Structure and phase transition of a uniaxially incommensurate in monolayer on Si(111)

Abstract

We have studied the atomic structure and phase transition of a dense metallic monolayer of In on Si(111). Although the monolayer phase was previously considered to have a (7×3) periodicity, low-energy electron diffraction and scanning tunneling microscopy observations have revealed that the phase has an incommensurate structure with the In overlayer uniaxially contracted by 2% from (7×3). The uniaxially contracted structure was found to be more stable than the commensurate (7×3) structure by first-principles calculations. We also observed a phase transition to a (7×7) phase at 250-210 K upon cooling. Angle-resolved photoelectron spectroscopy and macroscopic four-point-probe conductivity measurements demonstrated that the transition induces the disappearance of metallic surface states and a sharp drop in sheet conductivity, respectively. These results indicate an electronic metal-insulator transition.