Low Energy Alkali Ions Scattered From Au Nanoclusters

Metal nanoclusters have been intently investigated over the past 20 years because of their high catalytic activity at low temperatures. The experiments reported here employ a specialized method of low energy ion scattering (LEIS) to probe the electronic properties of deposited Au nanoclusters with and without adsorbates. Because the Au atoms are much more massive than the substrate atoms, the signal from the nanoclusters can be separated from that of the substrate. The experiments measure the neutralization probability of singly scattered alkali ions, which is acutely sensitive to the local electrostatic potential a few Å’s above the surface. Earlier work had demonstrated that the neutralization is a function of cluster size and that it is enhanced for the smallest clusters, but this result had not been previously understood. Recent DFT calculations, which show that the edge atoms are more positively charged than the center atoms, have enabled the development of a model to explain why the neutralization changes with cluster size. Data will be presented for metal clusters grown on various substrates, such as SiO₂, TiO₂ and graphene, and after reaction with halogen molecules.