Early Scanning Electron Microscopy

Abstract
The transmission electron microscope can be traced back to the work of K. Knoll and E. Ruska in Berlin who succeeded in 1931 in demonstrating a two lens electron microscope. The scanning electron microscope may also be traced back to the work of M. Knoll in 1935, during a study of secondary electron emission from surfaces. Two cathode ray tubes were used with a time-base generator supplying deflection signals to both tubes at once. The specimen under test was sealed into the first tube and the electron beam from the gun was scanned across the specimen surface and the variations in specimen current formed the signal. This signal was used to modulate the grid of the second cathode ray tube and the image displayed gave the variation in secondary emission on the specimen surface. In one case the word “Stuggart” was shown.

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