Raman spectroscopic characterization of submicron vapor-grown carbon fibers and carbon nanofibers obtained by pyrolyzing hydrocarbons

Variations of the properties of submicron vapor-grown carbon fibers (VGCFs) and nanofibers, with diameters around 0.1–0.2 μm and 80–100 nm, respectively, are observed by Raman spectroscopy as a function of heat-treatment temperature. The microstructural evolution strongly depends on the original properties of the material, such that the main transition temperatures associated with the onset for establishing two-dimensional graphene ordering are defined below 1500 °C for the nanofibers and 2000 °C for the submicron VGCFs, respectively. The relative intensities (I_D/I_G) of the as-grown phase for submicron VGCFs and nanofibers are 3.44 and 1.35, while those for the corresponding graphitized samples are 0.393 and 0.497, respectively.