AN INVESTIGATION OF WELL-CHARACTERIZED SMALL GOLD CLUSTERS BY PHOTOELECTRON-SPECTROSCOPY, TUNNELING SPECTROSCOPY, AND COGNATE TECHNIQUES

After microscopic characterization of the size distributions of gold clusters, deposited on carbon substrates by vacuum evaporation or by soft landing, Au(4f) binding energy of the clusters has been measured as a function of the mean cluster size. Similar measurements have been carried out on Au clusters prepared from sols by chemical means and high-nuclearity cluster compounds. In general, small clusters with a mean diameter of less than or similar to 2 nm show significantly larger binding energies than the bulk metal value, due to the onset of nonmetallicity. Nonmetallicity manifests itself in terms of a tunneling conductance gap only in clusters of diameter less than or similar to 1 nm containing 40 atoms or fewer.