Charge State Effect of High Energy Ions on Material Modification in the Electronic Stopping Region

Abstract

It has been observed that modifications of non-metallic solids such as sputtering and surface morphology are induced by electronic excitation under high-energy ion impact and that these modifications depend on the charge of incident ions (charge-state effect or incident-charge effect). A simple model is described, consisting of an approximation to the mean-charge-evolution by saturation curves and the charge-dependent electronic stopping power, for the evaluation of the relative yield (e.g., electronic sputtering yield) of the non-equilibrium charge incidence over that of the equilibrium-charge incidence. It is found that the present model reasonably explains the charge state effect on the film thickness dependence of lattice disordering of WO3. On the other hand, the model appears to be inadequate to explain the charge-state effect on the electronic sputtering of WO3 and LiF. Brief descriptions are given for the charge-state effect on the electronic sputtering of SiO2, UO2 and UF4, and surface morphology modification of poly-methyl-methacrylate (PMMA), mica and tetrahedral amorphous carbon (ta-C).