Electron and Ion Spectroscopy of Solids

485 Pages·1978·14.785 MB·English

by  G. D. Mahan (auth.), L. Fiermans, J. Vennik, W. Dekeyser (eds.)

Electron and Ion
Spectroscopy of Solids
NATO ADVANCED STUDY INSTITUTES SERIES
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Electron and Ion
Spectroscopy of Solids
Edited by
L. Fiermans, 1. Vennik, and W Dekeyser
Laboratory for Crystallography and the Study of Solids
State University Ghent
Ghent, Belgium
PLENUM PRESS. NEW YORK AND LONDON
Published in cooperation with NATO Scientific Affairs Division
Library of Co~ss Cataloging in Publication Dlla
Main entry under tille:
Eleetron and ion spcetroscopy or solid!.
(NATO advanced study institute! series: Series B, Physics; Y. 32)
"Based on leclufts presented al Ihe NATO Advaneed Sludy Institute held in Ghent,
Belgium, August 29-September 9,1971."
Indudes bibliographies and indexes.
1. Electron spcctroseopy. 2. 01nl-Spectra. 3. SolidJ-Spectra. 1. Fiermans, Lucien.
Il. Vennik, J. III. Dekeyser, Wîlly. IV. NATO Advanced SlUdy Instilule, Ghent,
Belgium, 1971. V. Sericl.
QC454.E4E4 539.7'2112 78.(;171
ISBN 978-1-4684-2819-3 ISBN 978-1-4684-2817-9 (eBook)
DOI 10.10071978-1-4684-2817-9
Based on Ihe leetures presentcd at thc NATO Advanced Sludy Inslilule held in
Ghenl, Bc"ium, AUlUst 29-Seplcmber 9,1977
01978 prcnum Press, New York
Softeovn rcprint or thc " ...d c:ovn 1$1 ~dition 1978
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Preface
Surface physics and chemistry have in recent years become one
of the most active fields in solid state research. A number of
techniques have been developed, and both the experimental aspect
and the correlated theory are evolving at an extremely fast rate.
Electron and ion spectroscopy are of major importance in this
development.
In this volume, which contains edited and extended versions of
eight sets of lectures given at the NATO Advanced Study Institute
held at Ghent, Belgium, from August 29 to September 9, 1977, a re
view of the state of the art in these fields is given from both an
experimental and a theoretical point of view. Electron emission
techniques such as UPS (ultraviolet photoemission spectroscopy),
XPS (x-ray photoemission spectroscopy), and AES (Auger electron
spectroscopy) constitute the major part of this volume, reflecting
the fact that they continue to be the most widely applied surface
techniques.
Recent developments in the application of synchrotron radiation
to angle-resolved photoelectron spectroscopy are extensively covered,
from an experimental point of view by Prof. W. E. Spicer (Stanford
University, U.S.A.) and from a theoretical point of view by Dr. A.
Liebsch (Kernforschungsanlage Julich, Germany). Emphasis is put on
the study of energy bands in layered structures, and on chemisorption
on well-defined surfaces. Chemisorption and catalysis on metals is
treated in detail by Prof. G. Ertl (Universitat Munchen, Germany).
This chapter contains a review of the application of the different
surface techniques to specific surface systems.
Fundamental problems involved in the interpretation of XPS and
AES spectra are discussed in chapters by Dr. G. K. Wertheim (Bell
Laboratories, U.S.A.) and Dr. T. E. Gallon (University of York,
U.K.), respectively. A general introduction to the theory of photo
emission is given in a chapter by Prof. G. D. Mahan (Indiana Univer
sity, U.S.A.). The chapter by Dr. H. D. Hagstrum (Bell Laboratories,
U.S.A.) in some respects can be considered to deal with the transi-
v
PREFACE
tion from e1ectron- and photon-stimulated electron emission tech
niques to techniques where ions are used as primary beams. In this
chapter Dr. Hagstrum comprehensively reviews the results obtained
with INS (ion-neutralization spectroscopy) in the study of chemi
sorption. A comparison with UPS is made. The last chapter on SIMS
(secondary ion mass spectroscopy) by Dr. H. W. Werner (Philips Re
search Laboratories, The Netherlands) is an extensive review of its
application to surface studies.
