Oxide Cathode Mechanisms: Electronic and Structural Features of Oxide Cathode Surfaces

摘要

This report describes studies made upon systems selected for their ability to model various important features of oxide cathodes and the mechanisms which enable them to function as efficient thermionic emitters at moderate temperatures. An account is given of experiments which aimed to simulate conditions upon the surfaces of polycrystalline samples of alkaline earth oxides (e.g. SrO and BaO/SrO or MgO and BaO/MgO) at various stages of their preparation in similiar fashion to that used in the thermal activation of oxide cathodes. Accounts are given of experiments which examined the interaction between the gases O2, N2O, H2 or Ch4 and appropriately preactivated surface of pure and mixed alkaline earth oxide samples. Accounts are given of experiments involving the controlled deposition in UHV conditions of zero-valent Ba ad-atoms-in amounts ranging from submonolayer to multilayer coverage - upon layers of SrO or BaO previously prepared in UHV conditions by evaporation of the corresponding metal and its subsequent oxidation. UPS spectra have been undertaken in order to examine surfaces of samples prepared by evaporation of barium metal or strontium metal and to study effects upon the UPS spectra by exposures to the gases N2O, O2 and CH4.