Who invented the electron microscope? A patent office and a Nobel committee disagree
Light microscopes hit a wall at about 200 nanometres, because visible light waves are simply too long. Swapping light for electrons, whose wavelength can be over 100,000 times shorter, pushed the limit down to roughly 0.1 nanometres. Nearly a century later, credit for the swap is still argued over.
Magnetic and electric fields do for an electron beam what glass lenses do for light, bending and focusing it. That toolkit grew slowly: Heinrich Hertz steered electron beams in a cathode-ray tube in 1883, Emil Wiechert focused them with a magnetic field in 1899, Arthur Wehnelt improved cathodes in 1905, and Hans Busch developed the electromagnetic lens in 1926. Leó Szilárd, by Dennis Gabor's account, tried in 1928 to persuade Gabor to build such a microscope and had filed a patent for one.
That year Max Knoll took charge of an electron-beam research group at the technical college in Charlottenburg, Berlin, which included the doctoral student Ernst Ruska. In 1931 the pair used two magnetic lenses to form magnified images of metal mesh, and in 1933 they built an instrument that beat an optical microscope's resolution. Meanwhile Reinhold Rüdenberg at Siemens-Schuckert filed patents in 1932 that legally make him the inventor, though nobody knows when his machine actually worked. Both he and Knoll had died by 1986, so neither could share that year's Nobel Prize.
Siemens hired Ruska, Bodo von Borries and Ruska's brother Helmut, who explored biological uses, and sold the first commercial model in 1938. Manfred von Ardenne pioneered the scanning version in 1937, and teams in Toronto and at Washington State University built North America's first instruments in the 1930s. Albert Crewe in Chicago added a field emission source to a scanning transmission design by 1965, and atomic-scale imaging arrived in the early 1980s.
Transmission machines fire electrons of roughly 80 to 300 keV through very thin slices, while scanning microscopes sweep a gentler beam, usually under 20 keV, across a surface and collect what bounces off. With aberration correctors, standard equipment in many commercial instruments by 2025, resolution can dip below 50 picometres and magnification can exceed 50 million times.
Source: Electron microscope
