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The development of the electron microscope

The electron microscope built by Ruska in 1933, it had a magnification around 12,000

In 1931, Ernst Ruska had a newly minted Ph.D. but no job prospects as the economic circumstances in Germany were dire; the Weimar Republic was suffering through an ultimately fatal bout of hyperinflation.  Ruska's thesis work, under the guidance of Max Knoll, had been a somewhat disappointing effort to build a new type of microscope that used electrons instead of light waves. However, because he couldn't find a job, he continued to perfect the electron microscope eventually winning a Nobel Prize for his work.

Light microscopes at that time were approaching the theoretical limits of their resolution due to the wavelength of light. The wavelength of electrons was smaller by a factor of 100,000, raising the prospect that individual atoms could be imaged.  Ruska had obtained images with his electron microscope as early as 1929, but they were scarcely better than viewing with the naked eye.

While unable to find a job, Ruska continued his work as a postdoctoral fellow. By 1933, he had built a new microscope that used dual magnetic coils as lenses by analogy with a compound optical microscope. This improvement allowed resolution beyond that of the light microscope, a critical selling point. Commercial developers were still underwhelmed. They questioned who would use the scope. The primary target, biologists, had a need for it but the electron beam heated up and destroyed the samples.

A fervent supporter of the electron microscope was Ruska's brother, Helmut, a young medical doctor. He convinced one of his former professors, Richard Siebeck, to write a favorable assessment of the new technology.  This impressed Siemens and Carl Zeiss sufficiently to fund commercial development of the instrument.  By 1938, Ernst Ruska had produced a prototype with a magnification of 30,000. In 1986, he was awarded the Nobel Prize for his invention, along with Gerd Binnig and Heinrich Rohrer who developed the scanning tunneling microscope.

Current electron microscopes have atomic level resolution, consistent with the very small wavelength of the electron. The problem of focusing the microscope kept it from fulfilling its promise for decades; fiddling with the fine focus with one's fingers was simply insufficient.  Computer technology finally enabled the microscope to be focused accurately, fufilling Ernst Ruska's long quest for a better microscope.   

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The electron microscope built by Ruska in 1933, it had a magnification around 12,000
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