0

0

0

1.41 ± 0.05

0

94B6

no

-2.3 ± 3.1

0

0

0

1.90 ± 0.04

0

92W2

4.1-71 Surface

Cu(110)+ (disordered)CF3COO

Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. PED no no -2.3 ± 3.1

Cu(110)+ PED (disordered)NHx (x=2 or 1)

no

no

0.0 ± 5.5

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

0

0

0

1.90 ± 0.04

0

92W2

0; -5.5 ± 5.5

0; 0

0; 0

1.33 ± 0.02

0

96H3

CF3COO (trifluoro-acetate) adsorption; both O down; O approx. atop so molecule bridges 2 Cu atoms; C-C axis and molecular plane perp. to surface; F atom sites in fluoro-methyl group not determined disordered overlayer of NH2 or NH in short bridge sites of unreconstructed relaxed substrate

admolecules at center sites (see Fig. 20) Ni(110)+ c(2x2)-CN

NE- no XAFS PD

no

98B1

unreconstructed; relaxed substrate with CN lying perpendicular to troughs across center site of rectangular hollow; N higher than C

added row reconstruction with multilayer relaxation; O in long bridge site atomic adsorption in long-bridge sites (O below top Cu layer); with missing Cu [001] rows atomic adsorption in long bridge sites with missing-row reconstruction and slight secondrow pairing away from O sites atomic adsorption in long bridge sites with missing-row reconstruction and slight secondrow pairing away from O sites

adsorption at long-bridge sites on cross-ridge missing/added-rows substrate Ag(110)+ (2x1)-O Cu(110)+ (2x1)-O

ICISS no

yes 14.9 ± 3.5

ICISS no

Cu(110)+ (2x1)-O Cu(110)+ (2x1)-O

0

0.08 ± 0.05 0

-0.03 ± 0.05

0

93C1

yes 25.2 ± 15.6 0

0

-0.60

0

86Y2

XRD no

yes 29.0 ± 3.9

0

0.03 ± 0.05 0

-0.34 ± 0.20

0

90F1

LEED no

yes 16.6 ± 3.9

0

0.03 ± 0.05 0

0.04 ± 0.05

0

90P1

0

4.1-72 ∆r0 [Å]

Ref.

Description

0.12 ± 0.07 0

-0.08 ± 0.20

0

91D2

0

0

0

-0.05 ± 0.06

0

93D2

yes 20.4

0

0

0

0.2

0.1 ± 0.1

90K

LEED no

yes -1.5 ± 5.9

0

0.0 ± 0.14

0

0.0 ± 0.08

0

95D2

LEED no

yes -3.7 ± 3.7

0

0.0 ± 0.05

0

0.09 ± 0.04

0

95G1

O in long bridge sites with missing row reconstruction; row pairing (away from O) of second Cu layer added-row reconstruction with O in long bridge site missing-row structure in which the O atoms are above long bridge sites in [001] direction with slight asymmetry; top 2 Ni layers have an expanded separation while the 2nd and 3rd have a contracted separation; the 3rd layer is slightly buckled missing/added row reconstruction; with N atoms in long bridge sites added-row reconstruction across ridges; N in long-bridge positions forming Rh-N-Rh chains; buckling in 3rd substrate layer

Cu(110)+ (2x1)-O Ni(110)+ (2x1)-O

LEIS no

yes 0

LEED no

Rh(110)+ (2x1)-N Rh(110)+ (2x1)-N

Cu(110)+ (2x1)-O

∆rls [%]

αls [°]

d01 [Å]

bls Tech- Clean Ads- ∆dl,l+1 [%] nique rec. ind [%] rec. ICISS no yes 18.2 ± 11.7 0

Surface

adsorption on missing-row/added-rows substrate along ridge; at outermost 3-fold sites Ir(110)-(1x2)+ LEED yes (2x2)-2S

yes -3.3 ± 7.4

0

0

0

0.94 ± 0.10

-0.20

87C1

missing-row structure of substrate; atomic S over outermost 3-fold fcc-hollow sites in zigzag arrangement (2 per cell); bonding to two top-layer Ir atoms and one second-layer Ir atom

-0.40 ± 0.12

92B2

atomic H resides at the pseudo-three-fold sites; Ni substrate is (1x2) missing-row reconstructed

adsorption on missing-row/added-rows substrate along ridge; at middle 3-fold sites Ni(110)+ (1x2)-2H

TOF- no SARS

yes 0

0

0

0

0.21

4.1-73 Surface


bls [%]

αls [°]

d01 [Å]

0

0

1.02 ± 0.04

∆rls [%]

∆r0 [Å]

Ref.

Description

0

94H4

(1x2) missing row reconstruction induced by K adsorption; K coverage < 0.5; so not ordered overlayer; K atoms occupy 4-fold coordinated hollows at bottom of missing-row troughs

mixed Au/K top layer; inducing spacing relaxations and buckling in deeper Au layers almost perfectly ordered mixed Mn-Cu top layer: 87% Mn on site 1; 94% Cu on site 2; no Mn diffusion into 2nd and deeper layers; buckling in top layer; relaxation of top 3 layers

adsorption on missing-row/added-rows substrate at in-trough hollow site PED Cu(110)(1x2)+ (disordered)K

no

yes 2.4 ± 6.3

0

adsorption at substitutional sites in top layer (see Fig. 25) Au(110)+ c(2x2)-K Cu(110)+ c(2x2)-Mn

MEIS yes

yes -13.0 ± 3.0

0

0

0

1.05 ± 0.20

0

89H1

LEED no

yes -5.7 ± 1.6

0

0

0

0.22 ± 0.05

0

98R

± 0.20 ± 0.02

0

0

0

87K

H-induced row pairing reconstruction (H positions not determined)

93B1

N-induced reconstruction of top Cu layer to form nearly square buckled lattice of higher density; N deep in 4-fold hollow sites of this layer; forming 'c(2x2)' superlattice wrt it; 2nd through 4th Cu layers slightly buckled

row-pairing reconstruction in top substrate layer Pd(110)+ (1x2)-H

LEED no

yes -11.0 ± 2.2

0

complex reconstruction Cu(110)+ (2x3)-4N

XRD no

yes

4.1-74 Surface

Cu(110)+ (2x3)-4N

Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. LEED no yes

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

94V1

N-induced reconstruction of top Cu layer to form nearly square buckled lattice of higher density; N deep in 4-fold hollow sites of this layer; forming 'c(2x2)' superlattice wrt it; 2nd Cu layer slightly buckled buckled pseudo-(100) surface reconstruction of topmost layer; which has 3 N and 6 Cu atoms per (3x2) unit cell; N atoms occupy 4-fold coordinated hollows; outermost N site occupation only 30%; the following 4 substrate layers are also buckled reconstruction with inserted Ni row in [1-10] direction; forming buckled top Ni layer with quasi-square lattice; 1 N atom in hollow sites slightly above deepest buckled Ni atoms and 2 N atoms below hollow site of inclined Ni square (interstitial site between top 2 Ni layers) missing-row-pair reconstruction; S adsorbed at hollow sites on remaining-Ni-row pairs; and near hollow sites substituting for missing Ni rows; buckling of top Ni layers substrate reconstruction with missing rows and overlayer Ni atoms; O adatoms between overlayer-Ni and next-layer Ni; and within next inter-Ni spacing substrate reconstruction with missing rows and overlayer Cu atoms; O adatoms between overlayer-Cu and next-layer Cu; and within next inter-Cu spacing

Cu(110)+ (2x3)-3N

LEED no

yes

97M4

Ni(110)+ (2x3)-3N

SEno XAFS

yes

94W2

Ni(110)+ (4x1)-3S

XRD no

yes

93F2

Ag(110)+ c(6x2)-4O

LEIS no

yes

93D1

Cu(110)+ c(6x2)-4O

LEIS no

yes

93D2

4.1-75 Surface

Cu(110)+ c(6x2)-4O

Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. LEED no yes

bls [%]

∆rls [%]

αls [°]

∆r0 [Å]

d01 [Å]

Ref.

Description

95L2

atomic adsorption on reconstructed substrate: two types of O; each bonded with 4 Cu; this structure is composed of double-stranded Cu-O chains and is similar to a modified (211) plane of bulk Cu2O; the basic building blocks are OCu-O 3-atom rods each P occupies an identical 6-coordinate site created by the reconstructed Cu(110); which itself corresponds to a quarter ML of added Cu atoms at hollow sites; each bonding to 2 P atoms and 5 other bulk-like Cu atoms combination of Bi overlayer in troughs and substitution of every fourth Cu row in the [001] direction of the topmost Cu layer by Bi atoms every 4th Cu row in the [001] direction (perp. to troughs) is substituted by Li atoms; remaining Cu rows are covered by 2 Li adatoms per unit cell

Cu(110)+ (2,2|-1,1)-2P

LEED no

yes

96L2

Cu(110)+ (4x1)-3Bi

GIXD no

yes

96L3

Cu(110)(4x1)-3Li

LEED no

yes

97M3

Table 16. Structures of clean hcp(10-10) surfaces. Surface

∆d12 [%] -25.0

∆d23 [%] 5.1

∆d34 [%] -11.0

∆d45 [%] 2.0

∆d56 [%] 0

Ref.

Description

96H4

-6.5 ± 2.0

1.0 ± 2.0

0.0 ± 4.0

0

0

90L2

relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface) relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface) and multilayer relaxations

1.436; -13.0 ± 0.4 3.0 ± 0.2 2.872

0.5 ± 0.6

0

0

91O2

Tech- Clean dbulk nique rec. [Å] Be(10-10) LEED no 1.319; 2.637 Co(10-10) LEED no 1.45; 2.9 Co(10-10) LEED no

relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface) and multilayer relaxations

4.1-76 Surface

Tech- Clean dbulk nique rec. [Å] Re(10-10) LEED no 2.4; 4.8

Ti(10-10)

LEED no

∆d23 ∆d12 [%] [%] -16.2 ± 12.6 2.0 ± 4.2

2.555; -4.3 ± 6.0 5.11

4.7 ± 3.0

∆d34 [%] 0

∆d45 [%] 0

∆d56 [%] 0

Ref.

Description

80D

bulk termination with top interlayer spacing contraction; second interlayer spacing may be expanded; termination between widely spaced layers

0

0

0

90W1

70% of surface bulk terminated with narrow top interlayer spacing (d12) contracted about 5%; second interlayer spacing (d23) expanded about 1-2%; 30% of surface bulk terminated with expanded (+6%) large (d23) interlayer spacing

Table 17. Adsorbate-induced structures on hcp(10-10) surfaces. Surface


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

0

0

2.44 ± 0.10 0

∆r0 [Å]

Ref.

Description

91B

atomic adsorption at 4-fold hollow of bulk terminated structure of lower corrugation

adsorption at center site (see Fig. 26) Co(10-10)+ c(2x2)-K

LEED no

no

-5.3 ± 14.0 0

adsorption in 3-fold hollow sites on sides of troughs; relaxations given relative to center sites (see Fig. 27) Co(10-10)+ (2x1)-2O

LEED no

no

25.4 ± 4.2 0 -3.2 ± 3.5 0

0 0

0 0

0.74 ± 0.05 0.97 ± 0.41 97G4

Ru(10-10)+ (2x1)-2O

LEED no

no

3.7 ± 1.3 0 -2.1 ± 1.3 0

0 0

0 0

0.96 ± 0.02 1.13 ± 0.05 98S1

relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface); oxygen forms zigzag chains; in hcp-hollow sites on sides of Co ridges relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface); oxygen forms zigzag chains; in hcp-hollow sites on sides of Ru ridges

4.1-77 Surface

Ru(10-10)+ c(2x4)-2O


∆dl,l+1 [%]

bls [%]

-4.0 ± 5.0; 0; -7.8 ± 5.0; 0; -1.4 ± 5.0 0

∆rls [%]

αls [°]

∆r0 [Å]

d01 [Å]

Ref.

2.0 ± 3.0; complex 1.02 ± 0.03 0.95 ± 0.06 98S1 0; 0

-1.4 ± 1.3 -3.8 ± 5.0; 0; 2.6 ± 5.0 0

0.01 ± 0.03; 0

Description

relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface); oxygen forms zigzag chains; in hcp-hollow sites on sides of alternate Ru ridges

adsorption at short-bridge sites and 3-fold hollow sites in sides of troughs (see Fig.s 27 and 28) Re(10-10)+ c(2x2)-3H

LEED no

no

98D1

Ru(10-10)+ c(2x2)-3H

LEED no

no

98D1

little change in top two Ru-Ru interlayer spacings; but contraction by 0.09 Å of third spacing; Re atoms of short-bridge site are possibly displaced laterally toward site by 0.02 Å little change in top two Re-Re interlayer spacings; but contraction by 0.05 Å of third spacing; Re atoms of short-bridge site are possibly displaced laterally toward site by 0.02 Å

Table 18. Structures of clean bcc(211) surfaces. Surface Fe(211) W(211)

Tech- Clean dbulk nique rec. [Å] LEED no 1.17

∆d23 ∆d12 [%] [%] -10.4 ± 2.6 5.0 ± 2.6

∆d34 [%] -1.8 ± 3.4

∆d45 [%] 0

∆d56 [%] 0

Ref.

Description

84S

TOF- no SARS

-9.4 ± 5.4

0

0

0

89R

bulk termination with multilayer relaxation perpendicular and parallel to surface bulk termination with registry shift by 6.0%; relative to bulk

1.29

-0.2 ± 5.4

4.1-78 Table 19. Adsorbate-induced structures on bcc(211) surfaces. Surface


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

89B3

atomic O in three out of four 3-fold coordinated sites on an unrelaxed and unreconstructed W substrate; as found consistent with experimental data

95H3

hydrogen induced missing row reconstruction of Fe(211); removal of close-packed rows in top layer; row pairing in 2nd layer and buckling in 3rd layer; adsorption site of H not determined

86S1

atomic adsorption in long-bridge sites; forming -FeO-Fe-O- strings perpendicular to clean-surface ridges; in which half the Fe atoms are missing ('missing-row' model)

adsorption at 3-fold coordinated sites of unreconstructed substrate W(211)+ (1x2)-3O

TOF- no SARS

no

adsorption on close-packed missing-row reconstruction Fe(211)+ (1x2)-2H

LEED no

yes

adsorption on non-close-packed missing-row reconstruction Fe(211)+ (2x1)-O

LEED no

yes

4.1-79 Table 20. Structures of clean bcc(111) surfaces. Surface

Clean rec. no no

∆d12 [%] -15.4 ± 3.6 -16.6 ± 3.0

∆d23 [%] 0 -9.3 ± 3.0

∆d34 [%] 0 4.0 ± 3.6

∆d45 [%] 0 -2.1 ± 3.6

∆d56 [%] 0 0

Ref.

Description

81S2 86S2

bulk termination with top spacing contraction bulk termination with multilayer relaxation perpendicular to surface bulk termination with multilayer relaxation perpendicular. to surface bulk termination with multilayer relaxation perpendicular to surface

Fe(111) Fe(111)

Technique LEED LEED

Mo(111)

LEIS no

0.909 -18.0 ± 2.0 4.0 ± 4.0

0

0

0

86O

Mo(111)

LEED no

0.907 -18.8 ± 2.0 -18.9

6.4

2.2

0

99A

dbulk [Å] 0.827 0.827

Table 21. Adsorbate-induced structures on bcc(111) surfaces. Surface


∆dl,l+1 [%]

bls [%]

∆rls [%]

αls [°]

d01 [Å]

∆r0 [Å]

Ref.

Description

-17.4 ± 1.5

0

0

0

0.03 ± 0.51

0

99A

H adsorbs in triplets around each deep hollow site; inducing little change in 1st Mo-Mo spacing; but large derelaxation of 2nd Mo-Mo spacing to near bulk value

adsorption at asymmetrical sites Mo(111)+ (1x1)-3H

LEED no

no

4.1-80 Table 22. Structures of clean Si; Ge and C(111) surfaces. Here; dbulk gives the spacing between the pairs of bilayers in the bulk. Surface

Tech- Clean dbulk nique rec. [Å] 2.35 Si(111)-(1x1) LEED no (laser annealed) Si(111)-(2x1) LEED yes 2.35 Si(111)-(2x1) MEIS yes 2.35 Si(111)-(2x1) LEED yes 2.35 Si(111)-(7x7) LEED yes 2.35 Ge(111)LEED yes 2.45 c(8x2)

d12 [%] -

ω (°) -

Ref.

description

86J

unreconstructed bulk termination with multilayer relaxations perpendicular to surface

-

-

84H1 85S 86S3 88T2 90T3

tilted π-bonded chain model with overall compression tilted π-bonded chain model; with tilt in lower chain in same direction as tilt in upper chain tilted π-bonded chain model with relaxations down to 4th bilayer optimized DAS (dimer-adatom-stacking fault) model 2 adatoms A and B in the top layer in T4 sites with identical local environments; relaxations found in the top 5 Ge layers (adatoms + 2 bilayers)

Table 23. Adsorbate-induced structures on Si; Ge and C (111) surfaces. Here; d01 is the local adsorbate height; while ∆d12 is the relative first bilayer spacing change. Surface


d01 [Å]

∆d12 [%]

ω [°]

Ref.

Description

atomic adsorption stabilizing unreconstructed substrate with relaxed top two interlayer spacings (H position not determined) unreconstructed; nearly unrelaxed ideal bulk Si termination (H position not determined)

adsorption at unknown sites Ge(111)+ (1x1)-H Si(111)+ (1x1)-H

LEED yes

no

-

0

87I

MEIS yes

no

-

-2 ± 2

94N4

1.32

1

91W2 atomic adsorption of Bi in T4 site (3-fold hollow above 2nd Ge layer) on unreconstructed; relaxed substrate

adsorption at T4 sites (see Fig. 29) Ge(111)+ (√3x√3) R30°-Bi

LEED yes

no

4.1-81 Surface

Ge(111)+ (√3x√3) R30°-Pb (1/3ML) Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Bi Si(111)+ (√3x√3) R30°-Ga Si(111)+ (√3x√3) R30°-Ga Si(111)+ (√3x√3) R30°-Ga Si(111)+ (√3x√3) R30°-In

Tech- Clean Adsnique rec. ind rec. LEED yes no

d01 [Å]

∆d12 [%]

1.7

LEED yes

no

LEED yes

RHEED PD

ω [°]

Ref.

Description

1

89H3

α structure: atomic adsorption of Pb in T4 sites on unreconstructed; relaxed substrate: buckling of second and third Ge monolayers (first is planar)

1.39

-22

90H2

no

1.38

-22

92N

yes

no

1.42 ± 0.06

-15

95H2

Al adsorbed at T4 site; the three 1st-layer Si atoms are moved radially inwards and up; the Si below the T4 site is moved down; pushing the Si right below it downwards; other 2nd- and 3rd-layer Si atoms below them are moved upwards Al at T4 site on unreconstructed; relaxed substrate; 1st-layer Si atoms are moved radially inwards and up; the Si below the T4 site is moved down; pushing the Si right below it downwards; other 2nd- and 3rd-layer Si atoms below them are moved upwards atomic adsorption in 4-fold coordinated T4 site; large rumpling in 2nd and 3rd layers of substrate

yes

no

1.30 ± 0.20

-

99S2

LEED yes

no

1.11

-14

MEIS yes

no

1.45

-23

RHEED

yes

no

1.51 ± 0.06

3±2

92W1 Bi centered at T4 site; nearest Si neighbors squeezed together; Si atom directly below Bi and third layer Si atom directly below pushed downwards; second-layer Si atoms surrounding the hollow H3 site are moved upwards 92C Ga centered at T4 site on unreconstructed; relaxed substrate; nearest Si atoms squeezed together; two Si atoms directly below Ga pushed downwards; 2nd-layer Si atoms surrounding the hollow H3 site are moved upwards 95H2 atomic adsorption in 4-fold coordinated T4 site; large rumpling in 2nd and 3rd layers of substrate

LEED yes

no

1.35

-24

88K

atomic adsorption in 4-fold coordinated T4 'top' site over top bilayer; with relaxations down into 2nd bilayer

XRD yes

no

1.85 ± 0.05

-15 ± 3

93F1

Ga centered at T4 site on unreconstructed; relaxed substrate; nearest Si atoms squeezed together; two Si atoms directly below Ga pushed downwards; 2nd-layer Si atoms surrounding the hollow H3 site are moved upwards

Al at T4 site on unreconstructed; relaxed substrate; 1st-layer Si atoms are moved radially inwards

4.1-82 Surface

Si(111)+ (√3x√3) R30°-In Si(111)+ (√3x√3) R30°-In Si(111)+ (√3x√3) R30°-In Si(111)+ (√3x√3) R30°-Pb (β phase) Si(111)+ (√3x√3) R30°-Sn Ge(111)+ (2x1)-2Sb

Tech- Clean Adsnique rec. ind rec. yes no SEXAFS XSW RH- yes no EED

d01 [Å]

∆d12 [%]

2.10 ± 0.06

0±2

93W6 In at T4 site on unreconstructed substrate with no appreciable surface relaxations within about 0.25Å

1.83 ± 0.06

-13 ± 3

95H2

atomic adsorption in 4-fold coordinated T4 site; large rumpling in 2nd and 3rd layers of substrate

PD

ω [°]

Ref.

Description

yes

no

1.70 ± 0.10

-

99S2

In at T4 site on unreconstructed; relaxed substrate; 1st-layer Si atoms are moved radially inwards

LEED yes

no

1.43 ± 0.05

-6 ± 2

91D1

XRD yes

no

1.59 ± 0.3

-25

89C

XRD yes

no

2.62 ± 0.03

3±3

92V

atomic adsorption above T4 site; the three first-layer Si atoms are moved in as well as up; the Si right below Pb is moved down together with the Si atom below it; all the other Si's in the 2nd; 3rd; and 4th Si layers are moved upwards; the 5th Si layer and below are in bulk positions atomic adsorption at T4 site; the three first-layer Si's are moved radially inwards; the Si below the T4 site is moved down; pushing the Si right below it downwards; other second-layer Si's and third-layer Si's below them are moved upwards; layers 4; 5; and 6 are laterally moved Sb forms 6° tilted zig-zag chains; saturating the dangling bonds of the unreconstructed; relaxed; full-bilayer-terminated substrate by slightly off-top adsorption

adsorption at top sites (see Fig. 30) C(111)+ (1x1)-H (diamond) Ge(111)+ (1x1)-Cl Ge(111)+ (1x1)-I Ge(111)+ (1x1)-PHx

MEIS yes

no

-

0

86D

unreconstructed bulk diamond termination between bilayers; probably stabilized by H; with minor C-C spacing contraction in top bilayer (H positions not determined; but probably terminate dangling bonds) atomic adsorption in top sites on unrelaxed unreconstructed substrate

SEyes XAFS SEyes XAFS XSW AR- yes PEFS

no

2.07 ± 0.03

0

83C

no

2.50 ± 0.04

0

89B2

atomic adsorption of I in top sites on unreconstructed; relaxed substrate: first substrate interlayer spacing contracted by 10%

no

2.26 ± 0.04

8

90T1

adsorption of partially dissociated PH3 in tilted top sites on unreconstructed; relaxed substrate; first Ge-Ge interlayer spacing contracted by 16%

4.1-83 Surface

Si(111)+ (√3x√3) R30°-Pb

d01 [Å]

∆d12 [%]

2.56

ω [°]

Ref.

Description

0

87D2

atomic adsorption in 1-fold coordinated top sites over unreconstructed; unrelaxed substrate terminated between bilayers

1.03 ± 0.05

8±2

87R3 atomic adsorption in bridge sites with shorter bond to 3rd Ge atom; with unreconstructed substrate relaxed perpendicular to surface

no

2.21

-21

92W1 Bi trimers centered at T4 site; nearest Si neighbors squeezed together; Si atom directly below Bi and third layer Si atom directly below pushed downwards; second-layer Si atoms surrounding the hollow H3 site are moved upwards

LEED yes

yes

-2.32

-25

90H1 B atom replaces a second layer Si atom; which becomes an adatom at the T4 site over the B atom; this B position is the B5 site

PD

yes

-2.21

-20

99B1 B atom replaces a second layer Si atom; which becomes an adatom at the T4 site over the B atom; this B position is the B5 site

Tech- Clean Adsnique rec. ind rec. XSW yes no

adsorption at bridge sites (see Fig. 31) Ge(111)+ (2x2)-S

AR- yes PEFS

no

adclusters at T4 site (see Fig. 29) Si(111)+ (√3x√3) R30°-3Bi

LEED yes

substitution below T4 site Si(111)+ (√3x√3) R30°-B Si(111)+ (√3x√3) R30°-B

yes

substitution of top half of top bilayer (see Fig. 32) Ge(111)+ (1x1)-Sb Si(111)+ (1x1)-As

HEIS yes

no

1.19

0

94G3

MEIS yes

no

0.99

0

87C2

atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; but relaxed substrate atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; unrelaxed substrate

4.1-84 Surface

Si(111)+ (1x1)-As Si(111)+ (1x1)-As

Tech- Clean Adsnique rec. ind rec. XSW yes no

d01 [Å]

∆d12 [%]

0.99 ± 0.03

MEIS yes

1.02 ± 0.06

no

ω [°]

Ref.

Description

0

87P

0

87H1

atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; unrelaxed substrate atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; unrelaxed substrate

partial substitution of top half of top bilayer (see Fig. 32) Si(111)+ (√3x√3) R30°-3Bi Si(111)+ (√3x√3) R30°-3Bi

XRD yes

yes

-0.8

14 ± 1

87T

triangles of 3 Bi replace every third Si in top layer; which is lower half of a bilayer

LEED yes

yes

2.21

41

91W1 triangles of 3 Bi replace every third Si in top layer; which is lower half of a bilayer

honeycomb-chained-trimer (HCT) structure Ge(111)+ (√3x√3) R30°-3Ag Si(111)+ (√3x√3) R30°-3Li Si(111)+ (√3x√3) R30°-3Ag Si(111)+ (√3x√3) R30°-3Ag Si(111)+ (√3x√3) R30°-3Ag

LEED yes

yes

0.70 ± 0.03

-1

94H5

honey-comb chained trimer (HCT) model: top Ge half bilayer replaced by Ag; 2nd layer Ge atoms form trimers

LEED yes

yes

0.45

-2

93O1

top Si half-bilayer substituted by Li (missing top layer); 2nd half-bilayer Si atoms form trimers

XRD yes

yes

0.80 ± 0.02

-4

93T

top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers; deep relaxations

LEED yes

yes

0.69

-2

93O1

top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers

QK- yes LEED/ CMTA

yes

0.79

0

93J

top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers; deep relaxations

4.1-85 Surface

Si(111)+ (√3x√3) R30°-3Ag

Tech- Clean Adsnique rec. ind rec. LEED yes yes

d01 [Å]

∆d12 [%]

0.78 ± 0.05

ω [°]

Ref.

