AUGER AND X-RAY PHOTOEMISSION SPECTROSCOPY STUDY ON CS2TE PHOTOCATHODES

Thin films of Cs2Te have been produced and analyzed by Auger depth pro filing and x-ray photoemission spectroscopy (XPS). The formation of th e 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 photoemi ssive film has been observed on photocathodes fabricated on Cu, The ru ggedness of the photocathodes has been tested by exposing them to a fe w 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 a fter the exposure to oxygen. The main reason for this is the formation of a thick cesium oxide layer at the surface of the photocathode. How ever, the oxygen pollution can be partially recovered by the combined effect of heating the photocathode at 230 degrees C and illuminating t he poisoned material with the 4.9 eV radiation. No rejuvenation has be en observed under the effect of the temperature or the radiation alone . (C) 1996 American Institute of Physics.