Atomic and electronic structures of rebondedB-type steps on theSi(001)−2×1surface

Abstract

Detailed atomic and electronic structures of rebonded $B$-type steps on the $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ surface are studied using scanning tunneling microscopy/spectroscopy (STM/STS). Both the step edge dimers on the upper atomic plane and the rebonded atoms in the lower atomic plane appear as bright protrusions in an empty-state STM image, indicating an enhancement in empty local density of states. A nonrebonded $B$-type step edge does not show these anomalous features. The differential conductance spectra on the bright protrusions indicate a strong enhancement in the local density of the empty state at the expense of the local density of the filled state. This change in the local density of states at the rebonded $B$-type step edge is tentatively interpreted in terms of the Haneman model, according to which rebonding-induced strain results in the rehybridization of the step edge atoms. Furthermore, we have found negative differential conductance (NDC) associated with the anomalous electronic states at the rebonded ${D}_{B}$ step. The responsible localized states that induce NDC at the $B$-type step sites are caused by rebonding at the step.