Ion impact energy distribution and sputtering of Si and Ge

The spatial distribution of ion deposited energy is often assumed to linearly relate to the local ion-induced sputtering of atoms from a solid surface. This—along with the assumption of an ellipsoidal region of energy deposition—is the central mechanism used in the Bradley and Harper [J. Vac. Sci. Technol. A 6, 2390 (1988)] explanation of ion-induced surface instabilities, but it has never been assessed directly. To do this, we use molecular dynamics to compute the actual distribution of deposited energy and relate this to the source of sputtered atoms for a range of ion energies (250 eV and 1500 eV), ion species (Ar, Kr, Xe, and Rn), targets (Si and Ge), and incidence angles (0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, and 80°). It is found that the energy deposition profile is remarkably ellipsoidal but that the relation between local deposited energy and local sputtering is not simple. It depends significantly upon the incidence angle, and the relation between energy and local sputter yield is nonlinear, though with a nearly uniform power-law relation. These results will affect, in particular, surface instability models based upon simpler approximations.