Influence of a single adatom on sputtering at grazing incidence - A molecular-dynamics case study of 5Â keV Ar impact on Pt (1Â 1Â 1)

Grazing incidence ion impact on a flat terrace lets the projectile reflect specularly off the surface, leading to little or no damage production or sputtering. The presence of isolated surface defects may change this behaviour drastically. We investigate this phenomenon for the specific case of 5 keV Ar ions impinging at 83° towards the surface normal onto the Pt (1 1 1) surface. Molecular-dynamics simulations allow to study the influence of isolated adatoms in detail. The scattering of the projectile from the adatom can redirect the projectile, or let the adatom recoil, such that either of them deposits considerable energy in the target surface, leading to abundant damage production and sputtering. Two distinct collision zones are identified: (i) When the projectile hits the surface in front of the adatom, it may collide with the adatom indirectly (after being specularly reflected off the surface); (ii) alternatively, it may hit the adatom directly. We quantify our results by measuring the zone of influence (≅13 Å2) around the adatom, into which the projectile must hit in order to collide with the adatom, and by the sputter cross section of roughly 110Å2. The data compare well with previous simulation results of sputtering from an atomically rough surface.