Table Of ContentSu rface and Interface
Characterization by
Electron Optical Methods
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Series B: Physics
Surface and Interface
Characterization by
Electron Optical Methods
Edited by
A. Howie
University of Cambridge
Cambridge, United Kingdom
and
U. Valdre
University of Bologna
Bologna, Italy
Plenum Press
New York and London
Published in cooperation with NATO Scientific Affairs Division
Proceedings of a NATO Advanced Study Institute
on the Study of Surfaces and Interfaces
by Electron Optical Techniques
held April 4-15,1987,
in Erice, Sicily, Italy
Library of Congress Cataloging in Publication Data
NATO Advanced Study Institute on the Study of Surfaces and Interfaces by Elec-
tron Optical Techniques (1987: Erice, Italy)
Surface and interface characterization by electron optical methods I edited
by A. Howie and U. Valdre.
p. cm.-(NATO ASI series. Series B, Physics; v. 191)
"Proceedings of a NATO Advanced Study Institute on the Study of Surfaces
and Interfaces by Electron Optical Techniques, held April 4-15, 1987, in Erice,
Sicily, Italy"-CIP t.p. verso.
Bibliography: p.
Includes index.
1. Surfaces (Physics)-Technique-Congresses. 2. Electron microscopy-
Congresses. 3. Electron microscope, Transmission-Congresses. I. Howie, A. II.
Valdre, U. (Ugo). III. Title. IV. Series.
QC173.4.S94N385 1987 88-28989
530.4'1-dc19 CIP
© 1988 Plenum Press, New York
Softcover reprint ofthe hardcover I st edition 1988
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All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted
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ISBN 978-1-4615-9539-7 ISBN 978-1-4615-9537-3 (eBook)
DOl 10.1007/978-1-4615-9537-3
STM image of the 7 x 7 reconstruction at the Si (111) surface. The distance between the main
6-fold symmetry centers is 2.6 nm. Color enhancement of the intensity scale reveals fine
details of atomic heights and bonding states at the surface. A surface step is visible as a
discontinuity running vertically near the center of the figure. Atoms are blue. Colors from blue
to red indicate details further away from the surface. (Courtesy Drs. J . E. Demuth, R. J .
Hamers, R. M. Tromp, and M. E. Weiland. Fig. 3 from chapter by Garcia.)
a b
I I
Magnetic domain images from an Fe (100) surface, measured simultaneously for the spin
polarization vector component along the horizontal axis (a) and the vertical axis (b). Areas of
the same color have the same magnetization (see arrows). Within the gray areas in (a) and (b)
the horizontal (a) and vertical (b) polarization components, respectively, are zero, while the ver-
tical and horizontal components are maximum. The scale markers each correspond to 60 I-'m
(Fig. 2 from chapter by Kirschner.)
PREFACE
The importance of real space imaging and spatially-resolved
spectroscopy in many of the most significant problems of surface and
interface behaviour is almost self evident. To join the expertise of the
tradi tional surface scientist with that of the electron microscopist has
however been a slow and difficult process. In the past few years
remarkable progress has been achieved, including the development of new
techniques of scanning transmission and reflection imaging as well as low
energy microscopy, all carried out in greatly improved vacuum conditions.
Most astonishing of all has been the advent of the scanning tunneling
electron microscope providing atomic resolution in a manner readily
compatible with most surface science diagnostic procedures. The problem of
beam damage, though often serious, is increasingly well understood so that
we can assess the reliability and usefulness of the results which can now
be obtained in catalysis studies and a wide range of surface science
applications.
These new developments and many others in more established surface
techniques are all described in this book, based on lectures given at a
NATO Advanced Study Institute held in Erice, Sicily, at Easter 1987. It is
regretted that a few lectures on low energy electron diffraction and
channeling effects could not be included.
Fifteen lecturers from seven different Countries and 67 students from
23 Countries and a wide variety of backgrounds attended the school.
Substantial problem-solving sessions and computer demonstrations were
arranged to back up the lectures and a number of these problems have been
reproduced in the book.
We wish to thank all the lecturers for their effort and patience in
producing the material for the book. For permission to include various
figures and quotations (specifically identified where appropriate in the
text) we are grateful to the American Institute of Physics, the American
Physical Society, the International Business Machines Corporation and the
Nobel Foundation.
The two enthralling lectures given enthusiastically by Dr Wolfgang
Telieps were a high point of the School. It was thus with great shock and
sorrow that we learnt of his death so soon afterwards. We are grateful to
his colleague, Professor Bauer, for providing the obituary notice included
here and for completing the write up of the relevant lecture notes.