Description

-2

95O3

top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers

conjugate HCT structure Ge(111)+ (√3x√3) R30°-3Au Ge(111)+ (√3x√3) R30°-3Au Si(111)+ (√3x√3) R30°-3Au Si(111)+ (√3x√3) R30°-3Au Si(111)+ (√3x√3) R30°-3Au

XRD yes

no

0.42 ± 0.02

6

93H3 conjugate honeycomb-chained-trimer (CHCT) model: Au trimers centered at T4 sites; replacing top half of top Ge bilayer; nearest Ge neighbors squeezed apart

LEED yes

no

0.51

0

95O4 conjugate honeycomb-chained-trimer (CHCT) model: Au trimers centered at T4 sites; replacing top half of top Ge bilayer; nearest Ge neighbors squeezed apart

LEED yes

no

0.56

0

92Q1 conjugate honeycomb-chained-trimer (CHCT) model: Au trimers centered at T4 sites; nearest Si neighbors in the missing-top-layer are squeezed apart

LEED yes

no

0.56

0

93O1 top Si half-bilayer substituted by Au (missing top layer); Au atoms form trimers

XRD yes

no

0.93

-8

94K

94W3 reconstruction with zigzag Si chains separated by CaF2 chains filling missing Si rows; Si chains oriented along [1-10]; obtained by mainly lateral displacements by +@ 7KLV GLVWDQFH LV PDFURVFRSLFDOO\ VWLOO D VKRUW GLVWDQFH ,Q RUGHU WR avoid any influence of the edge fields the lateral distance to such edges should be larger than z0. This is easily fulfilled for the case, where single crystalline surfaces of a diameter of several mm are studied. The above cited method of photoemission from adsorbed rare gases does not fulfill this criterion and has, therefore, to be used with care. The great advantage on the other hand is the small lateral extension of the rare gas atom probe which makes it possible to study surfaces of very small patches down to locally stoichiometric compound surfaces. Actually, the method was invented when it was found that photoemission from Xe physisorbed at steps gives rise to different binding energies compared to those from the terrace [79K3]. 4.2.1.4 Standardization of work-function change with coverage In Fig. 1 four different types of work-function changes with coverage are sketched. Types I and II are for electronegative adsorbates as, e.g., for oxygen or chlorine: the electronegative species attracts some negative charge which increases the barrier for the outgoing electron. Types III and IV are due to an inversion of the dipole moments of types I and II. Typical examples for electropositive species are the alkali metals. ∆Φ1

Type I

θ1

0

Work − function change ∆Φ

∆Φ1

Type II ∆Φ2

θ1

0

θ2

0

Type III ∆Φ1 θ1

0

θ2

∆Φ2 ∆Φ1 Coverage θ


Type IV

Fig. 1. Four different types of work-function changes ∆Φ as function of coverage θ. Characteristic maxima, minima, or saturation values are marked by (θi, Φi).

4.2-4

4.2 Electron work function of metals and semiconductors

[Ref. p 4.2-118

For all types in Fig. 1 is common that there is a more or less extended linear change with exposure θ for θ ĺ 0. This is quite easily understood assuming that each adsorbed species contributes by its own typical dipole moments p to the overall work-function change ∆Φ which is given by the Helmholtz equation ∆Φ = -4πepNa

(6)

where Na is the number of adsorbed atoms per unit area. Eq. (6) describes basically the types I and III. A linear change of Φ with Na is actually not observed, instead the change of Φ per adsorbed atom becomes smaller. This is formally explained by depolarisation due to lateral interaction between the dipoles. This has been modeled by Topping [27T] for mobile adsorption: ∆Φ = -4πeµ0Na(1 + 9αNa3/2)-1 = 3.77·10-15µθ(1 + 9αθ3/2)-1

(7) (7’)

where µ0 is the initial dipole moment (for Na ĺ 0) and α denotes an effective polarizability. In Eq. (7’) θ is the surface coverage in atoms cm-2, µ the dipole moment in D, and α the polarizability in cm3. This Topping formula is often used to extract p0 and α from the measured ∆Φ curves. It should be noted, however, that the depolarization may be a very involved process and may be differ among different systems. So, it was shown in calculations for Cs/W(100) that not only Cs 6s and W 5d contribute but also a significant counter-polarization of the Cs 5p shallow core level was found [83W2]. 4.2.1.5 Experimental methods This short paragraph is not intended to describe the experimental techniques to measure work function and work-function changes in detail. For this purpose one may look into chapter 2.4 or into older review articles [69R, 72H2, 79H3]. There are basically three absolute methods: Thermionic emission (Therm), field electron emission (FEM), and photoelectron emission (PYS, ARUPS). Besides this and even more important are relative methods which can be divided into three groups: secondary electron edge methods (SE edge), Kelvin methods (Kelvin) and the reflection of electron beams (diode). We have introduced here the acronyms used in the tables below. Before we start presenting the data collection we will briefly comment on the above listed methods: 4.2.1.5.1 Thermionic emission (Therm) According to the Dushman-Richardson equation, the electron current upon heating a substrate of work function Φ is given by I = A(1 – r) T2 exp(-Φ/kT)

(8)

where A is a known constant, T the temperature, k the Boltzmann constant and r the reflection coefficient of the outgoing electron at the surface potential barrier. The experiments to deduce Φ from Eq. (8) are very difficult; the current depends exponentially on Φ and space charge problems can introduce severe problems. Also the geometry of the emitting surface and fringe fields have to be controlled. Interestingly, it could be shown that the maximum of the energy distribution of thermoionic emitted electrons shifts with Φ [85E]. For many adsorbate-induced work-function changes this method is useless, since the adsorbate may desorb before the temperature is high enough to produce measurable current densities. 4.2.1.5.2 Field electron emission (FEM) If an electric field is applied to a metal surface the potential barrier at the surface may become narrower so that electrons may tunnel through the barrier. The field-emitted electron current I is given by the Fowler-Nordheim equation [28F] I = BE2 exp(-βE-1)

(9)

where B and β are constants containing Φ, and E is the electric field strength. A so-called FowlerLando lt -Börnst ein New Ser ies III/42 A2

Ref. p. 4.2-118]


4.2-5

Nordheim plot of ln(IE-2) vs. E-1 yields a straight line from which Φ can be derived. Usually, field emission sets in at fields of the order of 106 Volt cm-1. Such fields can easily be obtained if the metal surface is formed as a tip. As such a tip is composed of different surfaces with different Φ, measuring the total current leads to only an average value of Φ, weighted towards the surfaces of low Φ. Much more sensible results are achieved with the probe hole technique by which the current from different areas of the tip is analyzed separately. It became possible to follow the arrival of single evaporated atoms in the current jumps from a W(110) surface [77K]. During the sixties FEM was the best-choice method. Later, some drawbacks were clearly recognized [71F, 81S]: (1) (2) (3)

(4)

The shape of the emitter influences the strength of the electric field. If a planar facet is too large, the field gets reduced in its center region. The state of the adsorbate may be influenced by the electric field. There is a large uncertainty about the actual coverage of an adsorbed metal at an individual facet. The adsorbate under investigation is usually deposited onto one side of the tip which is kept at low temperature (room temperature) or below. Later the adsorbate is spread over the whole tip at elevated temperatures. Assuming that an equilibrium between the different faces is achieved this way, the coverage at the faces with the higher binding energy may be larger. There may be also structural changes within the adsorbate layer occurring during the preparation at higher temperatures.

In spite of these difficulties, reasonable results have been collected using the FEM method [79S2, 81S]. 4.2.1.5.3 Photoemission (PYS, ARUPS) We call this method photoemission yield spectroscopy (PYS) if photons near to threshold are used and all photoelectrons are collected [77S]. If VUV photons are used and photoelectron spectra are measured, we call the method ARUPS from angle-resolved UV-light photoelectron spectroscopy. Energy conservation in photoemission is given by F

Ekin = hν – E B – Φ ,

(10)

where the kinetic energy Ekin of the outgoing photoelectron is given by the photonenergy hν, the binding F

energy of the electron E B (with reference to the Fermi edge) and the work function Φ. Eq. (10) indicates that there is threshold photonenergy (hν)t so that photoelectrons with Ekin 0 are emitted for hν (hν)t. For a metal the electronic levels are filled up to EF so that (hν)t = Φ .

(11)

So, the photoemission process establishes the possibility to determine an absolute value of Φ. In practice there are several ways to make use of Eqs. (10) and (11). The first way was to use UV light with hν (hν)t § 5 eV. It can be shown [31F] that there is a narrow photon energy range (§ 0.5 eV) above threshold in which the yield of photoelectrons Y(hν) increases proportional to (hν-Φ)2. If one plots Y(hν)1/2 as a function of hν (Fowler plot) and extrapolates for hν ĺ 0, one can obtain Φ. The second way could be realized after development of VUV-light sources and energy analyzers for the photoelectrons. If one collects all electrons without cutting off some at the low energy end of the spectrum, one measures the width W of the photoelectron energy distribution curve. For a metal this is quite easy, since both the secondary electron threshold as well as the Fermi edge exhibit a large enough intensity. Thus, the work function can be determined from Φ = hν - W.

(12)

By this method absolute work function values can be determined with an accuracy of ±10 meV under the following conditions:


4.2-6 (1)

(2)


[Ref. p 4.2-118

The measurements have to be performed in an angle-resolved mode of photoelectron spectroscopy (ARUPS). Angle-integrated modes collect, with increasing kinetic energy, an increasing number of secondary electrons with kɊ 0. The threshold can therefore have a width of up to 1 eV and is not a sharp level. Therefore, an extrapolation procedure has to be used which always includes some degree or arbitrariness. The spectrometer sample configuration should be of such a geometry that a planar electric field is built in front of the sample, if one supplies the sample with a bias voltage of, e.g., -2 Volt. This voltage accelerates all photoelectrons by 2 eV and ensures that the full spectrum, including the electrons of the true secondary-electron threshold, enters the spectrometer.

Both conditions are fulfilled for the ARUP spectrometer (ADES 400, VG Scientific) which we use in our laboratory. For a Pt(111) surface and a pass energy of the spectrometer of 5 eV we have measured a linear increase of intensity from 10...90% within 120 meV at the secondary-electron threshold and a 10...90% drop of intensity within 140 meV at the Fermi edge. Under these conditions the secondary-electron threshold is as sharp as the Fermi edge. We have therefore included the energy resolution of our spectrometer at both edges. Furthermore, one can derive great benefit from the VUV-discharge lamps (e.g., the He-lamp) whose photon energy is precisely known. The energy of the HeIα line, e.g., is hν = 21.217 eV [70T]. Alternatively, one can perform two-photon photoelectron emission by using UV lasers. In this case one overcomes the surface barrier with the help of 2hν and hν is also known with high precision. 4.2.1.5.4 Secondary electron edge method (SE edge) If photons or charged particles, like electron or ions, interact with bulk material, inelastic processes occur and so-called secondary electrons (SE) are created. These electrons are in empty states above EF and even above the vacuum level. They can leave the bulk if their energy (with wave vector perpendicular to the surface) is larger than Φ (taking EF as the energy zero). The secondary-electron edge, i.e., the energy interval in which the current of secondary-electron drops to zero has a width of 0.05 to 1.0 eV depending on geometry and energy resolution of the electron energy spectrometer. Quite clearly, the SE edge shifts as Φ is changed. This shift can be used to determine a work-function change ∆Φ. The shift is measured very often at the half height of the SE edge where the SE current depends linearly from energy in most cases. In our tables, presented below, we have indicated this experimental method by SE edge (XPS) including in brackets the process which creates the SE edge, XPS given as an example here. Further probes to create SEs are electrons (E) or UV photons (UPS). 4.2.1.5.5 Diode method (Diode) If an electron beam is directed towards a surface, it gets reflected if its potential is equal to - (EP/e + ∆Φ), the negative value of the primary energy divided by e and corrected for ∆Φ between the surface and the electron emitter (in the widest sense: cathode, electron gun, etc.). Since the surface serves here as the anode in a diode configuration, the name diode method has been chosen. This method was introduced early by P.A. Anderson [35A]. Many details of different experimental set-ups are discussed in [73K2, 79H3]. It was pointed out [85K8] that for carefully chosen conditions and for a patchy surface, i.e., a surface consisting of a composite of smaller areas of different work function, the diode method measures the same arithmetical average of Φ as the Kelvin method (see below). How to use a HREEL spectrometer for the diode method is reported in Ref. [85S3]. 4.2.1.5.6 Vibrating capacitor method (Kelvin) The vibrating capacitor method is based on the work of Lord Kelvin [1898K] and of Zisman [32Z]. A condensor is formed of the surface to be studied and a reference electrode in front of it which are connected by a ammeter and a variable voltage source. If the capacitance between the plates (sample and reference electrode) is changed, e.g., by changing their distance, a current will flow. By compensating the


Ref. p. 4.2-118]


4.2-7

contact potential difference through the voltage source, the current can be brought to zero. Since Φ of the surface is part of the contact potential, its changes relative to the reference electrode can be measured. A more extended description can be found in Ref. [79H3]. A very versatile instrument of this kind was developed by Besocke [76B]. 4.2.1.6 Data collection Data have been collected for metal as well as semiconductor substrates. In the case of metals only elemental, single-crystalline samples were considered. There are a few exceptions to this general rule. Some metallic alloys are listed in case of single-crystalline samples of well defined (stoichiometric) composition. Some data are also incorporated for evaporated, mostly polycrystalline films of materials for which no single-crystal data are available. For semiconductor substrates, adsorbate-induced workfunction changes consist of two contributions: band-bending and electron-affinity changes. Systems were discarded for which the overall change in work function was small (-0.2 0.0

77

Kelvin

-0.9

77

Diode

0.0

10

ARUPS

0.0

15

Kelvin

-0.025

77 77 77 45 77

Kelvin Kelvin Kelvin ARUPS Kelvin SE edge (UPS) SE edge (UPS) Kelvin Kelvin

-0.47 45 L -0.47 -0.61(2) -0.61(2) -0.48 -0.58

LEED LEED LEED

-0.58

µ0 = 0.24 D

-0.53 -0.58

LEED LEED, AES

71C4 73C2 73C2 82M2 73C2 86J3

Al (polycr.) Au (polycr.) Au(100) Ba (polycr.) Ca (polycr.) Cr (polycr.) Cs (polycr.) Cs (polycr.) Cs (polycr.) Cu(100) Cu(100) Cu(110) Cu(110) Cu(111) Cu(111)

86E3

Cu(111)

74N 76M2 88A 53M 53M 74K 83R2 84C

76R3 Cu(211) 75P Cu(311)


40

77 77

Type

∆Φ [eV] at θ1

Xe/ Substrate 73C2 Ag(110) 73C2 Ag(111) 76M3 Ag(111) 76R3 86B5 Ag(111)

III

-0.48(1) monolayer TDS, XPS, UPS,LEED -0.6 multilayer UPS angle-integrated µ0 = 0.2 D -0.48 µ0 = 0.2 D

III

-0.45 -0.47

III

-0.29 -0.33 -0.25

III

III

LEED

1 ML multilayer 1 ML* *1 ML has been taken as 6·1014 atoms cm-2 ML AES, ELS, LEED ML 2. layer

ARUPS 1 ML

LEED µ0 = 0.24 D

4.2-10


Ref.

Xe/ Substrate 75P3 Cu(100) Cu(111) Cu(110) Cu(211) Cu(311) Cu(755) 71K Cu (polycr.) 74N4 Cu (polycr.) 53M Fe (polycr.) 80P Fe(110) 74N Fe (polycr.) 87J2

T [K]

Method

Type

∆Φ [eV] at θ1

77

Kelvin

III

77

Diode

-0.47 -0.48 -0.61 -0.53 -0.55 -0.53 -0.57

78

PYS

-0.63

77

Kelvin

-0.66

78

PYS

-0.3 -0.5

∆Φ values for surfaces annealed at higher temperatures do not vary much

82L4 53M

77

SE edge (UPS) SE edge (E) SE edge (UPS) Kelvin

78 78 78 78 78 78

FEM FEM FEM FEM FEM FEM

-1.6 -0.8 -1.8 -1.3 -1.0 -1.05

Kelvin

0.0 -0.05

1 ML*

Hg (polycr.) 74N2 Ir(100) Ir(110) Ir(111) Ir(210) Ir(321) 74N Ir (polycr.)

-0.22(1) ML

-0.23


K (polycr.) 77 K (polycr.) 15

84C

15

Kelvin

III

-0.1

1 ML*

15

Kelvin

III

-0.3

1 ML*

30...100 Kelvin

86M2 Ni(100)

20

µ0 = 0.14 D

-0.6

53M 84C

Li (polycr.) 84C Mg (polycr.) 74M6 Mo (polycr.) 71K Na (polycr.) 84C Na (polycr.) 82C Ni(100)

Comments, interpretation

ML

Ga 10 (polycr.) Ge(111)- 60 c(2 × 8) Gd(0001)

88P2

-0.25

[Ref. p 4.2-118

*1 ML has been taken as 6·1014 atoms cm-2 *1 ML has been taken as 6·1014 atoms cm-2 *1 ML has been taken as 6·1014 atoms cm-2

-0.70 77

Diode

15

Kelvin

SE edge (UPS)

0.0 III

-0.05

1 ML*

III*

-0.38

10 L

-0.3

ML

*1 ML has been taken as 6·1014 atoms cm-2 *very weak Type IV LEED, TDS, UPS µ0 = 0.29 D TDS, AES, influence of K


Ref. p. 4.2-118] Ref.

4.2 Electron work function of metals and semiconductors T [K]

Method

20

ARUPS ARUPS

53M

Ni (polycr.) 74N Ni (polycr.) 74N4 Ni (polycr.) 88J Ni(111)(7 × 7)Pb 85D2 NiO

77

Kelvin

78 590* 78

PYS PYS

-1.01 -0.6 -0.82

20

ARUPS

0.0 -0.4(2)

88J

Pb(111)

20

SE edge (UPS) ARUPS

71P

Pd(100)

77

Kelvin

80K

Pd(100)

40

84M

Pd(100)

SE edge (UPS) SE edge (E)

84W

Pd(100)

95

79K2 Pd(110)

100

84W

Pd(110)

95

84W

Pd(111)

95

ML 2. layer

ARUPS

*film annealed at 590 K ML Xe 5p and 4d levels

ML 2. layer at 6 L

-0.65

1 ML

III

-0.70(2)

SE edge (UPS)

III

-0.86(2)

SE edge (UPS) SE edge (UPS) SE edge (UPS)

III

-0.92(1)

III

-0.96(2)

III

-0.85(2)

LEED: no 2D island at 10 K µ0 = 0.45(3) D α = 3.6(8)·10-24 cm3 LEED, AES, UPS; hcp Xe layer µ0 = 0.61 D α = 8.4·10-24 cm3 LEED, TDS, UPS µ0 = 0.42 D LEED, TDS, UPS; hcp Xe layer µ0 = 0.44 D LEED, TDS, UPS; (¥î¥ 5ÛVWUXFWXUH µ0 = 0.70 D step edges µ0 = 1.12 D full layer µ0 = 0.49 D 2. layer µ0 = 0.11 D ∆Φ values for surfaces annealed at higher temperatures do not vary much *values taken from Fig. 3 of [74N3]

SE edge (UPS)

74N3 Pt(100) Pt(111) Pt(110) Pt(210) Pt(311) Pt(321) 86S2 Pt(111)

40

89A

95

FEM FEM FEM FEM FEM FEM SE edge (UPS) SE edge (UPS)


-0.75 -0.75 -0.90 -0.85


-0.085 -0.135 -0.94

40 83M2 Pd(810) [8(100)î (110)] 74N Pd 78 (polycr.)

Pt(111)

Type

∆Φ [eV] at θ1

Xe/ Substrate 82J Ni(110) 83R2 Ni(110)

4.2-11

-0.27(2) -1.03(2) -1.26 -1.12

PYS

-1.0 -0.85* -0.95* -1.1 -0.9 -0.9 -0.6 III

-0.55

LEED, ARUPS LEED, AES, Fig. 2 µ0 = 0.95 D α = 8.2·10-24 cm3

AES, UPS θXe = 1

UPS

4.2-12


[Ref. p 4.2-118

T [K]

Method

Type

∆Φ [eV] at θ1


< 50

Diode

IV

-0.58 -0.53

at 2θ1 at 3θ1

78 573* 78

PYS PYS

-0.90 -0.65 -0.95

ARUPS dips in ∆Φ var 3 different ordered structures µ0 = 0.3(1) D *film annealed at 573 K

ML

78

PYS

-1.09

74N4 Rh 78 (polycr.) 81W Ru(0001) stepped

PYS

-1.08

Ref.

Xe/ Substrate 96O3 Pt(111)

74N

Pt (polycr.) 74N4 Pt (polycr.) 74N Rh (polycr.)

86J3 86E3 87S5 74N

53M

Ru(0001)

SE edge (UPS) SE edge (UPS)

Ru(0001) Ru 78 (polycr.)

III

-0.50

-0.72

PYS

-0.65 -0.95

77

Kelvin

-0.1

77

Diode

0.0

77

Kelvin

-0.84

70E3

Se (polycr.) Sn (polycr.) Ti (polycr.) W(100)

FEM

-1.35

75W

W(100)

80

-0.99(5)

80W

W(100)

SE edge (UPS) Kelvin

70E3

W(110)

80C 80L 80W

W(110) W(110) W(110)

83O 70E3

W(110) W(111)

74K 53M

FEM

FEM FEM Kelvin

30

FEM FEM


µ0 = 0.25 D µ0 = 1.0 D at step edges µ0 = 0.34 D at step edges µ0 = 0.3 D ∆Φ values for surfaces annealed at higher temperatures do not vary much

µ0 = 0.97 at a Xe atom monolayer density of 6·1014 atoms cm-2

-1.05(2) at 4·1014 also co-adsorption of oxygen atoms cm-2 µ0 = 0.98 D α = 6·10-24 cm3 -2.4 µ0 = 1.67 D at a Xe atom density of 6·1014 Xe atoms cm-2 later it was noted that Fowler Nordheim equation breaks down for Xe/W(110) [80W] -2.0 ML -2.0 1 ML -0.45(2) also co-adsorption of oxygen µ0 = 0.35 D α = 6.6·10-24 cm3 -2.1 -1.13 µ0 = 0.41 D at monolayer density of 6·1014 Xe atoms cm-2


Ref. p. 4.2-118]


4.2-13

T [K]

Method

Type

∆Φ [eV] at θ1

74D

Xe/ Substrate W(111)

104

Diode

III*

70E3

W(120)

FEM

70E3

W(211)

FEM

53M

W (polycr.) Zn (polycr.)

77

-1.1 (1) at 1·1015 ∗shows a weak Type IV behavior, atoms cm-2 TDS µ0 = 0.66...0.75 D α = 3.5...4.9·10-24 cm3 -1.4 µ0 = 0.6 D at monolayer density of 6·1014 Xe atoms cm-2 -0.92 µ0 = 0.81 D at monolayer density of 6·1014 Xe atoms cm-2 -1.14

Ref.

53M

77

Kelvin


-0.21

4.2.3 Atomically chemisorbed adsorbates 4.2.3.1 Atomic Hydrogen (H), Atomic Deuterium (D) Fig. 3...10 Table 5. Atomic Hydrogen (H), Atomic Deuterium (D) Ref.

T [K]

Method

89Z3

H, D/ Substrate Ag(111)

100

93S3 95G

Ag(110) Ag(111)

100 100

SE edge (UPS) Diode Diode

80K3 Al(100)

300

Kelvin

90R

Be(0001)

100

94E

Co(10 1 0) 85

94R

Cu(110)


Kelvin

90.... Kelvin 400

Typ

∆Φ [eV] at θ1


-0.17

at saturation TDS, UPS

I I

0.22 0.32

1L 0.55

I

+0.24 +0.25 -0.55 -0.45 0.20 0.10

2L 200 L θ = 0.04 θ = 1.0 θH = 1 θH = 1.5

0.11 -0.5

20 L 500 L

II

IV

LEED, TDS, HREELS LEED, TDS, HREELS TDS: β2 (180 K), β1 (160 K) (shoulder) LEED: (2 × 2); 0.25 < θH < 0.5 (2 × 2) + (3 × 3); θH > 0.5 HREELS: threefold-hollow site; µ0 = 0.18 D

HREELS LEED, TDS, HREELS α and β states in TDS LEED: c(2 × 4), p2mg(2 × 1); p2mg(2 × 1) at θH = 1.5 used for calibration. (1 × 2) at θH = 1.5 assigned to a paired row structure. LEED, TDS The main effects in ∆Φ are due to changes in reconstruc-tion from (1 × 1) into (1 × 2).

4.2-14


[Ref. p 4.2-118

T [K]

Method

Typ

∆Φ [eV] at θ1


140 140 140 140 300

Kelvin Kelvin Kelvin

Ge(111)

300

Kelvin

IV

82D

Ir(100)

77

FEM

IV

80I

Ir(110) -(1 × 2)

140

Diode

-0.08 +0.07 +0.23 +0.22 +0.18 +0.05 +0.05 -0.05 +0.12 -0.22 -0.14 +0.3 -0.05

LEED, TDS, UPS

Kelvin

III I I I II

77D 73C

Ir(111) Ir(100) Mo(110)

89E

Mo(100) Mo(111) Mo(110)

Ref.

H, D/ Substrate 77B2 Fe(110) Fe(100) Fe(111) 81E Fe(111) 84S Ge(100)

FEM FEM

II

350

Diode

I I IV

74H2 Nb(100) 74D3 Ni(001) Ni(110) 83K Ni(100)

90 300 300 100

84P5

Ni(100)

95

74T

Ni(110)

85G

Ni(110)

170 300 175

Kelvin Kelvin Kelvin SE edge (UPS) SE edge (UPS, E) Diode?

