We have investigated the yields and emission velocity distributions of neutral In atoms and ${\mathrm{In}}_2$ dimers sputtered from a pure indium surface under bombardment with ${\mathrm{Au}}_m^{-}(m=1,2,3)$ projectile ions. It is shown that $5\text{−}\mathrm{keV}$ ${\mathrm{Au}}_1$ bombardment leads to results in full compliance with linear cascade sputtering theory. All polyatomic projectiles are found to generate an additional low-energy contribution to the sputtered flux, which increases with increasing projectile nuclearity and energy and completely dominates the spectra under $10\text{−}\mathrm{keV}$ ${\mathrm{Au}}_3$ bombardment. Analysis shows that this contribution cannot be explained in terms of thermal spike sputtering models. Instead, the results indicate a spike emission mechanism, which closely resembles a free expansion of a supercritically heated subsurface volume.

• Received 1 February 2005

DOI:https://doi.org/10.1103/PhysRevB.72.115417