Energy and angular distributions of atoms sputtered from polycrystalline surfaces: Thompson and beyond

We present a new analytic model for the energy and angular distributions of atoms ejected due to keV particle bombardment at normal incidence from polycrystalline solids. The main modification from the Thompson model is to assumed that the velocity distribution near the surface region is not isotropic. The model presented here predicts that the peak in the energy distribution shifts to lower energies as the polar angle increases and that the polar distribution becomes narrower as the energy of the particles increases. We have shown from computer simulations that the anisotropy in the surface region is due to the inherent asymmetry of the surface-vacuum interface. Finally, we and others have shown that the energy cost to remove an atom from the solid is greater than the heat of sublimation. (orig.)