Secondary-ion yields have been meas

Secondary-ion yields have been measured for a SiO 2 target bombarded by Ag ions at impact energies of 1.4–5.3 MeV, where the electronic and nuclear stopping powers compete with each other. Singly charged cluster ions as well as multiply charged monoatomic ions were observed. Dominant species of the cluster ions were Si(SiO 2 ) x + , SiO(SiO 2 ) x + and SiO 2 (SiO 2 ) x + . Oxygen rich positively charged species were not observed. All the cluster-ion yields were characterized by a power function of the electronic stopping power, of which exponent varies with cluster size. From this fact we can conclude that the cluster ions are produced directly through the collective process in the solid.