Electronic transport of Au-adsorbed Si(111)-3×3-Ag : Metallic conduction and localization

The electrical conductance of Au-adsorbed Si(111)-3×3-Ag surface was studied as a function of temperature (110-300 K) by a method of micro-four-point probe. In the pristine surface without Au adsorbates, the surface electrical conductance was inversely proportional to the temperature, indicating a metallic nature dominated by electron-phonon scattering. After deposition of small amounts of Au adsorbates [0.02 and 0.14 monolayer (ML)], the surface electrical conductance decreased with temperature, exhibiting a nonmetallic behavior in spite of nearly free-electron and metallic surface bands still existing. It is explained by localization of surface-state electrons due to randomly dispersed Au nanoclusters at 0.02 ML coverage and due to disordered and high-density domain boundaries in the 21×21 superstructure at 0.14 ML coverage of Au.