Theory of Non-equilibrium Single Electron Dynamics in STM Imaging of Dangling Bonds on a Hydrogenated Silicon Surface

TL;DR

This paper develops a 3D model to explain halo-like features observed around dangling bonds in STM images of hydrogenated silicon, attributing them to non-equilibrium charge transfer effects that alter local electronic structures.

Contribution

It introduces a comprehensive 3D model of charge transfer that explains the halo features as a consequence of non-equilibrium charging of dangling bonds during STM imaging.

Findings

Halo features are caused by localized charge distortions due to non-equilibrium current.

The model explains sharp edges of halos and their dependence on imaging conditions.

Charge-induced band distortions influence STM current around dangling bonds.

Abstract

During fabrication and scanning-tunneling-microscope (STM) imaging of dangling bonds (DBs) on a hydrogenated silicon surface, we consistently observed halo-like features around isolated DBs for specific imaging conditions. These surround individual or small groups of DBs, have abnormally sharp edges, and cannot be explained by conventional STM theory. Here we investigate the nature of these features by a comprehensive 3-dimensional model of elastic and inelastic charge transfer in the vicinity of a DB. Our essential finding is that non-equilibrium current through the localized electronic state of a DB determines the charging state of the DB. This localized charge distorts the electronic bands of the silicon sample, which in turn affects the STM current in that vicinity causing the halo effect. The influence of various imaging conditions and characteristics of the sample on STM images of DBs is also investigated.