Surface phonons of hydrogen-terminated semiconductor surfaces. I. The H:Si(111)-(1×1) surface

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Abstract
Surface-phonon dispersion curves and spectral densities for the hydrogen-terminated Si(111)-(1×1) surface have been calculated using a semiempirical total-energy approach. With an empirical tight-binding electronic structure and measured equilibrium properties of bulk Si and of the silane molecule as input, atomic force constants were calculated from the total energy. The dynamical matrix for a structure-optimized 36-layer Si slab, capped on both sides with a monolayer of hydrogen, was set up yielding the vibrational spectrum of H:Si(111)-(1×1). We analyze the resulting surface-phonon modes with respect to their physical origin, their spatial localization properties, and their polarization. The complete surface-phonon spectrum of localized and resonant modes is resolved by employing spectral densities of the slab. Contrary to the results of previous calculations, our calculated surface-phonon modes are in excellent agreement with recent high-resolution electron-energy-loss-spectroscopy data and largely account for the observed modes throughout the entire spectral range.