FRAGMENTATION AND REACTION PROCESSES IN CLUSTER-SURFACE COLLISIONS

We review the processes which have been observed from collisions betwe en alkali-halide clusters and solid surfaces. Soft impact of nanocryst alline NanFn-1+ clusters against solid surfaces causes them to cleave along the lowest energy (100) plane. At higher collision energies (E(i )>1 eV/atom), an evaporative cascade occurs which is characteristic of a transformation of the nanocrystal to a molten state. Efficient F- t ransfer from the cluster to the surface can occur for the larger clust ers (>60 atoms) scattering from Si(111), in direct competition with th e cleaving channel at low energies. In this regime, strong bonds can f orm between the F- and silicon surface. The reaction probability incre ases with cluster size indicating that an impact-initiated shock wave is needed to enhance the reactive process.