D. Des Chene (goclenius) wrote,
D. Des Chene

If I were filthy rich…

I’d buy a scanning electron microscope.* The image here, from a collection at the Museum of Science in Boston, shows a staple piercing a piece of paper: micro-violence in suspension.
The first electron microscope, constructed by Max Knoll and Ernst Ruska (in 1931 according to Ruska’s Nobel Prize Lecture (pdf); see also his autobiography), produced images using electrons transmitted through the specimen. Such microscopes, now capable of very high resolution, are called transmission electron microscopes. Scanning electron microscopes (SEMs) use either back-scattered or secondary electrons to produce images. The theory of the SEM was developed by Manfred von Ardenne in the late 30s; von Ardenne built an SEM or an STEM, a “scanning transmission electron microscope”) but published no images. Vladimir Zworykin, one of the inventors of television, and his student James Hillier built an SEM and published images made with it in 1942. The inferior resolution of the SEM led researchers to concentrate on the transmission EM until Charles Oatley at Cambridge decided that the technology was sound and proposed that his student Dennis McMullan should build an SEM; the result was a high-energy scanning microscope that detected backscattered electrons. Further improvements by K. C. A. Smith yielded an instrument which could “produce images comparable with those from modern microscopes” (McMullan 1993). The first commercial instruments were sold by Cambridge Scientific Instruments in 1965.
What’s instructive for philosophers in this history is the weaving together of what had been remarkable scientific achievements into an artifact whose principles of construction are so well-known, and whose operations are so reliable, that it can be mass-produced and used routinely for observation and quality control. The production of electrons from a cathode was discovered by J. J. Thomson (who also made the first “detectors” and showed that the particles emitted by the cathode were deflected by magnets); back-scattering was discovered by Ernest Rutherford, Hans Geiger, and E. Marsden; Ruska’s work developed out of the development of cathode-ray oscilloscopes under the tutelage of Max Knoll; the now standard Everhart-Thornley detectors, first constructed in 1956, required the development of efficient scintillators and photomultipliers capable of gathering enough secondary electrons for the production of images. The idea of scanning itself goes back to Alexander Bain, who in 1843 patented the first fax machine.
All this was brought together in 1965 by R. F. W. Pease and W. C. Nixon in the SEM V, whose design was used in the first commercial instrument (see Sampson 1996 and McMullan’s history). The participants themselves note that the development of the instrument was not straightforward. Oatley, for example, recognized that the new electron multiplier built by A. S. Baxter at Cavendish Labs would make it possible to measure secondary electron currents in the SEM—not knowing that von Ardenne had made a similar proposal. Against the advice of experts, he assigned Ph. D. students to the task of building an improved SEM; Dennis McMullan completed building the first, SEM1, in 1951. A decision was made to continue, even though many microscopists “believed that this new instrument could never compete with the well-established electron microscopical techniques of the time; in particular, with the replica technique which offered much superior resolution” (Smith 1997, online version p2); nevertheless the SEM promised many advantages, including “ease of specimen preparation, large depth of field, readily interpreted images, and great flexibility in the size and type of specimen that could be examined” (ib.). But only when technical difficulties in the use of the electron multipliers were overcome by Everhart and Thornley in 1955–1956 did the SEM advance from being a research project to become a research tool.
It was during this period, moreover, that the theory of the instrument—in particular, of mechanisms in backscatter, variations in the secondary output caused by differences in atomic number, and the reflection of electrons from solids (McMullan 1948, O. C. Wells 1957, Everhart 1958)—was developed further, so as to allow the data to be interpreted. Indeed it is not always clear in this period (at least to me) what should be called an application of the SEM to the study of something else and what should be called an investigation of the phenomena themselves that the SEM produces. The first photograph above is clearly an application; the second, whose label says that it is an image showing “electron channel contrast”—which is to say, an aspect of the phenomenon of scattering—, hovers somewhere between being a use of a scanning beam to form an image (though clearly this is what Knoll was after) and a study of its reflection. The eye tells us both about light and the things that reflect light; most often we ignore the light itself, but sometimes—when the afternoon sun slants into a room—we realize that light itself is an object of vision, and not just a medium. Then you may begin to wonder: am I seeing things or just the light affected by them? If that or is taken to be exclusive, the well-worn path opens to either a unwarrantable realism or an implausible idealism. Perhaps instead—as the SEM story suggests—the answer is both.
*How filthy? The cheapest instrument I came across in a cursory search was $6500 “as is”. You can lease a new Jeol JSM-6060LV low-vacuum SEM for just $2000 a month, minimum 5 years, at the end of which you can buy it for $1. A used Amray 1860 FE Field Emission SEM Electron Microscope is $29,000, which is about the price of a Lexus.
NB. References to printed sources are taken from McMullan 1995 and Smith 1997. My thoughts at the end of this post are of course not unaffected by the reading of authors like Latour, Pickering, and Aristotle.
David Sarnoff Library. “Electron Microscopy”. s.d. [2002?] Includes a collection of images.
INDARES, Aphrodite. “EPMA Course Notes, ch. 1”. Earth Sciences, Memorial University of Newfoundland, s.d.
KNOLL, M. “Aufladepotentiel und Sekundäremission elektronenbestrahlter Körper”. Z. tech. Phys. 16(1935): 467–475.
McMULLAN, Dennis. “Scanning electron microscopy, 1928–1965”. Scanning 17 (1995): 175–185. Online version. See also the brief biography of Oatley by K. C. A Smith listed below, and a bibliography of work at Cambridge.
McMULLAN, Dennis. “Von Ardenne and the scanning electron microscope”. Proc. Royal Microsc. Soc. 23 (1988): 283–288.
McMULLAN, Dennis. “The prehistory of scanned image microscopy Part 1: scanned optical microscopes”. Proc. Royal Microsc. Soc. 25(1990): 127–131.
OATLEY, Charles W., D. McMullan, and K. C. A. Smith. “The development of the scanning electron microscope”. In: P. W. Hawkes, ed., The beginnings of electron microscopy, Advances in electronics and electron physics Suppl. 16 (London: Academic Press, 1985): 443–482.
von ARDENNE, Manfred. “On the history of scanning electron microscopy, of the electron microprobe, and of early contributions to transmission electron microscopy”. title. In: P. W. Hawkes, ed., The beginnings of electron microscopy, Advances in electronics and electron physics Suppl. 16 (London: Academic Press, 1985): 1–21.
RUSKA, Ernst. “Autobiography”, nobelprize.org, Physics, 1986.
SAMPSON, Allen R. “Scanning Electron Microscopy”. Advanced Research Systems, 1996.
SMITH, K. C. A. “Charles Oatley: Pioneer of scanning electron microscopy”. In: J M Rodenburg, ed., Electron Microscopy and Analysis 1997: Proceedings of the Institute of Physics Electron Microscopy and Analysis Group Conference, University of Cambridge, 2–5 September 1997. Institute of Physics Publishing, 1997. (Institute of Physics Conference Series 153). Online version.
Tags: microscope history_of_science
  • Post a new comment


    Comments allowed for friends only

    Anonymous comments are disabled in this journal

    default userpic

    Your reply will be screened