Soft landing and fragmentation of small clusters deposited in noble-gas films

The collision between small silver clusters (AgN, N=2-7) and rare-gas films is investigated experimentally as a function of kinetic energy (2.5-50 eV per cluster atom), cluster size, and film material (Ar, Kr, and Xe). Cluster ions are produced by sputtering and size selected by a quadrupole mass spectrometer prior to deposition. The products are studied by UV-visible optical spectroscopic methods. The cluster fragmentation rate is found to decrease with the kinetic energy and when changing the film material from Xe to Kr and Ar. This agrees with previous molecular-dynamic predictions of larger clusters impinging on noble-gas films. In addition we find that the dimer fragmentation rate decreases when the binding energy increases. In order to explain the unexpectedly low dimer fragmentation observed at high kinetic energy, we suggest that after fragmentation partial reaggregation occurs by diffusion of the fragments within the hot region around the impact point.