Effect of substrate on the quantum efficiency of cesium telluride thin-film photocathodes

Molybdenum, in many cases, is chosen as a substrate of cesium telluride thin film photocathode for a radio frequency electron gun (RF-Gun), which shows high performance. Therefore, in this study, we chose molybdenum as a substrate for cesium telluride thin film. The dependence of quantum efficiency on the kinds of metals for substrate has not been measured entirely and not been well understood. In this report, showing the result of measurements, we report on the dependence of the quantum efficiency on substrate for the cesium telluride thin film photocathode. In addition to molybdenum, we use tungsten and copper for substrate. We also report on the dependence of the quantum efficiency on the average surface roughness of substrate for cesium telluride thin film when using tungsten and copper as well as molybdenum for the substrate. The rate in the measurement of the dependence of quantum efficiency on the kinds of metals for substrate to incident light wavelength 250 nm was 20% on molybdenum, on tungsten 8.6% and on copper 4.8%, when the tellurium thickness is 10 nm. In the measurement of the dependence of quantum efficiency on the average surface roughness Ra of the substrates, the rate a sample on a substrate of which Ra is less than 0.1 mu m shows was 20%, on a substrate of which Ra is 50 mu m was 15%. Thus, the quantum efficiency of cesium telluride thin film photocathode depends on the kind of metals for the substrate, and also on the roughness of the surface of substrates.