Characterization of the photoelectric effect on Kq-implanted W samples

Kq-implanted W samples with various implantation depths were investigated. Generally, implantation of alkali ions gives rise to two competitive effects: it lowers the surface work function, however it enhances surface oxidation too which in turn leads to a slight work function increase. In opposite to alkali overlayers, implanted species confined within a ‘metallic cage’ resist the applied laser irradiation and alkali removal occurs only to a small extent. Measurements of laser-induced photoelectric charge pulses indicate a variation of the photoemission yield as a function of surface oxide thickness. Moreover, following the charge pulse evolution over a longer period 2–3 h., one finds that the laser-induced oxide removal characteristics depends on the implantation parameters as well. Results are compared to those obtained for pure, non-implanted W and the mechanisms responsible for the work function lowering are discussed. q1999 Elsevier Science B.V. All rights reserved.