Threshold energies of light-ion sputtering and heavy-ion sputtering as a function of angle of incidence

The angular dependence of threshold energies has been investigated for light-ion sputtering and heavy-ion sputtering, and simple expressions for the angular dependences of threshold energies are derived for these two cases. For not-too-large angles of incidence, the threshold energy of heavy-ion sputtering is a decreasing function of the angle of incidence because of the anisotropy of the velocity distribution of recoil atoms, while the threshold energy of light-ion sputtering shows a weak angular dependence. For grazing angles of incidence, the threshold energies of these two cases are increasing functions of the angle of incidence because of surface scattering. In order to examine these theoretical angular dependences of threshold energies, the computer simulations have been performed using the ACAT code. It is found that in the near-threshold regime the angular dependences of sputtering yield by heavy ions are much different from those by light ions. (orig.)