Table Of ContentELECTRON PROBE
QUANTITATION
ELECTRON PROBE
QUANTITATION
Edited by
K.F .J. Heinrich
and
Dale E. Newbury
Chemical Science and Technology Laboratory
National Institute of Standards and Technology
Gaithersburg, Maryland
SPRINGER SCIENCE+BUSINESS MEDIA. LLC
L1brary of Congress Catalog1ng-in-Publicat1on Data
Electron probe quar.titat1on 1 edited by K.F.J. Heinrich and Dale E.
Newbury.
p. cm.
"Result of a gathering of Jnternational experts in 1988 at ...
National Institute of Standards and Technology"--Pref.
Includes bibl1ographical references and index.
ISBN 978-1-4899-2619-7 ISBN 978-1-4899-2617-3 (eBook)
DOI 10.1007/978-1-4899-2617-3
1. Electron probe m1croanalysis--Congresses. 2. Microchemistry-
-Congresses. I. Heinrich, Kurt F. J. II. Newbury, Dale E.
QD117.E42E44 1991
543'.08586--dc20 91-11807
CIP
ISBN 978-1-4899-2619-7
© 1991 Springer Science+Business Media New York
Originally published by P1enum Press, New York in 1991
Softcover reprint ofthe hardcover 1st edition 1991
Ali 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
In 1968, the National Bureau of Standards (NBS) published Special Publication 298
"Quantitative Electron Probe Microanalysis," which contained proceedings of a seminar
held on the subject at NBS in the summer of 1967. This publication received wide interest
that continued through the years far beyond expectations. The present volume, also the
result of a gathering of international experts, in 1988, at NBS (now the National Institute of
Standards and Technology, NIST), is intended to fulfill the same purpose.
After years of substantial agreement on the procedures of analysis and data evaluation,
several sharply differentiated approaches have developed. These are described in this publi
cation with all the details required for practical application. Neither the editors nor NIST
wish to endorse any single approach. Rather, we hope that their exposition will stimulate
the dialogue which is a prerequisite for technical progress. Additionally, it is expected that
those active in research in electron probe microanalysis will appreciate more clearly the
areas in which further investigations are warranted.
Kurt F. J. Heinrich (ret.)
Dale E. Newbury
Center for Analytical Chemistry
National Institute of Standards and Technology
v
CONTENTS
EARLY TIMES OF ELECTRON MICROPROBE ANALYSIS . . . . . . . . . . . . . 1
R. Castaing
STRATEGIES OF ELECTRON PROBE DATA REDUCTION . . . . . . . . . . . . 9
Kurt F. J. Heinrich
AN EPMA CORRECTION METHOD BASED UPON A
QUADRILATERAL !j>(pz) PROFILE.................................. 19
V. D. Scott and G. Love
QUANTITATIVE ANALYSIS OF HOMOGENEOUS OR STRATIFIED
MICROVOLUMES APPLYING THE MODEL "PAP".................. 31
Jean-Louis Pouchou and Fran~oise Pichoir
!j>(pz) EQUATIONS FOR QUANTITATIVE ANALYSIS................... 77
J.D. Brown
A COMPREHENSIVE THEORY OF ELECTRON PROBE
MICROANALYSIS................................................... 83
Rod Packwood
A FLEXIBLE AND COMPLETE MONTE CARLO PROCEDURE
FOR THE STUDY OF THE CHOICE OF PARAMETERS . . . . . . . . . . . . . . 105
J. Henoc and F. Maurice
QUANTITATIVE ELECTRON PROBE MICROANALYSIS OF
ULTRA-LIGHT ELEMENTS (BORON-OXYGEN)...................... 145
G. F. Bastin and H. J. M. Heijligers
NONCONDUCTIVE SPECIMENS IN THE ELECTRON PROBE
MICROANALYZER-A HITHERTO POORLY DISCUSSED PROBLEM 163
G. F. Bastin and H. J. M. Heijligers
THE R FACTOR: THE X-RAY LOSS DUE TO ELECTRON
BACKSCATTER..................................................... 177
R. L. Myklebust and D. E. Newbury
THE USE OF TRACER EXPERIMENTS AND MONTE CARLO
CALCULATIONS IN THE !j>(pz) DETERMINATION FOR
ELECTRON PROBE MICROANALYSIS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Peter Karduck and Werner Rehbach
