Ultraviolet and visible Raman spectroscopies of the graphitic BC_x phases

Ultraviolet (UV) Raman and visible Raman spectroscopies were applied to study the graphitic BC_x (g-BC_x) phases. The Raman spectra of the g-BC_x phases excited with UV laser at 244 nm have one main peak: a G peak (approximately at 1590 cm^{- 1}), and do not have the D peak (around 1350 cm^{- 1}) characteristic for Raman spectra of disordered graphitic phases. The D peak can be detected in all g-BC_x phases when green (534 nm) or near-infrared (785 nm) lasers are used for Raman scattering excitation. The positions of the G and D peaks were found to be independent (within the experimental errors) of the B/C ratio. The pattern of the peaks in UV Raman spectra of g-BC_2.1 phase indicates that the additional peaks centered at 1089 cm^{- 1} should be assigned to the E_g mode of B₄C vibration rather than to the T mode characteristic to amorphous graphite. The high signal-to-noise (S/N) ratio and lack of fluorescence of the UV Raman spectra allow an accurate measure of bandwidth and frequency of the G peaks.