of 5
Persistence pays off: Sir Charles Oatley and the scanning
electron microscope
T. E. Everhart,
a)
President
California Institute of Technology, Pasadena, California 91125
~
Received 29 May 1996; accepted 9 August 1996
!
Shortly after World War II, Sir Charles Oatley initiated research at the Cambridge University
engineering laboratories on what has evolved into the modern scanning electron microscope. While
much of the research was actually conducted by research students under Oatley’s supervision, he
continually provided ideas, resources, and encouragement. He then was instrumental in having this
instrument commercialized. His students often continued in the field for some time, making
contributions both to the instrument and to its applications that led to improved performance and
wider acceptance. This article attempts to capture some of the accomplishments of Sir Charles
Oatley as seen by those who worked closely with him. The author believes that Sir Charles deserves
the title: ‘‘Father of the Modern Scanning Electron Microscope.’’ ©
1996 American Vacuum
Society.
I. INTRODUCTION
I first met Charles W. Oatley in late September, 1955.
With my wife, Doris, I had arrived in Cambridge, England,
to study for a Ph.D. degree under his supervision in the en-
gineering laboratories of Cambridge University. Mr. Oatley,
as we called him then, was somewhat formal, always neatly
dressed, always helpful, yet a man of few words. He always
addressed his students by their surname, and comported him-
self as the English gentleman he was. When I arrived, one
student, Dennis McMullan, had completed his Ph.D. on the
scanning electron microscope
~
SEM
!
, a second, K. C. A.
~
Ken
!
Smith was starting his fourth year on McMullan’s
original instrument, which he had improved, and was starting
to write his dissertation. A third student, O. C.
~
Oliver
!
Wells, was starting his third year, having built a second SEM
from scratch. As the new student, I was to follow Ken Smith
on the original instrument, sharing it with him during my
first year.
Mr. Oatley had an impressive career before he arrived at
Cambridge after World War II as a member of the academic
staff. As an undergraduate, he had read natural sciences at St.
John’s College, Cambridge, and was a contemporary of Sir
John Cockcroft, Sir Nevill Mott, and Louis Leakey. After a
short time in industry, where he received a broad set of ex-
periences, in 1927 he joined the staff of the Physics Depart-
ment at King’s College, London, under E. V. Appleton. He
remained there until 1939, when he was invited to the Air
Defense Experimental Establishment, later the Radar Re-
search and Development Establishment, where he was first in
charge of research and then was deputy head under Cock-
croft. He was made director when Cockcroft left to work on
the atom bomb. In 1945, he was invited by Trinity College,
Cambridge, to become a fellow, and strengthen the postwar
teaching of engineering.
Mr. Oatley was made a Reader in Electrical Engineering
in 1954, which means he was second in the subject only to
the professor, who it turned out, was interested primarily in
his own research. Mr. Oatley was revising the curriculum,
introducing electronics and other more modern subjects, and
stimulating research in the other staff as well as in his stu-
dents. In short, he was busy.
Mr. Oatley became the Professor of Electrical Engineer-
ing in 1960, two years after I left Cambridge, and since then
has been affectionately known to his students as Professor
Oatley. He was elected a Fellow of the Royal Society in
1969, and retired from his chair in 1971, becoming Professor
Emeritus and remaining active both at Trinity College and in
the Engineering Labs for many years. He was knighted in
1974, and in 1976 became a founding fellow of the Fellow-
ship of Engineering, now the Royal Academy of Engineer-
ing. Figure 1 is the official Royal Society photograph of him,
probably taken about 1970. His students and colleagues held
symposia in his honor to help celebrate both his 80th and
90th birthdays. An avid gardener, he remained active until
shortly before he passed away on March 11 of this year at the
age of 92.
A person’s lifetime of accomplishments can properly be
thought of as the sum of their own accomplishments plus the
sum of their influence on other people: progeny, students,
associates, and others. I cannot represent his progeny, the
undergraduates he taught, or many others, such as many in
this audience who have used the SEM. I can represent myself
and try to represent research students who came before and
after me, as I try to give you some idea of why Sir Charles
Oatley, as I should refer to him now, deserves the title:
‘‘Father of the Modern Scanning Electron Microscope.’’
II. RESEARCH AND EDUCATION RATIONALE
In 1982, Sir Charles published an article in the Journal of
Applied Physics entitled ‘‘The early history of the scanning
electron microscope.’’
