Surface phonon dispersion of the deuterium-terminatedSi(111)−(1×1)surface

Abstract

The surface phonon dispersion was investigated by high-resolution electron-energy-loss spectroscopy on the deuterium-terminated $\mathrm{Si}(111)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$ prepared by an improved wet chemical method. The phonon modes were recorded over the entire surface Brillouin zone and compared with the theoretical phonon dispersion curves derived on the basis of semiempirical total-energy scheme calculated by Sandfort et al. [Phys. Rev. B 51, 7139 (1995)] and by Gr\"aschus et al. [Surf. Sci. 368, 179 (1996)]. The present results of the observation fairly agree with the theoretical curves, except a discrepancy for ${\mathrm{B}}_{3}$ and ${\mathrm{R}}_{1}$ branches exhibiting a sizable dispersion between 35 and $55\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, which was predicted to have no dispersion by the theory. The suface-projected bulk phonon is distributed below $65\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ of the vibration energy, and the Si-D modes with higher energies than that are independent of SPBP. The Si-D vibrations with energies between 35 and $65\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ strongly intermix with bulk phonons, and below $35\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, the Si-D's move together in phase and the surface phonons are the same as those of hydrogen-terminated $\mathrm{Si}(111)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$.