The nanoscale kinetics of surface topography evolution on silicon surfaces irradiated with 1 keV Ar${}^{+}$ ions is examined in both directions perpendicular and parallel to the projection of the ion beam on the surface. We use grazing incidence small angle x-ray scattering to measure in situ the evolution of surface morphology via the linear dispersion relation. We study the transition from surface ultra-smoothening at low angles of deviation from normal ion incidence to a pattern-forming instability at high incidence angles. A model based on the effects of impact-induced redistribution of those atoms that are not sputtered away explains both the observed ultra-smoothening at low angles from normal ion incidence and the instability at higher angles and accounts quantitatively for the measured two-dimensional dispersion relation and its dependence on incidence angle.

• Received 27 July 2011

DOI:https://doi.org/10.1103/PhysRevB.84.214108