Linearity and additivity in cluster-induced sputtering: A molecular-dynamics study of van der Waals bonded systems

Using molecular-dynamics simulation, we study sputtering of a condensed-gas solid induced by the impact of atomic clusters with sizes 1less than or equal tonless than or equal to10(4). Above a nonlinear onset regime, we find a linear increase of the sputter yield Y with the total energy E of the bombarding cluster. The fitting coefficients in the linear regime depend only on the cluster size n such that for fixed bombardment energy, sputtering decreases with increasing cluster size n. We find that to a good approximation the sputter yield in this regime obeys an additivity rule in cluster size n such that doubling the cluster size at the same cluster velocity amounts to doubling the sputter yield. The sputter-limiting energy epsilon(s) is introduced which separates erosion (epsilon>epsilon(s)) from growth (epsilon<epsilon(s)) under cluster impact.