1
After discussing the work of Knoll
and collaborators, Von Ardenne, and Zworykin, Hillier, and
Snyder, who were all excellent people, but did not produce a
viable SEM, he posed a question: ‘‘Why, in the face of the
a
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Electronic mail: everhart@cco.caltech.edu
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J. Vac. Sci. Technol. B 14(6), Nov/Dec 1996 0734-211X/96/14(6)/3620/5/$10.00 ©1996 American Vacuum Society
discouraging results that had hitherto been obtained, did I
think it worthwhile to reopen the matter in 1948?’’ He an-
swered the question by describing the conditions in the en-
gineering laboratories at that time, and providing his own
views on university research. These conditions and views
provide an important insight into the man, and his impact on
engineering at Cambridge, as well as on the SEM. I should
like to quote a few paragraphs from that article to illustrate.
‘‘Before the war, graduates from the Cambridge Univer-
sity Engineering Department normally left immediately after
obtaining their first degree and went into industry to take a
graduate apprenticeship which would later qualify them for
membership of a professional Institution. Very few remained
in the Department and such research as was done was carried
out largely by members of the teaching staff. In light-current
electrical engineering it was confined almost entirely to
problems relating to circuits.
By 1945 there was general agreement that the prewar pat-
tern could no longer meet the needs of rapidly advancing
technology and that a considerable research effort should be
built up in the Cambridge Engineering Department. To assist
with this program I was appointed to a lectureship in engi-
neering. At the time of my appointment I was in charge of
the army Radar Research and Development Establishment,
in which I had worked for the past six years. Prior to that I
had been a lecturer in a university physics department so it
was natural that, in thinking of possible future research
projects, I should look with favor on those which could be
broadly classified as applied physics.
From a different point of view, a project for a Ph.D. stu-
dent must provide him with good training and, if he is doing
experimental work, there is much to be said for choosing a
problem which involves the construction or modification of
some fairly complicated apparatus. Again, I have always felt
that university research in engineering should be adventurous
and should not mind tackling speculative projects. This is
partly to avoid direct competition with industry which, with
a ‘‘safe’’ project, is likely to reach a solution much more
quickly, but also for two other reasons which are rarely men-
tioned. In the first place, university research is relatively
cheap. The senior staff are already paid for their teaching
duties and the juniors are Ph.D. students financed by grants
which are normally very low compared with industrial sala-
ries. Thus the feasibility or otherwise of a speculative project
can often be established in a university at a small fraction of
the cost that would be incurred in industry. So long as the
project provides good training and leads to a Ph.D., failure to
achieve the desired result need not be a disaster.
~
The Ph.D.
candidate must, of course, be judged on the excellence of his
work, not on the end result.
!
The second reason is rather
similar. A Ph.D. student stays at the university for about
three years and his departure provides a convenient point at
which the promise of his project can be reviewed. If it seems
unlikely to succeed, it can be discontinued without the dis-
satisfaction and discouragement which sometimes attends
similar action in industry.’’
III. BRIEF HISTORY
Oatley knew of innovative work by A. S. Baxter in the
Cavendish laboratory on a secondary electron multiplier with
beryllium–copper dynodes, which could be operated suc-
cessfully in a demountable vacuum system. This new elec-
tron multiplier could amplify the nanoampere and smaller
electron currents expected in the SEM, and overcome one of
the problems faced by previous investigators. He also knew
of many electronic advances made during World War II,
which might improve performance of the SEM. He assigned
the task of building a new SEM to Dennis McMullan, who
was returning to Cambridge for Ph.D. work after five years
in industry working on radar, cathode ray tubes, and analog
computers. Oatley had acquired a loft full of war surplus
valves, cathode ray tubes, meters, and other electrical com-
ponents, as well as surplus vacuum pumps and equipment.
There was also access to an excellent machine shop with
skilled machinists, but there was little money, and he and his
research students had to rely on their own ingenuity. They
were also fortunate to have the skilled help of Leslie Peters,
technical assistant in the department. Peters spent much of
his life helping develop the SEM at Cambridge. On his re-
tirement, Oatley proposed him for an honorary MA, which
was granted.
McMullan built an electrostatic electron microscope, in-
cluding the electron lenses and a 40 kV stabilized power
supply. He also built a cathode ray tube display unit, added
scanning coils to the microscope, and he got all this electri-
cal, mechanical, and vacuum equipment to work as the de-
sired system! Those who followed him are grateful for his
F
IG
. 1. Professor Sir Charles Oatley, OBE, FRS, charter member, Royal
Academy of Engineering.
