Profile of Akira Tonomura

One of the most useful scientific instruments of the 20th century, the electron microscope, continues to be used worldwide to examine the atomic world. The first transmission electron microscopes were developed in the 1930s and began seeing institutional use in the 1940s. In the 1970s, the microscope was developed further into a device that could record not just the intensity of the electrons, but their phase as well, by using coherent field-emission electron beams. Physicist Akira Tonomura, elected to the National Academy of Sciences in 2000 as a Foreign Associate, was responsible for much of this technological development.

Transmission electron microscopes beam electrons through a thin sample of material and record changes in their trajectories upon passage. The intensity of the electrons that pass through are recorded and assembled into an image. Because of wave/particle duality, the electrons have a wavelength that can be used to probe the sample, as with a light microscope. However, because the electrons have a much shorter wavelength than a photon of light, much higher resolutions are possible as compared with light microscopy.

Tonomura invented a technique to produce more coherent electron beams for greater accuracy and to precisely record electron phases, providing even more atomic information than previously possible (1). Such phase information, when added to traditional pictures of intensity, generates an electron hologram. This technique of electron holography has opened up the “pico-world,” helping to reveal and study various physical quantum phenomena. In his Inaugural Article in this issue of PNAS (2), Tonomura reviews the development of more coherent electron beams and describes the direct observation of theoretical quantum effects and the motion of magnetic vortices in superconductors, as afforded by these more powerful microscopes.