87J Ni(110) 88H 86N3

175

II

I

? Kelvin

-0.8 -0.8 0.48 0.3 0.45 0.68 0.42 -0.015 +0.12 +0.52 +0.08 +0.40 +0.17 +0.11 +0.1 +0.05 0.58 0.50 +0.23 +0.50 0.25

0.5

98V

Ni(110)

(300)

Diode

I

0.35

500 L 500 L 500 L 20 L 0.05 ML 0.5 ML 1.0 ML 0.05 ML 0.6 ML 1L 100 L 0.25 L 25 L

5L 7L 16 L 40 L 50 L 0.2 L 3L at 10 L max 0.5 L 17 L (sat.) θD = 0.5 θD = 1.0 2L 9L

θH = 1 θH = 15

4L

TDS ELS surface conductivity

TDS β2 sites β1 sites

TDS, ESD

LEED LEED (1 × 2) UPS, TDS TDS, XPS co-adsorption with D LEED, AES (2 × 1) phase in LEED (1 × 2) phase in LEED (2 × 1) θH = 1.0 (β2 state) µ0 = 0.054 D (1 × 2)

µ0 = 0.1 D

θH = 1.5 (α state)

LEED, TDS, RBS, NRA See Figs. 3, 4. LEED, AES, TDS


Ref. p. 4.2-118]


H, D/ Substrate 74C3 Ni(111) Ni(100) Ni(110)

T [K]

Method

Typ

∆Φ [eV] at θ1


300 300 120

Kelvin, Diode

I I I

0.20 0.16 0.53

sat. sat. sat.

(1 × 1) (1 × 1) streaks, than 1 × 2 LEED, AES, TDS

77D4 Ni(111)

80

SE edge (E)

0.16

14 L

0.12 0.45 0.10 0.18 0.09 0.18 0.21 0.15

6L 6L 20 L 0.5 θmax 0.9 θmax θH = 1.0 θH = 1.25 θH = 2.0 θ = 1.35 1L

Ref.

300 86I

Ni(111)

79C2 Ni(111)

150

94W2 Pd(100)

SE edge (E) Kelvin

II II

Theory

Rh(100) 80B4 Pd(100) 83C Pd(110)

170 120

Theory Kelvin Kelvin

I I

+0.2 0.33

88H4 Pd(110)

140

Kelvin

I

0.30

89M

Pd(110)

130

Kelvin

I

0.30

90H2 Pd(110) 98M Pd(210) 77D4 Pd(111)

100 120 80

I I

0.30 0.17 0.14 0.18 0.18 0.32 0.20 +0.25 +0.07* -0.18*

99F 91P3

Pd(111) Pd(110) Pd(100) Pd(311) Pt(100)

120 100

Kelvin Kelvin SE edge (UPS) Theory Theory Theory Kelvin Kelvin

91P2

Pt(100)

35

Kelvin

98D


I IV

-0.37

4.2-15

LEED, AES, TDS, ESD LEED, TDS; see Fig. 5 Delocalisation of H discussed 4-fold hollow site for θH = 1.0 in addition subsurface sites up to θH = 2. See Fig. 6.

LEED, TDS. See Fig. 7. (2 × 1) at 0.3 L (1 × 2) > 0.5 L not observed as discontinuities in ∆Φ. LEED, TDS 4 L; θ = 1.5 LEED, TDS (2 × 1): θ = 1 (1 × 2): θ = 1.5 Authors discuss 2 surface phases and a subsurface hydrogen phase. LEED, TDS, NRA, RBS Authors discuss subsurface D! 1.5 ML TDS 5L LEED, TDS, HREELS 1L 2L good agreement with the given [74C] references [74C] [80B] LEED, TDS, HREELS θH = 1 LEED, TDS b state three (a1, a2, b) states; state b a1, a2, b states transfers the Pt(100) hex into the Pt(100) (1 × 1) surface at 330 K. *with respect to Pt(100) hex phase; see Fig. 8. at 100 L LEED, TDS 4 H-states: a1, a2, a3, b At 35 K (100)hex structure not lifted by H adsorption.

4.2-16 Ref. 76N

4.2 Electron work function of metals and semiconductors H, D/ Substrate Pt(111) Pt(100) ~Pt(110) Pt(210)

T [K]

Method

78

FEM probe-hole

Typ

[Ref. p 4.2-118

∆Φ [eV] at θ1


-0.56 -0.37 +0.10 +0.14

p H 2 = 2·10-9 Torr p H 2 = 2·10-9 Torr p H 2 = 2·10-9 Torr p H 2 = 2·10-9 Torr

76C Pt(111) 76C2 Pt(997)

130

Kelvin, Diode

III II

76C2 Pt(111)

300

III

77D4 Pt(111)

80

79N2 Pt(111) 87E Pt(110) -(1 × 2)

95 120

Kelvin, Diode SE edge (E) Kelvin Diode

92S

Pt(110) -(1×2) Pt(110)

170

Pt0.5Ni0.5 (110) Re film

-0.35 +0.02 -0.35 -0.23

sat. 0.25θsat θsat ∆φ = -0.23 × θ1.33 eV LEED, TDS, ELS

-0.2 III II

-0.45 0.17 -0,5

θH = 0.3 θH = 1.0

Diode (LEEM) Diode

IV

120

Diode

I

0.15 -0.7 +0.14 0.0 -0.4 -0.65 +0.60

θrel = 0.05 θrel = 1 0.1 L 0.2 L 0.6 L 20 L θH = 0.9

300

Diode

I

0.2

300

FEM

II

95M2 Re(10 1 0) 120

Kelvin

II

0.52 0.35 0.37 0.15

84P

100?

SE edge (UPS)

I

0.2

84H2 Rh(100) 84P6 Rh(100)

100 100

I

0.2 +0.20

87K

Rh(100) Rh(111)

300 300

Diode SE edge (UPS, E) PYS PYS

1.5·1014 molecules cm-2 (sat.) Also results for O, CO, C2H4 50 L * The central plane of the tip is 1000 L (10 1 0). 2L LEED, TDS 40...2000 L TDS: α, β1, β2 states LEED: c(2 × 2)-2H, (1 × 1)-2H sat. UPS, XPS, ELS A weak max. in ∆Φ is observed with coverage. sat. LEED, TDS UPS, TDS θD = 0.9

I II

0.27 0.23 0.18

87C2 Rh(110) 88E

100

Kelvin

I

0.9

92S6

94F2 76E2

82D2 Re*

Rh(100)

7·104 L (sat). 6·103 L 7·104 L (sat.) sat.

β2 state β1 state; saturation LEED, TDS LEED, TDS two H states in TDS: β1, β2

LEED, TDS, NRA

AES

LEED, TDS There are several changes in slope in ∆Φ (exposure) and several LEED structures.


Ref. p. 4.2-118]


Method

Typ

∆Φ [eV] at θ1

87K

H, D/ Substrate Rh(111)

300

PYS

IV

Rh(100) Rh(113)

300 90

PYS

III

91N

-0.23 -0.20 -0.28 0.97

min saturation saturation θH = 1

85F

Ru(0001) 95

0.025 -0.01 0.03

70 Ex

+0.030 +0.048 +0.030 +0.005 0.42 0.30 -0.25

0.5 L 0.8 L 1.1 L 2.5 L θ =1 θ =2

Ref.

Kelvin

86H3 Ru(0001) 80

Kelvin

91S2

Ru(0001) 45

Kelvin

89L2 96C 96B

Ru(10 1 0) 100

Kelvin

Si(100) -(2 × 1) W(100) (ribbon) W(100)

300

Diode

300

Diode

300

Thermoemission FEM FEM FEM

66E 69A 72P 73C

W(100) W(110) W(110)

74F2

W(100) W(112) W(100)

84H5 W(100) 86H2 W(100) W(110) 73R W(112)


300 300

II

II

II

I

0.2 I II II I I

300 300 450 300 300

SE edge (UPS) Diode Diode Diode Kelvin

0.9

I I I III II

0.9 -0.5 0.83 0.0 0.73 0.65 +0.9


LEED, TDS Low-coverage structures (1×3)−Η, (1×2)−Η, (1×3)−2Η have no influence on Rh surface structure. High-coverage structure (1×2) opens diffusion channels to subsurface sites. There are two states. depending on temperature LEED, TDS some small changes of Φ as observed in [85F] LEED 3 phases in LEED

LEED, TDS, HREELS three structures in LEED TDS atomic H used 1×1015 mole LEED -cules cm-2 sat.

0.1 L 10 L 6L 1.2 L UPS

+0.55 +0.27 0.97 -0.46 0.61

θH = 0.45 θH = 0.45 3L 35 L 1/2θsat

0.27

θsat

4.2-17

step at 0.2 L; ∆Φ = 0.25 eV linear increase β2 state (TD = 675 K) filled linear decrease β1 state (TD = 330 K) filled

4.2-18 Ref. 74B

4.2 Electron work function of metals and semiconductors H, D/ Substrate W(110) W(111) W(112)

T [K]

Method

Typ

∆Φ [eV] at θ1

*

Kelvin

III I II

-0.5 +0.26 0.6 +0.32 0.9

W(100)

97N

W(110)

72M3 W(111)

I

90

Kelvin

III

300 125 (300) 77

Diode

I

70A 97C

W(112) W(310)

77M

ZnO (0001)Zn (000 1 )O

FEM FEM

Zr(10 1 0) 100

Kelvin

96Z 96C

Kelvin I FEM II probe hole

370

-0.3 -0.5 +0.07(2) +0.21(2) 0.7 0.56 0.43 0.43

0.5θsat θsat

8L 240 L

[Ref. p 4.2-118


linear increase linear decrease linear increase See Fig. 9. TDS *dosed at 135 K LEED See Fig. 10. TDS LEED, TDS

0.5 L 4L 20 L

-0.2 -0.7 IV III

-0.01 +0.075 -0.06

0.25 L 3.0 L >0.7 L

AES, NRA, SIMS

Type

∆Φ [eV] at θ1


~+0.5 -1.1

LEED p(2 × 2) LEED: ringlike diffraction features LEED: ringlike diffraction features *hydrocarbons at a hot (500 K) Pt(111) surface AES gives coverage

Results are discussed in terms of two H sites: one site above the surface (∆Φ > 0) and one subsurface site (∆Φ < 0).

4.2.3.2 Atomic Carbon (C, C60) Table 6. Atomic Carbon (C) Ref.

C/ Substrate 74D3 Ni(001) 74G Pt(111) -(1 × 1) Pt(100) -(5 × 1) 86A3 Pt(111)

T [K]

Method

300 1170

Kelvin

1170 *

-1.1 Kelvin

-0.5

θC = 0.75


Ref. p. 4.2-118]


4.2-19

Table 7. C60 Ref.

C60/ Substrate 96M3 Al(111)

T [K]

Type

SE edge (UPS)

Al(110) 97K3 Cu(111)


94G2 GeS(001)

94J

Method

Rh(111)


93R3 Ta(110)

III

∆Φ [eV] at θ1


+0.95

1 ML

XPS

+0.95 -0.08

1 ML 1 ML

0.1

1 ML

-0.5

1 ML

+0.6

1 ML

LEED, UPS, XAS See also Table 8. LEED, X-Diffraction, SEM, XPS, UPS C60(111)-lage UPS, EELS ARUPS first C60 molecules are decomposed

Table 8. Work functions of clean metal surfaces and after adsorption of a monolayer C60. From [97K3]. Conclusion: All C60 monolayers are metallic showing a work function of about 5 eV. The dipole layer at the substrate-C60 interface is screened out by the C60 film. Ref.

Surface

[97K3] [97K3] [96M3] [96M3]

Cu(111) Ni(111) Al(110) Al(111) Au(119)a Rh(111) Ta(110)

[94J] [93R3] a

Clean surface Φ [eV] 4.94 5.36 4.35 4.25 5.37 5.4 4.8

Φ [eV] of 1 ML C60 on surface 4.86 4.93 5.25 5.15 4.82 4.9 5.4f

∆Φ [eV] -0.08 -0.43 +0.95 +0.95 -0.45 -0.5 +0.6b

) P. Rudolf et al, unpublished, quoted in [96M3] ) for reference only, since C60 decomposes on this surface at RT

b

4.2.3.3 Atomic Nitrogen (N) Table 9. Atomic Nitrogen (N) Ref. 90S

98G

79G

N/ Substrate Cr(110)

Cu(100)/ Fe(100) fcc Ni(110)


Type

∆Φ [eV] at θ1


-0.55

UPS adsorbed at 90 K and annealed stepwise to 300 K; transformation N2 ĺ1IROORZHG by UPS for epitaxial fcc-Fe films of thickness 1.2...8 ML Exposure 3000 L LEED, TDS p(2 × 3), authors discuss formation of surface nitride

T [K]

Method

300

SE edge (UPS)

75

Kelvin

I

0.8 ± 0.1

590

Kelvin

III

-0.5

4·105 L

4.2-20


N/ Substrate 91B4 Rh(111)

T [K]

Method

Type

∆Φ [eV] at θ1

I

+0.45

θN = 0.4

69A 71A

W(100) W(100)

300 300

SE edge (UPS) Therm Kelvin

300 300 300 400

Kelvin Kelvin Kelvin Kelvin

saturation 2L 4L 4L 4L

74F2 93O

W(210) W(310) W(100) W(100)

89S2

W(110)

200

Kelvin?

-0.7 -0.55 -0.50 0.25 0.18 -0.3 -0.4 -0.35 0.2

Ref.

IV I I IV

5L 300 L

[Ref. p 4.2-118

Comments, interpretation microwave discharge to produce atomic N

UPS ELS Chemisorbed N2 at 90 K irra-diated with electrons and heated to 200 K

4.2.3.4 Atomic Oxygen (O) Fig. 11 and 12 Table 10. Atomic Oxygen (O) T [K]

Method

Type ∆Φ [eV] at θ1

Kelvin

I III I

Ag(111)

300 300 400 300

85S3

Ag(110)

300?

Kelvin Diode

I

73D

Ag(111)

300?

I

Ref. 76E

O/ Substrate Ag(110) Ag(100)

78M2 Ag(331)

300

photoelectric Diode

77B5 Al(111)

300

Kelvin

79H4 Al(111) Al(110) Al(100) 77G4 Al(111) Al(110) Al(100) 80M Al(111) Al(110)

300 300 300 300

Kelvin Kelvin Kelvin PYS

88M

300

Al(100)

116

0.85 -0.15 +0.3 0.04 0.625 0.32 0.5 0.72 0.4

sat. 1000 L 1000 L p=10-5 Torr O2 sat. 5000 L θ = 0.25 θ = 0.3 θ = 0.50 1400 L

+0.7(1)

Kelvin

III III III I III III III

Kelvin

III II

-0.17 -0.21 -0.2 -0.48 -1.08 +0.12 -0.05 -0.48 -0.2 -0.8 -1.25 -0.7 -0.8 +0.25 +0.05

50 L 300 L 500 L 500 L 500 L 100 L 200 L 300 L 350 L 350 L 350 L 3·103 L 8·103 L 400 L 1600 L

Comments, interpretation (n × 1) LEED structures

no Auger signal! i.e. sticking coefficient very small LEED, AES LEED: (4 × 1) LEED: (3 × 1) LEED: (2 × 1)

LEED, AES facetted (2 × 1) chemisorbed layer oxidation

AES

LEED, AES

depending on pressure At low temperatures oxygen stays first on top.


Ref. p. 4.2-118] Ref.


O/ Substrate Au(111)

300

78G5 Be(0001) 83T Bi(0001)

300

98S3

T [K]

82C3 Co(0001) 300 93K3 Co(11 2 0) 100 300 95G2 Co(11 2 0) 100

Method

PYS SE edge (E) Kelvin?



I

0.85

1.3 ML

III III

-1.8 -1.1

3000 L sat.

I

0.55

5L

LEED, AES, TDS, HREELS, XPS oxidation through O3; see Fig. 11 LEED, AES LEED, AES, ELS presumably oxide formation LEED, AES, UPS


320

1.1

I IV

79P

Cr(100)

300

78G

Cr(111)

300 300


300* 300

Diode

300 300

Diode Diode

I I I

300 300 300

I

I II

97K2 Co(11 2 0)

82S7

Cr(110)

85F2

72E 78H

Cr(100) Cr(110) Cr2O3 (0001) Cu(111) Cu(100) Cu(110) Cu(110) Cu(100)

350

Kelvin Kelvin Kelvin Kelvin Kelvin

79H 80H

Cu(110) Cu(100)

475 600

Kelvin Kelvin

83N2 Cu(110) Cu(111) 84B Cu(110)

300 300 300 110

Kelvin Kelvin Kelvin

86F4 71D


4.2-21

IV

II III II

I II

LEED, UPS, XPS

-1.0 1.0

3L

0.8 0 -0.1 -0.4

1L 5L 12 L at 1.5 L

-0.2 +1.7 0 0.9 0.4 -1.2 +0.2 0.0 -0.25 0.0 +0.3 +0.15 +2.4 +1.2 +2.0

2L 20 L 2.7·1014 atoms cm-2

93R2 Pt(100)

650

PYS

85D

Pt(111)

370 570

Kelvin

I

0.30

7·1014 atoms cm-2

Pt(100)

370 570 300 120 560 1100

Kelvin

I

0.75

Diode Diode Diode Diode

I I

I

0.3 0.75 +1.15 +1.65 +2.5 0.2

1.4·1015 atoms cm-2 θ = 0.4 θ = 1.3 θO = 0.33 θO = 0.07 θO = 0.5

I

0.75

3.5 L

UPS good agreement between the two methods and with Ref. [86F2]

I

0.55

0.8 ML

LEED, AES, TDS, UPS, HREELS (2 × 2)-O at θ0 = 0.25 Exposure to NO2; see Fig. 12

86F2 92S6

Pt(110) -(1 × 2) Pt(110)

89R

Pt(111)

89F

Pt(112) (1 × 2)

89P2

Pt(111)


90...300 SE edge (E) 100 Kelvin and SE edge (UPS) 400 SE edge (UPS)

UPS

4.2-26 Ref. 92S2

4.2 Electron work function of metals and semiconductors O/ Substrate Pt(210)

72Z

Re(0001) Re(10 1 0) 74F Re(0001) (ribbon) 82D2 Re*

Method

330 430 >480

Kelvin

0.65 0.75 0.77

300 300 300... 850 300?

Diode Diode Diode

82L3 Re(10 1 0) 300? 88R Re(0001) 80 97B2 Rh(111) 40 87K

99S3


T [K]

FEM

I I I

0.5 1.2 0.9 1.2 0.94 1.15 1.33 1.3 0.45 0.75

I

0.38

I I I

Rh(100)

300

FEM? Diode SE edge (UPS) PYS

Rh(111)

300

PYS

I

0.28 +0.75 +0.95 0.2 0.8 1.0 +1.0 +0.2 +0.85 +1.15 1.1 0.7 0.5 0.3 0.92 0.3 1.12 +1.2 +0.4 +0.35 +0.35

Rh(111) 450 Rh(533) 340 Ru(0001) 300

Kelvin

I

Kelvin

I

100 77K5 Ru(10 1 0) 300 85S7 Ru(0001) 300

Kelvin Diode Diode

I I

86H3 Ru(0001) 80 300 87S Ru(0001) 300 93S2 Ru(0001) 400

Kelvin Kelvin Diode Kelvin

75M

I I I

640 99B

Ru(0001) 300

93S

300 500

Diode

20 300

Diode Kelvin

I II

SE edge (E) SE edge (UPS)

III

Si(100) -(2 × 1) + Ge 88S Si(111) 99P Si(111) -(7 × 7) 89B2 SiC(001) 92S3

SnO2(110) 150

II

+1.6 +0.95 +0.2 -0.25

500 L 500 L 500 L

[Ref. p 4.2-118

Comments, interpretation LEED, STM, TDS For T .D(5 × 2)-rect structure is observed which is found by STM as due to (110) and (310) microfacets LEED: (2 × 2) or (2 × 1) LEED: (1 × 3)

0.5 L * The central plane of the tip is 1L Re(10 1 0). 1L p = 10-5 Pa 2L SHG 2.3 L for exposures larger 2.3 L physisorbed O2 appears in UPS. 2·104 L AES (sat). 3·104 L (sat). LEED, TDS, PEEM θO = 0.2 θO = 0.25 1.6 L p(2 × 2) 2.5 L two states 2.5 L LEED, AES 3L FEM pictures θO = 0.25 AES, TDS θO = 0.50 θO = 0.70 2.5 L TDS 6L 4L AES, TDS, ELS 1L p(2 × 2) ĺSî 10 L 1L 10 L 1 ML TDS, UPS 6 ML 30 L 50 L 1L 2.5 L 70 L

0.25


Ref. p. 4.2-118]


Method


67F

O/ Substrate Ta(110)

300

Diode

IV

76T

Th(100)

300

Diode

IV

69A 72B 72M2 73P3 73B2 73D2 74F2

W(100) W(100) W(100) W(100) W(100) W(100) W(100)

300? 300 300 350 300 300

Ref.

76B2 W(100)

300 1050

84S7

W(100)

300

69T2

W(110)

300

Therm Kelvin Diode Diode Diode Kelvin SE edge (UPS) Diode Diode

I

I

I IV

SE edge (E) Kelvin

W(112)

69W

70E

W(110) W(111) W(211) W(100) W(100) W(211)

W(110) W(111) W(120) 74M3 W(100) W(110)

75E2

90 90 90 90 20 100 20 100 20 20, 100 20 20

FEM FEM FEM FEM FEM

I I I I

FEM

FEM FEM

I II

W(111)

FEM

II

W(112)

FEM

II

W(110)

300

Kelvin

IV

77B3 W(110)

700

Kelvin

I


-0.45 0 +0.2 -0.60min -0.46 0.94 1.45 1.6 1.4 1.75 +1.5 +1.5 1.4 -0.2 +0.8 1.2 +0.70 +0.75 +0.75 +0.92 +0.91 +1.05 1.3 1.4 1.6 1.7 1.2 1.4 1.4

0.6 1.4 1.3 +1.9 +0.9 +0.7 +1.3 +0.85 +0.4 +0.7 +2.1 +1.5 -0.05 +0.2 +0.1 +1.3

at θ1 at 2θ1 at 3θ1 8L 36 L sat. 50 L (sat.) 6L


LEED, AES

µ0 = 2.2 D ESD LEED

saturation UPS LEED, AES 1L 3L

6L 8L 1.2 L 2L 3L 8L

0.1 ML 0.5 ML θO = 0.5 θO = 1.0

p(2 × 2), AES, LEED p(2 × 1) p(1 × 1)

1018 atoms cm-2 2·1015 atoms cm-2 1016 atoms cm-2 1018 atoms cm-2 7·1014 atoms cm-2 8·1015 atoms cm-2 2·1017 atoms cm-2 2·1015 atoms cm-2 1018 atoms cm-2 LEED

4.2-27

4.2-28


Ref.

O/ Substrate 72M3 W(111)

72W

77E3

W(110) W(112) W(111) W(013) W(110) stepped 24(110)× (011) 10(110)× (011)

T [K]

Method



300 125 90 90 90 90 300

Diode Diode FEM FEM FEM FEM Kelvin

I I I I I I I

TDS

+1.2 +1.7 1.2 1.7 1.45 1.65

LEED, TDS 0.0 +0.25

300

Kelvin

I

78B4 W(110)

300

Kelvin

IV

300*

Kelvin

I

+0.1 +0.12 +0.48 -0.15 0.0 +0.8 +1.1

78W

W(110)

FEM

I

+0.9

80R

W(110)

50 100 300

Diode

IV

81M2 W(110)

300

Diode

I

83A3 W(110)

300

SE edge (E) Kelvin

-0.07 +0.3 0.0 0.4 1.0

88L

98W 80F

90 800 W(110) 90 W(100) 300 W(111) 300 W(110) 90 Zr polycr. 300

Kelvin FEM FEM Kelvin Diode

88G

Zr(0001)

Kelvin

IV

91Z4 94Z

Zr(0001) 475 Zr(10 1 0) 90

Kelvin Kelvin

IV

300

Kelvin

IV

470

Kelvin

IV

89S3 92Y

[Ref. p 4.2-118

W(110)

80

I I I

I IV

θO = 0.1 θO = 0.4 θO = 0.01 θO = 0.15 θO = 0.45 θO = 0.25 θO = 0.5 θO > 1 ML θO > 1 ML

LEED, TDS

LEED, TDS, AES oxygen dosing by adsorption of WO2 *plus annealing to 1300 K for 30 s

LEED, AES θ1 3 θ1 up to 0.8 L 10 L 11 L

1.0 1.5 0.95 1.6 1.1 1.0 -0.2 +0.55 -0.2 +0.9

LEED, AES, TDS, XPS

sat. sat. θ = 0.65 0.5 L 30 L 0.8 L 12 L

-0.32 -0.14 +0.55 -0.20 +0.25 -0.24 +0.06

θO = 0.5 0.8 L 5L 1L 5L 1.5 L 5L

LEED, AES, TDS

XPS, TDS

LEED, AES initial decrease of Φ is believed to be due to incorporation of oxygen into the bulk LEED, AES, NRA Although ordered surfaces are observed, the sticking coefficient of O2 is high. Only after a film thickness of 12.4 ǖSDVVLYDWLRQLV observed. It is concluded that atomic oxygen penetrates the bulk even at low temperatures.


Ref. p. 4.2-118] Ref. 98N

O/ Substrate ZrC(111)


Method



300 1050 1170 1270

SE edge (E)

I IV

UPS

1.0 -0.2 +0.6

LEED p(2 × 2) LEED c(2 × 2) θTe = 0.2 θTe = 0.4 θTe = 1 0.5 1.0 0.5 1.0 1.0 1.5 2θ1 sat. LEED, AES different ordered phases AES also studied at higher temperatures sat. c(2 × 4), LEED

1.8

sat.

I I

sat. sat. sat. sat.

LEED: (6 × 1) µ0 = 0.4 D at θ = 0.6

LEED, AES, TDS


Ref. p. 4.2-118]


4.2-33

Method

Type

∆Φ [eV] at θ1


Diode

I

+0.47

0.5

300

Diode

II

1.1 0.9 1.1

1.3 L 1.7 L 3.5 L

Ni(110)

300

I

1.1

sat.

