EXAFS Spectroscopy: Techniques and Applications

271 Pages·1981·5.989 MB·English

by  E. A. Stern (auth.), B. K. Teo, D. C. Joy (eds.)

EXAFS
Spectroscopy
Techniques and Applications
EXAFS
Spectroscopy
Techniques and Applications
Edited by
B.K. Teo and D.C. Joy
Bell Laboratories
Murray Hill, New Jersey
SPRINGER SCIENCE+BUSINESS MEDIA, LLC .
Library of Congress Cataloging in Publication Data
Main entry under title:
EXAFS spectroscopy, techniques and applications.
Based on proceedings of a symposium held at the meeting of the Materials Re·
search Society, Nov. 26·30, 1979, in Boston.
Includes index.
1. X·ray spectroscopy. 2. Absorption spectra. I. Teo, B. K. 1/. Joy, David C.,
1943· . 1/ I. Materials Research Society.
QC482.S6E9 543'.08586 81-199
ISBN 978-1-4757-1240-7 ISBN 978-1-4757-1238-4 (eBook)
DOI 10.1007/978-1-4757-1238-4
Based on the proceedings of a symposium on The Applications
of EXAFS to Materials Science, held at the 1979 Meeting of
the Materials Research Society, November 26-30,1979, in
Boston Massachusetts
© 1981 Springer Science+Business Media New York
Originally published by Plenum Press, New York 1981.
Sof'tcover reprint of the hardcover 1s t edition 1981
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted,
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
PREFACE
This book on Extended X-Ray Absorption Fine Structure (EXAFS) Spectroscopy
grew out of a symposium, with the same title, organized by us at the 1979 Meeting of
the Materials Research Society (MRS) in Boston, MA. That meeting provided not only
an overview of the theory, instrumentation and practice of EXAFS Spectroscopy as
currently employed with photon beams, but also a forum for a valuable dialogue
between those using the conventional approach and those breaking fresh ground by
using electron energy loss spectroscopy (EELS) for EXAFS studies.
This book contains contributions from both of these groups and provides the
interested reader with a detailed treatment of all aspects of EXAFS spectroscopy, from
the theory, through consideration of the instrumentation for both photon and electron
beam purposes, to detailed descriptions of the applications and physical limitations of
these techniques. While some of the material was originally presented at the MRS
meeting all of the chapters have been specially written for this book and contain much
that is new and significant.
As will be evident from reading this book, EXAFS measurements using photons as
the primary excitation source are well established, even though advances can still be
made in the areas of improvement of instrumentations, development of new tech
niques, understanding of the limitations, and applications to new systems. On the other
hand, the use of electrons in EXAFS data acquisition is still under intense develop
ment. While it is competitive in terms of counting statistics and potentially very useful
for EXAFS of low atomic weight elements and microscopic areas, much needs to be
done in ungrading the technique in order to compete or complement the photon tech
niques.
We hope that this first book on this important topic will be found valuable to those
now in the field as well as to those wishing to enter it, including researchers working in
the field of physics, chemistry, biology, materials science, and related areas.
Finally, we would like to thank all the authors for their valuable contributions to
this book. We are particularly indebted to Professor E. A. Stern and Dr. P. A. Lee, as
well as some of the authors, for their generous help in reading some of the chapters.
B. K. Teo and D. C. Joy
Bell Laboratories
Murray Hill, New Jersey
December, 1980
v
CONTENTS
Chapter 1 Historical Development of EXAFS ......................................................... 1
E. A. Stern
Chapter 2 Theory of Extended X-Ray Absorption Fine Structure .......................... 5
P. A. Lee
Chapter 3 EXAFS Spectroscopy: Techniques and Applications ............................ 13
Boon-Keng Teo
Chapter 4 Understanding the Causes of Non-Transferability
of EXAFS Amplitude ............................................................................ 59
E. A. Stern, B. Bunker, and S. M. Heald
Chapter 5 Near Neighbor Peak Shape Considerations
in EXAFS Analysis ............................................................................... 81
T. M. Hayes and J. B. Boyce
Chapter 6 Disorder Effects in the EXAFS of Metals and
Semiconductors in the Solid and Liquid States ..................................... 89
E. D. Crozier
Chapter 7 Structural Studies of Superionic Conduction ....................................... l03
J. B. Boyce and T. M. Hayes
Chapter 8 Extended X-Ray Absorption Fine Structure
Studies at High Pressure ..................................................................... 127
R. Ingalls, J. M. Tranquada, J. E. Whitmore,
E. D. Crozier, and A. J. Seary
Chapter 9 Structural Evidence for Solutions from
EXAFS Measurements ........................................................................ 139
Donald R. Sandstrom, B. Ray Stults, and R. B. Greegor
Chapter 10 EXAFS Studies of Supported Metal Catalysts ..................................... 159
G. H. Via, J. H. Sinfelt, and F. W. Lytle
Chapter 11 EXAFS of Amorphous Materials ........................................................ 163
S. H. Hunter
vii
viii Contents
Chapter 12 EXAFS of Dilute Systems: Fluorescence Detection .......................... 171
J. B. Hastings
Chapter 13 EXAFS Studies of Dilute Impurities in Solids .................................... 181
Matthew Marcus
Chapter 14 Materials Research at Stanford Synchrotron
Radiation Laboratory ........................................................................... 185
Arthur Bienenstock
