Charge state dependence of proton sputtering from solid surfaces with slowhighly charged ions

Proton sputtering from an uncleaned surface of a CuO mesh has been experime ntally studied for very slow highly charged ions of 500 eV Neq+ (q = 4-8), Arq+ (q = 4-13), Krq+ (q = 5-17) and Xeq+ (q = 7-24). It is found that (i) for q = 10, the sputtering yield of protons showed a power-law dependence ( similar to q(gamma)) with an exponent of gamma=5+/-1 for all ions measured, and (ii) for q < 10, the yield saturated and deviated from the power law. Such a characteristic feature has been reproduced well by a model based on the classical over-barrier model.