Monte Carlo simulations were used to model 3-dimensional distributions of cascade defects and energy deposition which were due to single ion impacts. The energy deposition profile served as the starting point for the formation and evolution of the thermal spike. In this case, the minimum deposited energy density per target atom for spike formation was of the order of the atomic binding energy. An effective spike that was created by a single-ion impact in the near-surface region was introduced in order to account for bump formation on the highly oriented pyrolytic graphite surface. A linear relationship between the bump volume and the effective spike energy was obtained on the basis of a thermal spike model. This agreed well with scanning tunnelling microscope results. It was suggested that the 1-dimensional energy deposition rate was not suitable for characterizing spike effects. Instead, a 3-dimensional parameter which took account of the nature of spike formation was proposed.

Q.Yang, T.Li, B.V.King, R.J.MacDonald: Physical Review B, 1996, 53[6], 3032-8