A model for the hillock formation on graphite surfaces by 246 MeV Kr+ ions

Scanning tunnelling microscopy has been used to study the effect of ion bom bardment at different angles of incidence on a graphite surface. The 246 Me V energy of Kr+ ions was selected in the medium energy range, where the ele ctronic and nuclear stopping is nearly balanced. The low dose (1 x 10(12)/c m(2)) of ions allows the characterization of single features caused by bomb ardment in perpendicular, at 30 degrees and at 60 degrees incidence. The de nsity of hillocks caused by the ion bombardment is significantly lower than the ion dose and this density depends on the angle of incidence. The hillo cks are attributed to knocked-on atoms leaving the sample surface. A simple model for the scattering process is presented to enlighten the hillock den sity differences. Other features produced by the ion bombardment, such as e longated traces and (root3 x root3) R30 superstructures are also reported. (C) 2001 Elsevier Science B.V. All rights reserved.