Roughening and ripple instabilities on ion-bombarded Si

Experimental studies of 10-40-keV ${\mathrm{Xe}}^{+}$ ion bombardment of Si at polar incidence angles between 0° and 45° to the surface normal at temperatures between 100 and 300 K show little roughening for near normal incidence but ripple production for 45° 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.