Defect-induced perturbation on the Sn–Si(111) surface: a voltage-dependent scanning tunneling microscopy study

We have measured the amplitude of the damped periodic lattice response to substitutional Si defect sites on the 13 ML Sn–Si(111) surface at room temperature by means of voltage-dependent scanning tunneling microscopy experiments. This perturbation, which in the case of Si defects mainly shows up as an increased apparent height of the defect first neighbors, is strongly voltage dependent and vanishes when tunneling at very low voltages (∼10 mV), both in filled and empty state images. The observed energy dependence is justified by the vertical hybridization of the surface dangling bond states at the Fermi level and by vertical charge rearrangement between the Sn adatoms and the subsurface Si atoms directly below the T4 site.