Nonlinear effects in ion emission from LiF induced by N + and N 2+ MeV ion impact

Abstract

Beams of N + and N 2 + in the 75–7500 keV/atom energy range have been used to bombard a LiF surface. Desorption yields and energy distributions of positive and negative secondary ions have been measured by the time-of-flight technique. Measurements of the energy distributions revealed the relative contribution to desorption due to collision cascades and electronic excitations in the solid. Experiments have shown that F − ions are desorbed as a result of elastic collision cascades and that the corresponding ion yield depends linearly on the number of constituents of the projectile, i.e. Y(N 2 +) > 2Y(N +). In contrast, emission of clusters, such as Li 2F +, were found to be caused by electronic excitation in the solid with the respective yields revealing a nonlinear dependence: Y(N 2 +) > 2Y(N +). Both processes were found to contribute to Li + desorption. Nonlinear effects are discussed in terms of effective stopping power which depends not only on the electronic stopping power of the primary ion, but also on the track size.