Sputtering of Ices: a Review

The sputtering of low temperature rare-gas and molecular-gas solids by ion bombardment occurs through two different routes. Collision cascades initiated by momentum transferring collisions of ions with atoms of the solid are effective as they are in metals. The apparent surface binding energy is, however, much lower than the sublimation energy and there is a substantial low energy component to the ejected energy distribution that is suggestive of a thermal or collisionat spike. In the ices sputtering is also produced by electronic excitation by ion or electron bombardment. This arises from conversion of electronic energy to translational kinetic energy and at low excitation densities may involve individual excitons or repulsive recombination events. At higher densities. cooperative effects lead to nonlinear sputtering yields. The current status of both the collisional and the eiectronic regimes of ice sputtering is briefly reviewed.