Difference between revisions of "History of the Electron Microscope"

Latest revision as of 16:26, 28 April 2010

A Snapshot of the EM:

To quote Slayter and Slayter: “At first many physicists doubted that a practical [electron microscope] could be devised, because electron beams are destructive, and specimens (especially biological specimens) are fragile. Nevertheless, electron lenses were described in 1926, a prototype electron microscope was constructed by 1932, and the first commercial instrument was launched by 1939. By 1970, the resolving power was 0.6nm, and by 1990, 0.1-0.2nm.” (1)

A Longer Exposure:

In 1925, the wave nature of electron was first accredited to de Broglie during the modern physics movement.

The Ruska/Knoll Early History:

According to several accounts, devices developed to form electron images came about in the late twenties and early thirties by engineers, apparently independent of de Broglie’s description(2). Theory and practice met when the experimental improvements in resolving power were attributed to the short wavelengths of electrons. This is evidenced by Ernst Ruska’s claim that he had not heard of de Broglie’s theory until after his and Max Knoll’s paper in 1931 on electron lenses and the electron microscope (2). These two are credited with first coining the term electron microscope, and Ruska was awarded the Nobel Prize in 1986 for the discovery. In his Nobel lecture, the prototype electron microscope is described, using the short iron clad coils, on which he had written his thesis, as lenses:

“Such an apparatus with two short coils was easily put together and in April 1931 I obtained the definite proof that it was possible. This apparatus is justifiably regarded today as the first electron microscope even though its total magnification of 3.6 x 4.8 = 14.4 was extremely modest.”(3)

In this microscope, the first TEM images were taken: mesh grids place over the anode aperture(3).

The Rüdenberg Early History:

Interestingly, it seems that though Ruska and Knoll are honored with the title of inventors of the EM, that Reinhold Rüdenberg of the Siemens company and later Harvard University actually patented the microscope in 1931 under the Siemens name. In this case, Rüdenberg based the patent and experiments on the theory of his friend, Hans Busch, who theorized the electron lens in 1926, and de Broglie’s wave nature of the electron to solve the resolution limit described by Helmholtz and Abbé (4). Rüdenberg was driven to develop the instrument by a desire see the polio virus, a disease affecting his son(4). He was unable to claim right to his invention upon immigration to the US, as this was the policy of the German government at the time(4).

Early Samples:

In either case, by the mid thirties and forties, many other engineers and scientists joined the fray to produce electron microscopes. During this period, the first electron micrographs appeared of biological specimens:

• In Brussels in 1934, Ladislaus L. Marton made a horizontal electron microscope to study the photoelectric effect, and went on to study biological specimens at a magnification of 20-30,000x. Later in 1937, he published the first electron micrographs of bacteria.
  • Ref: Marton, L. 1934. La microscopie electronique des onjectes biologiques. Bull. Acad. Belg. Cl. Sci. 20: 439-466
• Heinz Otto Mueller and Friedrich Krause, an electric engineer and a medical student respectively, worked to improve the instrument that Ruska built in 1933, taking micrographs of bacteria and other biological materials in the later thirties.
• In 1940, Helmuth Ruska, Ernst’s brother, used an electron microscope to obtain the first pictures of a virus.
  • Ref: Ruska, H. 1940. Die Sichtbarmachung der BakteriophagenLyse im Ubermikroskop. Naturwissenschaaften. 28: 45-6.
• In 1942, Thomas Anderson and Salvador Luria photographed bacteriophages with the aid of an electron microscope, confirming earlier work by Ruska. They demonstrated that a T2 phage has a head and a tail.
  • Ref: Luria, S. E. and T. F. Anderson. 1942. The identification and characterization of bacteriophages with the electron microscope. Proc. Natl. Acad. Sci. USA. 28: 127-13
• The first electron micrograph of an intact cell was published in The Journal of Experimental Medicine in March 1945, in "A Study of Tissue Culture Cells by Electron Microscopy," by K. R. Porter, A. Claude, and E. F. Fullam.

