Dynamical simulation for sputtering of B4C

Using ACAT-DIFFUSE code, we have simulated the fluence dependence of B4C sputtering and the associated surface composition change under D+ ion bombardment. The ACAT-DIFFUSE is a simulation code, which is based on a Monte Carlo method with a binary collision approximation and solves diffusion equations. In the case of near-threshold sputtering, the preferential sputtering of B atoms is enhanced by the threshold effect. As a result, the total sputtering yield at the steady-state is reduced by about 20% compared with low-fluence sputtering. The surface concentration at steady-state is determined by the competitive processes between diffusion and surface-atom removal due to sputtering. At normal incidence the interstitial diffusion contributes appreciably to the steady-state surface concentration, but at grazing incidence this effect is small. Therefore, the steady-state surface concentration ratio at grazing incidence is less than that of normal incidence. (author)