Local Structure of the Silicon Implanted in a Graphite Single Crystal

Abstract

Solid carbon forms two kinds of local structures, i.e., diamond-like and two-dimensional graphite structures. In contrast, silicon carbide tends to prefer only diamond structure that is composed of sp³ bonds. In order to clarify whether or not two-dimensional graphitic Si_xC layer exists, we investigate the local structures of Si_xC layer produced by Si⁺-ion implantation into highly oriented pyrolitic graphite (HOPG) by means of near-edge X-ray absorption fine structure (NEXAFS). The energy of the resonance peak in the Si K-edge NEXAFS spectra for Si⁺-implanted HOPG is lower than those for any other Si-containing materials. The intensity of the resonance peak showed a strong polarization dependence. These results suggest that the final state orbitals around Si atoms have π^*-like character and the direction of this orbital is perpendicular to the graphite plane. It is elucidated that the Si-C bonds produced by the Si⁺-ion implantation are nearly parallel to the graphite plane, and Si_xC phase forms a two-dimensionally spread graphite-like layer with sp² bonds.