Cluster impacts at keV and MeV energies: Secondary emission phenomena

Polyatomic projectiles of different types over a broad range of velocities have been used to bombard solid targets. Electron, ion and neutral secondary emissions were measured in experiments at low and high impact velocities. In both nuclear and electronic stopping power regimes, the non-linear effects which are observed in the secondary emission are characteristic of collective effects induced by cluster impacts. Several recent experiments are described and discussed. Massive clusters like C 60 at several tens of MeV can now be accelerated to large velocities and a large amount of matter containing high mass molecular ions can be emitted in single impacts. The collision of these exotic projectiles with solids is an emerging field and several aspects are discussed in this paper. The experimental results which are presented were obtained at Orsay.