Modulation of Si-H vibrational mode as a function of the hydrogen coverage on a H-Si(111)1x1 surface

In this study, we have observed a SFG microscopic image of the H-Si(111)1x1 surface after pump IR light irradiation. As the results, resonant SFG signals attributed to Si-H stretching vibration disappeared at the irradiated areas, and non-resonant signals were generated at these areas. We also found that there were boundary areas between laser irradiated and non-irradiated areas. Both SFG signals were weak at the boundary areas. As the reason of these modulations of SFG signals, we assumed that the temperature did not sufficiently increase for hydrogen desorption at the boundary areas, since the areas were located at edges of spatial distribution of the pump laser intensity. In order to verify the assumption, we heated the Si surface at 711K, slightly above threshold temperature for activation of hydrogen desorption, and then observe SFG spectra of the Si surface as a function of hydrogen coverage at room temperature. As the results, the intensity of the peak at 2083.7cm(-1) attributed to Si-H stretching vibration reduced as a function of hydrogen deficiency. Also, the peak position shifted toward red side. We simulated dipole-dipole interaction by using coherent potential approximation (CPA) method, and the simulated peak shift was qualitatively consistent with the experimental one. Thus, the peak shift corresponded to dipole-dipole interaction. On the other hand, the experimental peak width also broadened with the coverage reduction. However, the broadening was far wider than that of theoretical width. We suggest that the broadening was attributed to local structure defects and/or influence of neighbor dangling bonds.