Work function change of first wall candidate metals due to ion beam irradiation

A new device has been made for examining the work function (WF) change of metallic and ceramic materials due to ion irradiation. The charging effect on the performance of Kelvin probe (KP) was reduced efficiently using appropriate shielding. The oxygen adsorption test on nickel sample showed that the WF changed with the surface coverage monotonically. The surface and near-surface defects might be responsible for the WF increase in the low-energy (500 eV) ion irradiation experiment, as revealed with the TRIM simulation. When damages reached a dynamic equilibrium, the WF tended to saturate. The opposite behavior due to higher-energy (MeV) ion irradiation seemed to be induced mainly by the desorption of gases from the surface, and possible radiation-induced segregation and/or diffusion.