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 proces ses for GaAs(110). Scanning tunneling microscopy images reveal that mo st ion bombardment events at 300 K create pits that are 1-5 unit cells in size, indicating that direct knock-on collisions dominate. The ave rage pit size increases moderately with ion energy but shows a signifi cant variation with the incident angle. Vacancies are sufficiently mob ile at 625-775 K that vacancy islands form and the yield can be determ ined directly. The sputtering yields for these nearly ideal surfaces e xhibit structure that can be related to the nuclear stopping power and ion channeling, showing the influence of such geometric factors as su rface path length, ion radius, and projected atom column density. Temp erature 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 fl uence. While interlayer atomic transport is measurable at 625K and inc reases with temperature, it is not sufficient to achieve layer-by-laye r removal because As-x desorption competes with interlayer transport a bove similar to 800 K. (C) 1995 American Vacuum Society.