EFFECT OF COSTER-KRONIG TRANSITIONS ON
X-RAY GENERATION............................................... 219
JM.os L. LAb6r
vii
viii CONTENTS
UNCERTAINTIES IN THE ANALYSIS OF MX-RAY LINES
OF THE RARE-EARTH ELEMENTS.................................. 223
J. L. Labar and C. J. Salter
STANDARDS FOR ELECTRON PROBE MICROANALYSIS............. 251
R. B. Marinenko
QUANTITATIVE ELEMENTAL ANALYSIS OF INDIVIDUAL
MICROPARTICLES WITH ELECTRON BEAM INSTRUMENTS....... 261
John T. Armstrong
THE f(x) MACHINE: AN EXPERIMENTAL BENCH FOR THE
MEASUREMENT OF ELECTRON PROBE PARAMETERS . . . . . . . . . . . . 317
J. A. Small, D. E. Newbury, R. L. Myklebust, C. E. Fior~
A. A. Bell, and K. F. J. Heinrich
QUANTITATIVE COMPOSITIONAL MAPPING WITH THE
ELECTRON PROBE MICROANALYZER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
D. E. Newbury, R. B. Marinenko, R. L. Myklebust, and D. S. Bright
QUANTITATIVE X-RAY MICROANALYSIS IN THE ANALYTICAL
ELECTRON MICROSCOPE........................................... 371
D. B. Williams and J. I. Goldstein
INDEX................................................................ 399
EARLY TIMES OF ELECfRON MICROPROBE ANALYSIS
R. CASTAING
Universite de Paris-Sud
Orsay, France
Introduction
In 1967 I gave in London an after-dinner talk about "the early vicissitudes of electron
probe x-ray analysis." At this time, it was already an old story; now, it looks like prehistory.
I hope the reader will pardon me for evoking here, as an introduction to a series of papers
which will illustrate the present state of the art in that field, the reminiscences of an old
timer.
In January 1947, I joined the Materials Department of the Office National d'Etudes et
de Recherches Aeronautiques (ONERA), in a little research center 30 miles away from
Paris, near the village of Le Bouchet. My laboratory was equipped with an ill-assorted
collection of scientific apparatus, most of which had been obtained from Germany at the
end of the war; but in December I received the basic equipment I had been promised when
engaging at ONERA: two electron microscopes, at that time a real luxury. One of them
was a French electrostatic instrument manufactured by the C.S.F.; the other an R.C.A.
50 kV microscope built in 1945. I immediately turned my attention toward the R.C.A.
instrument; it was very pretty indeed and I was fascinated-! am ashamed to say-by the
American technology. I used that microscope, together with the oxide-film replica tech
nique, for studying the wonderful arrangements of oriented precipitates-platelets or
needles-which form when light alloys are annealed at moderate temperatures. That was
the occasion for me to meet Professor Guinier who studied the same alloys with x rays in
his laboratory at the Conservatoire des Arts et Metiers. I was astonished to learn from him,
in the course of one of our conversations, that the composition of most of the precipitates
or inclusions which appear on the light micrographs was in fact unknown, in spite of the art
of the metallographers, if their number was too small for recognizing the phase by x-ray
diffraction. On that occasion he asked me my opinion about identifying at least qualitatively
the elements present in such minute individual precipitates by focusing an electron beam
onto them and detecting the characteristic x rays so produced. I replied straightaway that
to my mind it was very easy to do; I was surprised that no one had done it before. We
agreed that I would try to do the experiment, even if it appeared a little too elementary a
subject for a doctoral thesis. In fact, there were some slight difficulties as I was to find out
during the next 2 or 3 years.
