field-emission electron gun, FEG

There are two types of field-emission electron gun (FEG); the cold cathode type and the thermal (thermally assisted) type. The FEG emits electrons from a sharpened tip of a cathode by applying a strong electric field. Compared with the thermionic-emission electron gun, the beam current of the FEG is small but its brightness is as high as 10⁷ to 10⁸. The FEG produces a small electron probe with a small energy spread. The FEG is essential for electron holography.

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