DISPERSION EFFECTS OF RAMAN LINES IN CARBONS

Raman spectra of highly oriented pyrolytic graphite (HOPG), natural po lycrystalline graphite (PCG), high pressure graphite (HPG), and low-te mperature pyrolyzed polyfurfuryl alcohol (PFA) have been measured. Com paring the Raman spectra of each sample illuminated with laser beams o f 488.0 nm and 1064.0 nm wavelengths, respectively, unambiguous disper sion effects have been observed for the D'-line in HOPG and in other f orms of PCG as well as for their D lines. Comparisons of the intensity ratios of the D' Line to the D line (I-D'/I-D) of HOPG and polycrysta lline indicate that the dispersion effects of the D' line and the D Li ne may have the same physical origin. In addition, it has also been ob served that the G-Line position of low-temperature pyrolyzed PFA is se nsitive to the excitation wavelength while that of HOPG, PCG, and HPG is not. This phenomenon is attributed to the nanometer size of the mic rocrystalline graphites by analyzing the factors that may induce such a dispersion effect. (C) 1998 American Institute of Physics.