Origin, symmetry, and temperature dependence of the perturbation induced by Si extrinsic defects on the Sn/Si(111) α surface: A scanning tunneling microscopy study

Abstract

We have studied with variable temperature scanning tunneling microscopy (STM) experiments the local structure of substitutional Si defects of the 1/3 ML Sn/Si(111) α surface. Empty state images show that most substitutional Si defects drift toward H3 sites leaving an unsaturated dangling bond from the first layer Si atoms. Consequently there is a charge transfer toward the Sn first neighbors of the defect. Filled state images show defect centered perturbations having 3×3 symmetry, which locally modifies the surface into a honeycomb pattern. Low temperature (120 K) STM images show undoubtedly the increase of the decay length of such perturbation, indicating the possibility of an overall phase transition at much lower temperatures.