G-band resonant Raman study of 62 isolated single-wall carbon nanotubes -: art. no. 155412

We report G-band resonance Raman spectra of single-wall carbon nanotubes (SWNTs) at the single-nanotube level. By measuring 62 different isolated SWNTs resonant with the incident laser, and having diameters d(t) ranging between 0.95 nm and 2.62 nm, we have conclusively determined the dependence of the two most intense G-band features on the nanotube structure. The higher-frequency peak is not diameter dependent (omega(G)(+)=1591 cm(-1)), while the lower-frequency peak is given by omega(G)(-)=omega(G)(+)-C/d(t)(2), with C being different for metallic and semiconducting SWNTs (C-M>C-S). The peak frequencies do not depend on nanotube chiral angle. The intensity ratio between the two most intense features is in the range 0.1<I-omega G(-)/I-omegaG(+)<0.3 for most of the isolated SWNTs (similar to 90%). Unusually high or low I-omega G(-)/I-omegaG(+) ratios are observed for a few spectra coming from SWNTs under special resonance conditions, i.e., SWNTs for which the incident photons are in resonance with the E-44(S) interband transition and scattered photons are in resonance with E-33(S). Since the E-ii values depend sensitively on both nanotube diameter and chirality, the (n,m) SWNTs that should exhibit such a special G-band spectra can be predicted by resonance Raman theory. The agreement between theoretical predictions and experimental observations about these special G-band phenomena gives additional support for the (n,m) assignment from resonance Raman spectroscopy.