Ion sputtering of GaAs(110): From individual bombardment events to multilayer removal

We have investigated the effects of ion mass (Ar+, Xe+), energy (0.3--5 keV), trajectory, and sample temperature on the ion sputtering processes for GaAs(110). Scanning tunneling microscopy images reveal that most ion bombardment events at 300 K create pits that are 1--5 unit cells in size, indicating that direct knock-on collisions dominate. The average pit size increases moderately with ion energy but shows a significant variation with the incident angle. Vacancies are sufficiently mobile at 625--775 K that vacancy islands form and the yield can be determined directly. The sputtering yields for these nearly ideal surfaces exhibit structure that can be related to the nuclear stopping power and ion channeling, showing the influence of such geometric factors as surface path length, ion radius, and projected atom column density. Temperature dependent results for monolayer and multilayer sputtering show that adatoms ejected onto the surface refill vacancies but that the surface roughness, as measured by surface width, increases with ion fluence. While interlayer atomic transport is measurable at 625 K and increases with temperature, it is not sufficient to achieve layer-by-layer removal because Asx desorption competes with interlayer transport above ∼800 K. copyright 1995 American Vacuum Society