Nanospace charge polarization of monatomic-layered platinum cluster disk constructed on silicon(111)-7×7 surface

We studied geometric and electronic structures of a platinum cluster disk consisting 30 Pt atoms on the Si(111)-7×7 surface by STM experiments (see left panel) and first principles calculations. It was found that the high stability of the cluster disk on the Si surface originates from the platinum-silicide bonds as strong as ∼45eV per cluster, which are formed by electron transfer from the 5d orbital of the Pt atoms to the 3s and 3p ones of the Si atoms. This finding gives an essential interpretation to the experimental discovery that valence electrons in an occupied molecular orbital of the Pt₃₀/Si system are distributed in a wider region than the locations of the Pt atoms. It appeared that electron accumulation at the interface between the cluster and the substrate induces two-dimensional charge polarization in a nanospace as shown in right panel due to a combination of a metallic nature of the cluster disk and a highly resistive nature of the Si surface. STM image (left) of a monatomic-layered platinum cluster disk, Pt₃₀, constructed on the Si(111) surface. Schematic image (right) of two-dimensional charge polarization; the Pt-5d electrons are distributed out of the cluster, so that the centre and the periphery of the cluster are charged positively and negatively, respectively.