Non-Linear Electronic Effects in Cluster-Solid Interactions

A review will be given of the effects of non- additivity under impacts of clusters, observed only in a variety of electronic energy loss phenomena. They include electron emission, luminescence, projectile charge state formation, electron-hole pairs generation causing the surface barrier detector response and the high-energy part of the secondary ion emission under cluster impacts. The sublinear effects consist in decreasing the yields per one incident atom with increasing number of cluster constituents at the same velocity. The ratio of the yields R_n = Y_n/nY_1, being the measure of the effect, is less than 1 and usually decreases with increasing projectile velocity, and the number of atoms in the cluster n. The reduction is caused by the mechanism of sweeping - out - electrons, that removes some electrons from the cluster trek in binary collisions between the front running cluster atoms and the target atoms, leaving fewer available for the tailing ones.