Electron Emission Spectroscopy: Proceedings of the NATO Summer Institute held at the University of Gent, August 28–September 7, 1972

513 Pages·1973·44.618 MB·English

by  C. B. Duke (auth.), W. Dekeyser, L. Fiermans, G. Vanderkelen, J. Vennik (eds.)

ELECTRON EMISSION SPECTROSCOPY
ELECTRON EMISSION
SPECTROSCOPY
PROCEEDINGS OF THE NATO SUMMER INSTITUTE
HELD AT THE UNIVERSITY OF GENT,
AUGUST 28-SEPTEMBER 7, 1972
Edited by
W. DEKEYSER, L. FIERMANS, G. V ANDERKELEN and J. VENNIK
State University, Gent
D. REIDEL PUBLISHING COMPANY
DORDRECHT-HOLLAND I BOSTON-U.S.A.
First printing: December 1973
Library of Congress Catalog Card Number 73-83559
ISBN-13: 978-94-010-2632-1 e-ISBN-13:978-94-01O-2630-7
DOl: 10.1007/978-94-010-2630-7
Published by D. Reidel Publishing Company,
P.O. Box 17, Dordrecht, Holland
Sold and distributed in the U.S.A., Canada, and Mexico
by D. Reidel Publishing Company, Inc.
306 Dartmouth Street, Boston,
Mass. 02116, U.S.A.
All Rights Reserved
Copyright © 1973 by D. Reidel Publishing Company, Dordrecht-Holland
Softcover reprint of the harcover 1st edition 1973
No part of this book may be reproduced in any form, by print, photoprint, microfilm,
or any other means, without written permission from the publisher
T ABLE OF CONTENTS
PREFACE VII
C. B. DUKE / ELECTRON SCATTERING BY SOLIDS 1
I. The Structure of Solid Surfaces 2
2. Elastic Electron-Solid Scattering: General Features 19
3. Elastic Low-Energy Electron Diffraction (ELEED) 35
4. Surface Crystallography 82
5. Inelastic Low-Energy Electron Diffraction (ILEED) 116
6. Synopsis 145
C. s. FAD LEY / THEORETICAL ASPECTS OF X-RAY PHOTOELECTRON
151
SPECTROSCOPY
1. Introduction 151
2. Core Electron Binding Energies 156
3. Valence Electron Binding Energies 111
4. Multiplet Splittings and Multi-Electron Processes 181
5. Relative Intensities and Angular Distributions 201
R. P. GUPTA AND S. K. SEN / CRYSTAL FIELD THEORY AND
CALCULATION OF THE INNER SHELL VACANCY LEVELS 225
I. Crystal Electric Potential 225
2. Multiplet Splitting in Crystalline Potential 233
3. Sternheimer Effect 250
E. LINDHOLM / MOLECULAR PHOTOELECTRON SPECTROSCOPY 259
1. Historical Development 259
2. Instruments 263
3. Diatomic Molecules: Photoelectron Spectra and Potential Energy
Diagrams 265
4. Intensities in Photoelectron Spectra 214
5. Polyatomic Molecules 218
6. Vibrational Structure of the Photoelectron Bands 280
7. Theoretical Calculation of Orbital Energies 283
8. Approximate Calculation of Orbital Energies 287
9. The Study of Large Molecules with Molecular Photoelectron Spectroscopy 289
10. The Dissociation of the Molecular Ion 292
VI TABLE OF CONTENTS
J. C. TRACY / AUGER ELECTRON SPECTROSCOPY FOR SURFACE ANALYSIS 295
1. Introduction 295
2. Secondary Electron Energy Distributions 296
3. The Auger Process 306
4. Electron Excitation of Auger Spectra 317
5. Experimental Considerations 329
6. Auger Spectroscopy for Surface Analysis 341
Bibliography compiled by D. T. Hawkins 352
D. T. CLARK / CHEMICAL ASPECTS OF ESCA 373
1. Introduction to ESCA, Applications to Chemical Analysis and Surface
Studies 373
2. Application of ESCA to Studies of Structure and Bonding in Organic
Molecules 409
3. Application of ESCA to Studies of Structure and Bonding in Inorganic
Chemistry 443
4. Application of ESCA to Structure and Bonding in Polymers 480
PREFACE
Electron emission spectroscopy became recently a major tool for the study of molecules
and solids. These volumes contain a rather complete review of the state of the art in
this field. Both the physical and chemical aspects are covered extensively by well
known specialists. Different modes of excitation are used in electron emission spec
troscopy.
