Work function of Mo(110) in mixed cesium and cesium monoxide vapors

Electron emission measurements from a Mo(110) emitter are performed in a diode containing both cesium and cesium monoxide vapors over a temperature range from 500 to 1800 K. The vapor pressures can be varied independently within a limited range: typical values are 1 x 10-3 and 2 x 10-4 Torr for cesium and Cs2O, respectively. At temperatures above 1000 K, the electron emission is increased by several orders of magnitude over that obtainable with cesium vapor alone by the addition of Cs2O. This is believed to result from the dissociation of Cs2O molecules adsorbed on the emitter surface to form an adsorbed oxygen layer. At temperatures below 700 K, the work function decreases with temperature to as low as 1.2 eV around 500 K. This is interpreted as resulting from multilayer deposition of Cs2O. Application to thermionic converters is discussed