Metal to semiconductor transition on Ag/Ge(111): Surface electronic structure of the root 3X root 3, root 39X root 39, and 6X6 surfaces - art. no. 195402

摘要

The root3 x root3, root 39 x root 39, and 6 x 6 phases of Ag/Ge(111) have been studied by angle-resolved photoemission and low-energy electron diffraction. The root3 x root3 surface, formed at a one-monolayer (ML) Ag coverage, shows a metallic behavior with two partially occupied surface bands resulting from a tiny amount of extra Ag atoms on the surface. The root3 x root3 surface transforms into a root 39 x root 39 periodicity, below similar to 250 K, when a small amount of Ag is added to the surface. The presence of the additional Ag atoms leads to an increased filling of two partially occupied surface bands. By depositing similar to0.2 ML of Ag on the root3 x root3 surface, it transforms into a 6 x 6 periodicity. We observe an interesting transition from the metallic root3 x root3 and root 39 x root 39 phases to a semiconducting phase for the 6 x 6 surface, with a gap of around 0.2 eV with respect to the Fermi level. On the 6 x 6 surface, the lower band of the partially occupied surface bands is pulled down entirely below the Fermi level while the upper band is missing in the photoemission spectra. These changes result in the observed band gap. [References: 11]