The electron-solid scattering is covered in detail by C. B. Duke, from a theoretical
point of view. Elastic and inelastic low energy electron diffraction are extensively
discussed in relation to the geometrical, electronic and vibronic structure of solid
surfaces.
Auger electron emission spectroscopy (AES) is covered by J. C. Tracy. The tech
nique is discussed from the point of view of surface research. This part also contains
a complete literature list concerning the application of AES up to the middle of 1972.
Electron emission produced by X-ray impact, is covered by C. S. Fadley, D. T. Clark,
R. P. Gupta and S. K. Sen.
The contribution by C. S. Fadley, entitled Theoretical Aspects of X-Ray Photo
electron Spectroscopy', is an up to date discussion of core electron binding energies,
valence electron binding energies, multiplet splittings and multi-electron processes.
R. P. Gupta and S. K. Sen's contribution provides an introduction to crystal field
theory and its application to electron energy level determination. D. T. Clark deals
with the more chemical aspects of X-ray photoelectron spectroscopy, i.e. the study
of chemical shifts and the relation to the bonding characteristics in molecules.
Finally, E. Lindholm considers the UV excitation in electron emission spectroscopy,
a branch known as 'Molecular Photoelectron Spectroscopy'.
These surveys are the rearranged and extended versions of six out of the nine sets
of lecture notes of the NATO Advanced Summer Institute held at Gent from August
28 to September 7, 1972. The editors are grateful to the lecturers of this school for
providing extended lecture notes and particularly to those who accepted to publish
them. In some cases this involved a major rewriting task in order to cover the subject
as completely as possible. The support of the NATO Science Committee is gratefully
acknowledged.
Our gratitude also goes to the following editors of books and periodicals and
authors who granted permission to reproduce figures, diagrams or other material, i.e.
Accounts of Chemical Research; American Chemical Society; American Institute of
Physics; Analytical Chemical Research; Applied Spectroscopy; Bulletin des Societes
Chimiques Belges; Chemical Physics Letters; Faraday Division of the Chemical
Society; Institute of Physics (London); Journal of the American Chemical Society;
Journal of Chemical Physics; Journal of the Chemical Society; Journal of Electron
VIII PREFACE
Spectroscopy; Journal of Physical Chemistry; Journal of Polymers Science; North
Holland Publishing Co.; Nova Royal Society Uppsala; Physical Society of Japan;
Plenum Publishing Corporation; Review of Modern Physics; Robert A. Welch Foun
dation Research Bulletin; Royal Society (London); Royal Society of Sciences of
Uppsala; Royal Swedish Academy of Sciences; Solid State Communications; Zeit
schrift fUr Naturforschung; Zeitschrift fUr Physik; J. Wiley and Sons Publishing Co;
I. Adams; S. Aksela; D. A. Allison; A. Bagchi; M. Barber; T. Bergmark;
S. A. L. Bergstrom; G. K. Bohn; H. P. Bonzel; G. Broden; C. R. Brundle;
J. M. Burkstrand; C. W. Caldwell Jr; T. A. Carlson; J. C. Carver; P. H. Cutler;
D. W. Davis; R. Ditchfield; A. R. Du Charme; C. B. Duke, D. E. Eastman;
C. S. Fadley; A. Fahlman; R. W. Finck; C. T. Foxon; T. E. Gallon; U. Gelius;
R. L. Gerlach; J. Gerstner; A. M. Gibbons; E. J. McGuire; C. Glupe; K. Hamrin;
S. B. M. Hagstrom; E. Hasilbach; D. M. Hercules; K. Hirabayshi; P. O. Heden;
J. Hedman; B. W. Hilland; J. M. Hollander; J. E. Houston; D. A. Huchital;
L. D. Hulett; D. W. Jespen; G. Johansson; W. L. Jolly; E. R. Jones; J. Jones;
R. C. Jopson; B. A. Joyce; S. Karlsson; J. T. McKinney; M. O. Krausse; A. B. Kunz;
