Thermal spike effects in low-energy single-ion impacts on graphite

Monte Carlo simulations have been used to obtain three-dimensional distributions of cascade defects and energy deposition due to single-ion impacts in graphite. This energy deposition profile serves 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 the spike formation is the order of the atomic binding energy. An effective spike created by a single-ion impact in the near-surface region is introduced to account for the bump formation on the highly oriented pyrolytic graphite surface. A linear relationship between the bump volume and the effective spike energy is obtained based on the thermal spike model, which agrees well with the scanning tunnel microscope results. It is suggested that the one-dimensional energy deposition rate dE/dx is not suitable to describe spike effects. On the other hand, a three-dimensional parameter corresponding to the nature of the spike formation should be used.