Investigation of Electron Emission by Cold Metals Using an Electron Microscope

As is known, large electric fields (of the order of \(10^7\ \mathrm{V/cm}\)) are capable of causing the emission of electrons from cold metals. In these cases the sources of electrons are usually individual submicroscopic asperities located on the cathode, near which a very strong field gradient is formed. The existence of such “point” sources of electrons on a cold metal placed in an electric field was confirmed in a recent work by Wehnelt and Schilling1. These authors succeeded in obtaining an image of the electron-emitting surface of a cold metal by using a magnetic electron microscope. In photographs obtained with the appropriate arrangement of the accelerating field, images of individual centers of electron emission can be seen. These centers emit electrons for several minutes and then suddenly disappear, while new emission centers arise at other places on the cathode. From the total current from the surface and from the number of emitting centers (submicroscopic), one can determine the current density of individual emission centers. This quantity may play an essential role in testing ideas about the emission of electrons by cold metals in an electric field.

L. Groshev, Moscow

Literature

1. Wehnelt and Schilling, Z. Physik 98, 286, 1936. ↩