Raman studies of benzene-derived graphite fibers

Carbon fibers prepared from thermal decomposition of benzene at ∼ 1100°C are studied by Raman spectroscopy as a function of heat-treatment temperature. The structural ordering at each heat-treatment temperature is monitored by observation of both the Raman-allowed $E_{2g_2}$ mode at 1580 ${\mathrm{cm}}^{-1\mathrm{}}$ and the disorder-induced lines at ∼ 1360 ${\mathrm{cm}}^{-1\mathrm{}}$ in the first-order spectra and at 2730 and 2970 ${\mathrm{cm}}^{-1\mathrm{}}$ in the second-order spectra. Raman and resistivity results indicate three characteristic heat-treatment temperatures relevant to the establishment of in-plane and interplanar ordering. Using fibers heat treated to the maximum available temperature of 2900°C, Raman spectroscopy shows that single-staged fibers can be prepared by acceptor intercalation, in agreement with direct Debye-Scherrer x-ray measurements. Resistivity measurements on pristine fibers previously heat treated to 2900°C show a metallic temperature dependence with $\rho =70\mathrm{}$ μΩ cm at 300 K and a residual resistance ratio of 1.5. Upon intercalation, a resistivity $\rho =7\mathrm{}$ μΩ cm at 300 K and a residual resistance ratio of 5 is achieved. Raman-spectroscopy and temperature-dependent resistivity measurements demonstrate that the benzene-derived fibers exhibit the highest degree of ordering achieved in fibers and provide an attractive host material for intercalation.