The editors are grateful to the lecturers of this Institute
for providing extended lecture notes. In most cases this involved
a considerable writing task in order to cover the subject in a
comprehensive way.
The support of the NATO Science Committee is gratefully ac
knowledged. Our gratitude also goes to the authors and editors of
books and periodicals who granted permission to reproduce figures,
diagrams, or other material.
Finally we also wish to thank Plenum Press for providing the
necessary support for the publication of these Proceedings.
L. Fiermans
J. Vennik
W. Dekeyser
Ghent, December 1977
Contents
Theory of Photoemission 1
G. D. Mahan
1. Introduction • • • • • 2
II. One Electron Theory 2
A. History • • • • • • 2
B. Atomic Photoionization • 3
C. Photoemission from a Solid • 8
D. Three Step Model • • • • • 11
III. Angular Dependence in Simple Metals 12
A. Interband Transitions •• • • • • 12
B. Internal Photoemission: Direction. 18
C. Internal Photoemission: Intensity 20
D. Experiments on Ag • • • • • 23
IV. Plasmon Satellites in XPS •• • • • • 29
A. X-ray Photoelectron Spectroscopy • 29
B. Electron Mean Free Path 30
C. Extrinsic vs. Intrinsic 34
V. Collective Effects • • • • • 40
A. Phonons 40
B. Electron-Electron Interactions 42
C. Auger Decay 45
D. Auger and Phonon • 47
References • • 51
The Use of Synchrotron Radiation in UPS: Theory
and Results • • • • • • • 54
W. E. Spicer
1. Introduction 54
II. Characteristics and Benefits of Synchrotron
Radiation • • • • • • 56
III. Fundamentals of the Photoemission Process •• 58
A. Introduction • • • • • • • • 58
B. The Three-Step Model • • • • • • • • • • 59
C. Effect of Various Scattering Events and
Contribution of Scattered Electrons • 62
vii
viii CONTENTS
IV. Benefits of Synchrotron Radiation
in Photoemission Studies • 63
A. Introduction • • • • 63
V. Tuning Synchrotron Radiation to
Minimize Electron Escape Depth
and Thus Maximize Surface
Sensitivity • • • • • • • • 65
A. Introduction • • • • • • • • • 65
B. GaAs Core Shifts Due to Oxygen
Adsorption • • • • • 67
VI. Use of Photon Energy Dependence of
Absorption Cross Section to
Separate Photoemission from Two
Sources Which Are Degenerate in
Energy . . . . . . . . . . . 72
A. Introduction • • • • • • • • • • 72
B. "Missing" Bonding Orbitals of
CO Adsorbed on Metal • • • • 72
VII. Angularly Resolved Photoemission Electron
Spectroscopy (ARPES) • . • • • 76
A. Introduction • • • • • • • • • • • • • 76
B. Studies of CO Adsorbed on Ni(lOO) •• 77
C. Use of ARPES to Obtain Information of
the Bulk Band Structure 81
D. Discussion of ARPES 86
VIII. Conclusions 86
References 89
Angle Resolved Photoemission: Theoretical
Interpretation of Results 93
A. Liebsch
I. Introduction 93
II. The Excitation Process 94
III. Atoms • • • • • • • • • • 99
IV. Molecules • • • • • • • 104
1. Gas Phase Molecules 104
2. Oriented Molecules 107
V. Adsorbates • • • • • 110
1. Core Levels • • • • 110
2. Surface Molecules • 116
3. Chemisorbed Overlayers 119
VI. Clean Surfaces 125
1. Formalism 125
2. TaS2 l3l
3. Cu(OOl) l34
4. Cu(l1l) : Surface State • • l37
References 141
CONTENTS ix
Chemisorption and Catalysis on Metals:
Applications of Surface · . . . . . . . . .
