Abstract
In the field of Raman spectroscopy, it is known that the full width at half maximum intensity of the G band (G-FWHM) in the first order Raman spectrum for carbon material is a parameter for graphitization, though it is qualitative evidence. In the present paper, this fact has been studied quantitatively using pyrolytic carbons having various values of interlayer spacing doce, 0.3367 nm≤d002≤0.3421nm. The crystal structures of the pyrolytic carbon samples with 0.3367nm≤d002≤0.3374nm are graphitic structures, while the samples with 0.3374nm<d002≤0.3421nm are turbostratic structures. The first order Raman spectrum for each pyrolytic carbon sample has been measured on a cleaved surface of the basal plane of the sample using a Raman microprobe. It has been found that the G-FWHM value for the largest d002 value of 0.342nm of the sample is 21.5cm-1, the value remains at the almost constant value of about 21cm-1 for the d002 values down to 0.3374nm and then decreases almost linearly to the lowest value of 16cm-1 for the lowest d002 value of 0.3367nm. This trend almost agrees with the results obtained for benzene-derived vapor grown carbon fibers heat-treated up to 2900°C by Chieu and his coworkers. The results obtained can be related well to the observation with a scanning electron microscope on a cleaved surface and fractured surface perpendicular to the cleaved surface for each pyrolytic carbon sample. The present findings are also related very well to the magnetoresistance results for the same pyrolytic carbon samples published by Kaburagi and his coworkers.