G. E. Laramore; U. Landman; M. G. Lagally; B. Lindberg; I. Lindgren; H. Lofgren;
P. M. Marcus; H. Mark; N. Mehlhorn; W. E. Moddeman; J. H. Neave;
T. C. Ngoe; R. Nordberg; C. Nordling; C. Norris; T. Novakov; G. A. Olah;
P. W. Palmberg; R. L. Park; L. G. Parrat; M. Pelavin; F. M. Propst; E. G. McRae;
H. Rosencwaig; D. A. Shirley; K. Siegbahn; D. L. Smith; L. C. Snydes; W. E. Swartz;
C. D. Swift; N. J. Taylor; T. D. Thomas; J. C. Tracy; C. W. Tucker; M. B. Webb;
G. W. Wertheim.
ELECTRON SCATTERING BY SOLIDS:
DETERMINATION OF THE CHEMICAL, GEOMETRICAL,
ELECTRONIC AND VIBRATIONAL STRUCTURE OF SURFACES
C. B. DUKE*
Dept. of Physics, Materials Research Laboratory,
and Coordinated Science Laboratory University of Illinois Urbana, Ill., U.S.A.
T ABLE OF CONTENTS
1. The Structure of Solid Surfaces 2
A. Introduction 2
B. The Chemical Structure of Planar Surfaces 4
C. The Geometrical Structure of Planar Surfaces 8
D. The Electronic Structure of Planar Surfaces 11
E. The Vibrational Structure of Planar Surfaces 16
F. Organization of the Remaining Lectures 18
2. Elastic Electron-Solid Scattering: General Features 19
A. The Elastic Scattering Problem 19
B. The Electron-Solid Force Law 23
C. Models of Elastic Electron-Solid Scattering 29
3. Elastic Low-Energy Electron Diffraction (ELEED) 35
A. Scattering from a Rigid Lattice: the Born Approximation 36
B. Scattering from a Vibrating Lattice: Linear-Response Theory 39
C. Beyond the Born Approximation 53
D. Dynamical Models of ELEED: Comparison of Theoretical Predictions
with Experimental Data 59
I. Historical Introduction 59
2. The Electron-lon-Core Potential 63
3. Boundary Conditions 67
4. Lattice Vibrations 68
5. Consequences of Different 'Bulk' Potentials 69
6. Specifically Surface Effects 71
7. The Low-Index Faces of Aluminum 74
8. Synopsis 80
4. Surface Crystallography 82
A. Definition of the Problem 82
B. Survey of Theoretical Approaches 86
C. Clean Surfaces 88
D. Adsorbed Monolayers 104
* Present address: Xerox Research Laboratories, Phillips Road, Webster, N.Y. 14580, U.S.A.
W. Dekeyser et al. (eds.), Electron EmiSSIOn Spectroscopy, 1-149. All Rights Reserved
Copyright © 1973 by D. Reidel Publishing Company. Dordrecht-Holland
2 C. B. DUKE
E. Summary and Perspective 113
5. Inelastic Low-Energy Electron Diffraction (lLEED) 116
A. Definitions and General Principles 116
B. Surface-Excitation Spectroscopy via ILEED 127
1. Dynamical Versus Two-Step Diffraction 128
2. Consequences of Instrumental Uncertainties 137
C. Surface-Plasmon Dispersion on Al(l\\) 140
6. Synopsis 145
1. The Structure of Solid Surfaces
A. INTRODUCTION
In these notes we examine the use of various experiments, primarily those associated
with generic labellow-energy-electron diffraction ('LEED'), to determine the atomic
identity, positions, vibrational amplitudes, and electronic structure of 'atoms' (i.e.,
ion-cores immersed in a sea of valence electrons) in the uppermost 1-5 layers of a
single-crystal solid. A general survey of mathematical models of the specifically sur
face microscopic properties of solids is available elsewhere. [1] Furthermore, the
construction of an adequate theory [2-6] of the electron-solid scattering phenomena
of primary interest to us requires extensive use of modern quantum-field-theory
methods with their concommitant algebraic complexity. Thus we focus our attention
on the applications of theories of particle-solid scattering to characterize the structure
of solid surfaces. We indicate only briefly the ingredients of models of the electronic,
geometrical, and vibrational structure of surfaces and the construction of theories
of the scattering process.
