Electronic structures of size-selected single-layered platinum clusters on silicon(111)-7×7 surface at a single cluster level by tunneling spectroscopy

Tunneling spectra of size-selected single-layered platinum clusters (size range of 5–40) deposited on a silicon(111)-7×7 surface were measured individually at a temperature of 77K by means of a scanning tunneling microscope (STM), and the local electronic densities of states of individual clusters were derived from their tunneling spectra measured by placing an STM tip on the clusters. In a bias-voltage (Vs) range from −3 to 3V, each tunneling spectrum exhibits several peaks assignable to electronic states associated with 5d states of a constituent platinum atom and an energy gap of 0.1–0.6eV in the vicinity of Vs=0. Even when platinum cluster ions having the same size were deposited on the silicon(111)-7×7 surface, the tunneling spectra and the energy gaps of the deposited clusters are not all the same but can be classified in shape into several different groups; this finding is consistent with the observation of the geometrical structures of platinum clusters on the silicon(111)-7×7 surface. The mean en...