Single Ne+, Ar+, Kr+ and Xe+ impacts on Pt(111) were analyzed by using variable-temperature (20 to 700K) scanning tunnelling microscopy. The adatom yield, the number distribution of adatoms created per impact, the radial distribution of the adatoms and the mean sizes of resultant adatom and vacancy clusters were determined. The Ne+ (4.5keV) impacts produced only isolated adatoms with a number distribution, of adatoms per impact, which was close to the Poisson distribution. The adatom yield was consistent with a linear cascade model. At an increased energy density, which corresponded to an Ar+ (4.5keV) impact, the adatom production mechanism changed. At this, and higher energy densities, adatom clusters were created which had number distributions that were much broader than the corresponding Poisson distribution. This, and an increased ratio of adatom yield to sputter yield, indicated that collective effects had to be taken into account in order to describe adatom production. Molecular dynamics simulations which were performed for Ne and Xe (4.5keV) impacts reproduced the experimental trends. Experiments using successively increasing fluences indicated that ion-induced adatom mobility occurred at lower energy densities. After Xe+ bombardment at higher energies (6.5keV), vacancy cluster formation was found below the surface.

Collective Effects in the Adatom Production by 4.5keV Rare-Gas Impacts on Pt(111): a Low-Temperature Scanning Tunnelling Microscopy Analysis. M.Morgenstern, T.Michely, G.Comsa: Philosophical Magazine A, 1999, 79[4], 775-94