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 dt 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 (ωG + = 1591 cm-1), while the lower-frequency peak is given by ωG - = ωG + - C/d- 2, with C being different for metallic and semiconducting SWNTs (CM>CS). 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<1ωG -/ 1ωG +<0.3 for most of the isolated SWNTs (∼90%). Unusually high or low 1ωG/1 ωG+ 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 E44 S interband transition and scattered photons are in resonance with E33 S. Since the Eii 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.
|Original language||English (US)|
|Number of pages||9|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Apr 15 2002|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics