microhist.htm

The Electron Microscope

The History of the Building of the 1938 Toronto Microscopy

Fig. 1B  The 1938 column with the revised camera and its cross-sections

Fig. 1C   Prebus left and Hillier right, working with the microsope in 1938.

Fig. 1D   The 1938 microscope with the revised camera, Prebus at the microscope, Professor Burton left and Ladd sitting right, 1940.

New ideas are never confined to one person or place and in 1937 when Hillier and Prebus were beginning their work, attempts at building electron microscopes had been going on in Europe for about 10 years. Hans Busch’s 1926 paper which showed theoretically that a coaxial magnetic or electric field could be expected to focus an electron beam and Louis deBroglie’s earlier hypothesis that electrons possess wave properties, suggested to physicists that an electron microscope was not only possible but that it might produce resolution far superior to that of an optical microscope. The basic principles of electron lenses had already been worked out in Europe and Ernst Ruska and his colleagues at the Berlin Technische Hochschule had developed the essential design of pole-pieces to concentrate a magnetic field. Ruska himself had already constructed in 1933 his early model of a two-stage transmission instrument with which he had achieved resolution only slightly better than that expected from a light microscope. By 1933, Marton in Belgium and Martin, Whelpton and Parnum in England had also built instruments, and developments were proceeding likewise in Japan and in the United States but with less success. Of all these attempts, only Ruska was able to produce micrographs and these did not demonstrate satisfactory resolution. As Hillier noted in his M.A. thesis (9), describing work going on elsewhere, "reports carried more details of problems than of their solutions." In general, the lenses demonstrated chronic distortion and astigmatism and the few published micrographs were badly blurred. The specimens seemed to have been damaged by the heat of the beam and many, as yet unknown factors were affecting images adversely. Leading microscopists, particularly in the United States, were very skeptical of the possibility of an electron microscope and had labeled the project of creating one as "impossible" and the few published electron micrographs as "fakes." It is with this background, that the success of the two Toronto graduate students, directed by Professor Burton, was so unforeseen and so remarkable.

The moving force behind the project to build a magnetic transmission electron microscope at the University of Toronto was Professor E.F. Burton, who had succeeded Sir John Cunningham McLennan as Chairman of the Department of Physics in 1932. Burton had graduated from Toronto with honours in mathematics and physics and had worked for two years as a Demonstrator under McLennan, before an Exhibition Scholarship took him to Cambridge and the Cavendish Laboratory, where he worked under J.J. Thomson, the recent discoverer of the electron. Several reasons can be advanced for Burton’s keen desire to develop an electron microscope. At Cambridge he had earned a second B.A. for his work with colloids and he reasoned that an electron microscope would have resolution¹ sufficient for him at last to be able to see and study colloidal particles directly in solution and aerosols. Working for J.J. Thomson must have stirred his interest in electrons, and his own diabetic medical history would have sensitized him to the development of science in medicine, where an electron microscope might be expected to play a part. For whatever of several reasons, Burton was quick to recognize the potential of an electron microscope for research.

¹ [Resolution with a light microscope is given by the expression 1/3(lambda), where (lambda) is the wavelength of the radiation being used. With ultraviolet radiation, where (lambda)=3000 A, and using quartz lenses, the best resolution would therefore be about 1000 A^c, where one A^c = 10^-8 cms. DeBroglie’s theoretical wavelength of an electron is given by (lambda)=h/mv, where h is Planck’s constant and m and v are the mass and velocity respectively of the electron. From this, it can be shown that the wavelength of an electron is equal approximately to 12.24/(square root)V x10^-8 cms, and that with V=50,000 volts the theoretical resolution of an electron microscope would be about 0.02Å-, a considerable improvement over the resolution expected with an optical microscope.]

He was catalyzed to action by his friendship with Dr. Walter H. Kohl, who had a Ph.D. in Engineering Physics from the Technical University of Dresden and was employed in Toronto as a development engineer with Rogers Radio Tubes Ltd., doing pioneer work in television on problems to do with the deflection of electron beams by magnetic and electric fields. Kohl repeated in his own laboratory much of the published work coming out of Germany. He attended seminars in the Department of Physics and became acquainted with Professor Burton and Burton came to rely on Kohl for his knowledge of electronics and for his ability to translate German papers. At Burton’s invitation, he gave many seminars in the Department on a variety of subjects to do with the emerging subject of electron optics. Kohl’s lectures and demonstrations in electron optics certainly must have encouraged Burton to develop his own electron microscope project.²

²[For more detail on Dr. Burton and Dr. Kohl, the reader is referred to references 1 and 3 of this paper.]

