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

摘要

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