High-voltage electron microscopy

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Abstract
A SECOND GENERATION of electron microscopes, using ten times the voltage of conventional instruments, is beginning to fulfill designers' hopes of allowing study of thicker specimens with less radiation damage. Voltages in the 1‐megavolt range have reduced the effect of chromatic aberration so that, a fixed value of resolution, usable specimen thickness can be increased roughly in the same ratio as voltage until it reaches a limit set by image visibility. Apart from a scaling up of the whole instrument, the only major difference in design is the insertion of an accelerator between the electron gun and the microscope itself. High‐voltage instruments are being used in metal studies by investigators who want a specimen thick enough to display bulk properties and, in biology, to probe living matter. A still larger machine is under construction in France.