Field Emission Scanning Electron Microscope Earns Milestone

The development made possible high-resolution imaging

20 January 2012
Photo: Hitachi

This month IEEE is honoring an invention that eventually led to the initial observation of the AIDS virus, among many other contributions. The first practical field emission–scanning electron microscope (FE-SEM), developed by Hitachi in collaboration with physicist Albert Crewe in 1972, made possible reliable ultrahigh-resolution imaging.

Electron microscopes let us observe cells and microorganisms, large molecules, biopsy samples, metals and crystalline structures, and the characteristics of various surfaces. They’re used in industry for quality control and failure analysis, among other applications.

To recognize the breakthrough, IEEE named Hitachi’s FE-SEM an IEEE Milestone in Electrical Engineering and Computing.

SIMULTANEOUS EFFORTS
Hitachi’s research on electron microscopes, which use a beam of electrons to illuminate the specimen and produce a magnified image, began close to 70 years ago. In 1942, Hitachi developed Japan’s first commercial electron microscope. The company then worked for decades to improve the technology.

But others, including Crewe, who in the early 1960s was director of Argonne National Laboratory, in Downers Grove Township, Ill., were also making advances in microscopy. Crewe had become interested in electron microscopy because of his lab’s extensive biology program. He wanted to improve the microscopic images that were so integral to biologists’ research. He came up with a design for a microscope that scans a sample with a high-energy beam of electrons in a rectangular, line-at-a-time pattern. Due to the narrow electron beam, scanning-electron-microscope images have a large depth of field, producing a characteristic three-dimensional appearance useful for understanding a sample’s structure.

Crewe set up a group at Argonne to turn his concept into reality, and in 1963 the researchers made a functioning device. A year later, he developed the first field emission (FE) gun, which improved the electron microscope’s optical quality. The gun produced an electron beam smaller in diameter and with greater current density and brightness than could be achieved by conventional thermionic emitters—which relied on the heat-induced flow of charge carriers from a surface. The gun also improved signal-to-noise ratio and spatial resolution.

BETTER FOCUS
Crewe wanted to spend more time researching microscopy, so he left Argonne in 1967 to become a professor of physics at the University of Chicago. In 1970, he developed an FE scanning transmission electron microscope and used it to observe individual atoms. (Crewe wasn’t the first to do so—the credit goes to German physicist Erwin Wilhelm Muller, who invented an FE electron microscope in 1936.) In the meantime, Hitachi had become interested in Crewe’s work and hired him as a consultant. During the next few years, he collaborated with Hitachi to enhance and commercialize the microscope. Among the greatest challenges in developing a commercial version was overcoming the instability of FE electron currents. Hitachi overcame that hurdle with ultrahigh vacuum technology, and in 1972 the company completed the world’s first commercial FE-SEM.

The microscope’s image resolution was vastly superior to others at the time, capable of capturing features as small as 3 nanometers, compared with the previous 15nm.

The FE-SEM’s initial application was to biology, and it captured the first high-resolution images of T2 bacteriophages, viruses that infect E. coli bacteria. More detailed images of bacteriophages were produced in the early 1980s with the addition of microprocessor control, which made ultrahigh resolution possible at a subnanometer scale. That capability also led to the first observation of the AIDS virus, in 1985 at Tottori University in Tokyo.

A ceremony for the Milestone is to be held on 31 January, with plaques unveiled at two Hitachi research laboratories in Tokyo. The plaques read:

Hitachi developed practical field emission electron source technology in collaboration with Albert Crewe of the University of Chicago, and commercialized the world’s first field emission scanning electron microscope in 1972. This technology enabled stable and reliable ultrahigh-resolution imaging with easy operation. Field emission electron microscopes have made invaluable contributions to the progress of science, technology, and industry in physics, biology, materials, and semiconductor devices.


For more information about this and other IEEE Milestones, visit the IEEE Global History Network.

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