1955: Individual atoms imaged
In 1951 the academic journal Zeitschrift für Physik published an article by Erwin Mueller, then a professor at the Kaiser-Wilhelm Institute in Germany, that described an instrument called a field ion microscope (FIM).
The underlying principle of FIM operation is simple: atoms of imaging gas, usually hydrogen or helium, are ionized by a high-voltage metal tip in an ultra-high vacuum. The ionized atoms, repelled by the tip toward the target surface, reflect off the surface onto a fluorescent screen detector.
Mueller’s theory that the FIM would provide enough precision and accuracy to image even individual atoms proved correct. By 1955, while teaching at the Pennsylvania State University, he had fine-tuned the FIM enough to obtain a clear view of the atomic structure of a metal atom. Thus Mueller was the first man to “see” atoms, and FIM was the first microscopy technique capable of atomic resolution.
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