Spectroscopies • • • • • 144
G. Ert1
I. Characterization of Chemisorbed Systems · · 144
1. The Molecular Nature of the Adsorbate • 144
2. The Surface Concentration (Coverage) 147
3. Electronic Properties · · · · · 150
4. Structure of Chemisorbed Layers 153
5. The Strength of the Substrate- . .
Adsorbate .B ond • · · · · · · · · · . . 155
6. Vibrations · · · · · · · · · · · · · 157
II. Factors Influencing the Chemisorption Bond 159
1. The Nature of the Substrate and
Adsorbate · · · · · · · 159
2. The Local Character of the
Chemisorption Bond • · · · · · · 159
3. The Crystallographic Orientation of
the Surface · · · · · · · 162
4. The Role of Monoatomic Steps · · · · · · 164
5. The Adsorption Site • · · · · · · 167
III. Interactions Between Adsorbed Particles 169
IV. Dynamics of S.u .r fa.c e Processes 179
References · · · · · · · · · · · · · 186
X-Ray Photoelectron Spectroscopy of Solids 192
G. K. Wertheim
I. Introduction · . . . 192
II. Valence Bands • • • • 198
A. Metals and Alloys • 198
B. Compounds with Metallic Conductivity 202
C. Insulators • • • • · . . 204
III. Photoemission from Open Shells •••• .. 205
A. The Rare Earths • • • • • • • • 205
B. Transition Metal Compounds • • • 208
IV. Core Level Spectra • • • • • 211
A. Shake-Up Satellites • • • • • • • • 212
B. Configuration Interaction • 213
C. Multiplet Splitting • • • • 215
D. Many-Body Effects in Metals • • 220
V. Summary • • • ••• 223
References • • • • • • • • 224
Current Problems in Auger Electron Spectroscopy • • 230
T. E. Gallon
.
·
Free Atom Auger Energies 230
· .
Auger Emission from Solids 233
x CONTENTS
Auger Energies in the Solid State • 235
Chemical Shifts in Auger Spectra 239
Line Broadening in the Solid State 242
Auger Spectra Involving Band Electrons 245
Quantitative Auger Spectroscopy . . . 260
References •••••• • • • • • 269
Studies of Adsorbate Electronic Structure Using
Ion Neutralization and Photo-
emission Spectroscopies 273
H. D. Hagstrum
I. Introduction • • • • • • • • • • • • • • • 273
II. Electronic Transition Processes • • • • • 275
III. What We Can Learn from Studying Particle-
Solid Electronic Interactions 277
IV. Experimental Apparatus and Techniques • • • 278
V. Transition Rate and Probability Functions 282
VI. The Auger Neutralization Process •• • • 284
VII. Evidence for Variation of Atomic Energy
Levels near a Surface • • • • 288
VIII. Transition Rate Parameters for Auger
Neutralization • • • • • • 290
IX. Tunneling Processes for Unexcited Ions 291
X. The Auger De-Excitation Process • 294
XI. Two-Stage Ejection Processes for
Unexcited Ions • • • • • • 296
XII. Two-Stage Ejection Processes for
Excited Ions • • • • • • • 298
XIII. Oscillatory Ion Scattering from Surfaces 302
XIV. Kinetic Ejection of Electrons by Ions ••• 304
XV. Energy Broadening in Auger Neutralization • 305
XVI. The Method of Ion Neutralization
Spectroscopy (INS) 309
XVII. What INS and UPS Measure 314
XVIII. Adsorbate Electronic Structure 317
XIX. Wave Function Variation Outside a Solid
Surface • • • • • • • • 319
XX. Uniqueness and Limitations of INS • 321
XXI. References • • • • 322
Introduction to Secondary Ion Mass Spectrometry (SIMS) 324
H. W. Werner
. . .
1. Introduction • • • • 324
2. Theory of SIMS • • • • 328
2.1. Physical Basis 328
2.2. Basic Formula for a SIMS Analysis. 338
2.3. Basic Experimental Embodiment ••• 353