ROUGHENING INSTABILITY AND EVOLUTION OF THE GE(001) SURFACE DURING ION SPUTTERING

We have investigated the temperature-dependent roughening kinetics of Ge surfaces during low energy ion sputtering using energy dispersive x -ray reflectivity. At 150-degrees-C and below, the surface is amorphiz ed by ion impact and roughens to a steady state small value. At 250-de grees-C the surface remains crystalline, roughens exponentially with t ime, and develops a pronounced ripple topography. At higher temperatur e this exponential roughening is slower, with an initial sublinear tim e dependence. A model that contains a balance between smoothing by sur face diffusion and viscous flow and roughening by atom removal explain s the kinetics. Ripple formation is a result of a curvature-dependent sputter yield.