82E2 80E

Pd(110) Pd(111)

300 300

SE edge (UPS) Diode Diode

LEED, AES ¥DQGDPRUHFRPSOH[VWUXFWXUH c(2 × 2), LEED, AES, TDS diffuse p(10 × 1) for exposures > 1.5 L µ0 = 0.51 D A dip in ∆Φ occurs at θCl = 0.5. AES, UPS

I I

1.22 0.57

1.7 L 1.8 L

88T2

Pd(111)

300

I

0.7

sat.

82E2

Pt(110)

300

Diode

I

0.55

1.0 L

80E

Pt(111)

300

Diode

IV

-0.08 +0.34

1L 2.3 L

Kelvin

IV

sat.

Ref.

T [K]

77E

Cl/ Substrate Ni(111)

82E2

Ni(110)

91Z2

98H2 Pt(111)

diffuse c(16 × 2), µ0 = 0.63 D (¥î¥ 5Û/(('VWUXFWXUH at 1.2...1.6 L Cl2; see Fig. 13. 4·1014 molecules cm-2 (¥î¥ 5ÛDW 2.5...3.0·1014 molecules cm-2 LEED, AES, TDS solid-state source for Cl2 diffuse p(2 × 1) for exposures > 0.8 L, for 0.3 L Pt(110)- (21× 2) reconstruction spots appear LEED, AES, TDS (3 × 3) LEED structure at 1.6...1.9 L Cl2; see Fig. 14. 1.2·1014 atoms cm-2 7·1014 atoms cm-2 LEED, AES, TDS, UPS 4 ordered surface structures For (110): high electronegativity, so that differences to Cl smaller so that Smoluchowski smoothing and polarization effects take over. explains decrease of Φ

83G

Ru(10 1 0) 300

?

I

-0.04 +0.38 0.55

83S

Ta(100) Ta(110)

?

I II

1.0 -1.0

sat. sat.

97W

Ta(110)

Theory

+0.6 -0.4 -1.0 -1.2

top site bridge site hollow site threefold site ML average ∆Φ 2ML

71A2 Ti,

300

FEM

I

69F2 81K 70J

300 300 300

Diode Diode K

I I III I I

300

FEM

370

SE edge (UPS)

W(100) W(100) W(110) W(100) W(111) 72H W(211) W(110) 79B4 W(100)


0.8 1.4 +0.64(2) 0.75 -0.26 +0.58 +1.03

sat. sat. sat. sat.

AES, LEED, TDS

±∆Φ depending on pressure I

0.65

1.5 L

UPS

4.2-34 Ref. 80B

79C

4.2 Electron work function of metals and semiconductors Cl/ Substrate W(110) W(111)

T [K]

Type

∆Φ [eV] at θ1


III I

-0.5 +0.7

Diode

I

Diode Diode

I I

0.64 0.73 0.81 1.0 0.85

LEED, TDS Prep.: surface ionization of KCl. W(111) facettes at higher coverages. * temperature before dosing Cl

Method

Diode

ZnO (000 1 )O

900* 1000* 1100* ZnO(0001) 300 300 ZnO (10 1 0)

[Ref. p 4.2-118

sat. sat.

4.2.3.9 Bromine (Br) Table 15. Atomic Bromine (Br) Br/ Substrate 78G2 Ag(111)

T [K] Method

Type

∆Φ [eV] at θ1

300

Diode?

I

1.4

85B

Ag(110)

120

Kelvin

I

1.4

80B3 Au(100)

320 300

Kelvin Kelvin

I

0.78

83R

300

(Diode)

I

1.1

Ref.

Cr(100)

1.10

3.5·1014 LEED, AES,TDS molecules cm-2 sat. LEED, AES, TDS p(2 × 1) at θBr = 0.5, fourfoldhollow site c(4 × 2) at θBr = 0.75, AgBr bilayer 16·1014 LEED, TDS molecules cm-2 0.4·1015 LEED, AES, TDS atoms cm-2 solid-state source for Br 3.3·1015 atoms cm-2 8·1014 LEED, AES, TDS atoms cm-2 solid-state source for Br; authors assume Br to metal charge transfer. 40·1014 atoms cm-2 sat. LEED, AES

1.8

sat.

+0.45 -0.28

sat. 0.7·1014 molecules cm-2 6·1014 molecules cm-2

1.6 84F

Cr(110)

300

(Diode)

IV

-0.45 -0.2

79D2 Fe(100)

300

88J3

300

82T2 79B

n-MoSe2 (0001) Pd(111) Pt(111)

300 300

SE edge (E)? SE edge (UPS) Diode Kelvin

I

I IV

520

70J

W(110) W(100) W(111)

300

+0.25

Kelvin

III I I


-0.32 +0.80 +0.88

TDS LEED, AES, TDS little charge transfer (3 × 3) ordered overlayer at 300 K order-disorder transition at 520 K

sat. sat. sat.


Ref. p. 4.2-118]


Ref.

Br/ Substrate 69F2 W(100) 79B4 W(100)

T [K] Method

Type

∆Φ [eV] at θ1


300 370

4.2-35

Diode SE edge (UPS) Kelvin

I I

+0.41(2) 0.4 3L

UPS

I

+1.1

UPS

T [K]

Method

Type

∆Φ [eV] at θ1


300

Kelvin

IV

130 Fe(100) 300 GaAs(110) 300

Diode Kelvin

III I

-0.1 +0.08 +0.6 -0.55 +0.6

sat.

LEED, TDS Correlated with LEED structures I2 on top of chemisorbed layer LEED, AES, TDS Surface states of acceptor character within the bulk band gap, Fig.3

0.9

sat.

IV

-0.7

0.33 ML

I

-0.55 0.35

sat. sat.

+0.8 -0.9 -0.78 -0.18 -0.13 -0.4

sat. sat.

0.5 ML

-0.4 +0.08 -0.37 -0.1

min saturation 1L UPS /

96M2 WSe2(0001) n-type 4.2.3.10 Iodine (I) Table 16. Atomic Iodine (I) Ref.

I/ Substrate 93N2 Au(100)

79J2 93T 88J3 92J

93C

n-MoSe2 (0001) Pt(111)

300 300 1000 300


300

SE edge (UPS) ? ? Kelvin

74A

Si(111) -(7 × 7) Ta(100) Ta(110) W(110) W(100) W(111) W(110)

300

Diode

I III III III III III

69F2

W(100)

300

Diode

IV

79B4 W(100)

370

SE edge (UPS)

IV

83S 70J

0.5 ML 1 ML

threefold-hollow site: ∆Φ < 0 on-top site: ∆Φ > 0

LEED, AES some different LEED patterns

4.2.4 Small molecules 4.2.4.1 Molecular Hydrogen (H2) Table 17. Molecular Hydrogen (H2) Ref. 83A

87J2

H2 / Substrate Cu(100)

Ga (polycr.)


T [K] 10 10 15 10

Method

SE edge (UPS)

Type

∆Φ [eV] at θ1

III

-0.18 -0.19 -0.23 -0.1


normal H2 HREELS para- H2 D2 UPS

4.2-36


[Ref. p 4.2-118

4.2.4.2 Molecular Nitrogen (N2) Table 18. Molecular Nitrogen (N2) T [K]

Method

Type

∆Φ [eV] at θ1


91H

N2 / Substrate Ag(111)

20

III

-0.45

1 ML

LEED, UPS, HREELS

89J2

Al(111)

20


III

-0.15

1 ML

LEED, UPS, HREELS physisorbed N2

82E

Fe(111)

125

I

0.10*

180 L

85S2

Fe(111)

65

(Kelvin)

IV

θ1 3 θ1

87J2

Ga (polycr.) Ir(111) Ir(100) ~Ir(110) Ir(210) Ir(731) Ni(110) Ni(110)

10

SE edge (UPS) FEM probe hole

-0.27 -0.23 0.0

TDS desorption temperature 155 K * at 2·10-6 Torr max. coverage 1·1014 molecules cm-2 TDS, this is the γ-N2

Ref.

73N

79G 82H

86B4 Ni(111)

80 80 80

90 20

Kelvin SE edge (UPS) Kelvin

I

-0.2 -0.7 +0.1 -0.3 -0.1 0.1 0.0 -0.56 -0.08

92B3 Pd(111)

73N2 Pt(111) Pt(100) Pt(331) Pt(320) 81N3 Rh(111) Rh(100) Rh(110) Rh(210) 77K5 Ru(10 1 0) 87D Ru(0001) 86D 92S7 Ru(0001) 76Y 80F

W(110) Zr (polycr.)

20

SE edge (UPS)

UPS

III

-0.7

chemisorbed physisorbed 1 ML*

LEED, TDS LEED, ARUPS chemisorbed + physisorbed N2 XPS, UPS, TDS chemisorption saturates for coverages smaller than 1 ML leading to coadsorption of a physisorbed species * from UPS chemisorbed + physisorbed N2 only chemisorbed N2

60 80

FEM

120 85

Diode Kelvin

III III

-0.6 -0.34 -0.31 -0.76 -0.77 -0.15 -0.5 +0.2 +0.3 -0.04 -0.54

40

SE edge (UPS)

III

-0.67

1 ML

ARUPS, HREELS ML from UPS

Diode

III

-0.19 -0.15

100 L

Authors conclude on dissociative adsorption. No proof that N2 sticks!

120 300

0.8 L LEED, AES, TDS


Ref. p. 4.2-118]


4.2-37

4.2.4.3 Molecular Oxygen (O2) Table 19. Molecurlar Oxygen (O2) Ref.

O2 / Substrate 79H2 Al(111)

T [K]

Method

20

82S4

Cu(111)

100


81S2

Ga polycr. 20

Type

III

SE edge (UPS)

∆Φ [eV] at θ1


+0.85

5 L O2

-0.4

1000 L

condensed O2 on Al(111) ΦAl(111) = 4.25 eV LEED, AES, UPS, ELS chemisorbed O2 2-peak spectrum in UPS condensed O2 layer (10 L) ΦGa = 4.0 eV physisorbed O2 monolayer after warming to 70 K unidentified O2 intermediate

+0.2 +0.5 +1.4

-

(presumably O ) 2

84S5

Ni(111)

5.5

Diode

I

0.07

89R

Pt(111)

20

SE edge (UPS)

I

-0.45

6 L O2

∆Φ = 0.07 eV = const. for exposures up to 12 L UPS, XPS

4.2.4.4 Carbonmonoxide (CO) Fig. 15...21 Table 20. Carbonmonoxide (CO) Ref.

CO/ Substrate 76M3 Ag(111) 82K Al(100)

83K2 Al(111)

T [K] Method 77 300

300


Kelvin Kelvin

-0.2 0.0

3L 2L

LEED, UPS, XPS NO dissociates. UPS, XPS

LEED, TDS, XPS 1 Ex = 1018 cm-2 At higher T different curves with some dips occur. Authors discuss the results in terms of two different NO species. dissociative adsorption Small (-0.15 eV) dip at the beginning due to subsurface species.

Table 22. N2O Ref. 84S6

N2O/ Substrate Cu(110)


0.25 0.08

0.5 L 1L

4.2-44


[Ref. p 4.2-118

4.2.4.6 NH3, PH3, PF3, P(CH3)3, AsH3 Fig. 22 Table 23. NH3 NH3 / Substrate 78G3 Fe(111) Fe(100) 79W Fe(110)

T [K]

Method

Type

∆Φ [eV] at θ1


135 135 120

Kelvin Kelvin (Kelvin)

III III III

-2.0 -2.0 -2.3

sat. sat. 15 L

LEED, AES, TDS, UPS

80P

Ir(111)

190

III

-2.5

sat.

77A

Mo(110)

200 300

SE edge (UPS) FEM (probehole)

Mo(100)

Ref.

-2.25 -1.2

For all faces: NH3 decomposes at higher T N increases Φ

80S5

Ni(111)

200 300 200 300 200 300 200

81F

Pt(111)

100

95K4 97V3 96V2 88R 90R2 91A 96V

Pt(111)

100

Kelvin

Pt(111) Re(0001) Re(0001)

90 80 (80)

Kelvin Diode Kelvin

III III

-0.29 -2.1 -2.3

6L sat.

SE edge (E) SE edge (E)

III

-2.3

θ = 0.25

III

-2.4

θ = 0.73

(300)

PYS

III

-0.5

sat.

(300) 300

PYS PYS

III III

-0.59 -0.6

sat. sat.

III

-0.3

2L

Mo(211) MO(111)

Rh(111)

83B5 Ru(0001)

91C

Si(111) -(7 × 7) 91C2 Si(100) 92C Si(111) -(2 × 1) 92R TiO2(110)

300


LEED, AES, UPS, TDS µ0 = 2.2 D ARUPS

III

-1.95 -1.1 -1.9 -1.0 -1.55 -0.9 -1.7(2)

sat.

ARUPS, TDS

III

-3.0

sat.

UPS, TDS ∆Φ corresponds to the sum of α state (TD = 350 K) and β state (TD = 150 K) LEED, AES, TDS, IRAS

-3.0

IRAS SHG SHG (2 × 1) in LEED, a1 + a2 state µ0 = 1.9 D LEED, TDS, ESDIAD three states from TDS α, β, γ α state: θ = 0.25, disordered β state: bilayer formed through hydrogen bonds γ state: multilayer µ0 = 1.9 D see Fig. 22

LEED, AES Authors conclude dissociation to happen. UPS


Ref. p. 4.2-118]


4.2-45

Table 24. PH3 T [K]

Method

Type

∆Φ [eV] at θ1


89Z2

PH3/ Substrate Ag(111)

105

III

-1.4

TDS, UPS

98Y

Au film

100


85H

Rh(100)

100

SE edge (E)

III

-0.24 -0.32 -0.45 -1.2

T [K]

Method

Type

∆Φ [eV] at θ1


105

SE edge (UPS)

III

-0.15

TDS, UPS

T [K]

Method

Type

∆Φ [eV] at θ1


105

SE edge (UPS)

III

-2.2

TDS, UPS

T [K]

Method

Type

∆Φ [eV] at θ1


100

Kelvin

-0.24 -0.32 -0.45

under ambient conditions; rise time of Kelvin probe signal was 10 s; same behavior for AsH3.

Ref.

20 ppb 50 ppb 80 ppb 3L

under ambient conditions; rise time of Kelvin probe signal was 10 s; same behavior for AsH3. LEED, AES, TDS Bonding to surface via P concluded.

Table 25. PF3 Ref. 89Z2

PF3/ Substrate Ag(111)

Table 26. P(CH3)3 Ref. 89Z2

P(CH3)3/ Substrate Ag(111)

Table 27. AsH3 Ref. 98Y

AsH3/ Substrate Au film

20 ppb 50 ppb 80 ppb

4.2.4.7 H2O, D2O Sass and Richardson [84S8] pointed out earlier that in studies of water adsorption on clean metal surfaces, thermal desorption spectra, characteristically, show a two-peak behavior in the temperature range 150...200 K, although in certain cases a considerably more complex pattern is observed. In the usual interpretation, the higher temperature peak (ca. 170...200 K) is attributed to molecular H2O in the first monolayer at the surface, whereas the lower temperature peak (ca. 150...160 K) accompanies the onset of multilayer ice formation. These temperatures can be correlated with binding energies of ca. 48...57 and 43...45 kJ mol-1, respectively. The latter corresponds, as expected, to the enthalpy of vaporization of ice whilst the former lies in the upper part of the range generally considered to characterize physisorption. With respect to the work-function changes induced by H2O adsorption there is always a decrease of 0.6 to 1.3 eV observed indicating that the lower half of the bilayer –pointing to the metal substrate – interacts with the oxygen part. For higher exposures multilayer ice is condensed which does not contribute very much to a further work-function decrease as the H2O dipoles are apparently randomly oriented. Figs. 23...25


4.2-46


[Ref. p 4.2-118

Table 28. H2O, D2O H2O, D2O/ T [K] Substrate 87B2 Ag(110) 80

Method

Type

∆Φ [eV] at θ1


(Kelvin)

III

-0.65

2L

LEED, ESDIAD, TDS no long-range order at 80 K

89M2 Al(100) 93B3 Al(100)

100 100

Kelvin Kelvin

III IV

82H2 Co(0001) 100 Co(11 2 1) 100

Kelvin Kelvin

I I

-0.95 -1.2 -0.9 -1.1 -1.2

12 L 2.5 L 16 L 10 L 10 L

94G

Co(11 2 0)

III

-1.3

0.7 L

82S

Cu(110)


FT IR-RAS, NRA at 100 K no dissociation of H2O UPS, TDS H2O adsorption reversible below 300 K; ∆Φ > 0 XPS, UPS

III

-0.9

1L

UPS, LEED, ELS

III III

-0.95 -0.85

Ref.

90

83B4 84B Cu(110) Cu(111)

110 110

Kelvin Kelvin

-0.09 -0.8

LEED, UPS, TDS µ0 = 0.85 D µ0 = 0.5 D see Fig. 23 *mirror electron microscopy saturation UPS

83P5 85S5

Cu(110) Cu(100)

350 80

93B2 Cu(100)

120

* SE edge (UPS) Kelvin

III

-0.9

10 L

Diode

III

-0.7

1L

HREELS, TDS defects stabilize H2O clusters TDS, XPS

81W2 Ir(110) -(1 × 2) 81B Ni(110) 84P4 Ni(100)

140 150 100

Kelvin SE edge (UPS) (Kelvin)

III

-0.7 -1.05

1.2 L sat.

UPS, TDS, ELS UPS, XPS, TDS

87N

Ni(111)

100

III

-0.65

2.5 L

III

-1.1

θ = 0.66

130


III

-1.15

92B2 Ni(665)

150

Kelvin

III

-0.7

1.2 L θ § θ = 0.75

Ni(221)

150

Kelvin

III

-1.4

92C2 Ni(110)

180

Kelvin

III

-0.6

93M

140

Kelvin

III

-1.05

disordered layer LEED, UPS ARUPS, LEED, XPS, TDS Authors propose bilayer model. LEED, TDS, NRA c(2 × 2) structure LEED, TDS H2O decorates the steps (665): 11 (111) terraces + 1 (11 1 )step (221): 3 (111) terraces + 1 (11 1 )step LEED, ESDIAD, TDS, FTIR-RAS c(2 × 2), H2O plane highly inclined to surface normal LEED, TDS (11 11 9): 10.5 (111) terraces + 1 (11 1 )step µ0 = 1.2 D Steps are decorated by H2O:

89P

Ni(111)

(100)

90C

Ni(110)

Ni(11 11 9)

4L 4L


Ref. p. 4.2-118]


Ref.

H2O, D2O/ T [K] Substrate 94M2 Ni(775) 150

98R 90H4 86F3 89R

NiO(100) 120 Pd(110) 100 Pt(110) 100 Pt(111) 90

97V3 Pt(111) 90 81T Ru(0001) 95

91P

Ru(0001) 120

95H

Ru(0001)

Method

Type

∆Φ [eV] at θ1


Kelvin

III

-0.75

1.5 L

LEED, AES also: co-adsorption with Na

III III III

-1.0 -0.73 -1.0 -1.15

1 ML θ = 0.5 5L

III III

-1.1 -0.6

5L 2L

III

-1.2

5L

III

-1.28

θ = 0.66 bilayer

? Kelvin Kelvin SE edge (UPS) Kelvin Diode

SE edge (UPS)

4.2-47

LEED, TDS ESDIAD, TDS UPS see Fig. 24 LEED, AES, IRAS LEED, HREELS, TDS hydrogen bonded bilayer (¥î¥ 5ÛVWUXFWXUHE\/((' LEED, UPS, XPS see Fig. 25 LEED, TDS, p(¥î¥ µ0 = 0.34 D

ȝ '0 = 0.65 D;

+0.20 +0.75

0.25 ML 0.5 ML

III

+0.20 +0.77 -1.3

Kelvin

III

-1.7 -1.34

1.6 L 6L bilayer at 1.3 L 3.5 L 2L

SE edge (XPS)

III

-1.1

100... ARUPS 140

III

-1.4

III

-0.7

III III

-0.9 -0.9

10 L

Kelvin

III

-0.2

3L

(Kelvin)

III

-1.1 -1.3

1. layer LEED, TDS, NRA, FTIR-RAS 2. layer (θ = 0.75)

96K2 Ru(0001) 400

96L3

97H

Ru(0001) 82

Ru(0001) 120

94H2 TiO2(110) 90

92M5 WSe2 (p-type) WSe2 (n-type) InSe GaSe (p-type) 96M2 WSe2 (0001) (p-type) 97B Zr(0001)


depolarization included with two A states for the H2O bilayer one A state for the D2O bilayer LEED, HREELS, TDS similar result for Ru(12(001) × (010)) similar result for Ru(12(001) × (010)) MDS, TDS

80

Kelvin

Kelvin

TDS: 2 states A1, A2 for the H2O bilayer only one A state for D2O θ* = 0.75 * θ = 1.0 refers to the saturation value for the 275 K TDS peak. Band bending only 0.1 eV. XPS, TDS 10 L UPS band bending also determined 6L

UPS

4.2-48


[Ref. p 4.2-118

4.2.4.8 H2S Table 29. H2S Ref. 79F

H2S/ T [K] Substrate Ru(11 2 0) 80

Method

Type

∆Φ [eV] at θ1


SE edge (UPS)

II

0.16 -0.36

H2S dissociates molecular adsorption

0.8 L /

4.2.4.9 CO2, SO2, (CH3)2SO, (CH3)3PO3 Table 30. CO2 CO2/ Substrate 94B3 Cu(332) 96H2 Cu(111)

T [K]

Method

Type

∆Φ [eV] at θ1


95 100

Kelvin Kelvin

III

-0.4

200 L

86B3 Fe(111)

140

SE edge (UPS)

1.25

1.5 L

69O

Ni(100)

300

0.3

60 L

LEED, AES, UPS, TDS TDS, UPS, XPS also with co-adsorbed K UPS unclear which species this is LEED dissociative adsorption CO2 ĺ&22

87B

Ni(110)

80

W(100) W(100)

140 300 300

1L 2L 3L

69A 76H

Therm Diode

I

0.6 0.5 0.9 0.44 0.56

T [K]

Method

Type

∆Φ [eV] at θ1


Kelvin

I III

-0.22 0.24 0.3

LEED, AES, TDS

0.4 1.3

SO2 dissociates LEED, UPS, XPS dissociative adsorption leading to TiO2 and TiS2

Type

∆Φ [eV] at θ1


III

-0.77

TDS, XPS

Ref.

SE edge (UPS)

II I

ARUPS, HREELS CO2 parallel to surface ±20° anionic bent species LEED, AES, TDS

Table 31. SO2 Ref. 92A 88O

85S4

SO2/ Substrate Cu(111)

80 200 TiO2(110) 300 TiO2(441) 300 Ti2O3 300 (1012)


SO2 dissociates

Table 32. (CH3)2SO Ref. 97S2

(CH3)2SO / T [K] Substrate Au(100) 100

Method

25 L


Ref. p. 4.2-118]


4.2-49

Table 33. (CH3)3PO3 Ref.

(CH3)3PO3/ T [K] Substrate 85H3 Rh(100) 100

Method

Type

SE edge (UPS)

∆Φ [eV] at θ1 -2.25 -2.50


ML TDS, XPS, UPS multilayer conclusion: PO points to the surface: µ0 = 2.5 D

4.2.4.10 C2N2, HCN Table 34. C2N2 Ref.

C2N2/ Substrate 89R2 Pd(110)

78N

Pt(111)

T [K]

Method

Type

∆Φ [eV] at θ1


300 80

SE edge (UPS)

I ?

1.0 1.8

sat. sat.

300

SE edge el.

I

0.5

sat.

LEED, ARUPS, TDS, several LEED structures; above 200 K C2N2 is believed to decompose into 2 CN. LEED, AES, TDS

I

+0.8

2.5 L

LEED, AES, TDS, UPS

83G3 Ru(10 1 0) 300 Table 35. HCN Ref.

HCN/ Substrate 88H6 Pt(111)


T [K]

Method

Type

∆Φ [eV] at θ1


90

Kelvin

III

-1.15

TDS, LEED

4L

4.2-50


[Ref. p 4.2-118

4.2.4.11 CH3CN, HCOOH, HNCO Table 36. CH3CN (Acetonitrile) Ref. 83S2

CH3CN/ Substrate Pt(111)

T [K]

Method

100

SE edge (UPS)

92O2 Pt(111) 95K4 Pt(111) 97V3

100

Type

∆Φ [eV] at θ1 -1.5 -1.75


ML XPS, TDS, HREELS multilayer conclusion: CŁ1UHK\EULGL]HVWR Cő1DQGFKHPLVRUEVQHDUO\ parallel to surface 2L LEED, AES, IRAS, TDS 4L (multilayer) LEED, AES, TDS, IRAS

III

-1.4 -1.5 -1.5

Method

Type

∆Φ [eV] at θ1


K

III

-0.5 -0.65 -0.9

sat. sat. sat.

n-type, see Figs. and p-type molecularly adsorbed

-0.7

sat.

molecularly adsorbed

Kelvin

Table 37. HCOOH (formic acid) Ref. HCOOH/ T [K] Substrate 83M GaAs(110) 300 88O TiO2(110)

300

TiO2(441)

300


Table 38. HNCO Ref.

HNCO/ T [K] Substrate 83G3 Ru(10 1 0) 300

∆Φ [eV] at θ1


I

+0.80

LEED, AES, UPS, TDS

Method Typ

2.5 L

4.2.4.12 KOH, KCl, HCl, HBr Table 39. KOH Ref. 95M

KOH/ Substrate Si(100)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode

III

-3.0

assumed intact KOH to be adsorbed. µ0 = 1 D

T [K]

Method

Type

∆Φ [eV] at θ1


100 670 100 300 670

FEM

III III III

-1.1 -0.35 -1.0 -0.9 -0.35

quartz microbalance, AES

2 nm

Table 40. KCl Ref. 86S

KCl/ Substrate Ag(111)

89S

Ag(110)

FEM

sat. sat. sat. sat. sat.

completely reversible


Ref. p. 4.2-118]


4.2-51

Table 41. HCl, HBr Ref. 78M

HCl, HBr/ T [K] Substrate Si(111) 300

Method

Type

SE edge

∆Φ [eV] at θ1


0.2

both for HCl, HBr both adsorb as molecular entities

sat.