The plan I drew up for my work was simple. Electron probes less than 10 nm in
diameter had been produced by Boersch just before the war; Hillier used 20-nm probes in
his attempts to microanalyze thin samples by the characteristic energy losses of the elec
trons. With the self-assurance of youth, I planned using such probe diameters for exciting
the x rays, so that scanning microscopy was necessary for locating the points to be ana
lyzed. The only problem I was foreseeing was the intensity of the x rays; the expected
electron beam current was much less than a thousandth of a microampere and, from mea
surements carried out with Guinier on his conventional x-ray tubes, we concluded that even
with a Geiger Muller counter, the counting rates from a curved quartz spectrometer would
be of the order of one pulse per minute. Surely we were too pessimistic, as we disregarded
Electron Probe Quantitation, Edited by K.F.J. Heinrich and
D. E. Newbury, Plenum Press, New York, 1991
2 ELECTRON PROBE QUANTITATION
the fact that a bent crystal does not reflect correctly the radiation from a broad source, but
at that moment we concluded that we would have to fall back on nondispersive methods
such as balanced filters. In short, the basic idea was to build an instrument provided with
nondispersive spectrometry and with a scanning electron microscope for viewing the ob
ject. We had little hope, in view of the small number of counts obtainable in a reasonable
time and the supposed complexity of the laws governing the emission of characteristic lines
by compounds, to get any accuracy for quantitative analysis. By the way, the instrument
planned was nothing more than a modern scanning microscope equipped with E.D.S. How
ever, for the years to come, things were to be quite different.
First I realized that in massive samples which concerned the metallurgists I would
have to give up the splendid spatial resolving power that I had cheerfully envisaged, as I
became aware of the terrific path that my electrons would perform haphazardly in the
sample before agreeing to stop. I had to limit my ambitions to analyzing volumes of a few
cubic micrometers. That was a big disappointment despite the gain of several orders of
magnitude in resolution over localized spark source light spectrometry, which at this time
was the best technique available for microanalysis. That disappointment showed a little
when I presented my first results at the first European Regional Conference on Electron
Microscopy held in 1949 in the lovely city of Delft.
I have happy memories of that Delft Conference. It was the first time my wife and I
left France. I had prepared my presentation in French and was astounded when the orga
nizers told me, the day before my talk, that I had better give my paper in English. By
chance, when arriving at the conference place, we had made friends with young British
participants Alan Agar and his wife. Agar kindly proposed to help me by translating my
paper, which took half of the night. He is perfectly right when he claims that the first paper
on the microprobe, attributed to Professor Guinier and me, was in fact written by him.
The experimental arrangement that I presented in that paper was quite simple indeed.
I had modified my C.S.F. microscope, replacing the projector lens with a probe forming
lens; the objective operated as a condenser. The probe formed 6 mm below the lower
electrode; the specimen could be moved by a crude mechanical stage, but in addition, an
electrostatic deflector allowed controlled displacement of the probe across the sample sur
face. The experiment consisted of demonstrating the spatial resolving power by plotting the
changes in the total x-ray emission, as registered by a Geiger Muller counter, when the
probe passed over chemical discontinuities. The first sample I observed was a plating of
copper on aluminum; from the steep change of the emission one could estimate the resolv
ing power to 1 or 2 micrometers. Similar intensity drops were observed on a sample of cast
iron when the probe passed over the graphite flakes.
