A facility for electron microscopy of specimens in controlled environments

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Abstract
A controlled environment for specimens in the electron microscope is produced within a space formed by two 20 mu m apertures 0.75 mm apart in the gap of the objective polepiece. An additional diffusion pump makes it possible to operate the microscope with gas at 1 atm pressure in the space without covering the apertures with membranes. A side entry stage permits rapid specimen changing and enables the whole of a normal grid to be scanned. Preliminary experiments using this system indicate that repeat periods less than 100 AA can be distinguished in wet catalase when helium pressure is used in the specimen chamber and the current density at the specimen is 0.1 nA mu m-2 or less. With higher beam currents, bubbling occurs in the specimen and the structure of the crystal is no longer observable.