4.2.5 Nonpolar hydrocarbons Table 42. Methane (CH4) T [K] Method

Type

∆Φ [eV] at θ1


96A

CH4/ Substrate Pt(111)

55

III

-0.42

96M

Pt(111)

40

TDS, UPS µ0 = 0.54 D XPS, TDS

Ref.

71Y W(100) 72M3 W(111) 78S W(100)

110 125 300

SE edge (UPS) SE edge (XPS) FEM Diode FEM

W(111)

300

FEM

III

-0.5

0.3 ML

I III IV

sat.

I

-0.34 -0.30(5) -0.3 0.2 0.35

θ1 3θ1 θ1

TDS adsorbed species is probably CH2 probably CH3 + H

Table 43. Propane (C3H8) Ref. 71L

C3H8/ Substrate Ni(111)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode

III

-0.3

LEED

∆Φ [eV] at θ1

Comments, interpretation LEED, UPS, TDS max. coverage < 0.5 at 100 K C2H4 π-bonded to surface c(2 × 2) structure bonding via the O-atom LEED, TDS, HREELS conclusion: O interacts with Ag surface; µ0 = 0.4 D LEED, AES

Table 44. Ethylene (C2H4) Ref.

C2H4/ Substrate 86K3 Ag(110) 86B

T [K]

Method Type

100...300 K

III

-0.7 -1.45

2L sat

90...750 K

III

-0.35

1L

80K3 Al(100)

300

K

II

84R2 Cu(110)

90

θ1 θ2 sat.

97L2

90

SE edge III (UPS) K III

+0.24 -0.4 -1.1 -0.9

1.8 L

300

Diode

-0.3

sat.

96H

Ag(110)

Cu(111)

74D2 Ni(111)


III

UPS LEED, HREELS, TDS conclusion: π-bond to surface adsorption is reversible TDS

4.2-52 Ref. 75F

4.2 Electron work function of metals and semiconductors C2H4/ T [K] Substrate Ni(111)*+ 80

Method Type

∆Φ [eV] at θ1

FN

II

Pd(111)*+ 80

FN

II

Pt(111)*+ Cu(111)* Au(111)* Al(111)*

FN FN FN

III III III II

+0.13 -0.44 +0.08 -0.8 -1.45 +0.28 -0.46 +0.04 -0.06 -0.3

θ1 θ2 θ1 θ2 sat. sat. sat. θ1 θ2 sat.

80 80 80 80

79B2 Ni(111)

300

76G

300 525 300 525

Diode Diode Diode Diode

-1.5 -1.7 -1.2 -1.5

1·10-8 1·10-8 1·10-8 1·10-8

300

SE edge III (E)

-1.6

sat.

-1.4 -1.3 -0.7 -1.4 -1.2 -0.9 -1.1 -1.0 -0.9 -1.5 -1.2 -0.18 0.0 -0.35

sat. sat. sat. sat. sat. sat.

Pt(111) Pt(100) -(5 × 1)

78N 79V

Pt(111) stepped Pt(111)

Pt(533) Pt(110) Pt(210) 86A2 Pt(111) 88Z

Pt(111)

88M2 Rh(111) 76E2 Re film

84K 74B

Si(111) W(100) W(111) W(211) W(110)

90 210 325 210 210 210 300 120 100 320 300 300

III III III III III SE edge III (E) III Diode III Diode II

330 300 300 300 300

K K K K K

FEM FN FN FN FN Kelvin

III

III III III III III

-0.15 -0.5 -0.45 -0.45 -1.1

[Ref. p 4.2-118

Comments, interpretation *film + dissociation at the beginning

torr torr torr torr

LEED, TDS, HREELS conclusion: dehydrogenation to C2H2 LEED: diffuse (1/2 O) features disordered LEED: substrate: (1 × 1) adsorbate: (¥î¥ 5Û (1 × 1) disordered LEED, AES, TDS

TDS, SIMS also other temperatures 6L 1·1014 molecules cm-2 2.5·1014 molecules cm-2 5.5·1014 molecules cm-2 104 L sat. sat. sat. sat.

TDS


Ref. p. 4.2-118]


4.2-53

Table 45. Acetylene (C2H2) C2H2/ Substrate 74D2 Ni(111)

T [K]

Method

Type

∆Φ [eV] at θ1

300

Diode

III

77D2 Ni(111)

180

at 4·10-9 mbar at 1·10-8 mbar saturation

Pd(111)

180

-1.4

saturation

Pt(111)

180


-0.6 -1.0 -1.2

-1.6

saturation

Ni(111) Pt(111)

300 300

-1.3 -1.5

6L

Diode

Diode

-1.65 -1.8 -1.65

LEED, TDS, HREELS LEED (2 × 2) p = 1·10-8 torr after 10 min, disordered, 1·10-8 torr, disordered LEED: substrate changes to (1 × 1) Adsorbate structure (¥î¥ 5Û 4·10-7 torr , no further change in structure.

0.2 L 0.7 L 5L

AES, ELS

Ref.

78B 76G

III

420 Pt(100) -(5 × 1)

300 420

86A2 Pt(111) 78R

W(100)

300 120 300

-1.7 Kelvin

Comments, interpretation TDS UPS

III III II

-1.3 -1.4 +0.3 0.0 -0.6

Type

∆Φ [eV] at θ1


Diode

-1.3

LEED: (2 × 2)

Diode

-1.2

LEED: ½ order streaks

∆Φ [eV] at θ1


Diode

Table 46. Propylene (CH3CH:CH2) Ref. 76G

CH3CH:CH2 T [K] /Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)

Method

Table 47. Cyclopentane (C5H10) Ref. 76G

C5H10/ Substrate Pt(111) -(1 × 1) Pt(100) -(5 × 1)

T [K]

Method

Type

300

Diode

-1.0

300 300

Diode

-0.7 -0.4 -0.3


7·10-9 torr LEED: (1 × 1) low background 4·10-7 torr disordered 7·10-9 torr LEED: (5 × 1) low background 4·10-7 torr diffuse features at ½ order

4.2-54


[Ref. p 4.2-118

Table 48. Pentadiene (C5H8) C5H8/ Substrate 84A2 Pt(111)

Ref.

T [K]

Method

90

Diode

Type

∆Φ [eV] at θ1


-1.5

TDS, HREELS conclusion: tilted C5-ring

sat.

Table 49. n-hexane (C6H14) Ref. 76G

C6H14/ Substrate Pt(111) -(1 × 1) Pt(100) -(5 × 1)

∆Φ [eV] at θ1


Diode

-1.1

LEED: disordered

Diode

-0.8

LEED: disordered

∆Φ [eV] at θ1


T [K]

Method

300 300

Type

Table 50. Cyclohexane (C6H12) Ref. 76G

C6H12/ Substrate Pt(111)

Pt(100)(5 × 1)

T [K]

Method

300 300 420 573 300 300

Diode

Type

-1.2 -0.7 -1.1 -1.4 -0.75 -0.4

III

-1.5 -0.89

LEED: (1 × 1) very poorly ordered apparent (2 × 2) disordered LEED: (5 × 1) LEED: (1 × 1) and diffuse streaked (2 × 1) pattern 4·10-7 torr LEED: (1 × 1) and diffuse streaked (2 × 1) pattern 4·10-7 torr LEED: (1 × 1) disordered at 1.2 L

III

-0.6

sat.

Type

∆Φ [eV] at θ1

Diode

420

91E

Pt(111)

97S

Pt(111)

-1.2

573 130

SE edge (UPS) 160... SE edge 380 (UPS)

6·10-9 torr 4·10-7 torr 4·10-7 torr 4·10-7 torr 6·10-9 torr 4·10-7 torr

TDS, HREELS

Table 51. Cyclohexene () Ref. 76G

C6H10/ Substrate Pt(111) -(1 × 1)

T [K]

Method

300

Diode

425 Pt(100) -(5 × 1)

300

-1.7 -1.6

Diode

-1.6 -1.5

Comments, interpretation LEED:

 2 4

2   − 2

LEED: apparent (2 × 2) LEED: (1 × 1) diffuse (½ O) features LEED: (1 × 1) streaked (2 × 1)


Ref. p. 4.2-118]


4.2-55

Table 52. 1,3 Cyclohexadiene (C6H8) Ref. 76G

C6H8/ Substrate Pt(111) -(1 × 1)

Pt(100) -(5 × 1)

Type

∆Φ [eV] at θ1

T [K]

Method

300

Diode

-1.8 -1.3 -0.8

300

Diode

-1.7 -1.6 -1.4


2·10-8 torr LEED: poorly ordered 1h  4 − 2 2·10-8 torr LEED:  0 4    5h -8  4 − 2 2·10 torr LEED:   0 5  2·10-8 torr LEED: diffuse, ½ order streaks LEED: diffuse, ½ order streaks 1h 2·10-8 torr 5h LEED: diffuse, ½ order streaks 2·10-8 torr

Table 53. Benzene (C6H6, C6D6) Ref. 90Z2

C6H6, C6D6/ T [K] Substrate Ag(111) 100

Method

Type

∆Φ [eV] at θ1

I III

-0.7 -0.9 -0.9

98V2 Cu(111)

85

SE edge (UPS) 2PPE

74D2 Ni(111)

300

Diode

III

88N3 Pd(110)

80

SE edge (UPS)

III

73G

Pt(111)

300

ret. field

IV

Pt(100)(5 × 1)

300

ret. field

IV

Pt(111)

300 300 300

Diode

76G

-1.2 -0.8 -1.1

-1.4 -0.7 -1.6 -1.1 -1.8 -1.4 -0.7

Pt(100)(5 × 1)

300

Diode

-1.6

85A Pt(111) 95K4 Pt(111) 82R Pt(100)(5 × 20) 88M2 Rh(111)

300 100 300

Kelvin Kelvin SE edge (UPS) Diode

III

-1.5 -1.3 -1.5

III

-1.4


300


1 ML TDS, XPS, UPS multilayer sat. LEED, 2PPE Fig. 3 TDS 3.5 L after pumping ARUPS, LEED, c(4 × 2), AES 3L linear decrease of Φ azimuthally oriented, tilted by 10 - 20º with respect to the surface LEED, ordered structures θ1 θ2 LEED, ordered structures θ1 θ2 4·10-7 torr, poorly ordered  4 − 2 5 min at 4·10-7 LEED:   0 4   4 − 2 40 min at 4·10-7 LEED:   0 5  LEED: substrate changes into (1 × 1) adsorbate: diffuse mig-like ½ order streakes saturation AES, HREELS, TDS LEED, AES, TDS, IRAS 10 L ARUPS C6D6

4.2-56 Ref. 88J2

99W


[Ref. p 4.2-118

C6H6, C6D6/ T [K] Method Substrate Ru(0001) 120...25 K 0

Type

∆Φ [eV] at θ1


III

-1.8

sat.

W(110)

III

-1.5

2.5·1014 atoms cm-2

LEED, HREELS C6H6-mig parallel to surface max. coverage: 0.14 molecule/Ru atom; µ0 = 2.2 D TDS, XPS

Type

∆Φ [eV] at θ1


Diode

-1.7

LEED: streaks at 1/3 order

Diode

-1.5

Kelvin

-1.6

Kelvin

Table 54. Toluene (C6H5CH3) Ref. 74G

85A

C6H5CH3/ T [K] Substrate Pt(111) 300 -(1 × 1) 425 Pt(100) 300 -(5 × 1) 425 300 Pt(111)

Method

(4 × 2) LEED: (5 × 1), streaks at 1/3 order (1 × 1) high background saturation AES, HREELS, TDS

Table 55. Ethylbenzene (C6H5C2H5) C6H5C2H5/ Substrate 98R2 Pt(111) Ref.

T [K] Method

Type

∆Φ [eV] at θ1


135

III

-1.8

0.5 ML

UPS, TDS

III

-1.2

1 ML

III

-0.2 -0.5

1 ML 2 ML

Type

∆Φ [eV] at θ1


-1.5

LEED: disordered

-1.5

LEED: (1 × 1) disordered

∆Φ [eV] at θ1


Diode

-1.7

LEED: disordered

Diode

-1.8


Fe3O4(111) 135

FeO(111)

135


Table 56. N-butylbenzene (C6H5C4H9) Ref. 74G

C6H5C4H9/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)

Method Diode Diode

-

Table 57. T-butylbenzene (C6H5C(CH3)3) Ref. 74G

C6H5C(CH3)3 T [K] /Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)

Method

Type


Ref. p. 4.2-118]


4.2-57

Table 58. M-xylene (C6H4(CH3)2) Ref. 74G

C6H4(CH3)2/ T [K] Substrate Pt(111) 325 -(1 × 1) Pt(100) 325 -(5 × 1)

∆Φ [eV] at θ1


Diode

-1.8

LEED: streaks at 1/2.6 order

Diode

-1.7

LEED: (5 × 1) streaks at 1/3 order

∆Φ [eV] at θ1


Diode

-1.9

LEED: very poorly ordered

Diode

-1.8


Method

Type

Table 59. Biphenyle (C6H5C6H5) Ref. 74G

C6H5C6H5/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)

Method

Type

Table 60. Naphtalene (C10H8) Ref. 73G 76G

C10H8/ Substrate Pt(100) -(5 × 1) Pt(111) Pt(100) -(5 × 1)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode

III

-1.7

sat.

LEED

300 425 300

Diode Diode Diode

-1.95 -2.0 -1.7

9·10-9 torr LEED: apparent (3 × 1) 9·10-9 torr LEED: (6 × 6) 9·10-9 torr LEED: substrate: (1 × 1) adsorbate: disordered 9·10-9 torr LEED: substrate: (1 × 1) adsorbate: disordered

-1.65

Table 61. 2-Methylnaphtalene (C10H7CH3) Ref. 74G

C10H7CH3/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)


∆Φ [eV] at θ1


Diode

-2.0

LEED: very poorly ordered

Diode

-1.6

LEED: disordered

Method

Type

4.2-58


[Ref. p 4.2-118

4.2.6 Polar hydrocarbons Table 62. Methanol (CH3OH) Ref. 92S8

CH3OH / Substrate Cr(110)

T [K]

Method

Type

∆Φ [eV] at θ1


90

III

-2.2

UPS

III

-1.6

at 6 L

TDS, UPS

-1.2

at 80 L

TDS, HREELS

III

-1.1 -1.8

at 3 L

TDS, UPS LEED, AES, TDS, IRAS

77R2 Ni(111)

80

85S6

80

SE edge (UPS) SE edge (UPS) Diode

77 100

Kelvin Kelvin

Si(111) -(7 × 7) 82C2 Pd(100) 95K4, Pt(111) 97V3

Table 63. Ethyleneoxide (C2H4O) C2H4O / Substrate 86K3, Ag(110) 86B Ref.

87B4 Fe(100) 87B4 Ni(111) 90N

Ni(111)

93W

Ni(110)

93W2 Pt(110) -(1 × 2)

T [K]

Method Type

100...300 Kelvin

III

100...300 SE edge IV (UPS) 100...300 SE edge III (UPS) 100 Kelvin III

140

SE edge III (UPS) SE edge III (UPS)

∆Φ [eV] at θ1


-1.45

sat.

-2.2 -1.9 -1.3

0.5 ML 0.75 ML sat.

LEED, UPS, TDS c(2 × 2) structure bonding via the O-atom ARUPS

-1.6

2L

-2.9

0.5 ML

-2.1

0.5 ML

ARUPS TDS co-adsorption with K LEED, TDS, ARUPS c(2 × 2) structure LEED, TDS, ARUPS two differently oriented species

Table 64. Ethylenedioxide ((CH2)4O2) Ref. 96H

(CH2)4O2/ T [K] Method Substrate Ag(110) 90...750 Kelvin

Type

∆Φ [eV] at θ1


III

-0.35

LEED, TDS, HREELS conclusion: O interacts with Ag surface; µ0 = 0.4 D

Type

∆Φ [eV] at θ1


-1.6

LEED, AES, TDS, IRAS

1L

Table 65. Acetone (C3H6O) Ref.

C3H6O / Substrate 95K4, Pt(111) 97V3

T [K]

Method

100

Kelvin


Ref. p. 4.2-118]


4.2-59

Table 66. Furan (C4H4O) C4H4O / Substrate 96O2 Pd(111) Ref.

T [K]

Method

Type

∆Φ [eV] at θ1


175

SE edge (UPS)

III

-1.5

XPS, UPS

Method

Type

∆Φ [eV] at θ1


ARUPS

III

-0.6

Table 67. Benzenethiol (C6H5SH) Ref.

C6H5SH / T [K] Substrate 99W2 Au(111) 300 82A

Cu(111)

300

SE edge (UPS)

-1.0

at 10 L

LEED, HREELS, ARUPS, XPS µ0 = 1.6·1030 Cm saturation ARUPS at 10 L

Table 68. Pyridine (C6H5N) Ref.

C6H5N / Substrate 88N2 Pd(110)

73G

76G

Pt(111) Pt(100) -(5 × 1) Pt(111) -(1 × 1)

Pt(100) -(5 × 1)

T [K]

Method

Type

∆Φ [eV] at θ1


300

SE edge (UPS)

III

-1.07

sat. (5 L)

300 300

Diode Diode

III III

-2.4 -2.4

sat. sat.

LEED, ARUPS c(4 × 2) structure orientation parallel to surface LEED LEED

300

Diode

-2.7

1·10-8 torr LEED: diffuse (1/2 O) features

525

Diode

-1.7

300

Diode

-2.4

1·10-8 torr LEED: well defined streaks at 1/3, 2/3, 3/3 order 1·10-8 torr LEED: (1 × 1) and disordered

525

Diode

1·10-8 torr LEED: (1 × 1) plus (¥ × ¥ 5Û

Table 69. Aniline (C6H5NH2) Ref. 74G

C6H5NH2/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)

∆Φ [eV] at θ1


Diode

-1.8

LEED: streaks at 1/3 order

Diode

-1.8


∆Φ [eV] at θ1


Diode

-1.5

LEED: 1/3 order features

Diode

-1.4


Method

Type

Table 70. Nitrobenzene (C6H5NO2) Ref. 74G

C6H5NO2/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)


Method

Type

4.2-60


[Ref. p 4.2-118

Table 71. Cyanobenzene (C6H5CN) Ref. 74G

C6H5CN / T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)

∆Φ [eV] at θ1


Diode

-1.6

LEED: 1/3 order features

Diode

-1.5


Method

Type

4.2.7 Halohydrocarbons Table 72. Chloro-methane (ClCH3) Ref.

ClCH3/ Substrate

89Z

Ag(111) 100

97Y2 Al(111)

T [K]

90

90S2

Pd(100)

99L

Ru(0001) 100

97K4 Si(111)

100

100

Method

Type

∆Φ [eV] at θ1


SE edge (UPS)

IV

-0.8 -0.6

0.9 ML 1.3 ML

XPS, UPS, TDS 1 ML = 4.6(3)·1014 molecules cm-

SE edge (UPS) SE edge (UPS) Kelvin

III

-0.55

at 7 L

IV IV

K

I

-0.9 -0.75 -1.9 -1.5 -1.7 0.4

3L UPS, TDS 12 L min, 1.8 L 3.5 L 6L 4L CH3Cl weakly bound at 100 K does not react

2

UPS

Table 73. Chloro-ethane (ClC2H5) Ref. 91Z3

ClC2H5/ Substrate Ag(111)

T [K]

Method

Type

∆Φ [eV] at θ1


100

SE edge (UPS)

III

-1.0

TDS, UPS, XPS

Type

∆Φ [eV] at θ1


-0.6

LEED, AES, TDS, IRAS

Method Typ

∆Φ [eV] at θ1


SE edge (UPS)

+1.0

LEED, UPS

1 ML

Table 74. Di-chloro-methane (Cl2CH2) Ref.

Cl2CH2/ Substrate 95K4 Pt(111)

T [K]

Method

100

Kelvin

Table 75. Tri-chloro-methane (Cl3CH) Ref.

Cl3CH / T [K] Substrate 84G1 Ag(111) 300


Ref. p. 4.2-118]


4.2-61

Table 76. Tetra-chloro-methane (Cl4C) Ref.

Cl4C / Substrate

T [K]

Method

79J3

Fe(100)

300

Diode

Type

∆Φ [eV] at θ1


1.30

mobile precursor

sat.

Table 77. Bromo-methane (BrCH3) T [K]

Method

Type

∆Φ [eV] at θ1

100


IV

-1.0 -0.7 -2.2 -1.85

89Z

BrCH3/ Substrate Ag(111)

99L2

Ru(0001) 82

Ref.

IV


0.9 ML XPS, UPS, TDS 1.4 ML 1 ML = 4.6(3)·1014 molecules cm-2 min, 3.5 L TDS, also with a ML of Cu 6.5 L

Table 78. Di-bromo-methane (Br2CH2) Br2CH2/ Substrate 84G2 Ag(111) Ref.

T [K]

Method

300

SE edge (UPS)

Type

∆Φ [eV] at θ1


+0.7

LEED, UPS

Table 79. Tetra-bromo-methane (Br4C) Ref.

Br4C / Substrate

79D3 Fe(100)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode

I

0.95

LEED, AES CBr4 dissociates

Type

∆Φ [eV] at θ1


+0.3

LEED, UPS

sat.

Table 80. Iodo-methane (ICH3) ICH3/ Substrate 80G2 Ag(111)

T [K]

Method

300

95Y

Au(100)

105

SE edge (UPS) Diode

93S8

Pd(100)

85

Ref.

SE edge (UPS)

III

-1.0 min at 5...15 L TDS, IRAS, HREELS -0.8 30 L -1.5 1.5 L UPS

Type

∆Φ [eV] at θ1


-0.85 min 7 L +0.1 25 L

TDS, IRAS, HREELS

Table 81. Iodo-ethane (IC2H5) Ref. 95Y

IC2H5/ Substrate Au(100)

T [K]

Method

105

Diode

Table 82. Chloro-tri-fluoro-methane (ClCF3) Ref.

ClCF3/ Substrate

T [K]

Method

Type

∆Φ [eV] at θ1


92K

Pt(111)

50

SE edge (UPS)

III

-0.15

XPS, UPS, TDS CF3Cl does not react at 50 K


2.5 ML

4.2-62


[Ref. p 4.2-118

Table 83. 1,2-di-chloro-ethane (ClCH2CH2Cl) ClCH2CH2Cl T [K] /Substrate 92W2 Cu(111) 110

Ref.

Method

Type

SE edge (UPS)

∆Φ [eV] at θ1 -0.55 -0.45


at 1 ML UPS multilayer

Table 84. 1,2-di-chloro-ethene (ClCH:CHCl) Ref. 97Y

ClCH:CHCl / T [K] Substrate Cu(100) 120

Method

Type

SE edge (E)

∆Φ [eV] at θ1


-0.25* -0.45**

NEXAFS * CHClő&&O2 ** cis-CHClő&+&O

Table 85. 1,2-chloro-bromo-ethane (ClCH2CH2Br) ClCH2CH2Br T [K] /Substrate 93K2 Cu(111) 111

Ref.

99T

Cu(111)

100

Method

Type

∆Φ [eV] at θ1


SE edge (E) SE edge (UPS)

I

0.8

sat.

-0.55 -0.4 +0.75

12 L 30 L 10 L

at 300 K Br/Cl adsorbate is formed and C2H4 desorbed LEED, AES, UPS

300

Table 86. Iodo-benzene (IC6H5) Ref. 92X

Substrate Cu(111)

T [K] 110

Method SE edge (E)

Type

∆Φ [eV] at θ1 0.6 2L

Comments, interpretation AES, TDS, HREELS

Table 87. Chloro-benzene (ClC6H5) Ref.

ClC6H5/ Substrate

T [K]

Method

Type

∆Φ [eV] at θ1


82R

Pt(100)(5 × 20)

300

SE edge (UPS)

III

-0.85

ARUPS

Method

Type

∆Φ [eV] at θ1


IV

-1.1 -0.6 -1.3

10 L

4.2.8 Other hydrocarbons Table 88. Di-ethyl-zink ((C2H5)2Zn) Ref.

(C2H5)2Zn / T [K] Substrate 94K2 Pd(100) 90 99K4 Rh(111)

90

III

θ1 4θ1 2L

Comments, interpretation XPS, TDS XPS, TDS, HREELS


Ref. p. 4.2-118]


Table 89. glycine (α-amino acetic acid) (H2NCH2CO2H) Ref.

89E3

H2NCH2 – T [K] CO2H / Substrate Pt(111) 120

Method

Type

∆Φ [eV] at θ1

SE edge (UPS)

III

-1.7


10·1014 LEED, TDS, UPS atoms cm-2

Table 90. Closo-1,2-di-carbado-decaborane (C2B10H12) Ref. 94Z2

C2B10H12/ T [K] Method Substrate Cu(100) 150... SE edge 400 (UPS)

Type

∆Φ [eV] at θ1

I

2.0


sat.

Table 91. TCNQ (Tetra-cyano-quino-dimethane) (C12N4H4) T [K]

Method

Type

∆Φ [eV] at θ1


86E2

C12N4H4/ Substrate Cu(111)

100

Diode

I

86E4

Cu(111)

100

Diode

I

0.8 1.36 0.78 1.28 1.36

HREELS supports negatively charged layer HREELS

Ref.

at 1 ML at 2 ML 1. layer 2. layer 3. layer

4.2.9. Alkali metals Table 92. Lithium (Li) Ref. 86P2

Li/ Substrate Ag(111)

86P3 Ag(111) 85P4 89H2 Al(111)

T [K]

Method Type

∆Φ [eV] at θ1


300

Kelvin

IV

300

Kelvin

IV

AES

140

Kelvin

III

-1.86 -1.76 -1.9 min -1.8 ML -1.20

Diode

III

-1.8

95G3 CdTe(100) 94M3 Cu(100)

180

96L

160

Cu(111)

87A4 GaAs(100) (IBA) 79G2 Mo(211) 77 84K4 Mo(110) 5, 77, 300


SE edge IV (E) Diode IV Kelvin Diode Diode

III IV

min ML θLi = 0.5 θLi = 1.0

1 1015 atoms cm-2 LEED, AES, TDS µ0 = 2.1 D ML LEED, AES, ELS µ0 = 3.2 D LEED, AES θLi = 0.55 θLi = 0.8 min ELS ML

-2.0 -1.7 -2.4 -1.85 -1.8 min -1.6 ML -1.5 ML -2.6 min θLi = 0.35 -1.7 ML θLi = 1

4.2-63

4.2-64


Ref.

