Auger and x‐ray photoemission spectroscopy study on Cs2Te photocathodes

Thin films of Cs2Te have been produced and analyzed by Auger depth profiling and x-ray photoemission spectroscopy (XPS). The formation of the photoemissive material passes through different phases, each of them has been characterized by XPS and by its total yield in the spectral region 3.5-5 eV. Copper and molybdenum substrates have been considered. While Mo behaves to all practical purposes like an ideal support for Cs2Te, strong diffusion from the substrate material into the photoemissive film has been observed on photocathodes fabricated on Cu, The ruggedness of the photocathodes has been tested by exposing them to a few hundred Langmuirs of different gases, namely O-2, CO2, CO, N-2, and CH4. The last three have no effect on the photocathode lifetime, while a substantial reduction of the quantum efficiency has been observed after the exposure to oxygen. The main reason for this is the formation of a thick cesium oxide layer at the surface of the photocathode. However, the oxygen pollution can be partially recovered by the combined effect of heating the photocathode at 230 degrees C and illuminating the poisoned material with the 4.9 eV radiation. No rejuvenation has been observed under the effect of the temperature or the radiation alone.