During the summer of 1935, Burton attended a conference in Berlin on the subject, Possible Areas for the Application of the Electron Microscope. In the autumn, he returned, enthusiastic, to Toronto to meet a young Cecil E. Hall, from the University of Alberta, who was expecting to do graduate work in spectroscopy. Burton was able to convince Hall, as he would later convince Prebus, to change his interests from spectroscopy to electron optics and to become his first graduate student in the new field. It is said that the general attitude of graduate students in the Department toward electron optics at that time was negative but Hall was attracted to it and agreed to construct a simple electrostatic emission type electron microscope. He built two emission microscopes during the next two years, the second with two magnetic lenses with which he took micrographs of the emitting surfaces of hot cathodes at 3000X. For this work, he received an M.A. in 1936 (10). Burton had been able to find financial support for Hall in spite of the Great Depression and the great scarcity of research moneys. The situation has a modern-day ring to it! The figure secured by Burton for Hall’s second year is interesting by today’s standards: 800 dollars from the N.R.C. to cover both equipment and stipend.³

³[Things had not improved much salary-wise by the autumn of 1939, when I, as a graduate student, was demonstrating Physics for a stipend of $800. for the term.]

In May of 1935, Burton turned again to N.R.C. for funds, "to attempt to take electron micrographs of substances placed in the path of an electron beam," i.e. to construct a true transmission electron microscope. Burton asked for $724.50, $250 for equipment and the balance for the investigator’s salary at $62.50 per month.⁴ On the grounds that the work could be as well done by a scholarship holder, Burton’s request was refused and Hall, unfunded, was forced to leave the project. As Hall’s career was to show, his departure from Toronto was a huge loss for the Department and the University. Hall accepted a position at the Eastman Kodak Company in Rochester, New York., where there was interest in building an electron microscope in the United States in 1939 at Kodak. I shall not follow Hall’s outstanding career any further than to remark that he went to M.I.T. from Kodak and did remarkable work there in the Biology Department. At M.I.T., he completed the requirements for the Ph.D. and published his book on electron microscopy (11), still a worthwhile read for electron microscopists.

⁴[From these figures, it appears that Burton must have thought that Hall would be able to construct a microscope in about 7 ½ months. He wasn’t far wrong. As it turned out, it took Hillier and Prebus about 4 months!]

As has been pointed out earlier, expectations for electron microscopy were viewed with extreme skepticism by many scientists. Hall has told me that optics of the electron variety was a rather "cool" subject at Toronto in the thirties when low temperature physics and spectroscopy were the "hot" topics. Dr. M.F. Crawford had been made head of spectroscopic research in 1937 and had accomplished a large body of well recognized research. He was already an authority in atomic spectroscopy, attracting many graduate students to his well equipped laboratory, including Hall and Prebus. Some of the local antipathy to Burton’s electron microscope project may well have been caused by his penchant for convincing graduate students to work in electron optics rather than in the well established field of spectroscopy. Albert Prebus had come to Toronto in the autumn of 1937 fully intending to continue his interest in atomic spectra, but Burton convinced him too, to change his research interests into the new field. During the years that I knew them, I must admit that I never heard either Hall or Prebus complain that they had deserted spectroscopy for electron optics.

When Prebus arrived in Toronto, he had an M.Sc. from the University of Alberta, and Burton teamed him up with a 1937 B.A graduate in M and P from the University of Toronto, James Hillier, who had already been working since graduation on the electron microscope project. While the two are quite different in personality, with Hillier outgoing and Prebus more introspective, both are highly intelligent and diligent and were enthusiastic for the project. They worked exceptionally well as a team. Their project was to build a compound, transmission, magnetic electron microscope and to apply it to biological and colloidal materials. In order to accomplish this, in addition to their own wits, they had only Hall’s M.A. thesis, his emission microscopes and translated publications by Knoll, Marton and Ruska to help them.

The design, machining and construction for the column, particularly of its more sensitive components, such as the pole-pieces, were done mostly by Hillier and Prebus themselves. Prebus recalls that the shop work was done on a two-shift basis, with the day crew.⁵ from 8:00 a.m. to 5:00 p.m., Hillier and Prebus the night shift (without the unqualified approval of the day crew), often until 4:00 a.m. Working drawings were submitted at the end of the Christmas vacation of 1937 and active construction was begun in January of 1938. Impossible as it may seem to us now, they succeeded in assembly of the high voltage and the vacuum systems, and in construction of the column in less than four months and realized success in April of 1938 with quality micrographs at measured resolution of 140 Å, soon improved to 60 Å by use of a solid objective pole-piece, machined en bloc and designed by Prebus (12). I can witness personally that many micrographs with 20 Å or better measured resolution were taken with the 1938 model during the years that followed. Prebus has confided in me since, that he and Hillier were somewhat surprised at their initial quick success. I imagine that they must have been, but there must have also been extreme gratification and pleasant excitement for both of them.

⁵[The personnel of the McLennan Laboratory machine shops were very important to the develop-ment of electron microscopy at the University of Toronto. Mr. Grantley Woodward, particularly, did much of the construction of the Toronto microscopes and he acknowledged the efforts of his colleague, Mr. Frank Shepherd, who, like Grant, worked on both the 1938 and 1940 models. Grant was mainly responsible later for the machining and construction of the 1944 model. For his technical contributions to early electron microscopy, Mr. Woodward was awarded an honorary membership in the Electron Microscopy Society of America in 1978. He worked with each of us and much of his time was spent deciphering our amateur engineering drawings, on which we left our spurts of genius. In the basement of the McLennan Laboratory there was a true genius, a blower of glass, Harold Chappelle, who blew our first mercury and diffusion vacuum pumps, and whose talented hands could produce any object of glass, however complicated, for us or others at the Laboratory.]