Chapter 15 Cornell High Energy Synchrotron Source: CHESS ............................ 197
Boris W. Batterman
Chapter 16 National Synchrotron Light Source (NSLS):
An Optimized Source for Synchrotron Radiation ................................ 205
J. B. Hastings
Chapter 17 Electron Energy Loss Spectroscopy for
Extended Fine Structure Studies - An Introduction ......................... 213
David C. Joy
Chapter 18 Extended Core Edge Fine Structure in
Electron Energy Loss Spectra .............................................................. 217
R. D. Leapman, L. A. Grunes, P. L. Fejes,
and J. Silcox
Chapter 19 Extended Energy Loss Fine Structure Studies
in an Electron Microscope ................................................................... 241
S. Csillag, D. E. Johnson, and E. A. Stern
Chapter 20 A Comparison of Electron and Photon Beams
for Obtaining Inner Shell Spectra ........................................................ 255
M. Utlaut
Chapter 21 Some Thoughts Concerning the Radiation Damage
Resulting from Measurement of Inner Shell Excitation
Spectra Using Electron and Photon Beams ......................................... 269
M. S. Isaacson
Index ............................................................................................................................. 273
HISTORICAL DEVELOPMENT OF EXAFS
E. A. Stern
University of Washington
Seattle, VA 98195
The Extended X-ray Absorption Fine Structure (EXAFS) has been known for over
50 years, but only recently has its power for structure determination been appreciated.
The first experimental detection of fine structure past absorption edges were by Fricke
(1920)1 and Hertz (1920).2 The first structure detected was the near edge structure
(Coster 1924,3 Lindh 1921,4 19255) which could be explained by the theory of Kossel
(1920).6 However, as the experimental measurements extended the detected fine struc
ture to hundreds of eV past the edge (the EXAFS) (Ray 1929,7 Kievet and Lindsay
19308) a new explanation was required. The temperature dependence in EXAFS was
first experimentally noted by Hanawalt (1931).9,10 Kronig (1931)11 first attempted an
explanation of the EXAFS in condensed matter using the newly developed Quantum
Mechanics. His explanation utilized the energy gaps at the Brillouin zone boundari~s
and thus depended explicitly on the long range order in the solid. Following Azaroff
(1963) 12 we will call this theory a long range order (LRO) theory and the other class of
theories short range order (SRO). LRO theory is fundamentally in error, but it took
over 40 years for the error to be discovered (Stern 1974).13
Kronig (1932) 14 also germinated the idea of the SRO theory which he employed to
explain EXAFS in molecules. Some elements of the modern theory were missing in
his original theory but the basic physical idea was correct. Kronig, apparently, never
realized that the same basic physics explains EXAFS in both solids and molecules.
Kronig's SRO theory explains EXAFS by the modulations of the final state wave func
tion of the photoelectron caused by the backscattering from the surrounding atoms.
Petersen (1932, 1933, 1936) 15-17 developed the Kronig ideas further for molecules by
adding the phase shift in the photoelectron wave function caused by both the potentials
of the excited atom and the backscattering atoms. The next advance was made by Kos
tarev (1941, 1949)18,19 who realized that the Petersen SRO theory was also applicable to
matter in the condensed state. The lifetime of the excited photoelectron and core hole
state was first accounted for by Sawada et al. (1959)20 through a mean free path. The
remaining missing element was supplied by Shmidt (1961, 1963)21 who pointed out that
the interference of the backscattered waves from atoms at a given average distance (a
2 Chapter 1
coordination shell of atoms) will not be all in phase because of the disorder in their dis
tances due to thermal vibrations or structure variations. He introduced a Debye-Waller
type factor to account for the thermal disorder based on the Debye theory of lattice
vibrations.
The historical development outlined above is not an exhaustive description of all of
the contributions to EXAFS theory. The review. by Azaroff and Pease (1974)22 covers
the field until 1970 (even though it was published in 1974)22 and gives a more complete
exposition. It is our purpose here to take advantage of hindsight, which was not avail
able at the time of the Azaroff and Pease review, and emphasize just those contribu
tions that we now know are correct. At the time of the above developments, the issue
was quite confused. Although the various elements of the modern theory were around,
no one put them completely together. In fact, there was even confusion whether the
SRO or LRO theory was the correct one. In their review to 1970, nine years after the
various elements of the theory had been proposed, Azaroff and Pease (1974)22 stated:
"it is premature to draw any conclusions regarding the most appropriate calculational
approach to employ for EXAFS". A clever experimental study of EXAFS which
attempted to distinguish between the SRO and LRO theories states in its summary
(Perel and Deslattes 197023): "Neither of the (EXAFS) theories discussed here (SRO
and LRO) can account for even the 'gross' characteristics of the absorption spectra ... "
In spite of this confusion, there were some applications made of EXAFS as an
experimental tool. Chemical bond information using near edge structure was obtained
by Mitchell and Beaman (1952)24 and van Nordstrand (1960).25 Nearest neighbor dis
tance determinations were made by Lytle (1965, 1966)26,27 and Levy (1965).28 How
ever, these efforts did not attract general attention because of the confusion surround
ing the subject.