Li/ Substrate 88G3 Ni(100)

T [K]

Method Type

∆Φ [eV] at θ1


310

Diode

-2.8 -2.5 -2.4 -2.1 -3.5 -2.8 -3.6 min -2.5

min ML

RP

-2.4 -1.8 -1.9 -2.2 -2.4

min

NMR, TDS

1 ML 3 ML

AES, LEED

98M3 Ni(775)

IV IV

94J2

Ru(0001)

96E

Ru(0001) 200

SE edge IV (MDS) Kelvin IV

98E

Ru(0001)

Kelvin

88N4 Si(111)(7 × 7) 91C3 Si(111) 93F

300

66G

77

73M

IV

SE edge III (UPS) IV

Si(111)(7× 7) 94E2 Si(100) 95K3 n-type p-type 95K6 Si(100)(2× 1) 95K7 Si(100)(2× 1) W(211)

360 360

SE edge III (E) Diode III Diode Diode

300

III III III

FEM

III

W(110)

FEM

FEM

W(111) W(211)

FEM Diode

III III III

300

Diode

IV

W(110)

77

Diode

IV

W(110)

77

FEM

IV

W(211)

300

Diode

IV

W(100) W(111)

300 300

Diode Diode

III III

74M5 W(110)

[Ref. p 4.2-118

77 300

µ0 = 1.5 D

TDS, MDS 3 θLi = 0.46 α = 12.8 Å θLi = 0.45 NMR θLi = 1.0 µ changes from 4 to 0.5 D with coverage -3.5 min θLi = 0.5 µ0 = 4.9 D -2.5 -2.3 AES, MDS

-2.2 -1.8 -2.4 -2.3

-1.5 -1.8 -3.0 -2.4 -1.7 -1.5 -1.8 -1.5 -1.8 -2.9 -1.9 -2.3 -2.8 -2.2 -3.0 -2.4 -1.5 -2.0 -1.9 -1.4 -1.4

AES, TDS

1 ML 2 ML AES, LEED, UPS different Li induced superstructures ML 2. layer

ML 2. layer ML 2. layer min ML 2. layer min ML min ML 1 min 2 min ML ML

5 1014 atoms cm-2 12 1014 atoms cm-2 5 1014 atoms cm-2 LEED

5 1014 cm-2 12 1014 cm-2 20 1014 cm-2

5 1014 12 1014 16 1014 12 1014 12 1014

cm-2 cm-2 cm-2 cm-2 cm-2


Ref. p. 4.2-118] Ref.

Li/ Substrate 84K4 W(110)


Method Type

∆Φ [eV] at θ1

5, 77, 300

Diode

IV

Diode

IV

-2.9 min -2.0 ML -2.6 min -1.7 ML

Mo(110) 5, 77, 300

4.2-65


θLi = 0.35 LEED θLi = 1 θLi = 0.35 θLi = 1

Table 93. Sodium (Na) Figs. 26 and 27 Ref.

Na / Substrate 77B4 Ag(110)

T [K]

74P

Al(111)

300

87P2

Al(100) Al(100)

300 100 350

Method

Type

∆Φ [eV] at θ1


III

-2.0

θNa = 0.45

UPS, XPS

III

-1.6

ML

µ0 = 3.4 D

III IV

-1.6 -2.0 -1.6 -1.6

ML min ML ML

-1.5 -1.4 -1.7 -1.4 -2.7 -2.5 -2.5

θNa = 0.3

-2.0 -2.0 -2.3 -2.7 -2.3

at θNa =0.1 θNa = 0.25 θNa = 0.55 min ML

-2.1 -1.8 -2.2 -2.0

min ML min ML

-2.8 -2.3

min ML


III

89H2 Al(111)

140

Kelvin

IV

Al(111)

300

Kelvin

IV

95N2 Au(100)

130

Kelvin

IV

300

III

95S5

Au(100)

80L

Cu(111)

300

Diode

IV

83W

Cu(100)

100

Diode

IV

91T

Cu(111)

300

Diode

IV

93S4 93S5

Cu(111)

Diode

IV


Kelvin

θNa = 0.3 min ML ML


µ0 = 3.2 D µ0 = 3.2 D linear decrease for 0.08 < θNa < 0.5 explained by 2D clustering. See Fig. 26. LEED, UPS, ELS µ0 = 1.8 D µ0 = 2.1 D θNa = 0.22 θNa = 0.45 θNa = 0.45, no minimum observed LEED, XPS, AES lifting of (5 × 20) reconstruction XPS

θNa = 0.13, µ0 = 11.3 D θNa = 0.5, close-packed layer LEED, AES, ELS, ARUPS

θNa = 0.2 θNa = 0.4 LEED, TDS θNa = 0.2, µ0 = 4.3 D, UPS θNa = 0.4

4.2-66 Ref. 93S6 93T2

4.2 Electron work function of metals and semiconductors Na / Substrate Cu(110)

94F

Cu(111)

96L2

Cu(110)

67P

Ge(111)

69W2 Ge(111) 81B2 Ge(100)

T [K]

Method

Type

∆Φ [eV] at θ1

Diode SE edge (UPS)

IV

θNa = 0.5 θNa = 1.0, µ0 = 2.7 D UPS -2.0 > θNa = 0.5 LEED, IPES -2.75 min, θNa =0.33 2PPE -2.3 ML, θNa = 1 -2.4 2 ML AES, ARUPS -2.2 min θNa = 0.3 -1.8 ∆Φ is different after heating to θNa = 0.7 370 K -2.5 LEED

ARUPS (2PPE) 100 (370)

300

Ge(111) 40

III IV

SE edge (E) Diode FEM

III III IV

FEM

IV

SE edge (UPS) Diode

III

-2.5 -2.5 -2.3 -2.4 -2.3 -2.5

III

-2.6

1 ML

LEED, AES, ELS, TDS

-1.9 -1.8 -3.1 -2.2 -3.1 -2.5 -2.1 -2.0 -3.3 -2.6 -3.2 -2.4 -2.9 -2.3 -3.2 -2.6

min ML min ML min ML min ML min ML min ML

LEED

-2.2 -1.5 -2.8 -2.3 -3.6 -2.8 -3.0 -2.8 -3.6 -2.9

min thick layer min, θNa = 0.25 ML, θNa = 0.55 min ML min, θNa = 0.5 ML, θNa = 1.0 min ML

Diode

IV

70G

Ni(111)

300

Kelvin

IV

Ni(100)

300

Kelvin

IV

Ni(110)

300

74A2 Ni(100)

300

Diode

IV

88G3 Ni(100)

325

Diode

IV

IV

98M3 Ni(775)

IV Diode

IV

SE edge (UPS) Diode

IV IV

85K7 Ru(0001) 300

Diode

IV

87K2 Ru(10 1 0) 300

Diode

IV

87R

Diode

IV

94B4 NiO

180

88M2 Rh(111)

310

Ru(0001) 300

min ML

IV

77

Ni(111)

-2.1 -1.9


ARUPS

96K3 Ge(111) (2 × 8) 97N4 Ge(100)(2 × 1) 80G Mo(211)

93S5

[Ref. p 4.2-118

7·1014 atoms cm-2 10·1014 atoms cm-2 7.5·1014 atoms cm-2 10·1014 atoms cm-2 UPS

θNa = 0.21, µ0 = 3.7 D θNa = 0.45 θNa = 0.26, µ0 = 3.6 D θNa = 0.5 See Fig. 27 θNa = 0.23, µ0 = 3.4 D θNa = 0.45 µ0 = 4.3 D

min ML

θNa = 0.18 θNa = 0.40 UPS UPS, XPS

µ0 = 3.4 D TDS co-adsorption with CO θNa = 0.3 θNa = 0.6, µ0 = 4.3 D TDS, ELS


Ref. p. 4.2-118]

4.2 Electron work function of metals and semiconductors Method

Type

∆Φ [eV] at θ1

IV

94H3 Ru(0001) 50


-3.5 -3.0 -3.7 -2.9

69W2 89G2 89G3 91T2

Diode SE edge (E) Diode

Ref. 91P6

Na / T [K] Substrate Ru(0001) 120

Si(111) Si(001)(2 × 1) Si(001)(2 × 1) 92R2 Si(111)(2 × 1) 93H Si(100)(2 × 1) 93J Si(001)(2 × 1) 94O Si(111)

300 430 300

100

300

SE edge (UPS) ARUPS

97C2 Si(100)- 300 (2 × 1) 67O W(100) W(110) W(111) W(112) Re(10 1 1) Re(1120) Re(10 2 2) 68K W(110)

SE edge (UPS) SE edge (UPS) FEM FEM FEM FEM FEM FEM FEM FEM

68K

W(112)

FEM

W(100)

FEM

IV

-2.5 -2.9

III

-3.0

at θNa = 1 min

IV III

-2.7 -2.4 -2.7 -2.2 -3.0

min ML

III

-2.5 -2.3 -3.0 -2.45 -3.90 -2.0 -2.35 -3.6 -2.6 -2.9 -3.6 -2.9 -2.6 -2.4 -2.5 -2.2 -2.1 -2.0 -3.4 -2.5 -2.8 -3.5 -2.5 -2.0 -2.3 -2.1

min min min min min min min min

-2.0

at 0.5 ML at θNa = 0.75 ML

IV IV IV IV IV IV IV

W(111) 70M

W(110)

77

Diode

IV

W(110)

300

Diode

IV

71C5 W(112) 73M3 W(112)

300 77

Diode Diode

III IV

300 W(112) W(112) + 1 ML oxygen

Diode

70C



min, θNa = 0.30 ML, θNa = 0.44 min θNa = 0.2, µ0 = 5.0(5) D ML θNa = 0.55 LEED, TDS

III III

LEED, AES

min ML

LEED, AES, ELS clustering for θNa > 0.5 IPES UPS LEED, IPES UPS ARUPS

min min

4.2-67

5·1014 atoms cm-2 10·1014 atoms cm-2 8·1014 atoms cm-2 15·1014 atoms cm-2 7·1014 atoms cm-2 10·1014 atoms cm-2 7·1014 atoms cm-2 10·1014 atoms cm-2

min ML 2. layer

7·1014 atoms cm-2 10·1014 atoms cm-2 200 K and 400 K similar LEED

4.2-68 Ref.


85C

Na / Substrate W(100)

97O

ZrC(100)

[Ref. p 4.2-118

T [K]

Method

Type

∆Φ [eV] at θ1


300


IV

-3.0 -2.7 -0.6 -0.1

LEED, AES, ARUPS

IV

min

θNa = 0.25, AES, UPS θNa = 0.8

Table 94. Potassium (K) Ref.

K/ Substrate 82F2 Ag(111)

T [K] Method

88A2 Ag(111) 89B4 Ag(111)

100

91O

Ag(100)

325 140

86P2 Al(111)

300

87P2 Al(100)

100 350


Diode

IV

Kelvin

IV

SE edge IV (UPS) SE edge III (E) IV SE edge III (E) or Diode SE edge IV (E) SE edge III (E)

89H2 Al(111)

140

Kelvin

IV

95N2 Au(100)

130

Kelvin

IV

95S4 Au(100)

300 130

Kelvin Kelvin

III IV

90

87D2 Cu(100)

120

85W

Cu(110)

300

86A4 Cu(100)

330

92A2 Cu(100) 95H3 Cu(111)

90

min, θΚ = 0.15 ML, θΚ = 0.33 θΚ = 0.55 θΚ = 1.5 min, θΚ = 0.5 ML, θΚ = 1.2 θΚ = 1.2 min, θΚ = 0.2 ML, θΚ = 0.4

-2.8 -2.3 -2.3

min ML

-2.2 -1.7 -3.3 -3.0 -3.0 -3.3 -3.1 -2.7 -2.7 -3.1

SE edge (XPS) SE edge IV (E) SE edge IV (UPS) SE edge IV (E)

-3.0 -2.9 -3.6 -2.3 -3.1 -2.3 -3.0 -2.5

Kelvin

IV

Kelvin

IV

-2.87 -1.9 -2.9 -2.4

min, at θ1 at 5θ1 min, θΚ = 0.25 θΚ = 0.6

III

LEED, AES UPS, XPS, ELS

AES

min ML min, θΚ = 0.15 ML, θΚ = 0.4 ML θΚ = 0.15 θΚ = 0.45 θΚ = 0.1 θΚ = 0.2 θΚ = 0.45 θΚ = 0.5 θΚ = 1.0 min ML min ML min, θΚ = 0.17 θΚ = 0.3

300

99W3 Cr2O3(0001)

-2.9 -2.4 -2.8 -2.1 -3.5 -2.8 -2.2 -2.4 -2.1 -2.2


LEED, AES, TDS µ0 = 4.6 linear decrease for 0.05 < θΚ < 0.4 explained by 2D clustering µ0 = 4.1 D LEED, AES, XPS

LEED, XPS K-induced (5 × 20) ĺ (1 × 1) “deconstruction”

LEED, XPS, Laser induced desorption AES, TDS, ELS MDS LEED, AES, ELS µ = 16 D, goes to 3 D with coverage

TDS CO-adsorption of CO Lando lt -Börnst ein New Ser ies III/42 A2

Ref. p. 4.2-118]


4.2-69

T [K] Method



90

Kelvin

IV

LEED, AES, TDS, UPS

79B5 Fe(110)

300

81L

Fe(100)

300

SE edge IV (UPS) Kelvin IV

Fe(110)

300

Kelvin

IV

Fe(111)

300

Kelvin

IV

GaAs(110)*

300

Kelvin

300 300 300 300

Ref. 98B

92O

K/ Substrate Cu(332)

min, 0.8 ML 2 ML min, θΚ = 0.18 ML, θΚ = 0.31 min ML min ML min ML

III

-2.7 -2.3 -3.7 -2.8 -2.4 -2.1 -3.5 -3.0 -2.5 -2.4 -2.8

Kelvin

III

-3.5

1 ML

LEED, AES *prepared by ion bombardment and annealing **cleaved

Kelvin Diode Diode FEM

III III III IV

1 ML

**cleaved

at

Ge(111)

FEM

IV

4.5·1014 atoms cm-2 7.5·1014 atoms cm-2 4.5·1014 atoms cm-2 7.5·1014 atoms cm-2

Graphite(0001) 160 85

-2.4 -3.0 -3.4 -2.9 -2.65 -2.8 -2.65 -2.2(1)

GaAs(110)** p-type n-type 69W2 Ge(111) Ge(100) 81B2 Ge(100)

at

76B4 Mo(100)

77

Mo(110)

77

FEM

IV

-3.1 -2.3

Mo(211)

77

FEM

IV

-2.5 -2.1

Mo(111)

77

FEM

IV

-2.1 -1.7

300

Diode

III

-1.1

min, 5·1014 atoms cm-2 ML, 9·1014 atoms cm-2 min, 3·1014 atoms cm-2 ML, 6·1014 atoms cm-2 min, 4·1014 atoms cm-2 ML, 8·1014 atoms cm-2 min, 2.5·1014 atoms cm-2 ML, 7.5·1014 atoms cm-2 0.2 ML

SE edge III (UPS) SE edge IV (UPS) Diode

-2.0

θΚ = 0.5

-3.2 -2.8 -3.5 -2.9

θΚ = 0.3 θΚ = 1.0 min, θΚ = 0.2 ML, θΚ = 0.33

91P5 MoS2 (basal) 96O

NbC(100) NbC(111)

73A

Ni(100)


-2.4 -2.1

µ0 =4.4 D µ0 = 3.8 D

θK = 0.35

SE edge III (UPS) Diode FEM IV

99O

LEED, AES, UPS µ0 = 6.0 D µ0 = 7.0 D

LEED, AES, TDS 2 D and 3 D clusters for coverages θΚ > 0.2

LEED, UPS LEED µ0 = 6.3 D

4.2-70


K/ Substrate 74A2 Ni(100)

T [K] Method


300

Diode

IV

84S11 Ni(100)

120

88G3 Ni(100)

325

SE edge IV (UPS) Diode IV

70G

300

Kelvin

Ref.

Ni(110)

85L2 Ni(111)

IV

86U

Ni(111)

90

90N

Ni(111)

100

SE edge III (UPS) SE edge IV (E) Kelvin IV

40

Kelvin

91H2 Ni(100) 98M3 Ni(775)

IV IV

87B6 Pd(100)

300

83K3 Pt(111)

300

85L

Pt(111)

300

88W

Pt(111)

IV

96L2 Pt(111)

140

SE edge (UPS) SE edge (UPS) SE edge (E, UPS) ARUPS

78L3 Re(10 1 0)

245

Diode

IV

97V2 Re(0001)

105

Kelvin

IV

92J2

45

Rh(111)

IV IV IV

IV

85D3 Ru(0001)

80

Kelvin

85M

60

Ru(0001)

IV

IV

86H4 Ru(10 1 0)

430


87R

Ru(0001)

300

Diode

IV

88D

Ru(0001)

450

Diode

IV

91P6 Ru(0001)

120

SE edge IV (UPS)

-3.5 -2.8 -3.6 -2.9 -3.7 -3.3 -2.7 -2.5 -4.1

min, θΚ = 0.2 ML, θΚ = 0.40 min, θΚ = 0.15 ML, θΚ = 0.33 min ML min, θΚ = 0.38 ML, θΚ = 0.5

-4.0 -3.5 -3.8 -3.1 -3.3 -2.5 -3.5 -2.8 -4.15 -3.2 -4.6 -3.9 -4.6 -4.0 -4.8 -3.2 -4.3 -3.7 -3.0 -2.6 -4.3 -3.0 -3.8 -3.4 -4.3 -2.4 -4.0 -3.3 -2.6 -2.4 -3.9 -3.2 -3.7 -3.2 -3.8 -3.0

min ML min, θΚ = 0.2 θΚ = 0.7 min ML

[Ref. p 4.2-118

Comments, interpretation µ0 = 6.7 D

µ0 = 5.3 D; see Fig. 27 MDS LEED, IRAS, TDS µ0 = 3.7 D TDS

µ0 = 6.3 D

min, θΚ = 0.17 ML, θΚ = 0.33 min, θΚ = 0.5 ML, θΚ = 1.0 min, θΚ = 0.3 ML, θΚ = 0.5 min ML min, θΚ = 0.45 ML, θΚ = 1.0 min, θΚ = 0.35 ML, θΚ = 1.0

min ML min ML min, θΚ = 0.17 ML, θΚ = 0.35 min min, θΚ = 0.2 ML, θΚ = 0.4

LEED, AES, TDS µ0 = 6.4 D XPS, UPS µ0 = 9.4 D AES, TDS, UPS, HREELS AES, TDS, UPS incorporation of K 4.5·1014 atoms cm-2 7·1014 atoms cm-2 TDS, SHG UPS

LEED, AES, UPS, TDS µ0 = 3.6 D µ0 = 3.9 D TDS, ELS µ0 = 7.8 D LEED, AES, TDS XPS, UPS


Ref. p. 4.2-118]

4.2 Electron work function of metals and semiconductors T [K] Method


300 300

Diode Diode

III IV

83T2 Si(100)-(2 × 1) 86O Si(100)

200

Diode Kelvin

III IV

Si(111)

300

Kelvin

Ref.

K/ Substrate 69W2 Si(111) Si(100)

89E2 Si(100)-(2 × 1) 90M Si(111)-(7 × 7)

300

90N2 Si(100)-(2 × 1) 90R3 Si(100)-(2 × 1)

300

92B4 Si(111)

300

92M3 Si(100)-(2 × 1)

300

ARUPS SE edge (UPS) SE edge (UPS) SE edge (UPS) Diode

III IV IV IV IV

55 93F

Si(111)-(7 × 7)

300

-3.0 -3.4 -3.1 -2.1 -2.9 -2.6 -3.1 -2.9 -3.3 -3.2 -3.1 -3.3 -3.0 -3.45 -3.0 -3.1 -3.0 -3.3 -2.5 -3.3 -2.5 -3.4 -3.2 -3.0

94W

SE edge IV (E) Diode III

97N5 Si(111) cleaved 76B4 Ta(100)

77

Diode SE edge (UPS) SE edge (UPS) FEM

IV

Ta(110)

77

FEM

IV

-3.1 -2.2

Ta(111)

77

FEM

IV

-1.6 -1.3

Ta(211)

77

FEM

IV

-2.0 -1.8

95H2 TiO2(110)

ARUPS

IV

65S

FEM

-3.8 -3.4 -2.6 -2.2

Si(111)-(7 × 7) 300 Si(111) (¥î¥ 5Û% 300 97C3 Si(100)-(2 × 1) 300

W (averaged)


300

III III

-3.0 -3.5

III

-3.20 (-3.56) -2.3 -2.1

4.2-71


min θΚ = 0.5 min

LEED, AES, ELS AES

min

min min, θΚ = 0.5 θΚ = 0.75 min ML min ML min ML min ML min, θΚ = 0.5 ML, θΚ

LEED, IPES, UPS

LEED, IPES, UPS TDS, LEED, AES LEED, AES, UPS, TDS includes band bending of 0.3 eV at 300 K. LEED, AES LEED, AES, ARUPS

min

LEED, AES, ARUPS ARUPS UPS second experiment

min, 2.2·1014 atoms cm-2 ML, 4·1014 atoms cm-2 min, 2.3·1014 atoms cm-2 ML, 4·1014 atoms cm-2 min, 2.2·1014 atoms cm-2 ML, 3.5·1014 atoms cm-2 min, 3·1014 atoms cm-2 ML, 4·1014 atoms cm-2 min, θΚ = 0.4 ML, θΚ = 0.7 min

LEED, ARUPS

4.2-72 Ref. 66S

4.2 Electron work function of metals and semiconductors K/ Substrate W(100)

T [K] Method


300

FEM

IV

W(110)

300

FEM

IV

W(111)

300

FEM

IV

W(211)

300

FEM

IV

FEM

IV

67O2 W(100) W(110)

IV

W(111)

IV

W(112)

IV

min, θΚ = 0.8 ML, θΚ = 1.2 min, θΚ = 0.85 ML, θΚ = 1.1 min, θΚ = 0.85 ML, θΚ = 1.1 min, θΚ = 0.85 ML, θΚ = 1.1

min, 3.6·1014 atoms cm-2 ML, 6.2·1014 atoms cm-2 min, 2.8·1014 atoms cm-2 ML, 4.6·1014 atoms cm-2 min, 4·1014 atoms cm-2 ML, 7·1014 atoms cm-2 min, 3.5·1014 atoms cm-2 ML, 6·1014 atoms cm-2

74M5 W(211)

245

74M7 W(112)

245

Diode

75B

W(100)

77

FEM

IV

-3.0 -2.6

W(110)

77

FEM

IV

-4.1 -3.2

W(111)

77

FEM

IV

-2.5 -2.3

W(211)

77

FEM

IV

-2.9 -2.7

76B4 W(110) 85C W(100)

77 300

91D

78

FEM SE edge (UPS) FEM IV

W(112)

IV

-2.8 -2.4 -2.8 -2.4 -2.7 -2.4 -2.8 -2.4 -3.0 -2.6 -4.3 -3.4 -2.5 -2.3 -3.2 -2.8 -2.9 -2.7 -2.9 -2.2

-3.1 -2.7 -3.0 -2.7

min, ML min 2. layer

min ML, θΚ = 0.6 min ML

[Ref. p 4.2-118

Comments, interpretation µ0 = 4.7 D µ0 = 7.8 D µ0 = 5.7 D µ0 = 6.8 D

4·1014 atoms cm2 12·1014 atoms cm2 LEED µ0 = 4.8 D

µ0 = 4.1 D

µ0 = 4.1 D

µ0 = 8.6 D LEED, AES, ARUPS


Ref. p. 4.2-118]


4.2-73

Table 95. Rubidium (Rb) Fig. 28 Ref.

Rb / Substrate 89H2 Al(111) 99S2

T [K]

Method

Type

∆Φ [eV] at θ1

140

Kelvin

IV

-2.3 -1.8 -2.8 -2.5

min ML min, θRb = 0.15 θRb = 0.3

-3.5

min

Cu(100)

97C3 Si(100) -(2 × 1)

IV

300

SE edge (UPS)

III

Comments, interpretation LEED, AES, UPS µ0 = 4.1 D; see Fig. 28 data of H. Schief, Diploma Thesis, University Göttingen, 1990 ARUPS

Table 96. Cesium (Cs) Fig. 29 T [K]

Method Type

∆Φ [eV] at θ1


83H

Cs / Substrate Ag(110)

300

SE edge IV (UPS)

-2.5 -2.4

min ML

86D

Ag(110)

300

Kelvin IV

100

Kelvin Kelvin IV

-2.4 -2.2 -2.6 -3.1 -2.7 -2.9 -2.3 -2.6 -2.3 -2.4 -1.8 -2.4 -1.8 -2.57 -2.0 -2.4 -1.6 -1.7

min ML min θCs = 0.6 θCs = 1.3 min, θCs = 0.4 ML,θCs> 0.9 min ML min ML min ML min, θCs = 0.22 ML, θCs= 0.4 2·1014 atoms cm2

LEED, AES small amounts of alkali drive a (1 × 2) reconstruction θCs = 0.26 θCs = 0.4

Ref.

88A2 Ag(111) 93S7

Ag(100)

80

Kelvin IV

86P2

Al(111)

300

87H

Al(111)

140

SE edge IV (E) Kelvin IV

89H2 Al(111)

140

Kelvin IV

94K3 Al(111)

85

Diode

87T

Be (polycr.)

