Origin of atomic clusters during ion sputtering

Previous studies have shown that the size distributions of small clusters ( n≤40; n=number of atoms/cluster) generated by sputtering obey an inverse power law with an exponent between −8 and −4. Here we report electron microscopy studies of the size distributions of larger clusters ( n≥500) sputtered by high-energy ion impacts. These new measurements also yield an inverse power law, but one with an exponent of −2 and one independent of sputtering yield, indicating that the large clusters are produced when shock waves, generated by subsurface displacement cascades, ablate the surface.