A major reason for the confusion was the lack of detailed agreement between any
theory and the experiments. The experimental measurements were not always reliable
themselves, but this was not a critical factor since there were many reliable measure
ments available which did not agree with the theories. The SRO theory, though correct
in principle, suffered because the atomic parameters that enter it were not calculated
accurately.
The situation changed when Sayers, Stern and Lytle (1971 )29 pointed out, based on
a theoretical expression of the EXAFS (Sayers et al. 1970)30 which has since become
the accepted modern form, that a Fourier transform of the EXAFS with respect to the
photoelectron wave number should peak at distances corresponding to nearest neighbor
coordination shells of atoms. The introduction of the Fourier transform changed
EXAFS from a confusing scientific curiosity to a quantitative tool for structure determi
nation. Instead of comparing EXAFS measurements to theoretical calculations based
on atomic parameters whose values were difficult to calculate, it was now possible to
use EXAFS to extract structure information directly and to determine experimentally
all of the required atomic parameters. The correctness of the SRO theory was now
obvious since the transform revealed only the first few nearest neighbor shells of
atoms.
The accessibility of EXAFS measurements was greatly enhanced with the availability
of synchrotron radiation sources of X-rays several years after the potential of EXAFS
was first shown. Because synchrotron sources typically have x-ray intensities 3 or more
orders of magnitude greater in the continuum energies than do the standard x-ray tube
Historical Development of EXAFS 3
sources, the time for measuring a spectrum for concentrated samples dropped from the
order of a week (Lytle et al. 1975)31 to the order of minutes. At the same time, these
sources expanded possibilities by making feasible the measurement of dilute samples
which could not be even contemplated before.
REFERENCES
I. H. Fricke, Phys. Rev. 16,202 (1920).
2. G. Hertz, Zeit. f. Physik, 3, 19 (1920).
3. D. Coster, Zeit. f. Physik, 25, 83 (1924).
4. A. E. Lindh, Zeit. f. Physik 6, 303 (1921).
5. A. E. Lindh, Zeit. f. Physik 31,210 (1925).
6. W. Kossel, Zeit. f. Physik 1,119; 2, 470 (1920).
7. B. B. Ray, Zeit. f. Physik 55,119 (1929).
8. B. Kievit and G. A. Lindsay, Phys. Rev. 36,648 (1930).
9. J. D. Hanawalt, Zeit. f. Physik 70,20 (1931).
10. J. D. Hanawalt, Phys. Rev. 37,715 (1931).
11. R. de L. Kronig, Z. Physik 70,317 (1931).
12. L. V. Azaroff, Rev. Mod. Phys. 35, 1012 (1963).
13. E. A. Stern, Phys. Rev. BI0, 3027 (1974).
14. R. de L. Kronig, Zeit. f. Physik 75, 468 (1932).
15. H. Peterson, Zeit. f. Physik 76, 768 (1932).
16. H. Peterson, Zeit. f. Physik 80,528 (1933).
17. H. Peterson, Zeit. f. Physik 98,569 (1936).
18. A. I. Kostarev, Zh. Eksper. Teor. Fiz. 11,60 (1941).
19. A. I. Kostarev, Zh. Eksper. Teor. Fiz. 19,413 (1949).
20. M. Sawada, Rep. Sci. Works Osaka Univ. 7, 1 (1959).
21. V. V. Shmidt, Bull. Acad. Sci. USSR, Ser. Phys. 25, 998 (1961); V. V. Shmidt,
ibid., 27, 392 (1963).
22. L. V. Azaroff and D. M. Pease, X-ray Absorption, in: "X-ray Spectroscopy," L. V.
Azaroff, ed., McGraw-Hill, N.Y. ch. 6 (1974).
23. J. Perel and R. D. Deslattes, Phys. Rev. 82, 1317, (1970).
24. G. Mitchell and W. W. Beeman, J. Chern. Phys. 20, 1298 (1952).
25. R. A. Van Nordstrand, Advances in Catalysis 12, 149 (1960).
26. F. W. Lytle in: "Physics of Non-Crystalline Solids", J. A. Prins, ed., North-Holland,
Amsterdam, p. 12 (1965).
4 Chapter 1
27. F. W. Lytle, Adv. X-ray Analysis 9,398 (1966).
28. R. M. Levy, 1. Chern. Phys. 43, 1846 (1965).
29. D. E. Sayers, E. A. Stern and F. W. Lytle, Phys. Rev. Lett. 27, 1204 (1971).
30. D. E. Sayers, F. W. Lytle and E. A. Stern, Adv. X-ray Anal. 13, 248 (1970).
31. F. W. Lytle, D. E. Sayers and E. A. Stern, Phys. Rev. B11, 4825 (1975).