The environmental scanning electron microscope and its applications.

Abstract

An environmental scanning electron microscope can be made by incorporating a pressure limiting aperture at some distance below the objective aperture of an SEM, and by providing independent pumping between these two apertures. Tilting of the pressure limiting aperture with respect to the axis of the electron optics column redirects the gas jet which develops above the pressure limiting aperture and which otherwise would inject excessive gas through the objective aperture into the column. The detection of backscattered and multiple-backscattered electrons is achieved below the pressure limiting aperture in the region confined by the sample, the detector and the aperture grid. Wet specimens can be examined in the environmental scanning electron microscope at 7kV and TV rates by placing them at a sufficiently close distance to the pressure limiting aperture. Live seedlings and ants have been observed in this way. Wet (fresh) rat tissues, wool fibers subjected to various treatments, crystallization and rewetting of salts, and some radiation effects have been observed and recorded under the environmental scanning electron microscope. Examination of specimens in the full pressure range, 0-1013 mbar, is possible. A detector-aperture system which will allow the signal originating from the sample to be detected simultaneously both below and above the aperture is under construction. Further development of environmental scanning electron microscopy now depends upon close co-ordination between microscope manufacturers and research groups involved in such fields as biology, fiber technology, radiation and physical chemistry.