In the materials science world, far less was being accomplished early on due to limitations in specimen preparation. During the early forties, the main types of samples being studied were carbon black particles and those particles that colored cosmetics. It wasn’t until 1949 when Heidenreich thinned metal foils to electron transparency (2) that a lot of the early materials science work in EM took off.

Building Better EMs:

The first industrially (regularly) produced EM was by Siemens in 1939, starting with a series of events described by Ernst:

"As first collaborators [Max Knoll and I] secured Heinz Otto Mueller for the practical development and Walter Glaser from Prag as theorist. We started in 1937, and in 1938 we had completed two prototypes with condenser and polepieces for objective and projective as well as airlocks for specimens and photoplates. The maximum magnification was 30,000x. One of these instruments was immediately used for first biological investigations by Helmut Ruska and several medical collaborators. […]By the end of 1939 the first serially produced Siemens instrument had been delivered to Hoechst. The instrument No. 26 was, by the way, delivered to Professor Arne Tiselius in Uppsala in autumn 1943. By Februrary 1945 more than 30 electron microscopes had been built in Berlin and delivered."(3)

WWII, of course, disrupted a lot of this early push for EM, including the bombing of first visiting scientist laboratory that Siemens built in 1944, and Kruase and Mueller’s deaths during the early forties. Even so, by 1954 Siemens was again able to produce a scope with mass appeal: the Elmiskop. This was the first to have two condenser lenses, allowing for less heat irradiation of the sample(3).

According to Dykstra, the latter half of the 20th century was mainly focused on improving the auxiliary devices, and the overall operational systems. By 1946, the gross resolution improvements had essentially been done, after Hillier and Vance improved on their RCA TEM model to a 1.0nm resolution(5). The decade breakdown for improvements goes as follows from Dykstra’s chapter on the TEM(5):

• 1950s and 1960s: Improvements in power supplies (smaller, solid-state circuit controlled supplies instead of vacuum tubes), lens manufacture (the Philips 75 had sliding objective lenses), vacuum systems (the addition of a LN2 cold trap improved pressure from 10^-4 to 10^-6 Torr), and mechanical controls (the Philips 200 now allowed for screw adjustments of the column elements, and the Hitachi HU-11E allowed for mechanical and electron alignments). For the user-friendly side of things, phosphorescent viewing screens were developed.

• 1970s: Development of high voltage (1meV) TEMs, as well as an overall industry standard of a 0.344nm resolution on all TEMs sold in the latter half of the decade.

• 1980s: Development of intermediate voltage EMs (300 to 400keV), and EMs with resolutions less than 2Å. Also, a boom in the development of better accessories occurred in this decade. Vacuum systems were made cleaner with better diffusion oil pumps, turbomolecular pumps, and ion getter pumps. New techniques including AFM, STM, and electron energy loss spectroscopy were invented, aiding in comparisons. Additionally, in the interest of increasing user-friendliness and precise control, the Philips CM and the Hitachi H-7000 were among the first to move to partial computer control in the 1980s.

• 1990s: JEOL’s JEM-1210 was the first software driven TEM(5). Further improvements in user-friendliness and the reduction of noise and image defects seem to have been the main points of interest for the past decade or so.

Main References:

1. Slayter, EM, Slayter, HS. Light and Electron Microscopy. Cambridge University Press, NY:1992.
2. Williams and Carter. Transmission Electron Micrscopy: A Textbook for Materials Science. Springer, NY: 1996.
3. Ruska, E. The development of the electron microscope and of early electron microscopy. Nobel Lecture: 8 December 1986.
4. Rüdenberg, R. The Early History of the Electron Microscope. Journal of Applied Physics, 27 May 1943. p. 434-436.
5. Dykstra, MJ. Biological Electron Microscopy: Theory, Techniques, and Troubleshooting. Plenum Press, NY: 1992.