SPUTTERING DAMAGE IN THE PT(111) SURFACE BY HE+ ION-BOMBARDMENT

The morphology of an initially almost ideal Pt(111) surface upon bombardment with 1 keV He+ ions at 735 K has been investigated by scanning tunneling microscopy. In addition to vacancy islands previously observed upon Ar+ ion bombardment, the He+-damaged surface exhibits a large density of hexagonal adatom islands with threefold symmetry and of subatomic height bumps with smooth height profiles already after fluences as low as 5.3 x 10(19) ions/m2. The formation of bumps is ascribed to strain fields resulting from subsurface helium bubbles. The observed adatom islands are pushed out of the surface by such bubbles. With increasing fluence the density of dislocations penetrating the surface is drastically enhanced.