IV

94G3 CdTe(100)

Diode

III

78L2 80L

Cu(111)

300

Diode

IV

-3.4 -3.0

min ML

82P7

Cu(100)

300

Diode

IV

-3.0 -2.5

min ML


LEED, AES LEED, TDS AES UPS, µ0 = 4.1 D LEED, AES, UPS µ0 = 4.1 D TDS, HREELS AES θCs = 0.33 ML LEED, AES θCs = 0.16, µ0 = 9.6 D θCs = 0.26, p(2 × 2) closepacked layer LEED, AES, ELS, ARUPS θCs = 0.14 θCs = 0.27

4.2-74 Ref. 91S

4.2 Electron work function of metals and semiconductors Cs / Substrate Cu(110)

[Ref. p 4.2-118

T [K]

Method Type

∆Φ [eV] at θ1


100

Kelvin IV

260

IV

-2.8 -2.4 -2.6 -2.4

min ML min ML min ML

θCs = 0.16 θCs = 0.28 θCs = 0.22 θCs = 0.33 θCs = 0.45, IPE θCs = 1.0

LEED, AES

97A

Cu(100)

300

Diode

IV

71M

GaAs(110) (cleaved) p-type GaAs(110) cleaved in air GaAs(110) 300 (cleaved) n-type Ge(111) 300 p-type GaAS(111) B GaAs(100) GaAs(110)* 300

Diode

III

-3.1 -2.6 -4.0

Diode

III

-3.4

saturation

Kelvin III

-3.3

θCs = 0.6

Kelvin III

-3.3

θCs = 0.8

Diode

III

-3.2

saturation

SE edge III (UPS) Diode III

-3.7

*prepared by IBA

-1.8(2)

LEED: (1 × 1)

77D3

78C2

84R3

89M3 75D

GaP(111) 80 or 300 GaP( 1 1 1 ) 69W2 Ge(111) 300 Ge(100)

300

86H5 Graphite (0001) 81G

Mo(211)

77

82S5

Mo(100)

?

92E2

Mo(110)

94G4 Mo(110)

77

300 MoS2 cleaved in 200 air 85K9 MoS2(0001) 300 85K10 170 78P2 NbSe2 200 NbSe2 300 70G Ni(110) 300 78P3

Diode

IV

Diode

IV

Diode

IV

IV

?

IV

Diode

IV

Diode

Diode

-3.2 -3.0 -3.4 -3.1 -2.4

-2.8 -2.7 -2.3 -3.6 -3.4 -3.6 -2.9 -2.5 -1.9

III III

-1.8 -2.8

III III Diode III Diode III Kelvin IV

-2.3 -3.0 -3.0 -0.6 -3.1

Diode

min min min 5·1014 atoms cm2 min ML 2. layer min ML min ML

LEED: (¥î¥ 5ÛSDWWHUQ LEED

ELS

3 1014 atoms cm−2 15·1014 atoms cm-2 LEED, ELS

AES, TDS LEED min

θCs = 0.33; see Fig. 27 Lando lt -Börnst ein New Ser ies III/42 A2

Ref. p. 4.2-118]


4.2-75

T [K]

Method Type

∆Φ [eV] at θ1


300

Diode

LEED

77K4 Ni(100) 88G3 Ni(100)

325

ARUPS III Diode IV

89D

100

-3.4 -2.9 -3.0 -3.8 -3.3 -3.8 -3.2 -3.0 -4.5 -4.0 -4.1 -3.8 -4.2 -3.5

Ref. 75P2

Cs / Substrate Ni(100)

Ni(111)

IV

SE edge IV (UPS) Diode III ARUPS IV

91K4 NiO(100) 89C Pt(111)

300

85H4 Ru(0001)

80

87R

Ru(0001)

300

SE edge IV (E) Diode IV

90D2 Ru(0001)

300

Diode

91P6

120

Ru(0001)

IV

Diode

III

-3.0

Diode

IV

-3.1 -3.0 -2.2

min ML 1 ML

-3.9 -3.2 -3.0 -2.8 -3.1 -2.3

min ML min ML min, (2 × 2) ML

300

Diode

82T

IV

SE edge IV (UPS) IV 200

Kelvin IV ARUPS IV

300

W(110)

SE edge III (XPS) FEM IV

W(100)

IV


130

300

SE edge IV (E)

TDS, also oxidation of Cs LEED, ARUPS

µ0 = 10.5 D see Fig. 29 θCs = 0.14 θCs = 0.3 TDS, ELS; µ0 = 11 D min LEED, TDS ML µ0 = 16.4 D min, θCs = 0.19 XPS, UPS ML,θCs= 0.40 min

300

Si(100)

69M2 W(100)

min, θCs = 0.25 ML, θCs= 0.4 min ML min ML

300

300

67S

min, θCs = 0.5 θCs= 1.0

SE edge IV (UPS) Diode III

69W2 Si(111)

97G2 TiO2(110)

XPS

-3.8 -3.6 -4.0 -3.7 -3.2 -2.9 -3.6 -3.2 -3.7 -3.3 -3.7 -3.2 -3.4 -2.8 -3.6 -3.1 -3.25 -3.0 -3.0


Si(100) -(2 × 1) 85I2 Si(100) -(2 × 1) 87O2 Si(100) -(2 × 1) 89E2 Si(100) -(2 × 1) 90M Si(111) -(7 × 7) 94W3 Si(111) -(7 × 7) Si(111) -(¥î¥ R30Û% 67F Ta(110)

min ML

min min θCs = 0.7 θCs = 1.0 min ML min ML min ML

LEED, AES, ELS, UPS

AES

LEED, IPES, UPS LEED, AES, ARUPS

µ0 = 6 Band bending 0.3 eV D

LEED

4.2-76 Ref. 69S

4.2 Electron work function of metals and semiconductors Cs / Substrate W(110)

T [K]

Method Type

∆Φ [eV] at θ1

FEM

-3.6 -3.4 -3.0 -2.8 -3.2 -2.0 -2.6 -2.8 -3.7 -3.2 -3.1 -2.6 -3.0 -2.8 -3.1 -2.4 -3.8 -3.2

IV

W(100)

IV

70F

W(211) W(111) W(115) W(103) W(110)

77

72V

W(100)

300

III III III III SE edge IV (E) Diode IV

71P2

W(211)

300

Diode

IV

73P2

W(100)

300

Diode

IV

80D2 W(110)

250

Kelvin IV

87L

WSe2*

97K5 WSe2

Diode 85

III

-3.1

IV

-4.1 -3.9

[Ref. p 4.2-118


min ML

1.8·1014 atoms cm-2 2.5·1014 atoms cm-2

min ML min ML min ML min ML min ML

θCs = 0.25, (2 × 2) LEED θCs = 0.43, close-packed layer

6·1014 atoms cm-2 min

3.5·1014 atoms cm-2 5.5·1014 atoms cm-2 LEED, AES AES, LEED, TDS *cleaved in air θCs = 0.4 θCs = 0.8 AES, TDS

4.2.10 Noble metals Besides the alkali metals, the noble metals (Cu, Ag, Au) are most thoroughly studied. The work-function changes reflect a larger number of effects which may occur during adsorption. The most sensitive coverage range is the monolayer, but some changes are also observed up to 10 ML. The work-function changes are mainly affected by the growth mode: pseudomorphic or not in registry, distributed single atoms or islands, cluster growth in three dimensions, layer-by-layer growth or clusters on a wetting layer (the so-called Stranski-Krastanov growth mode). These different modes depend on atomic fluxes and substrate temperature. Superimposed to these different growth modes, a change of the substrate reconstruction may occur which also may influence Φ. Obviously, work-function measurements alone can not discriminate all those different processes. The high melting metal surfaces (W, Mo, Ta) have been preferred substrates from the beginning of UHV technology in surface science, since they can easily be cleaned by high-temperature flashes. There are some interesting reviews on this topic (e.g. [85K6]). Also Figs. 30 and 31 show the richness of the observed Φ variations. As mentioned already in the introduction, Cu was selected to represent this class of adsorbates and some more figures are added to the Cu table.


Ref. p. 4.2-118]


4.2-77

Table 97. Copper (Cu) Figs. 32...41 Ref.

Cu / Substrate 87B7 Al(111)

94H

T [K]

Method

Type

∆Φ [eV] at θ1

300

ARUPS

I

0.0 +0.4 0.0 +0.2 -1.1+ -1.4

Al(100)

300

Ir(100)

380

I FEM

III


1 ML LEED, AES, ARUPS 4 ML 1 ML 4 ML 4...8 ML + average value 1.5...4.5 ML Cu grows as Cu(100) φ sat = 4.55 ± 0.02 eV 100

80S3

Mo(100)

300

Diode

90T

Mo(110)

300

Diode

87B5 Pd(111)* 88V 85P Pt(111)

95N

3 ML 1 ML

SE edge (E) Kelvin Kelvin

min, θCu = 1 θCu = 3.5 2 ML

quartz crystal microbalance; θ [ML] is given in relation to the number of substrate atoms, which is taken as 1.0×1015 Ir atoms cm-2. AES see Fig. 32 AES, LEED, TDS * film on mica LEED, AES T>475 K: alloy formation θ = 1: p(1×1), pseudomorphic Figs. 33 and 34

LEED, AES, TDS *from AES, annealed to 900 K following to deposition without annealing

* thick Ru(0001) film on Mo(110) LEED, AES growth mode: 2 D layer-bylayer; see Fig. 35 MDS, IRAS, TDS ∆Φ measured during Cu deposition: ∆Φ-oscillations Cu compresses oxygen on the surface.

4.2-78 Ref.


85T2

Cu / Substrate Si(111)

T [K]

97V

V(100)

65M

W(110)

6 ML

LEED, AES, first 2D alloy formation then epitaxial growth of Cu LEED, AES, UPS, TDS

-0.65 -0.5

FEM

II

300

FEM

II


IV

W(100)

300 (800) 300

75C

W(100)

77

FEM

II

+0.42 -0.20

76M

W(211)

300

Diode

II

0.35 0.0 -0.42 -0.28

77J2

W(100)

77J3

W(111)

400... FEM 700 500 FEM

II

W(112)

600

II

W(211)

74B3 W(110)

W(110) 77M3 W(112) 77R W(100) 79R

FEM

600 80...200 Diode 20 FEM

II

0.25 -0.3 -0.1 0.2 -0.7 -0.5 -0.80 -0.52 0.15 -0.75

II

III II II

[Ref. p 4.2-118

sat. Φ Cu(111)

strained Cu(111) film Cu(111) film * plus annealing (T not given) to spread the Cu over the tip face.

sat. Φ Cu(100)

2.0·1015 cm-2 LEED, AES, TDS 4.8·1015 cm-2 0.8·1015 cm-2 LEED, AES, TDS 1.8·1015 cm-2 0.5·1015 cm-2* µ0 = 0.5 D 1.2·1015 cm-2* * assignment of coverage by [77 R] θ1 2 θ1 3.5 θ1 8 θ1 Fig. 36

+0.4 -0.3 +0.2 +0.3 -0.9 -0.5 -0.7

θ1 4θ1 7θ1 1.5θ1 3.5θ1 5 θ1

+0.42 -0.32

0.5·1015 cm-2 1.2·1015 cm-2

W(310) similar to (112)

25·1014 atoms/cm2 Fig. 37 Fig. 38


Ref. p. 4.2-118] Ref.

Cu / Substrate 78B2 W(100)

81S


Method

Type

∆Φ [eV] at θ1


78

FEM

II

Fig. 39

300... FEM 930

II

+0.16 -0.24 +0.20 f(θ1,T)

W(100) W(110) W(211) W(111) 85K6 W(110) 86C2 W(110)

800 300*

Diode Kelvin

III

87C

W(110)

300

Kelvin

III

87A2 W(100)

300

SE edge (E)

II

800 98Y2 ZnO(0001) Zn

IV SE edge (UPS)

IV

T [K]

Method

Type

300

SE edge (E)

-0.65 -0.72 -0.67 -0.72 -0.35 0.25 -0.89 -0.45 0 -0.15 +0.42

4.2-79

discussion of existing data Figs. 40 and 41

1 ML saturation θ = 1* θ=4 θ = 4** 0.5 2.0 0.5 1.0 θCu = 0.05 θCu = 1.3

µ0 = 0.7 D at 800 K LEED *annealed to 850 K LEED, AES, TDS *from AES **annealed to 850 K LEED, AES, TDS surface alloy formation reinterpretation of Bauer XPS, ISS

Table 98. Silver (Ag) Figs. 42...47 Ref. 91T3

Ag / Substrate Cu(110)

-0.1 -0.05 -0.40 -0.35 -0.22 -0.53

120

92M2 Cu(111)

300

94N

Cu(111)

95W 94H

Cu(111) Ir(100)

∆Φ [eV] at θ1

300

SE edge (E) Diode

IV III

78*

ARUPS FEM

III III

-0.35 -0.33 -0.45 -0.3 -1.05+ -1.20¹

θAg = 0.5 θAg = 1.0 θAg = 10 θAg = 0.3 θAg = 1.0 θAg = 10 min saturation 1 ML 1 ML 3...4 ML

Comments, interpretation AES, LEED

ML determination: Auger and ∆ĭ * spreaded at 442 K7 ML 0.7 ML 3 ML 0.1 ML 0.1 ML 0.1 ML

AES AES also measured at 573, 863 K only low coverages; diluted disordered layer see Fig. 42

4.2-80


[Ref. p 4.2-118

Type

∆Φ [eV] at θ1


SE edge (UPS) SE edge (UPS) 310... SE edge 600 (E)

III

-0.50

1 ML

AES, UPS

III

-0.54

1 ML

III

-1.2 -1.5

1 ML 2.5 ML

82D2 Re*

300?

FEM

III

-0.55

83A2 Re-tip

350... FEM 600

IV

-0.72

— — — — — —

AES, LEED, TDS ML from TDS Stranski-Krastanov-growth: φ of the rough surface at θAg = 2 smaller than for the epitaxial ML. * The central plane of the tip is Re( 10 1 0 ). The final work function is 4.32 eV. average ∆Φ µ0 = (1.5±0.5) D *jump of Φ during spreading of Ag onto the indicated area

1 ML 2 ML 4 ML at 5 ML

TDS, XPS

θAg = 0.6

Ref. 83S3

Ag / Substrate Pt(100) Pt(997)

85P3

Pt(111)

T [K]

Method

98S4

Re(0001)

300

Kelvin

III

88P

Ru(0001) 300

Diode

ΙΙΙ

-0.80* -1.00* -0.48* -0.78* -0.70* -0.55* -1.00* -0.90* -0.60 -0.75 -0.70 −0.16

95N3 Ru(0001) 350

Kelvin

ΙΙΙ

−0.33

—

0.0±0.15 2 ML

Re( 10 1 0 ) Re( 10 1 1 ) Re( 10 2 0 )

Re( 11 2 2 )

95V

V(100)

70S

W(100)

250... SE edge 900 920 FEM

72J

W(100)

?

FEM

II

77K2 W(100) W(110)

300 300

Diode Diode

III IV

W(111)

300

Diode

IV

W(110)

300 500 300 600 800

Diode Diode Diode Diode Diode

IV

77B

W(100)

IV

-0.55 -0.35 +0.15 -0.35 -0.35 -0.87 -0.72 -0.45 -0.35 -0.75 -0.62 -0.30 -0.30 -0.25

AES; layer by layer growth; Ag(111); change in slope = transition to next layer ∆Φ measurements during Ag evaporation. At higher T change in slope of ∆Φ. AES, UPS layer growth for 2 ML

0.7 ML 1.5 ML

— — — — — 2 ML >3 ML 2.5 ML 2.5 ML >4 ML

1×1015 Ag atoms cm-2 5×1015 Ag atoms cm-2 Fig. 43

LEED, AES, TDS Fig. 44


Ref. p. 4.2-118]


4.2-81

Ag / Substrate W(110) W(100) W(211) W(111)

T [K]

Method

Type

∆Φ [eV] at θ1


300 300 300 300

FEM

III III III II

various changes at annealing temperatures up to 900 K

W(110)

var.

Diode

IV

-0.8 -0.15 -0.7 +0.1 -0.3 see Fig. 45

84K2 W(211)

300 900 800 800 90 300 700 300

Diode

IV

Diode Diode Kelvin

— — III

Ref. 79S2

79K

85K6 W(110) W(211) 93Z W(110)

95D

W(110)

FEM

-0.65 -0.35 — — -0.80

— — 1 ML

see Fig. 47

µ0 = 1 D for surface gas µ0 = 0.1 D for strained Ag(111) µ0 = 0.05 D for unstrained Ag(111) 1.2×1015 atoms cm-2, AES 3 ×1015 atoms cm-2 µ0 = 0.6 D at 800 K µ0 = 0.2 D at 800 K Fig. 46

quartz crystal microbalance at Φsat: 5.25±0.25×1015 Ag atoms cm-2 θ [ML] is given relative to the number of substrate atoms which is taken as 1.0×1015 Ir atoms cm-2

Table 99. Gold (Au) Figs. 48...52 Ref. 95W 94H

Au / Substrate Cu(111) Ir(100)

83S3

Pt(100) Pt(111) Pt(997)


T [K]

Method

Type

∆Φ [eV] at θ1

78*

ARUPS FEM

I —

+0.6 0.10+ -0.20+ ±0.1

4 ML 1 ML 2 ML 1...5 ML


IV III

-0.45 -0.4 -0.3

1 ML 3 ML 1 ML

III

-0.25

1 ML


quartz crystal microbalance DWĭsat: 2.25±0.18î1015 Au atoms cm-2 ɴ (ML) is given relative to the number of substrate atoms, which is taken as 1.0î1015 Ir atoms cm-2 * spreading temperature 445...520K + average value depending on spreading temperature AES, UPS

4.2-82 Ref. 77C

77C

4.2 Electron work function of metals and semiconductors Au / T [K] Substrate Re tip with 600* [11 2 0] orientation

Method

Type

∆Φ [eV] at θ1

FEM

II

0.35 0.20

θ = 1+

—

0.20

θ4

state 2, Au(111)

—

0

θ < 2.5

—

0.20

33 qualitatively similar to W(100) *measurements are performed also ș = 0.6 at higher temperatures ș=2 AES, ELS θ1 2θ1 6θ1 0.7 ML 2 ML 4 ML —

AES nearly no difference between 300 and 930 K µ0 = 0.7 D at 800 K µ0 = -0.3 D at 800 K

see Fig. 52

4.2.11 3d transition metals Table 100. Titanium (Ti) Ref.

Ti / Substrate 74B2 W

T [K]

Method

Type

FEM

∆Φ [eV] at θ1


-0.6

Table 101. Vanadium (V) Ref. 92Z3

V/ T [K] Substrate TiO2(110)


4.2-83

Method

Type

∆Φ [eV] at θ1

SE edge (UPS)

IV

-0.3 +0.25 +0.5


LEED, UPS, XPS min ML thicker layer

4.2-84


[Ref. p 4.2-118

Table 102. Chromium (Cr) Ref. 93P

Cr / T [K] Substrate TiO2(110)

89B3 W(110) W(100)

100 1100

Method

Type

∆Φ [eV] at θ1


SE edge (He+) SE edge (SE)

IV

-1.5 min 1.8 Å -0.9 >6Å -1.3 ~0.5 ML -0.5 1 ML

LEED, XPS, LEIS

III

Fig. 53 pseudomorphic ML on both substrates at 100 K

Table 103. Iron (Fe) T [K]

Method

Type

∆Φ [eV] at θ1

82S6

Fe / Substrate Ag(100)

300

ARUPS

II

90T

Mo(110)

300

Diode

IV

85K4 MoS2

300

Diode

III

0.0 +0.75 +0.2 -0.55 -0.17 -0.45 -1.0

0.5 ML 1.0 ML 3 ML min,θFe = 2 θFe > 4 θ1 2θ1

88H3 Re(0001)

980

Diode

III

Diode SE edge (He+) FEM

III IV

-0.21 -0.26 -0.58 -1.3 -1.0 -0.6 -0.4

1 ML 2 ML 5 ML min, 1 Å >4Å

Kelvin

III (IV)

see Fig. 54

see Fig. 55 see Fig. 56.

Ref.

99K3 Ru(0001) 300 93P TiO2(110) 78J2

W(001)

97N2 W(110)

97N3 W(110) 83G2 W(110) W(112) W(111) W(001) 99K W(111)

300 600 1000

IV

90 300 300 + 600 90 ≥ 300 300

Kelvin

IV

Diode

IV

300

Diode

II

+0.03 -0.22 -0.1

Comments, interpretation UPS Stranski-Krastanov growth mode AES, LEED, TDS Phase I: island formation Phase II: reaction with substrate LEED, AES

LEED, AES LEED, XPS, LEIS at 12×1014 atoms cm-2 at 24×1014 atoms cm-2 also deposited at 600 and 1000 K without larger changes extension of Ref. [97N3]

AES kinks 1 ML = 1.4×1015 atoms cm-2 µ0 = 1.3 D (W(110)) LEED, AES, TDS 1 ML 28 ML


Ref. p. 4.2-118]


4.2-85

Table 104. Cobalt (Co) Ref. 95W 90T

91F 96S

Co / Substrate Cu(111) Mo(110)

Pt(110) -(1 × 2) W(110) W(100) W(111)

89J

W(110) W(100)

T [K]

Method

Type

∆Φ [eV] at θ1

300

ARUPS Diode

I IV

+0.15 -0.35 0.0 +0.1 +0.2

SE edge (UPS)

III

-0.8

IV IV III II IV IV IV IV

-1.5 -0.45 -1.2 -0.55 -0.55 -0.55 see Fig. 57

µ0 = 4.6 D


300 580 300 580 300 580 1100

SE edge (E)


7 ML min, θCo = 0.8 AES, LEED, TDS θCo = 1.3 θCo = 1.5 θCo = 3 1 ML LEED, AES

µ0 = 3.3 D µ0 = 1.3 D strained pseudomorphic ML

Table 105. Nickel (Ni) Ref. 90T

Ni / Substrate Mo(110)

85P2

MoS2

T [K]

Method

Type

∆Φ [eV] at θ1

300

Diode

IV

-0.35 0.0 +0.23 +0.20

IV

-0.25 -0.05 -0.16 >0 -0.4 -0.3 -0.24 -0.12 -0.75

80

300 450 88B3 Ru(0001) 100* 99K3 Ru(0001) 300

SE edge (UPS) Diode

IV

84K3 W(110)

300 1100

Diode

IV

85K6 W(110) W(211) 94B W(110) W(100)

800 800

Diode Diode

W(111) W(112) 94W4 W(110)


IV

IV II

Kelvin

— — IV

-1.05 +0.35 -0.4 10 ML

Kelvin

IV

-0.25 +0.65

0.3 ML 3.5 ML

300

Kelvin

IV

-0.25 +0.65

0.2 ML > 3 ML

300

Kelvin

-0.18 0.0 +0.55 +0.60

θ1 1.5 θ1 2.5 θ1 3 θ1

I

LEED, AES, XPS

4.2-88 Ref. 98S2

4.2 Electron work function of metals and semiconductors Pd / Substrate Mo(211)

T [K]

Method



Diode

I

LEED, AES

100

I

300

I

800

I

80W2 Nb(110) (foil)

IV

0.2 0.52 0.07 0.7 0.08 0.48 -0.2 +0.65

1 ML* *from kinks in AES sat. at 3 ML µ0 = 0.3 D 1 ML* sat. >4 ML 1 ML* sat. >4 ML 1 ML UPS

0/

Ru(0001) 300 film on Mo(110) 99K3 Ru(0001) 300

SE edge (UPS) Diode

IV

-0.03 +0.12

~0.5 ML ~3 ML

Diode

I

86N

Si(111)(7 × 7)

SE edge

(I)

+0.04 +0.15 +0.12 +0.32

1 ML 3 ML 1 ML 2.5 ML

89R

Ta(110)

80S4

W(110)

300 830

Diode

IV IV

-0.35 0.0 +0.70 -0.45 -0.60

θPd = 0.75 θPd = 1.1 θPd = 0.5 1 ML 1 ML

81P

W(100)

300

Diode

II

0.3 0.17 0.5

85K6 W(110)

800

90Z

W(110)

900*

Kelvin

IV

-0.54 -0.38

98F

W(011)

110

Diode

IV

99K

W(111)

800 300

Diode

III II

-0.85 -0.40 -0.55 +0.25 +0.17 +0.7

88P

300

[Ref. p 4.2-118

IV

Fig. 3 2-dim. pseudomorphic islands later pseudomorphic Pd(111) LEED, AES θ = 1: 7.8·1014 atoms cm-2 (quartz oscillator) UPS

second layer metastable T > 700 K 3-dim. cluster see Fig. 58 1 ML AES, ML from kinks in AES 2 ML Also annealed to 460, 510, 620, 4 ML and 1020 K resulting in gradual changes. Behavior similar to other fcc metals on W(100); see Fig. 59 value from θ ĺ µ0 = 0.74 D 1 ML** *annealed to 900 K 1.8 ML*** **from TDS ***presumably cluster formation min,θ=0.35 LEED, metastable metal clusters θ = 1.2 1 ML LEED, AES, TDS 1 ML 2 ML 8 ML


Ref. p. 4.2-118]


4.2-89

4.2.13 5d transition metals Table 111. Lanthanum (La) Ref. 82L2

La / Substrate Mo(112)

T [K]

Method

Type

∆Φ [eV] at θ1


Diode

IV

discussion of structures by LEED

77G2 W(100)

300

Diode

IV

77V

W(110)

300

Diode

IV

Mo(110)

300

Diode

IV

FN (FEM)

III

-1.8 -1.4 -1.8 -1.5 -2.5 -1.8 -1.8 -1.5 -2.8

Type

∆Φ [eV] at θ1

IV

-1.3** -0.5**

91B

W(110)*

at 0.6 ML at 1.2 ML at 0.5 ML at 0.8 ML 4·1014 cm-2 8·1014 cm-2 6·1014 cm-2 8·1014 cm-2 at 1 ML

at higher T up to 1350 K the minimum is more shallow on 0.3 eV LEED, AES; µ0 = 4.5 D LEED, AES; µ0 = 3.9 D also for (111) and (112) plans

Table 112. Hafnium (Hf) Ref. 94S

Hf / T [K] Method Substrate W tip with 300* FEM (111) center

θ1 6θ1

Comments, interpretation *measured at 300 K after spreading of Hf at 1300 K **average value

Table 113. Tantalum (Ta) Ref. 79R 90A

77K

Ta / Substrate W(100) Si(111) -(7 × 7)

T [K]

Method

Type

∆Φ [eV] at θ1

77 300

FEM SE edge (UPS)

III

-0.65 +0.22 +0.2 -0.45

W(110)

0.5 ML at 5 ML at 3 ML at 30 ML

FEM


silicide silicide Nb value LEED, UPS µ0 = 0.5 D

Table 114. Tungsten (W) Ref.