At this time preliminary trials with a Johannson curved quartz crystal that Guinier had
brought from his laboratory, where he used it as a monochromator, had shown that count
ing rates of several hundred per second could be obtained on the Cu K a line with that
1-J.Lm, 30-kV probe, in spite of the weakness of the beam intensity, less than one hundredth
of a microampere. That opened the way to quantitative measurements of the lines and I
hastened to fit the instrument with a Johannson focusing spectrometer manufactured at the
ONERA workshop. It was ready at the beginning of 1950 when the Materials Department
moved to the present building of Chatillon-sous-Bagneux. This spectrometer was a nice
piece of work; it could be adjusted to allow very good separation of the K a doublets. The
wavelength range was limited; it gave access to the K radiation of the elements between
titanium and zinc. The L radiation allowed detecting heavier elements between cesium and
rhenium. I also equipped the probe forming lens with an electrostatic stigmator, whose
operation could be controlled quite satisfactorily by looking at the symmetry of shadow
CASTAING 3
images of extremely thin plexiglass filaments, coated by vacuum deposition with chromium
to avoid their melting under the beam. All was ready for attacking the problem of quantita
tive analysis.
I had undertaken a theoretical calculation of the intensity of the x-ray lines; the princi
ple generally accepted at this time for x-ray emission analysis consisted of comparing the
concentrations of two component elements by measuring the intensities of the correspond
ing characteristic radiations. I was quite excited indeed when I realized, in the course of
that calculation, that the number of parameters, instrumental and others, would be consider
ably reduced if I did away with the comparison of different lines and proceeded by compar
ing the same x-ray line when emitted by the sample and by a known standard such as the
pure element. That amounted to comparing directly-apart from a correction for self-ab
sorption in the targets-the total number of ionizations that an electron produces in the
sample on a given atomic level to the corresponding number in the standard. It was clearly
the key to absolute quantitative measurements.
The best way for checking that principle was to analyze diffusion couples where the
pure elements and various intermetallic phases would be found together, and· the first one I
observed was a silver-zinc couple. In principle I had only to move the specimen under the
beam and to plot the Zn K a emission while the probe crossed the diffusion zone. But the
apparatus was not equipped at this time with a viewing device and my crude specimen stage
could not ensure calibrated displacements. I was reduced to moving the sample more or less
haphazardly, watching the abrupt changes of the zinc emission, then scanning the probe
across the discontinuity for exploring locally the diffusion curve near the phase boundaries.
I remember my delight when I noticed, by observing the diffusion couple under the micro
scope after hours of fight against the beam instabilities, that all the phase boundaries were
covered with myriads of contamination spots. I realized that the discontinuities of emission
I had observed really corresponded to changes of composition. This was a revelation and
since then I really believed in electron probe microanalysis.
That exhausting experiment made clear to me that a viewing device was a pressing
necessity. That was not a simple job; I had to insert a mirror in the 6-mm clearance between
the probe forming lens and the sample where part of the space was occupied by the stigma
tor. I still remember the wonder I felt when I was able to see the specimen during the
bombardment; the counter became crazy when I brought a precipitate under the cross
wires of the eyepiece. Some of those precipitates were good enough to become fluorescent
under the beam. That somewhat monstrous apparatus was the most splendid toy I ever had.
Then things became serious. Measurements on homogeneous samples showed that the
simple ratio k of the two readings, on the sample and on a pure standard, was not far from
giving directly the mass concentration, at least in the case of neighboring components; but
estimations of the electron penetration from Lenard's law made clear that the self-absorp
tion of the x-ray photons in the target was far from negligible. It was clear that if a simple
relation was to be confirmed between the k-ratios and the concentrations, it would hold for
the k-ratios of the generated intensities only, and not for those of the emerging ones which
had to be corrected for their absorption in the target. Another correction had to be made
for subtracting the contribution of the fluorescence, but it was generally low and calculat
ing it was not too complicated. Estimating the self absorption required the knowledge of
the depth distribution of the characteristic emission, which was at this time practically
unknown, at least at the required level of accuracy. I realized that the correction curve
could be obtained by plotting the emerging intensity as a function of the angle of emergence
of the beam-an extension of a simple method originally proposed by Kulenkampff. Rotat
ing the whole spectrometer around the bombarded point raised serious technical diffi-