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T. E. Everhart: Persistence pays off: Sir Charles Oatley
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JVST B - Microelectronics and Nanometer Structures
ingenuity and hard work, for had he failed, the story of the
scanning electron microscope would be very different. Fig-
ure 2 is a photograph of his microscope in Scroope House,
where much of the early work took place.
McMullan examined samples with the scanning beam in-
cident obliquely on the surface, in order to increase both the
number of reflected primary electrons and to produce more
contrast than could be obtained at normal incidence. Ken
Smith believed that secondary electrons actually produced
more of the video signal that was used to modulate the in-
tensity of the display cathode ray tube, and I carried out a
series of experiments to determine what fraction of the video
signal was due to secondary electrons, and what fraction was
due to the reflected electrons. But I digress: this talk is about
Sir Charles Oatley, not about individual contributions to the
SEM by particular research students.
McMullan’s microscope was promising enough that Oat-
ley asked Ken Smith to carry on. Ken improved the reliabil-
ity of the microscope, and investigated several fields of
application.
2
This showed how the SEM was complementary
to the transmission electron microscope
~
TEM
!
, and drew
some attention. However, the resolution was a few hundreds
of angstrom units for the SEM versus 10 or 20 for the TEM.
The fact that sample preparation was minimal to zero for the
SEM compared to replica preparation for the TEM did not
seem important, especially to people who had spent a good
deal of time learning how to prepare replicas. This hard won
knowledge became obsolete if one used the SEM! Oatley
persevered in his faith, and each student who operated a
SEM spent some time extending the applications to help
prove the worth of the instrument.
For example, Oliver Wells showed that one could exam-
ine fibers without burning them, a problem in the TEM, and
he examined the inside bore of spinnerets used to spin arti-
ficial fibers, impossible in the TEM. I looked at
p
-
n
junc-
tions, and developed an understanding of voltage contrast as
well as electron beam induced currents produced by the
scanning electron beam. Richard Thornley examined pow-
ders. Others continued this tradition.
Keeping an electron microscope operating at peak effi-
ciency, especially one built with war surplus components,
was not always easy. In particular, I had difficulty with the
first electronic amplifier that followed the electron multiplier.
The first dynode of the electron multiplier had to be a few
hundred volts positive with respect to the sample, which was
normally grounded. Each succeeding dynode was a few hun-
dred volts more positive yet. By the time the final collector
of the multiplied current was reached, the potential was sev-
eral thousand volts positive, and the amplifier and its power
supply had to float at this potential, amplifying the signal so
that when it came through a high voltage capacitor to
ground, the signal would dominate over any noise introduced
at that step. I sought a much simpler solution to this problem.
Mr. Oatley had suggested a fast plastic scintillator called
Pamelon used in high energy physics for particle detection to
Ken Smith for his water vapor cell. He procured a supply of
this material for me to use in contrast experiments. This scin-
tillator proved useful for transmitted and reflected electrons,
and with a special detector that I constructed so that the
scintillator material could be at 10–15 kV, it proved possible
to detect secondary electrons in this way as well. By guiding
the light produced to a photomultiplier, a noise free detection
system useful for any of the three signals resulted. Richard
Thornley later carried out detailed measurements on the ap-
propriate voltage needed to accelerate the secondary elec-
trons for noise free operation, to characterize the detector
more completely. Each of Oatley’s graduate students could
undoubtedly recite similar suggestions he made that helped
them solve problems they faced.
F
IG
. 2. D. McMullan’s scanning electron microscope, as modified by K. C.
A. Smith. Photograph taken about 1955.
F
IG
. 3. The Canadian Pulp and Paper Research Institute SEM, constructed
by Dr. K. C. A. Smith at Cambridge University engineering laboratory.
Photograph taken in Cambridge by Les Peters about 1957 or 1958.
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J. Vac. Sci. Technol. B, Vol. 14, No. 6, Nov/Dec 1996
After Ken Smith received his doctorate, Oatley also ar-
ranged for him to design and construct an improved SEM for
the Pulp and Paper Research Institute of Canada. This instru-
ment, shown in Fig. 3, had magnetic lenses, and incorporated
the improved detector mentioned above. Its performance
gave confidence that a stable, reliable instrument could be
built for routine work. It performed well in Canada for a
decade or more.
