Material-dependent emission mechanism of secondary atomic ions from solids under MeV-energy heavy ion bombardment

Yields and emission energy distributions of secondary ions have been measured for GaP and GaAs targets bombarded by MeV-energy Si ions for studying roles of the electronic collision in the formation process of secondary atomic ions. In the case of the GaP target, single- and multiple-charged positive P ions were observed in a way similar to Al and Si targets. In the case of GaAs, however, the production rates of positive As ions are strongly depressed. Negative atomic ions were not observed for both targets. The emission energy distribution extends asymmetrically over the high-energy side for all the positively charged atomic ions. The most probable and mean emission energies are in general proportional to the electric charge of the secondary ions. These results combined with the yield dependence on the incident energy show that sputtering of the ions is related to several processes of (1) the thermalization model for the singly charged ions and (2) the combined force of kinetic recoil and Coulomb repulsion in a highly charged track region for the multiply charged ions