On Universality in Sputtering Yields Due to Cluster Bombardment

Molecular dynamics simulations, in which atomic and molecular solids are bombarded by Ar-n (n = 60-2953) clusters, are used to explain the physics that underlie the universal relation of the sputtering yield Y per cluster atom versus incident energy E per cluster atom (Y/n vs E/n). We show that a better representation to unify the results is Y/(E/U-0) versus (E/U-0)/n, where U-0 is the sample cohesive energy per atom or molecular equivalent, and the yield Y is given in the units of atoms or molecular equivalents for atomistic and molecular solids, respectively. In addition, we identified a synergistic cluster effect. Specifically, for a given (E/U-0)/n value, larger clusters produce larger yields than the yields that are only proportional to the cluster size n or equivalently to the scaled energy E/U-0. This synergistic effect can be described in the high (E/U-0)/n regime as scaling of Y with (E/U-0)(alpha), where alpha > 1.