Activation of Thermionic and Photoelectric Cathodes

Abstract

Thermal regeneration of an adsorptive capacity in oxidized metals and semiconductors is identified with a nonspecific tendency for oxygen atoms to bury themselves. This process, which often occurs at room temperature, leads to a positive surface potential, and the thermionic or photoelectric emission of electrons is enhanced. Photoelectric measurements which are in line with this view are presented for titanium undergoing interaction with oxygen. The emission value of the clean metal was doubled after thermally regenerating the surface at 400°C. Activation of the electron emission of surfaces bearing thin skins of foreign oxides is ascribed to a surface configuration which is essentially similar to that of thermally regenerated metals and semiconductors. The emission from oxide-coated cathodes (thick layers of foreign oxides), is regarded as a maintained form of exoelectron emission which arises from innumerable donor centers produced during the activation process; electrons which have been emitted are replaced from the underlying metal. Attention is finally drawn to the use of electronegative elements other than oxygen for increasing the electron emission of metal surfaces.