Physical Mechanism of Operation of Osmium-Coated Cathodes of Microwave Devices

The electronic structure and physical chemistry of an osmium-coated cathode are determined, and the physical mechanism of the effect of osmium on the electronic structure and emission properties of a dispenser cathode is investigated. The studies are carried out by optical spectroscopy, electron spectroscopy for chemical analysis, and electron energy-loss spectroscopy. The emission properties of standard dispenser cathodes are determined by oxygen vacancies in BaO crystallites; the surface oxygen vacancies form acceptor surface states, which is accompanied by upward bending of the oxide energy bands. In osmium-coated dispenser cathodes, osmium atoms are dissolved in BaO crystallites and form extra donor surface states at the surface of crystallites, which results in downward bending of the oxide energy bands and, correspondingly, a decrease in the work function of the cathode material.