Isotopic shift and broadening of Si–D bending vibration on Si(111)

Abstract Surface infrared spectroscopy was carried out on unreconstructed H:Si(111)1×1 and D:Si(111)1×1 and the spectra obtained were compared precisely. Two narrow absorption peaks of Si–H bond-stretching and bond-bending were clearly observed on H:Si(111), while on D:Si(111) a narrow peak for the Si–D stretching was observed. But the corresponding bending peak split into two and these widths were from three to four times larger than that of Si–H. The splitting of the bending vibration is direct evidence of the coupling of the vibration of the surface layer composed of D and Si with the second layer of Si. Isotope exchange from H to D leads to the decrease in bending vibration frequencies down to those of the substrate. The broadening suggests the interaction of the deuterized surface layer with the rest of the substrate.