Emission energy distribution of secondary ions produced through the electronic sputtering process under heavy ion bombardment

The emission energy distribution of secondary ions has been systematically measured for a SiO2 bombarded by Si, Cu and Ag ions at an impact energy region of MeV, where the electronic stopping power dominates over the nuclear stopping power. The obtained emission energy for atomic Oq+ and Siq+ (qe: electric charge) ions depends not only on projectiles but also on the electric charge qe. The energy distribution is asymmetric extending to a high-energy side. Conversely, the energy distribution for cluster ions is very narrow compared with that for the atomic ions. The mean energy for the cluster ions hardly depends on the size of clusters. However, in the case of the Cu projectiles, the mean energy of the (SiO2)(x) series (x: number of molecules) is overall less than those of the Si(SiO2)(x) and SiO(SiO2)(x) series. These results combined with the yield dependence on the electronic stopping power show that the atomic ions are produced from the hot track region and forced to move by the electric repulsive force. The cluster ions are formed in the periphery of the track region. (C) 2000 Elsevier Science B.V. All rights reserved.