W/ Substrate 86A Si(111) -(7 × 7) 90A Si(111) -(7 × 7) 75B2 W(110) 76B 77K


T [K]

Method

300

SE edge (UPS) SE edge (UPS) Kelvin

300

FEM

Type

∆Φ [eV] at θ1


+0.28

UPS, LEED sharp interface at 300 K LEED, UPS reaches W value abrupt interface This change of Φ decreases with decreasing terrace width. µ0 = 0.2 D

+0.36

at 3 Å thickness at 2 ML

-0.6

θW = 0.5

4.2-90


[Ref. p 4.2-118

Table 115. Rhenium (Re) Ref. 96S6 77K

Re / Substrate Si(111)(7 × 7) W(110)

T [K]

Method

400

Type

∆Φ [eV] at θ1


I

+0.6

UPS, XPS sharp interface, µ0 = 0.11(5) D µ0 = 0.1 D


FEM

Table 116. Iridium (Ir) Ref.

Ir / Substrate 79R W(100) 77K W(110) 91K2 W(110)

T [K]

Method

Type

∆Φ [eV] at θ1

77

I

0.8

var.

FEM FEM Diode

350*

Diode

IV

450* 77K 96K

W(110) W(110)

FEM 1100... Diode 1500

-0.55 -0.2** -0.3 -0.15**

0.5 ML

0.25 ML 0.75 ML 0.35 ML 1 ML

µ0 = 0.0 D with LEED and ∆Φ transition 1 D – 2 D islands *also annealed at 1250 K and 1650 K **no saturation

>-0.1

µ0 = 0.0 D LEED

Table 117. Platinum (Pt) T [K]

Method

Type

∆Φ [eV] at θ1


300, 1300 350

Diode

I

0.78

LEED, AES

PE-Kante IV

77K W(110) 91K2 W(110)

var.

FEM Diode

94 K

W(110)

400

Diode

IV

96K

W(110)

880... 1240

Diode

III

Ref. 98S2

Pt / Substrate Mo(211)

87A

Re(0001)

-0.1 +0.6

ML 1 ML

Pt grows epitaxially µ0 = 0.0 D LEED and ∆Φ indicate transition from 1D to 2D islands

-0.4 +0.5 >-0.1

ML 2 ML up to 1.5 ML

LEED


Ref. p. 4.2-118]


4.2-91

4.2.14 Rare-earth metals Table 118. Neodymium (Nd) Ref.

Nd / Substrate 87N2 Cu(100)

88N5 Cu(111)

92S2

Mo(112)

92S5

87G

T [K]

Method

Type

∆Φ [eV] at θ1

300

?

III

-2.0

1.3 ML

III III III

-1.7 -1.4 -2.0 -1.7 -1.7 -1.6 -1.2 -1.3 -1.4 -1.9 -1.25 -1.45

1.3 ML 1.3 ML at 2.5 θ1 at θ1 at 2.5 θ1 0.5 ML 1.2 ML 1.2 ML 1.2 ML 4·1014 cm-2 7.5·1014 cm-2 12·1014 cm-2 0.5 LEED 1.0

550 800 300 900*

SE edge (UPS) Diode

IV

Mo(110)

300 300 600 900 300

(Diode)

IV

W(112)

300

Diode

IV

-1.8 -1.5

Comments, interpretation θ by kinks in Auger different sub ML phases Frank von der Marwe growth alloy formation alloy formation LEED, AES, ARUPS *annealed to

Table 119. Samarium (Sm) T [K]

Method

Type

∆Φ [eV] at θ1

89J3

Sm / Substrate Cu(111)

300

Diode

III

87S2

Mo(110)

300

Diode

IV*

88F 95R

Pd(100) Ru(0001) 500

Diode SE edge (UPS)

III IV

-1.9 -1.9 -2.2 -2.4 -1.5 -2.4 -2.2 -2.4 -2.2 -2.4

Ref.

θSm = 0.4 θSm = 1.0 θSm = 2.0 0.2 ML 1.0 ML 3 ML ? 0.3 ML 0.8 ML 3.0 ML

Comments, interpretation AES, LEED

*special: local maximum at 1 ML

valence charge = 2.75 at surfaces UPS

Table 120. Gadolinium (Gd) Ref. 97L

Gd / Substrate Mo(112)

T [K]

Method

Type

∆Φ [eV] at θ1

300

SE edge (E)

IV

-1.4 -0.8 -1.5 -1.2 -2.6

1100 76B5 W tip


FEM

1 ML 2 ML 1 ML 2 ML ?

Comments, interpretation LEED

specific discussion for W(111), (110), (121)

4.2-92


Ref.

Gd / Substrate 86K2 W(110)

87G

W(112)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode

IV

0.33 ML 0.66 ML

Auger, LEED, TDS

1200 300

Diode

IV

-2.5 -1.8 § -1.6 -1.4

0.5 ML 1.0 ML

linear chains of adatom for θ < 1 LEED, ordered structure

-2.1 -1.5 -1.3 -0.8 -1.7 -1.5 -1.7

5·1014 cm-2 7·1014 cm-2 5·1014 cm-2 Typ IV ĺ,,,DWKLJK7 8·1014 cm-2 4.5·1014 atoms cm-2 7.5·1014 atoms cm-2 9 ·1014 atoms cm-2

88G2 W(111) 91M2 W(100) 99S

[Ref. p 4.2-118

Diode 300 1200

Diode

IV

FEM

IV

T [K]

Method

Type

∆Φ [eV] at θ1

300

CPD

IV

300 up to 1050 300

Diode

IV

-1.9 -1.45 -1.55 -2.9 -2.7

4·1014 cm-3 8·1014 cm-3 13·1014 cm-3 0.5 ML 0.7 ML

Diode

IV

-2.8 -2.0 -1.7 -1.5

0.6 ML LEED, AES, TDS 1.0 ML 5·1014 cm-3 Typ IV ĺ,,,DW. 7·1014 cm-3

IV

-1.4 -0.9

5·1014 cm-3 Typ IV ĺ,,,DWKLJK7 8·1014 cm-3

Type

∆Φ [eV] at θ1

W(111)

Table 121. Terbium () Ref. 92S5

Tb / Substrate Mo(110)

85K

W(211)

86K2 W(110) 88G2 W(111)

91M2 W(100)

300 Ļ 1200 300 Ļ 1200

Diode

Diode

Comments, interpretation AES, LEED quartz microbalance Fig. 4 Auger, LEED, TDS electropositive material

Table 122. Dysprosium (Dy) Ref. 91P4

Dy / Substrate Mo(110)

T [K]

Method

300

Kelvin

-1.9 -1.2 -1.4

4·1014 atoms cm-2 7·1014 atoms cm-2 >12·1014 atoms cm-2

Comments, interpretation LEED, AES also at 850 K

Table 123. Holmium (Ho) Ref. 89G

Ho / Substrate W(112)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode?

IV

-1.9 -1.3

LEED

0.5 ML 1.1 ML


Ref. p. 4.2-118]


4.2-93

Table 124. Erbium (Er) Ref. 92S5

95K 95S6

Er / Substrate Mo(110)

T [K]

Method

Type

∆Φ [eV] at θ1

300

CPD

IV

III

4·1014 cm-2 7·1014 cm-2 12·1014 cm-2 5 Å Er

µ0 = 1.9 D

Kelvin

-1.85 -1.35 -1.45 -1.6

Kelvin

III

-1.1 -1.7

1 ML 9 ML

XPS µ0 = 1.1(5) D intermixing at higher T

T [K]

Method

Type

∆Φ [eV] at θ1

300

Diode

IV

-1.7 -1.55 -2.0

Method

Type

∆Φ [eV] at θ1


Diode

IV

-2.4 -1.8

0.5 ML 1 ML

AES, LEED (1 ML: 0.55 substrate units)

Diode

IV

0.6 ML 1 ML 0.6

AES, LEED

III

-1.75 -1.65 -0.6

300 αSiC(0001) Si(100) 230


Table 125. Thulium (Tm) Ref. 92N

Tm / Substrate Mo(110)


0.8 ML ML 2.5 ML

Table 126. Yterbium (Yb) Ref.

Yb / Substrate Mo(110)

87S4 also in 87S3 97K2 Si(111)

T [K]

300 800

Si forms a step layer

4.2.15 Group IIa metals Table 127. Beryllium (Be) T [K]

Method

Type

∆Φ [eV] at θ1

79Z

Be / Substrate W(110)

300*

Diode

IV

91D

W(100) W(112)

300* 300

FEM

I II

-0.75 -0.50 +0.28 +0.4 -0.6 0.0

Ref.


at θ1 at 2 θ1 saturation 1 ML saturation

Comments, interpretation *measured also at higher T

4.2-94


[Ref. p 4.2-118

Table 128. Strontium (Sr) Ref. 77V

Sr / Substrate Mo(110)

T [K]

Method

Type

∆Φ [eV] at θ1


300

Diode

IV

W(110)

300

Diode

IV

-2.6 -2.0 -3.3

0.25 ML 1.0 ML 0.3 ML

-2.1

1.0 ML

IV

-2.1 -1.8

IV

-2.9 -1.9

4·1014 cm-2 7·1014 cm-2 = ML 0.3 1.0

LEED, AES µ0 = 5.1 D LEED, AES µ0 = 5.1 D several ordered structures µ0 = 6.6 D LEED, structures in sub-ML regime discussed

79M

Mo(112)

73K

W(110)

Diode

77, 300 FEM

Table 129. Barium (Ba) Ref.

T [K]

Method

Type

∆Φ [eV] at θ1

300

Kelvin

IV

-2.3 ML

(θmin = 2.3 eV) (θsat = 2.7 eV) in Russian language

96W 98C

Si(100) -(2 × 1) Si(111)(7 × 7) Si(100) -(2 × 1)

99K2 Si(100) -(2 × 1) 69F W(100)

IV

SE edge IV (E) (SE edge)

1140 300

SE edge (UPS) ?

-2.1

ML: 6.8·1014 atoms cm-2

LEED


Ref. p. 4.2-118] Ref.

Ba / Substrate 74G2 W(110)


Method

300

?

Type

∆Φ [eV] at θ1


IV

-3.5 -2.6

2.35·1014 cm-2 5.5·1014 cm-2

FEM

IV

-3.6 -2.7

2.4·1014 cm-2 5.5·1014 cm-2

77G3 W(110)

Diode

IV

92L

Diode

-3.1 min -2.5 ML -2.1 -1.7 -2.7 -2.4

2.2·1014 cm-2 5.5·1014 cm-2 1 ML >2 ML 4·1014 cm-2 6·1014 cm-2

75G

W(110)

300

W(100)

73M2 W(112)

77

Diode

IV

4.2-95

LEED, linear branches in the ĳ FXUYH Φmin = 2.0 eV Φsat = 2.5 eV Φmin = 2.0 eV Φmax = 2.9 eV interaction with co-adsorbed Si µ0 = 13.5 D, LEED LEED, IPES LEED

4.2.16 Group IIIa metals Table 130. Aluminum (Al) Method

Type

∆Φ [eV] at θ1

SE edge (E)

III

91K3 Mo(110)

Diode

IV

90D

1 ML 2 ML 4 ML θ1 >θ1 2 ML

Ref. 92P

Al / Substrate Ag(111)

T [K]

Kelvin

III

98S

Pd(111) on mica Pd(100) 325

-0.2 -0.3 -0.38 -0.47 -0.44 -1.3

Kelvin

III

-1.3

2 ML

96P2

Re(10 1 0) 300

Kelvin

III

-1.2

1.3 ML

96K4 Ru(0001) 300

Kelvin

III

84P3

PYS

III

-0.8 -1.2 -0.45

1 ML 2.5 ML 1 ML

74M2 W

FEM

IV

-0.4* -0.3*

θ1 θ2

74M8 W tip

FEM

IV

-0.2 -0.15

at 2 θ1 at 3 θ1

Si(111) -(2 × 1)


300

Comments, interpretation LEED, AES

Stranski-Krastanov growth mode for θ > 2 ML; µ0 = 0.29 D At low θAl surface disordered. Alloying for T at 750...950 K. AES, LEED, TDS dips in ∆Φ at specific LEED structures STM LEED: (2 × 1) ĺ¥3 × ¥ ĺ × 1) AES Problem: 0xygen growth with time and number of Al-doses. *average W(001) and W(111) show complicated dependencies

4.2-96


[Ref. p 4.2-118

Table 131. Gallium (Ga) Ref.

Ga / Substrate 85K5 W(100)

T [K]

Method Type

∆Φ [eV] at θ1

700...1600 FEM

Comments, interpretation nearly constant at 4.5 eV (?)

Table 132. Indium (In) Ref. 96R

In / T [K] Substrate Au(111) 300

Method

Type

∆Φ [eV] at θ1


SE edge (E)

III*

-0.7

LEED, AES A disordered AuIn2 compound is formed. *from Ref. [ ]


4.2.17 Group IVa elements For Carbon (C) see Table 6 and 7. Table 133. Silicon (Si) Si / Substrate 71C3 W(100)

T [K]

Method

Type

∆Φ [eV] at θ1

295

FEM

II

+0.55 +0.2

73B3 W(110)

300

Diode

III

Ref.

θ1 5θ1 LEED

Table 134. Germanium (Ge) T [K] Method

Type

∆Φ [eV] at θ1


300

IV

n- and p-type

III I

-1.1 -1.0 -0.5 -0.45 -0.10 -0.08 -0.3 +0.65

Mo average 900* FEM

I

+0.85

W

I

+0.28

Ref.

Ge / Substrate 85K2 InP(110) 92B

Nb tip 300 (110) center 92S4 Si(100) -(2 × 1) 73B3 W(110) 300 73Z W average 900*

83Z

500

Kelvin

FEM IV probe hole Diode IV Diode FEM

FEM

0.4 ML >2 ML θGe = 1 θGe = 2 1 ML 3 ML >2 ML

LEED, AES LEED *spreading temperature final value: Φ = 5.2 ± 0.1 *spreading temperature final value: Φ = 5.2 ± 0.1


Ref. p. 4.2-118]


4.2-97

Table 135. Tin (Sn) T [K]

Method

Type

∆Φ [eV] at θ1


91Z

Sn / Substrate Au(111)

300

SE edge

III

-0.9

1 ML

88T

Mo(110)

350

Diode

IV

-0.2 -0.9

0.2ML 0/ Fig. 7

300

PYS

+0.5

1 ML

AES AuSn forms which grows laterally as a double layer AES, LEED, TDS Stranski-Krastanov growth after 2 ML alloying at 600 K, repulsive interaction in ML. AES, LEED

300

PYS

III

-0.25

2 ML

Method

Type

∆Φ [eV] at θ1


SE edge (E)

III

-0.48

2 ML

LEED

III

-0.6 -0.45 -0.4 -0.36 -0.78 -1.5

1 ML 1 ML 0.7 1.0 2.5 1 ML

LEED, AES

+0.15 -0.3 -0.13 0 -0.2 -0.1 -0.45 -0.40 -0.15 0.0 -0.17 -0.13

3·1014 atoms cm-2 22·1014 atoms cm-2 3·1014 atoms cm-2 Â14 atoms cm-2 3·1014 atoms cm-2 10·1014 atoms cm-2 5·1014 atoms cm-2 8·1014 atoms cm-2 6·1014 atoms cm-2 surface reconstruction at Â14 atoms cm-2 800 K 3·1014 atoms cm-2 *deposition temperature 10·1014 atoms cm-2

Ref.

85T4

Si(111) -(2 × 1) 87A3 Si(100) -(2 × 1)

LEED, AES, PYS layer growth till 2 ML, then Stranski-Krastanov growth. Between θGe = 0.5...1.0 ML a (2 × 1) ĺ × 1) structure transition occurs.

Table 136. Lead (Pb) Ref.

Pb / Substrate Ag(111)

T [K]

300

88T

Cu(111) Cu(100) Mo(110)

300

Diode

IV

92M

Pt(111)

300

Kelvin

I

77J

W(211)

526

FEM

II

W(100)

463

FEM

IV

843

FEM

IV

W(110)

290

FEM

IV

W(100)

300*

FEM

IV

80T 84A

78J2

800*


IV

LEED, AES

After ML formation intermixed region occurs at the Pb/Pt interface

4.2-98


[Ref. p 4.2-118

4.2.18 Group Va elements Table 137. Antimon (Sb) Ref.

Sb / Substrate 93M2 Au(111) 92E

T [K]

Method

300

GaAs(110) cleaved

Type

∆Φ [eV] at θ1

IV

-0.8 -0.7


θ1 >2θ1

Kelvin

p-type

300

I

+0.5

1 ML

n-type

300

I

+0.6

0.4 ML

p-type

90

I

n-type

90

I

+0.75 +0.5 +0.66 +0.6 +0.7

5 ML 1 ML 10ML 1 ML 4 ML

control by electric field induced Raman spectroscopy from which band bending is derived no dipole contribution, only band bending no dipole contribution , only band bending 0.55 dipole contribution 0.25 dipole contribution 0.3 dipole contribution 0.3 dipole contribution 0.45 dipole contribution

Table 138. Bismuth (Bi) Ref. 90P

Bi / Substrate Au(111)

T [K]

82C4 Bi(0001)

Method

Type

∆Φ [eV] at θ1

SE edge (E)

III

-1.5

SE edge (E)

-1.0

86P

Pt(111)

640

IV

93G

Pt(110) (1 × 2)

150

III

-2.05 -1.98 -1.2


1 ML

LEED, AES Bi forms monolayer followed of Bi-Au compound at the interface 3 ML AES linear decrease of ∆Φ ĺ subsurface O 0.75 ML* *adsorbate 1 ML* LEED, AES, TDS


Ref. p. 4.2-118]


4.2.19 Other elements Table 139. Mercury (Hg) Ref. 68S

Hg / T [K] Method Substrate Mo tip with FEM (110) center

90S3

Ni(111)

68S 78J3

W tip with (110) center W(100) 295

92Z4

W(110)

Type

∆Φ [eV] at θ1

II

+0.4 +0.4 +0.1 -0.37

θHg = 0.2 θHg = 0.6 θHg = 1.8 12 L

+0.4 +0.3 +0.12(2) 0.0 -0.75 -0.65

θHg = 0.3 θHg = 0.75 θHg = 0.75 LEED, AES θHg = 1.0 4 ML LEED, TDS > 5 ML

SE edge (UPS) FEM

III II

Diode

II

Kelvin

IV


LEED, UPS

Table 140. Uranium (U) T [K]

Method

Type

∆Φ [eV] at θ1


68C

U/ Substrate W

300*

FEM

IV

*annealed to T > 1040 K

71C

W(100)

300*

W(110)

FEM IV probe hole IV

W(111)

IV

W(112)

IV

W(113)

IV

W(116)

IV

-1.3 -1.1 -1.0 -0.75 -1.20 -1.15 -1.25 -0.77 -1.75 -1.15 -1.1 -0.9 -0.95 -0.7

Ref.


min ML θ1 6θ1 θ1 2θ1 θ1 6θ1 θ1 3θ1 θ1 3θ1 θ1 2θ1

*deposition temperature

4.2-99

Figures for 4.2 0.5

Pd(110)Xe

Ni(110)D 2 Work − function change ∆Φ [eV]

Work − function change ∆Φ [eV]

0 − 0.2

a

b

− 0.4 c − 0.6

0.4

0.3

0.2

0.1

−0.8 2

1

3 5 4 Xe exposure L [Langmuir]

6

Fig. 2. Xe adsorption on Pd(110) at 77 K. (a) work-function change, (b) Xe Auger peak-to-peak amplitude, (c) Xe overlayer LEED beam intensity vs. Xe exposure. From [71P]. 0.8

4

0.4 β2 β1

D2 pressure p [arb.units]


0.5

α

0.6 0.8 1.0 1.2 D2 coverage θ [ML]

1.4

1.6

0.20

6

0.2

0.4

Ni(111)H

0.6

0.3

0.2

Fig. 3. Work-function change ∆Φ vs. coverage θ for D2 adsorption on Ni(110). T = 175 K, θ = 1 ML Ł·1015 atoms cm-2. From [87J]

8

Ni(110)D 2

0.7

0

7

2


0

0.15

0.10

0.05

0.1 0 190

230

270 310 Temperature T [K]

350

0 390

Fig. 4. Thermal desorption spectrum and work-function change for desorption of D2 from Ni(110). Initial coverage = 1.5 monolayer; adsorption temperature = 175 K; heating rate 0.5 K s-1.From [87J].

0

0.2

0.4 0.6 H coverage θ [ML]

0.8

1.0

Fig. 5. Work-function change caused by H2 adsorption at 150 K on Ni(111) as a function of the absolute coverage θ. From [79C2].


Ref. p. 4.2-118]

4.2 Electron work function of metals and semiconductors 0.24

0.25

Pd(100)H

0.20



Pd(100)H

0.15

0.10

0.05

0.5

1.0 H coverage θ [ML]

2.0

1.5

Fig. 6. Hydrogen adsorption on Pd(100). Calculated coverage dependence of work-function change (filled circles) and experimental results (crosses) from Ref. [80B4]. The work functions were calculated for ordered structures where the hydrogen occupies surface hollow sites up to θ = 1 followed by an occupation of subsurface (Oh) sites by the additional hydrogen atoms. From [94W], [94W2].

0.12 0.08

0.2

0.4

1.2

1.0 0.6 0.8 H coverage θ [ML]

1.4

Fig. 7: Work-function change for H on Pd(100) with coverage θ. From [80B4].

1.0

Pt(100)H2 Tad = 100K

a1

a2

b

0

− 0.1


0.2 0.1

W :H 2

0.8

H 2 desorption rate


0.16

0

0.4

− 0.2

0.20

0.04

0

0.3

4.2-101

W(100)

0.6 W(211) 0.4 0.2 W(111)

0 − 0.2

W(110)

− 0.4 − 0.6

100

300 200 Temperature T [K]

400

500

Fig. 8. Thermal desorption spectra (upper curve) and work-function change (lower curve) for 5 L H2 adsorbed on the (1 × 1)-like structure of Pt(100) at 100 K. The most prominent peaks are labeled a1, a2, and b, respectively. No hydrogen desorption below 100 K could be detected. A work-function change of 0 eV corresponds to the work function of the clean hexrot surface (Φ = 5.75 eV). From [91P3].


0

0.2

0.4 0.6 H 2 coverage θ [ML]

0.8

1.0

Fig. 9. Work-function change vs. coverage for H2 on W(110), W(100), W(211), and W(111). From [74B].

4.2-102


[Ref. p 4.2-118

5.3

0

5.3

−0.1

5.2

−0.1

5.2

− 0.2

5.1

− 0.2

5.1

− 0.3

5.0

− 0.3

5.0

− 0.4

4.9

− 0.4

4.9

0

− 0.5

0

5

10

a

15 20 25 H 2 exposure L [L]

30

35

40

− 0.5 0

4.8

40

b

80 120 H 2 exposure L [L]

Work function [eV]


Work function [eV]


W(110)H 2

4.8 200

160

Fig. 10. Work function and work-function change vs. exposure in Langmuir of H2 for hydrogen adsorption on clean W(110) at 90 K. (a) shows the region from 0 to 40 L and (b) the entire curve. From [97N].

1.0

0.6

Pt(111)0 0.5

0.8



Au(111)0

0.6

0.4

0.2

0

0.4 0.3 0.2 0.1

0.2

0.4

1.0 0.6 0.8 O coverage θ [ML]

1.2

1.4

Fig. 11. Work-function change measured as a function of oxygen coverage. The solid curve is a fit for the data using equation (7’). The authors consider that the first steep increase in Φ could be due to lifting of the clean Au(111) surface reconstruction. The remainder range 0.1

Measuring Techniques and Surface Properties Changed Adsorption

Adsorption, Surface Area and Porosity

Surface Properties

Measuring Slipperiness: Human Locomotion and Surface Factors

Adsorption, Surface Area, & Porosity, Second Edition

Martian Surface: Composition, Mineralogy and Physical Properties

Adsorption Engineering

Surface characterization methods: principles, techniques, and applications

Surface analysis: The principal techniques

Surface Analysis: The Principal Techniques

Surface characterization methods - principles, techniques and applications

Principles of adsorption and adsorption processes

Surface Characterization Methods: Principles, Techniques, and Applications

Surface Analysis - The Principal Techniques

Capillary Condensation and Adsorption

Principles of Adsorption and Adsorption Processes

Petrophysics - Theory and Practice of Measuring Reservoir Rock Properties etc

Adsorption and Diffusion

Changed

Changed

changed

Large-Scale Adsorption and Chromatography

Measuring Efficiency in Health Care: Analytic Techniques and Health Policy

Surface and Underground Excavations: Methods, Techniques and Equipment

Safety Metrics: Tools and Techniques for Measuring Safety Performance

Palpation Techniques: Surface Anatomy for Physical Therapists

Materials Surface Processing By Directed Energy Techniques

Catalysis and Adsorption by Zeolites

Advanced Techniques for Assessment Surface Topography

Measuring Efficiency in Health Care: Analytic Techniques and Health Policy

Adsorption analysis: Equilibria and kinetics

Measuring Techniques and Surface Properties Changed Adsorption

Adsorption, Surface Area and Porosity

Surface Properties

Measuring Slipperiness: Human Locomotion and Surface Factors

Adsorption, Surface Area, & Porosity, Second Edition

Martian Surface: Composition, Mineralogy and Physical Properties

Adsorption Engineering

Surface characterization methods: principles, techniques, and applications

Surface analysis: The principal techniques

Surface Analysis: The Principal Techniques

Surface characterization methods - principles, techniques and applications

Principles of adsorption and adsorption processes

Surface Characterization Methods: Principles, Techniques, and Applications

Surface Analysis - The Principal Techniques

Capillary Condensation and Adsorption

Principles of Adsorption and Adsorption Processes

Petrophysics - Theory and Practice of Measuring Reservoir Rock Properties etc

Adsorption and Diffusion

Changed

Changed

changed

Large-Scale Adsorption and Chromatography

Measuring Efficiency in Health Care: Analytic Techniques and Health Policy

Surface and Underground Excavations: Methods, Techniques and Equipment

Safety Metrics: Tools and Techniques for Measuring Safety Performance

Palpation Techniques: Surface Anatomy for Physical Therapists

Materials Surface Processing By Directed Energy Techniques

Catalysis and Adsorption by Zeolites

Advanced Techniques for Assessment Surface Topography

Measuring Efficiency in Health Care: Analytic Techniques and Health Policy

Adsorption analysis: Equilibria and kinetics

Recommend Documents