AVS 59th Annual International Symposium and Exhibition
    Surface Science Monday Sessions
       Session SS-MoA

Paper SS-MoA10
Glide-Plane-Specific Selectivity of HREELS Demonstrated in H:Si(110)-(1x1) Phonon Dispersion

Monday, October 29, 2012, 5:00 pm, Room 21

Session: Surface Dynamics
Presenter: T. Yamada, RIKEN, Japan
Authors: T. Yamada, RIKEN, Japan
S.Y. Matsushita, Tohoku University, Japan
H. Kato, Science University of Tokyo, Japan
A. Kasuya, Tohoku University, Japan
S. Suto, Tohoku University, Japan
Correspondent: Click to Email
We observed the consequence of surface glide-plane symmetry over the phonon vibration on a typical, well-defined silicon wafer. We recorded surface phonon dispersion curves on hydrogen-terminated Si(110)-(1×1) by means of high-resolution electron energy loss spectroscopy (HREELS). This surface, H:Si(110)-(1×1), was prepared by etching a Si(110) wafer in 40% aqueous solution of NH4F. H:Si(110)-(1×1) structure involves a glide-plane symmetry, denoted as p2mg, along the short segment of the rectangular unit cell, containing two H-Si bonds. This glide-plane symmetry is also lucid in the extinction rule observed in the pattern of low energy electron diffraction (LEED). The normal vibrational modes are doubled into the in-phase and anti-phase modes. However, for the phonons propagating along the glide plane, ones of those pairs are excluded according to the wave vector. The H-Si symmetric stretching, anti-phase out-of-plane bending, and anti-phase in-plane bending exist only for the wave vectors in the 1st Brillouin zone, and the others exist only in the 2nd Brillouin zone. The impact scattering selection rule furthermore limits the normal modes visible to HREELS.We have verified this special case of phonon dispersion by recording angular-resolved vibrational spectra. The surface phonon dispersion curves were recorded over the 1st and 2nd Brillouin zones, by adjusting the angular configuration as well as the incident electron energy. The experimental dispersion curves are in a fair agreement with the theoretical prediction [2]. However, along Γ-X direction, the H-Si stretching mode (~2080 cm-1) just composes a single branch as a concatenation of the symmetric mode in the 1st Brillouin zone, and the asymmetric mode in the 2nd Brillouin zone. Similarly, the out-of-plane bending (~680 cm-1) curve is also single. This is due to the glide-plane symmetry. The in-plane bending modes are all cancelled by the EELS impact selection rule. As for the propagating direction vertical to the glide plane (Γ-X' direction), the pairs of stretching and out-of-plane bending appear simultaneously. The sub-surface phonon modes (< 600 cm-1) also follow the same rule. This is a special case for the glide-plane symmetry, reflected over the reciprocal unit cell as the property of phonon waves propagating along the surface.[1] M. Eremtchenko et al., Surf. Sci. 582 (2005) 159.[2] V. Gräschus et al., Phys. Rev. B 56 (1997) 6482.