Fragmentation of aluminum-cluster anions in collision with a solid surface

Dynamical processes involved in the scattering of aluminum-cluster anions, Al_N^- (4 ≤ N ≤ 25), from a silicon surface were investigated. The scattered anions observed were fragment cluster anions, Al_n^- (n ≤ N). The recoil velocities of these fragment anions were evaluated by analyzing both the angular dependence of their intensity and the collision-energy dependence of their time-of-flight. The recoil energy of each fragment anion thus obtained suggests that the fragmentation process involves not only sequential evaporation of aluminum atoms but also fission into fragment clusters. Comparison of the present result with that of the collision-induced dissociation with a rare-gas atom indicates that the electron transfer between the cluster and the surface plays an important role.