Electronic and dynamic studies of boron carbide nanowires

Abstract

The electronic and vibrational properties of boron carbide nanowires grown by plasma-enhanced chemical vapor deposition have been examined with the techniques of near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and Raman spectroscopy. The B 1s absorption edge is characterized by a narrow ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ resonance characteristic of ${sp/sp}^{2}$ hybridization followed by a broad ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ resonance characteristic of ${\mathrm{sp}}^{3}$ hybridization. The C 1s NEXAFS spectrum is dominated by the ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ resonance indicating that C bonding in the nanowires is predominantly ${\mathrm{sp}}^{3}$ in character. The NEXAFS spectra are equivalent to corresponding spectra of single-crystal $({\mathrm{B}}_{4}\mathrm{C})$ boron carbide, consistent with the ${\mathrm{B}}_{4}\mathrm{C}$ structure of the nanowires as determined by selected area electron diffraction. Four corresponding Raman modes of crystalline boron carbide have been observed for the boron carbide nanowires. Two previously unobserved Raman modes of boron carbide at 1365 and 1965 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ have also been observed, which are specific to boron carbide nanowires.