The successful outcome of the project was reported by Burton to the University in his very casual way, "Mr. James Hillier, assistant demonstrator and Mr. Albert Prebus, holder of a studentship from the National Research Council have continued the work of perfecting the electron microscope and have succeeded in taking many photographs of submicroscopic structures up to a primary magnification of 30,000 times". The first scientific report was submitted to the Canadian Journal of Research in January 1939, just one clear year after work had been begun, and appeared in April 1939 (13). A short note was published in Physical Review in December 1939 (14) and other reports, describing the work, appeared in 1939 (15) and 1940 (16). Some of the first micrographs were reproduced on December 17, 1938 in the popular magazine Saturday Night with a descriptive text by Burton, and a second popular article appeared in MacLean’s magazine on April 1, 1939 authored by the journalist R.E. Beamish. The book by Burton and Kohl (17) which described the 1938 microscope appeared in 1942, with its second edition, describing the 1944 model, in 1946.

I happened to read the MacLean's story in the spring of 1939, when I was in my graduating. year in Mathematics and Physics at McMaster University in Hamilton, Ontario. I was intrigued by the description of a new type of microscope which used a magnetic field instead of glass as a lens, and electrons instead of light as radiation, and wishing, in any case, to continue with University life, I wrote to Professor Burton asking if I could be considered for a situation as a graduate student in Physics under his direction. To my delight, and somewhat to my surprise, Dr. Burton accepted my application and offered me a fellowship in his laboratory. Thus, by reason of reading the MacLean's article, the generosity of Professor Burton and my own good fortune were my feet placed on the pleasant and rewarding paths of electron microscopy.

William A. Ladd, a 1939 graduate in Mathematics and Physics at the University of Toronto, whose name is familiar to electron microscopists as the founder of the Ladd Research Instruments Inc., also joined the electron microscope team in the Fall of 1939. He was assigned to Hillier and I to Prebus as our mentors. Ladd’s activity took him primarily into work with Hillier and Prebus as the second, or 1940 model electron microscope was built. Funds for this were provided by the Colombian Carbon Company of Brooklyn, New York, whose far-sighted research director, Dr. W.B. Wiegand, a graduate in physics of the University of Toronto and a close friend of Burton, had realized early the potential of the microscope for determining the particle sizes and other properties of carbon blacks. Ladd left the laboratory after receiving his M.A. (18) in 1940 and went with the 1940 microscope to Brooklyn.

My M.A. studies were related to basic electron optics with Prebus and my M.A. thesis (19) was entitled. "The Measurement of the Magnetic Field Along the Axis of an Electron Lens". I also used the 1938 microscope with biological specimens, helped to improve its operation and received the M.A. degree in 1940. I stayed on at Toronto to receive my Ph.D. in 1943 (20), after applying the microscope to a wide range of specimens from both biological and material science and developing the designs of the third, or 1944 model Toronto microscope, which became a part of my Ph.D. thesis. In September of 1943 I joined the Physics staff of the University of British Columbia, where I stayed for two years and did no electron microscopy except to talk about it. I returned to the Toronto laboratory only for the summer of 1944 to help bring the 1944 microscope into operation. In September of 1945 I took up a new position as physicist with the Shawinigan Chemicals Ltd. in Shawinigan Falls, Quebec, where I stayed for two years doing industrial electron microscopy before taking a position in medical research in the Henry Ford Hospital in Detroit, Michigan, where I stayed.

Prebus and Hillier left Toronto in 1940 to continue their careers in the United States. Hillier who had received his M.A. in 1938 and who returned to his alma mater for his Ph.D. in 1941 (21), accepted a position at R.C.A. where he enjoyed great success, received many honours and became R.C.A. Executive Vice-President and Senior Scientist. Prebus also did extremely well, accepted a post-doctoral position at Ohio State University, later became a full Professor at O.S.U. and continued his interests in theoretical electron optics. He had received his Ph.D. degree from the University of Toronto in 1940 (22).

The "Golden Age" of electron microscopy at Toronto coincided with the years of World War II, 1939 through 1945, when many of the electron microscopy projects were related to the war effort and were classified. Consequently, few publications from those years exist. In the Department of Physics the development of the electron microscope, as an instrument, ended with the completion of the third microscope, which had involved my self with Dr. Lorne T. Newman. Dr. Newman was a University of Toronto graduate, a colloid physicist who came on staff in 1940, advised me on my Ph.D. program, and left the laboratory later to join the Manhattan Project in Oak Ridge, Tennessee. At the same time as Dr. Newman arrived, Dr. Beatrice Deacon, also a colloid physicist, and a Toronto graduate, came on board. Her work was confined exclusively to war-related quantitative studies of the filtration efficiency of a variety of fibrous materials and of the particle sizes of debilitating solid-particle aerosols, incident upon those materials, studies in which both Dr. Newman and I were also involved.

The 1938 Model Toronto Electron Microscope and its Operation

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