Above-surface potential sputtering of protons by highly charged ions

We present a description for potential-energy-induced sputtering of protons by slow, highly charged ions in front of insulator surfaces, based on the classical over-barrier model. Proton emission results from the localized Coulomb explosion after breaking the covalent C-H bond in hydrocarbons at the surface. The model describes the very steep dependence on the projectile charge (similar to Q(4)-Q(6)) for moderately high charge states (Q less than or similar to 10), in agreement with the experiment. It furthermore predicts the saturation of the Q dependence for even higher charge states.