Garry Stewart, Fabian Pease, Alec Broers, and Phillip
Chang were the final four doctoral students that Oatley ac-
cepted, although the latter three finished their dissertation
under Dr. W. C. Nixon, who joined Oatley as Assistant Di-
rector of Research in October, 1959. Stewart built an im-
proved instrument, and studied basic mechanisms in ion
sputtering, watching the process dynamically. Pease con-
structed a high resolution SEM using a much improved mag-
netic lens design, and improving many other aspects of the
instrument as well. He held the resolution record for the
SEM for several years. A picture of his instrument is shown
in Fig. 4. Broers inherited Stewart’s instrument and studied
selective ion beam etching. Stewart meantime went to work
for Cambridge Instruments Company, and played a major
role as that company commercialized the Stereoscan SEM.
Chang has had a distinguished career at IBM, and recently
has developed a pocket-sized SEM column.
IV. EDUCATION AT CAMBRIDGE
In order to appreciate Mr. Oatley’s considerable influ-
ence, it is necessary to understand the university system in
which he operated. Cambridge University is a collection of
colleges and members of the university are generally also
members of a college. As such, they contribute to and inter-
act with members of the college, as well as with their own
university department. In Mr. Oatley’s case, he was both a
fellow of Trinity College and a member of the engineering
faculty. Individual supervision of undergraduate students
was arranged through the college; lecture classes were taught
in engineering. Students were expected to learn the material,
but were examined on it only at the end of the year, a pre-
liminary exam being taken at the end of the first year, and the
Tripos exams at the end of their second and third year. More
studying often went on during vacations, which were long,
than during term time when lectures were given and there
were many student activities.
At that time, there were few lecture courses for graduate
students, and they were purely voluntary. Graduate students
were given great freedom, but also considerable responsibil-
ity. Research supervisors would advise, point you in the right
direction, refer you to articles to read, but the detailed
knowledge you had to dig out for yourself. It took consider-
able discipline to make each day count.
The normal work week was Monday through Friday, plus
Saturday morning. Morning coffee at about 10:30 a.m. was
when I could count on finding Mr. Oatley for a few mo-
ments, to ask a question, gain permission for a purchase, or
discuss a point. All the research students gathered there, as
did several members of the staff. A good deal of informal
questioning, discussion, and learning took place then. Mr.
Oatley made many suggestions during these moments that
helped my research move forward. He also would ask about
my wife and daughter. Perhaps because there were very few
married students at Cambridge in those days, his wife, Enid,
would look in from time to time on my wife and infant
daughter, often bringing a little gift, a word of cheer, and
confirming that the entire Everhart family was important to
both the Oatleys.
One morning at coffee, Mr. Oatley asked me about a re-
cent development in traveling wave tubes, a topic of my
earlier research at the Hughes Research Labs. A lecturer in
the department who had some radar experience during WW
II interjected that he didn’t know why Oatley asked me, a
lowly research student, about such a topic. Mr. Oatley, with
a smile, responded that since I had three publications on the
subject, he thought the question was appropriate. We then
continued our discussion, while the lecturer listened. Mr.
Oatley treated people well, respected them for what they
knew, and was able to educate them when they needed it.
Because of his age
~
over 50 at the time
!
and distinguished
bearing, both the academic and electronic shop staff often
referred to Mr. Oatley as ‘‘Uncle’’ when he was not present.
He never let on that he knew this, until one day when two
members of the academic staff were having a discussion
about a difficult question. He was asked for advice, solved
the problem on the spot, and then left the room. As they were
expressing wonder and appreciation about this feat, he stuck
his head back through the door, and reportedly said: ‘‘Uncle
F
IG
. 4. High resolution SEM constructed by R. F. W. Pease. Photograph
taken in 1963 by Les Peters.
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is a cagey bird’’, and then left. This added to his legend as a
leader who was aware of what was going on around him!