To specify the microscopic 'structure' of a solid surface, one must provide four
types of information: the atomic identity of ion cores in the uppermost few layers;
the positions of these ion cores; their vibrational amplitudes; and the ground
state properties and excitation spectrum of the valence electron fluid in which they
are immersed. Much of this information can be determined in more than one way.
Thus the choice of which experiments to perform to obtain it often is based on con
siderations of experimental convenience and/or ease in theoretical interpretation,
rather than on a fundamental limitation of the experimental methods not used. How
ever, two general features of sample preparation are common to all methods. First,
the samples must be prepared in high vacuum (p'" 10-1°_10-12 torr) in order that
the surface conditions remain constant for the duration (I'" 1 h) of the experiment.
Second, single-crystal specimens are almost a necessity because of the difficulties in
herent in trying to characterize the surface conditions on polycrystalline or powder
samples. For some applications (e.g., the study of impurity segregation at grain
boundaries [7]), the second criterion may be relaxed, but in these lectures I shall
presume it to be satisfied.
Given the requirements of high-vacuum environment and a single-crystal sample,
a further important distinction between types of experiments is based on the
ELECTRON SCATTERING BY SOLIDS 3
geometry of the sample. In the 'tip' geometry, characteristic of field-emission and
field ionization microscopy, [8] multiple atomic planes are exposed on a more-or-less
spherical tip and electron emission from or ion formation near these planes is used
to project a greatly expanded image of the tip on a spherical screen. The area of each
planar surface is small (A'" (100 A)2), the electric fringing fields at the surface are
large, [9] and the samples generally are confined to the mechanically-strong transition
metals. In the 'planar' geometry, characteristic of electron-diffraction and photo
emission experiments, a macroscopic area (A ",(I cm)2) of a single atomic plane is
sought by combinations of polishing, etching, ion-bombardment, and heat treatment.
Perhaps the most serious shortcoming of this type of experiment is that usually no
independent measurement of the surface topography is possible. [10] As, however,
essentially all theoretical models of electron-solid and photon-solid interactions either
implicitly or explicitly assume the planar geometry, we concentrate our attention on
this latter class of experiments. A synopsis of these general experimental design
criteria is given in Figures 1 and 2.
Characterization of Solid Surfaces I
A. Maintenance of Constant Surface Condition
During Measurement (T "'lmin):
U HV ( p '" 10-10 Torr)
B. Cia sses of Experiment 'T----,
(11
1. Tip-Geometry
a. V> 0 FEM
b. V < 0 FIM 11
Fig. 1. Schematic indication of some of the design criteria for experiments utilized to characterize
the structure of solid surfaces. The use of ultra-high vacuum (UHV) field-emission microscopy (FEM)
and field-ion microscopy (FIM) is discussed in the text.
Characterization of Solid Surfaces IT
2. Planar -Geometry
a. Large-Area [lO-2-1O-4mm2]
b. Small External Fields
c. Probe via Scattering Experiments:
Do They Disturb the Surface?
d Need Slng.!f Crystal Surfaces
for Well-Defined System
Fig. 2. General features of experiments used to characterize planar solid surfaces. The probes usea
in the scattering experiments can be atomic species (1), photons (y), or electrons (e).