On the Investigation of Specimen Contamination in the Electron Microscope

A number of experiments directed toward determining the nature and cause of deposits which occur on electron microscope specimens under electron bombardment are described. From these the conclusion is drawn that the material is a result of chemical reaction, occurring at any surface simultaneously bombarded by electrons and organic molecules. The organic vapors are shown to arise in two ways: (1) by diffusion out of the metal walls, gaskets, and greases exposed to the vacuum, (2) by the outgassing of metal parts of the instrument exposed to electron bombardment. To eliminate the effect both sources must be removed.