Energy Distributions of Sputtered Metal Aluminum-Clusters

The energy distributions of neutral clusters escaping from metal targets under ion bombardment have been measured by nonresonant laser post-ionization and a time-of-flight (TOF) technique. Measurements of various aluminum- and tin-atoms, dimers and trimers from pure Al and AlSn alloy targets show that the ionization process is crucial for the interpretation of the measured spectra. In particular, fragmentation of large clusters can easily mask and disturb the measured energy distribution of clusters with fewer atoms and of monomers, if the ionization probability is low, as is the case for multiphoton ionization. The results obtained for the energy distribution of Al-atoms, dimers and trimers show that simple theories for the cluster formation cannot predict the correct energy distributions, but molecular dynamic simulations agree well with the experiments.