CLUSTER-SOLID INTERACTIONS

It is expected that during the impact of a cluster ion with a surface the interactions among the participating atoms will create transient conditions that are more extreme than those found for the impacts of individual atoms. At energies of keV per atom molecular dynamics simulations suggest a variety of experimental observations that may provide diagnostic information about the impact. Among the phenomena predicted are: an enhanced probability for the rebound (''splash'') of energetic atoms from the projectile; the emission of sharp-line Auger electrons well below their kinematic threshold due to collisions among the moving atoms; the existence of highly excited rebounding projectile fragments that decay by thermionic electron emission and fragmentation/fission. MeV cluster beams (e.g., C-n(+), Au-n(+)) are now available, which also offer a potentially rich variety of new phenomena. For them the cooperative effect of the associated atoms in the cluster for electronic excitation and nuclear recoil may produce extreme conditions both at the point of impact and along the cluster ''track'' in the target. This talk will review to what extent such effects have been observed already, the optimum choices for future experiments, and the relation of the observations to the conditions during the cluster impact.