LOCAL DIPOLE FIELD CONTRIBUTIONS TO BOND-STRETCHING SILICON–HYDROGEN VIBRATIONAL MODES ON FLAT AND VICINAL Si(111) SURFACES
Bond-stretching frequencies for bonded-H (and D) on flat and vicinal Si(111) surfaces have been calculated using a model that includes (i) short range valence forces and (ii) dynamic effects due to dipole–dipole interactions. Dipole–dipole interactions have been calculated exactly for flat surfaces, and for vicinal surfaces off-cut in the [Formula: see text] and [Formula: see text] directions terminated respectively by monohydride, Si–H, and dihydride, Si–H 2, bonding at the step edges. Using short range force constants and effective charges obtained from isolated Si–H and Si–H 2 stretching modes in hydrogenated amorphous Si, a-Si:H, as input parameters, the calculated coupled mode frequencies are in excellent agreement with experiment, i.e. using 5 empirical parameters, 16 frequencies in the range of 1500–2150 cm-1 are fit to better than 0.14%, or ±2–3 cm-1.