The Erosion of Frozen Argon by Swift Helium Ions

The temperature, energy, and thickness dependence of the erosion rates of frozen argon films when irradiated with 0.1–3 MeV helium ions have been measured. The erosion yields Y are much too high to be explained by the concentional collisional cascade-sputtering theory and are furthermore unequivocally associated with electronic processes generated by the bombarding particle. In the present energy region, it is found that Y scales approximately as the electronic stopping power squared, depends on the charge state of the incoming helium ions, and perhaps more important, is independent of the substrate temperature and current density up to a temperature at which beam-induced thermal sublimation sets in. Different models such as, e.g., Coulomb explosion and ionization spikes, which may explain the experimental results, are discussed.