Surface phonon dispersion of the deuterium-terminated Si (111) - (1×1) surface

The surface phonon dispersion was investigated by high-resolution electron-energy-loss spectroscopy on the deuterium-terminated Si (111) - (1×1) 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 [Phys. Rev. B 51, 7139 (1995)] and by Gräschus [Surf. Sci. 368, 179 (1996)]. The present results of the observation fairly agree with the theoretical curves, except a discrepancy for B3 and R1 branches exhibiting a sizable dispersion between 35 and 55 meV, which was predicted to have no dispersion by the theory. The suface-projected bulk phonon is distributed below 65 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 meV strongly intermix with bulk phonons, and below 35 meV, the Si-D's move together in phase and the surface phonons are the same as those of hydrogen-terminated Si (111) - (1×1).