Thermionic emission from dispenser cathodes

Abstract

ABSTRACT The invalidity of the classical dipole theory as an emission mechanism for dispenser cathodes is discussed. A model of dynamic surface emission centres, proposed for explaining the observed phenomena in oxide cathodes, is extended to describe the thermionic emission from dispenser cathodes. The essential points of this model are: (1) on the solid surface, when a high-energy electron meets the low potential field, this electron has a chance of being emitted into the vacuum; (2) the metal-like barium atoms provide high-energy electrons while oxygen, in the form of doubly charged negative ions, may provide a low potential field; (3) on the actual cathode surface, different conditions of adsorption form local emission centres; and (4) at high temperatures, these centres are not stagnant but ever-changing, so that the cathode operates in a state of dynamic equilibrium. Recent data from various electron spectroscopies on prepared films as well as dispenser cathodes seem to support this new model.