Electronic and dynamic studies of boron carbide nanowires

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 π* resonance characteristic of sp/sp² hybridization followed by a broad σ* resonance characteristic of sp³ hybridization. The C 1s NEXAFS spectrum is dominated by the σ* resonance indicating that C bonding in the nanowires is predominantly sp³ in character. The NEXAFS spectra are equivalent to corresponding spectra of single-crystal (B₄C) boron carbide, consistent with the B₄C 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 cm^-1 have also been observed, which are specific to boron carbide nanowires.