The protection of KCsSb photocathodes with CsBr films

We report on photoemission properties of visible KCsSb reflective photocathodes coated with thin CsBr protective films. We present the absolute quantum efficiency and its stability under prolonged contact with oxygen. It is found that KCsSb photocathodes coated with 280 Å thick CsBr films have 5% quantum efficiency at 312 nm and can withstand an exposure to 150 Torr of oxygen for half an hour. We discuss the possible role of good lattice constants matching between the photocathodes and the protecting film.