Roughening and ripple instabilities on ion-bombarded Si

Experimental studies of 10-40-keV Xe+ ion bombardment of Si at polar incidence angles between 0 degrees and 45 degrees to the surface normal at temperatures between 100 and 300 K show little roughening for near normal incidence but ripple production for 45 degrees incidence. It is shown that inclusion of the directed flux of atoms parallel to the surface and generated by ion bombardment in a stochastic differential equation description of the dynamics of surface evolution during sputtering erosion can induce smoothing for near-normal ion incidence. For oblique incidence, roughening and ripple production occurs with a late stage dynamics dictated by the competition between curvature-dependent sputtering processes and surface relaxation (which is also, probably, irradiation motivated), gradient-dependent sputtering, and other higher-order effects.