Lifetime test of photoemission from Cs_3Sb photocathode coated with W or Cr film

摘要

Cs_3Sb photocathodes were fabricated at 8-16 ℃ with sandwiched layers of Sb, Cs, and Sb deposited onto the fine tips of three cathodes at 15℃ After examining the influence of the cathode tip temperature on the changes in the quantum efficiencies of the Cs_3Sb photocathodes during and after additional Cs depositions, we performed lifetime tests of the three Cs_3Sb 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 Cs_3Sb photocathode during the lifetime test at 0.9-1.0 × 10~(-7) Pa. We found that the passive WO_3 or Cr_2O_3 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 Cs_3 Sb photocathode by effectively protecting its surface against oxidation and evaporation of Cs. This protection effect was most effective at approximately 90 ℃.