Raman spectra of nano-structured carbon films synthesized using ammonia-containing feed gas

We examined the Raman spectra of nanostructured carbon films grown using the ammonia-containing feed gas at two excitation wavelengths, 514.5 and 1064 nm. The increase of the ammonia concentration in the feed gas resulted in two prominent changes: the complete morphology change (from nanoparticle dominance to nanotube dominance) and the degradation of the graphitic sheet quality. However, the Raman spectra preserved strong resemblance to those of graphite and glassy carbon and showed only systematic variation in the peak position, width, and the intensities. We noted that the ammonia-concentration-dependent broadening of D and G bands, the up-shift of D band, and the increase of the intensity ratio I(D)/I(G) of these films could be interpreted as the signature for the increase of disorder in the graphitic structure and/or the reduction of the graphitic crystallite size in accordance with the similar observation from other carbon-based films. We attributed the observed excitation-energy-dependent shift of the D-band position and the variation of I(D)/I(G) value to the resonance phenomena in Raman scattering. Moreover, we showed that the dispersion of the D band was in good quantitative agreement with the model proposed by Matthews [Phys. Rev. B 59, R6585 (1999)]. (C) 2002 American Institute of Physics.