The success of the School was greatly assisted by a contribution from
NATO and from the facilities of the Ettore Majorana Centre for Scientific
Culture. For secretarial support we are grateful to Mrs Irene Salerno, Mrs
Mary Waterworth and Miss Vanna Valdre.
A. Howie and U. Valdre
June 1988
v
OBITUARY
Wolfgang Telieps, who gave one of the most interesting lectures in
this school, died in a tragic car accident on May 31, 1987 at the age of
36. He had studied physics at the Technical University Clausthal, where he
received a M.S. degree in physics in 1977 and his Ph.D. in 1983. For his
M.S. thesis work he studied the imaging column of the low energy electron
microscope; in his Ph.D. project he took over the responsibility for the
complete instrument . In spite of strong discouragement by referees, he
succeeded in demonstrating the viability of LEEM . This achievement and the
work which he did in the following years in the course of his preparation
for the "habilitation" rapidly brought him international recognition.
Wolfgang Telieps was not only an outstanding physicist but also a
great human being who was liked by all who knew him for his pleasant
personality, his objectiveness, his tolerance, his willingness to help and
many other positive characteristics which made him an ideal collaborator.
His untimely death has thus robbed, not only the scientific community of a
very talented young member, but also his colleagues of an unforgettable
friend.
vi
CONTENTS
Principles and techniques of transmission imaging of surfaces . . . . .
A. Howie
Catalyst studies by scanning transmission electron microscopy 11
A. Howie
Localised surface imaging and spectroscopy in the scanning
transmission electron microscope . . .. ..... 19
A. Howie
Fundamentals of high resolution transmission electron microscopy. 31
D.J. Smith
Profile imaging of small particles, extended surfaces and dynamic
surface phenomena. . . . . . . . . . . . . . .. .... 43
D.J. Smith
Transmission electron microscopy and diffraction from semiconductor
interfaces and surfaces. . . . . . . . . . . . . . . . . . . . 55
J.M. Gibson
The transmission electron microscopy of interfaces and multilayers. .. 77
W.M. Stobbs
Surface microanalysis and microscopy by X-ray photoelectron
spectroscopy (XPS), core-loss spectroscopy (CLS) and
Auger electron spectroscopy (AES) .......... . 89
J. Cazaux
Reflection electron microscopy ..................... 127
J.M. Cowley
An introduction to reflection high energy electron diffraction ..... 159
P.J. Dobson
Intensity oscillations in reflection high energy electron
diffraction during epitaxial growth. . ........... 185
P.J. Dobson, B.A. Joyce, J.H. Neave, J. Zhang
Emission and low energy reflection electron microscopy ......... 195
E. Bauer and W. Telieps
Scanning tunneling microscopy and spectroscopy ............. 235
N. Garcia
Spin-polarized secondary electrons from ferromagnets .......... 267
J. Kirschner
Electronically stimulated desorption: mechanisms, applications
and implications ....................... 285
D. Menzel
Structure and catalytic activity of surfaces .............. 301
V. Ponec
Subj ect Index . . . . . . . . . . . . . . . . . . . . . . . • • . . . . 315
viii
PRINCIPLES AND TECHNIQUES OF TRANSMISSION IMAGING OF SURFACES
A. Howie
Cavendish Laboratory
Madingley Road
Cambridge CB3 OHE, U.K.
INTRODUCTION
Although many surface characterisation techniques are essentially
broad beam methods yielding diffraction or other information averaged over
large areas of surface, crucial properties of the surface may depend on
steps or other inhomogeneities. There is indeed an instability, shown
schematically in figure 1, whereby even a uniform single crystal overgrowth
such as an expi taxial layer or adsorbed oxide tends to become
inhomogeneous, forming island structures or localised defects. The
overgrowth has an energy E proportional to thickness t at small t where it
matches its lattice parameter with the substrate crystal at the cost of
elastic strain energy (point A). At larger values of t, when elastic strain
energy becomes prohibitive, misfit dislocations are introduced to relieve
it. Eventually where the overgrowth has completely relaxed to its own
lattice parameter, E becomes the characteristic interfacial energy of the
boundary, independent of t (point C). Since the E versus t curve is concave
downwards, a homogeneous film represented by point B can reduce its energy
to the point D by breaking up into regions A and C.
The study of these important and almost inevitable inhomogeneous
features of extended surfaces, as well as of more obviously heterogeneous
surface structures like catalyst particles, clearly requires a high
resolution, real space imaging technique. For such a purpose, electron
E Ifn' 1111 'fIIJ 11110111111111
\
- B
I\I ~ ~ ~ ~ ~ ~ C
~ 0
A
Fig. 1. Energy per unit area of an epitaxial overgrowth as a function of
thickness t, showing instability at B.