V. PERSISTENCE PAYS OFF
Even in 1960 detractors well outnumbered champions of
the SEM. Indeed, Mr. Oatley himself still defended his pro-
gram largely on the grounds of the SEM being a valuable
educational vehicle in that mastering it required developing
competence in a wide variety of disciplines including elec-
tron optics, circuitry, signal processing, mechanical engi-
neering, high voltage engineering, and, often, solid state
physics. Indeed, the SEM faced competition from the trans-
mission electron microscope because the latter was perceived
to be much simpler and had far better resolution. In addition,
the TEM could operate in reflection, which allowed exami-
nation of surfaces at higher resolution than that obtained with
the SEM. Nonetheless, there were a growing number of ap-
plications for which the reflection and replica techniques
were impractical
~
e.g., the
in situ
examination of surfaces
undergoing changes or very fragile surfaces
!
and, although
not appreciated by professional microscopists at the time, the
convenience
~
minimal specimen preparation
!
and extraordi-
narily lifelike images made believers out of those who had
access to the SEM. V. E. Cosslett, who led the electron mi-
croscope research group at the nearby Cavendish laboratory,
recognized that the scanning operation allowed decoupling
of the mapping operation from the contrast operation so that
the information from the sample did not have to be focused.
This allowed Dr. Peter Duncumb on Cosslett’s team to de-
velop the scanning electron x-ray microanalyzer
~
which
mapped elemental content by collecting characteristic x
rays
!
.
Mr. Oatley pressed hard for the commercialization of the
SEM. He hoped Metropolitan Vickers, a company that made
electron microscopes, would make and sell them, but this
came to naught. Drs. Ken Smith and Bill Nixon persuaded
the chief development engineer of the Cambridge Instrument
Company that, in addition to the scanning x-ray microprobe,
mentioned above, the company should manufacture the SEM
as well. Sir Charles received permission from Metropolitan
Vickers to turn elsewhere, then approached the managing
director of the Cambridge Instrument Company, and the first
commercial SEM was under way. Since the mid 1960’s,
commercial SEMs have enabled many people to see the
world we live in with more clarity and detail, and to both
see, and then make, smaller devices which have benefited
mankind.
VI. OATLEY’S SEM STUDENTS
The people who worked on the SEM under Sir Charles
Oatley have had successful careers, often using the expertise
they learned in Cambridge. Dennis McMullan, after a suc-
cessful career at Imperial College, London, and at the Royal
Greenwich Observatory, is carrying on research in Cam-
bridge during his retirement. Ken Smith helped Dr. V. E.
Cosslett develop a high voltage TEM in the Cavendish, and
later was a member of the team that developed a high reso-
lution electron microscope. He became a Reader in the engi-
neering laboratory, and is now retired. Oliver Wells has had
a successful career in industry, for many years at IBM, and
has written a book on the SEM, as well as made many con-
tributions to its operation and applications. I was active in
the field for about twenty years while a professor at Berke-
ley, and more recently have been active in academic admin-
istration. Peter Spreadbury, who developed a simplified SEM
as a Master’s degree project, is a lecturer at Cambridge.
Richard Thornley has had a successful career at IBM, and
more recently at Storage Technology. Garry Stewart worked
for a considerable period of time at Cambridge Instruments
Company and, more recently, at deBeers, where he has put
his considerable expertise at instrumentation to good use.
Fabian Pease is a professor at Stanford University, after a
successful period at Bell Laboratories. He has made impor-
tant contributions to a host of fields, including electron beam
micro fabrication and commercial instruments for this pur-
pose. Alec Broers had a very successful career at IBM, rising
to become an IBM fellow and department manager. He re-
turned to Cambridge, becoming Professor of Electrical Engi-
neering, head of the engineering laboratories, Master of
Churchill College, and in October 1996 became the Vice
Chancellor of Cambridge University.
Sir Charles Oatley told me on a recent visit to Cambridge
that he took considerable satisfaction in the accomplishments
of his students, such as Ian Ross, an early student who be-
came President of Bell Labs. He would be delighted that
Alec Broers will become the first engineer to ever lead Cam-
bridge University. Sir Charles was a modest man, who sent
his students off to conferences to give papers, who immersed
himself in bettering his university while others gave the
talks, and who quietly paved the way for others. Through his
ideas, his encouragement, his provision of resources, and his
push for a commercial SEM, I believe that Sir Charles Oat-
ley truly deserves the title: ‘‘Father of the Modern Scanning
Electron Microscope.’’
1
C. W. Oatley, J. Appl. Phys.
53
, R1–R13
~
1982
!
.
2
The contributions mentioned in this article are documented in Ref. 1 in
more detail, and are not included here to save space.
3
I am indebted to D. McMullan, K. C. A. Smith, O. C. Wells, R. F. W.
Pease, and A. Broers for help in preparing this manuscript. I have also
referred to obituaries that appeared in the London Times, The Guardian,
and Nature.
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