Theory of scanning tunneling microscopy and spectroscopy of the hydrogen-terminated Si(001) surface

Abstract

The hydrogen(H)-terminated Si(001)-2 × 1 : H and 3 × 1 : H surfaces are theoretically investigated. For this purpose, the electronic states are calculated in the density functional approach with the DV (discrete variation)-Xα-LCAO method. We also simulate the scanning tunneling microscopy (STM) images and the scanning tunneling spectroscopy (STS) spectra in a first-principles approach. Our results reproduce well the observed features of the images, especially those of the monohydride units appearing on the surfaces. It is found that the ball-like spots forming a bean shape indicate the H atoms of the units. In this case, the atomic geometry effect predominates over the tunneling current of the STM on the surfaces. In the STS spectra, however, we cannot find any characteristic structure due to the H-Si anti-bonding state. This result seems to contradict the STS observation on the initial hydrogenated Si(001) surface. Finally, we discuss on a possible origin of this discrepancy.