Raman scattering studies of the graphitization process in anthracene- and saccharose-based carbons

We report Raman scattering studies of the graphitization process in a series of carbons produced by the pyrolysis of saccharose and anthracene and then annealed at 1000, 1900 and 2300°C. Using 488 nm light, the first- and second-order Raman spectra of six samples have been examined in the range 50-4000 cm-1. The low-frequency Raman range 50-1000 cm-1 has been carefully examined using the laser excitation wavelengths 457.2, 476.5, 488.0 and 514.3 nm. A dependence of the Raman spectra in the first- and second-order ranges on annealing temperature and degree and size of ordered domains has been observed and correlated with neutron diffraction observations, indicating almost complete graphitization of the carbon prepared from anthracene and a disordered structure of the saccharose carbon at 2300°C. The occurrence of a sharp peak at about 464 cm-1 and broadened peaks in the range 75-210 cm-1, which shift with excitation energy as result of the one-dimensional quantum confinement effect of electrons in such structures, provide evidence for the presence of fullerene- and nanotube-like elements in the investigated materials. The presence of curved elements with odd-membered rings at an early stage of preparation and their sizeable increase at higher temperatures distinguish non-graphitizing from graphitizing carbons.