Beam Sensitivity in the Electron Microscope: Strategies for Examination
A large proportion of the specimens, both organic and inorganic, examined in the electron microscope undergo some form of alteration during examination in the electron beam. That deleterious consequences often result should not be surprising when one considers that, to be resolved, an atom requires interaction with > 104 electrons which deposit energy in the specimen at a rate > 104 W/mm3. It is indeed more surprising that reliable information can be extracted at all from so many materials under these conditions. The first evidence of beam sensitivity was reported in 1947 by Burton, Sennett and Ellis in NaCl crystallites. They concluded in commendably cautious language: We have recently observed changes in a number of substances, chiefly ionic crystals, when subjected to intense electron bombardment in the electron microscope. While the results are not readily interpretable, they do suggest that the effects may not be entirely due to the heating effect of the electron beam.