Electron and ion emission from a copper surface in the presence of oxygen, cesium, and oxygen plus cesium

Abstract

Thermionic work functions, electron emission S curves, and cesium ion emission characteristics are reported for a polycrystalline copper surface in oxygen only, and in oxygen plus cesium vapor, in the ranges of oxygen pressure from below 10 −7 to above 10 −4 Torr and cesium arrival flux between 10 13 and 10 16 atoms/ cm 2- sec. The data are compared to similarly obtained data from an identical copper surface in vacuum and in cesium vapor only, and to other data for copper in oxygen plus cesium vapor. Three adsorption regimes are discussed and postulated to be (a) a photostimulated emission at low temperatures, (b) thermionic emission from the surface system Cs-CuO at intermediate temperatures, and (c) thermionic emission from the surface system Cs-O-Cu at higher temperatures. Two thermionic emission maxima were observed in the electron emission S curves. Electron emission was greatly enhanced by the combined presence of oxygen and cesium in the central regime. Electron emission from copper was sharply decreased by the presence of oxygen only. The adsorption energy for cesium on copper increased with increasing oxygen pressure (coverage).