Abstract
Auger and work function measurements have been made on a tungsten surface containing absorbed layers of (a) barium, and (b) barium and oxygen. The experimental techniques employed enabled one to distinguish the quantitative effects of oxygen on the barium-oxygen- tungsten surface reaction. It was found that the barium on an impregnated tungsten cathode is not oxidized barium (BaO), nor is it present as metallic barium chemisorbed on tungsten; rather it seems to be in an intermediate state probably as a coadsorbed (barium and oxygen) layer on tungsten. As a result of these studies a physical model for the impregnated tungsten cathode is proposed. The model assumes that the surface of the cathode, during life, has an adsorbed surface layer of a monolayer or less of both barium and oxygen on the surface. With life the barium is depleted leading to a higher work function surface. End of life occurs when the barium partial monolayer is so low that the resultant high cathode work function cannot sustain the required emission level. Recent NASA life test results on TWT type tubes are reported and explained by the proposed model.
Published Version
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