The mechanism of emission from the silver-oxygen-cesium photocathode

Photoelectron energy distribution measurements were made on silver-oxygen-cesium photocathodes by a retarding-potential method. For incident photon energies below 2.1 eV, the distributions consist of a single peak; as the photon energy is increased, structure due to fast and slow electrons may be resolved. The fast-electron structure is identified as being due to emission from a maximum in the density of states for silver at about 0.3 eV below the Fermi level. A slow-electron peak appears to be due to pair production in cesium monoxide, the threshold occurring at a photon energy of about 3.4 eV. The distributions confirm the Sommer-Borziak model of the cathode, in which silver particles are supposed to be dispersed in a semiconducting cesium monoxide matrix. For photon energies up to about 4 eV, emission is due to excitation of electrons from the silver particles and the tunnelling of these electrons into the conduction band of the cesium monoxide. For photon energies greater than about 4 eV, emission from the valence band of cesium monoxide may become important.