Dissociation Energies of Surface Films of Various Oxides as Determined by Emission Measurements of Oxide Coated Cathodes

Abstract

A mechanism of falling emission in vacuum tubes is discussed. It is demonstrated that when an electron achieves a critical kinetic energy in moving from the cathode to the anode, and if the anode is an oxide, the electrons will cause a dissociation of the oxide. The liberated oxygen will return to the cathode and falling emission will result. The critical energy of the electron starting the dissociation is found to be equivalent to the heats of formation of the oxides bombarded in the case of five different oxides. Using this equivalence principle, the heats of formation of two compounds are found which have not been recorded in the literature, Ta₂O₄ and ZrO. In addition, the contact potential between barium oxide cathodes and seven various oxides are determined and the work function of the seven oxides computed.