Comparison of CsBr and KBr covered Cu photocathodes: Effects of laser irradiation and work function changes

Thin films of CsBr and KBr were deposited on Cu(100) to investigate photoemission properties of these potential photocathode materials. After prolonged laser ultraviolet irradiation photoemission, quantum efficiency increases by factors of 26 and 77 for KBr/Cu(100) and CsBr/Cu(100) photocathodes, respectively. Immediately following thin film deposition, a decrease in work function is observed, compared to bare Cu, in both cases. Quantum efficiency enhancements are attributed to the decrease in photocathode work function, and photo-induced processes that introduce defect states into the alkali halide bandgap. Our results suggest that KBr, a relatively stable alkali-halide, also has potential for photocathode applications.