Step structure on H/Si formed in hot water as revealed with angle-resolved polarized infrared spectroscopy

Stretching, scissoring, and wagging due to H atoms chemisorbed on Si surfaces were observed on several vicinal (111) surfaces by infrared spectroscopy in nitrogen atmosphere while surface electric fields were controlled. By analyzing the response to the electrical field, orientation of the dynamic polarization, Pdyn, for each vibration mode was determined. These vibration modes were associated with specific bulk-terminated chemisorption sites for H atoms on these surfaces. The H-terminated vicinal (111) surfaces with 〈112¯〉 steps were characterized by H atoms forming monohydrides on the (111) terrace and monohydride chains at the 〈112¯〉 step-edges. The anisotropy of the Pdyns showed that these step edges were atomically straight along 〈1¯10〉 and had the translational symmetry of Si crystal. On the surface with 〈1¯1¯2〉 steps, we detected scissoring of the SiH2 structures, which was missing in the previous investigation, as well as stretching and wagging of the Si-H bonds. By rotating the surface electrical field in the (1¯10) plane we obtained angle-resolved absorption spectra. By analyzing the absorption features we determined the direction of the dynamic polarization of each vibration. The step-edge structure was deduced by adopting the three-layer model with an experimentally determined screening factor. It was revealed that this step edge was formed by a strained vertical dihydride and a strained monohydride complex and that the dihydride was rotated to the 〈1¯10〉 axis at 21° from its bulk-terminated position resulting in a large angle of 65° to the optical surface.