Raman studies of benzene-derived graphite fibers

Abstract

Carbon fibers prepared from thermal decomposition of benzene at \ensuremath{\sim} 1100\ifmmode^\circ\else\textdegree\fi{}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 ${E}_{2{g}_{2}}$ mode at 1580 ${\mathrm{cm}}^{\ensuremath{-}1}$ and the disorder-induced lines at \ensuremath{\sim} 1360 ${\mathrm{cm}}^{\ensuremath{-}1}$ in the first-order spectra and at 2730 and 2970 ${\mathrm{cm}}^{\ensuremath{-}1}$ 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\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}C show a metallic temperature dependence with $\ensuremath{\rho}=70$ \ensuremath{\mu}\ensuremath{\Omega} cm at 300 K and a residual resistance ratio of 1.5. Upon intercalation, a resistivity $\ensuremath{\rho}=7$ \ensuremath{\mu}\ensuremath{\Omega} 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.