Lifetime test of photoemission from Cs3Sb photocathode coated with W or Cr film

Cs3Sb photocathodes were fabricated at 8-16 °C with sandwiched layers of Sb, Cs, and Sb deposited onto the fine tips of three cathodes at 15 °C. After examining the influence of the cathode tip temperature on the changes in the quantum efficiencies of the Cs3Sb photocathodes during and after additional Cs depositions, we performed lifetime tests of the three Cs3Sb photocathodes using a 405-nm semiconductor laser and 488-nm Ar ion laser. The decrease in the photocurrent with time was more rapid with the 488-nm laser irradiation than with the 405-nm laser irradiation, and continuous laser irradiation caused a much more rapid decrease in photoelectrons with time than intermittent laser irradiation did. We deposited a 0.32-0.64-nm-thick W film or a 0.43-nm-thick Cr film onto the Cs3Sb photocathode during the lifetime test at 0.9-1.0 × 10−7 Pa. We found that the passive WO3 or Cr2O3 film, which was formed at a reduced vacuum level of 1.6 × 10−7 Pa or during the continuous 405-nm laser irradiation, increased the lifetime of the Cs3Sb photocathode by effectively protecting its surface against oxidation and evaporation of Cs. This protection effect was most effective at approximately 90 °C.