Mechanisms of pattern formation and smoothing induced by ion-beam erosion

We have investigated bombardment-induced pattern formation and smoothening during Ar(+) ion erosion of Al(2)O(3) surfaces. The experiments show that ion smoothening of a patterned surface is explained by a mechanism where collisions with near-surface atoms produce an effective downhill current. Quantitative agreement is obtained using ion-collision simulations to compute the magnitude of the surface current. The results lead to predictions for the surface morphology phase diagram as a function of ion energy and incidence angle that substantially agree with experimental results.