First-principles study of tunnel current between scanning tunneling microscopy tip and hydrogen-adsorbed Si(001) surface

TL;DR

This study uses first-principles calculations to analyze the tunnel current in STM images of hydrogen-adsorbed Si(001) surfaces, revealing the dominant role of $ ext{pi}$ states and explaining experimental observations.

Contribution

It provides a detailed theoretical analysis of STM images of hydrogen-adsorbed Si(001), highlighting the role of $ ext{pi}$ states and edge currents, aligning with experimental data.

Findings

$ ext{pi}$ states dominate tunnel current contributions.

Tunnel currents pass through dimer edges, not centers.

Hydrogen-adsorbed dimers appear lower in STM images.

Abstract

A scanning tunneling microscopy (STM) image of a hydrogen-adsorbed Si(001) surface is studied using first-principles electron-conduction calculation. The resultant STM image and scanning tunneling spectroscopy spectra are in agreement with experimental results. The contributions of the $\pi$ states of bare dimers to the tunnel current are markedly large, and the $\sigma$ states of the dimers rarely affect the STM images. The tunnel currents do not pass through the centers of the dimers but go through the edges of the dimers with local loop currents. In addition, when the tip exists above the hydrogen-adsorbed dimer, there are certain contributions from the $\pi$ state of the adjacing bare dimers to the tunnel current. This leads to the STM image in which the hydrogen-adsorbed dimers neighboring bare dimers look higher than those surrounded by hydrogen-adsorbed dimers. These results are consistent with the experimental images observed by STM.