G-band resonant Raman study of 62 isolated single-wall carbon nanotubes

Abstract

We report G-band resonance Raman spectra of single-wall carbon nanotubes ͑SWNTs͒ at the singlenanotube 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 (G ϩ ϭ1591 cm Ϫ1), while the lower-frequency peak is given by G Ϫ ϭ G ϩ ϪC/d t 2 , with C being different for metallic and semiconducting SWNTs (C M ϾC S). The peak frequencies do not depend on nanotube chiral angle. The intensity ratio between the two most intense features is in the range 0.1ϽI G Ϫ /I G ϩϽ 0.3 for most of the isolated SWNTs (ϳ90%). Unusually high or low I G Ϫ /I G ϩ 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.

Type- and Species-Selective Air Etching of Single-Walled Carbon Nanotubes Tracked with in Situ Raman Spectroscopy

“…For a fixed diameter, a metallic GÀ is approximately twice as far in energy from the Gþ for a semiconductor. 71,72 A1nm diameter semiconducting nanotube has a GÀ at about 1550 cm À1 , 70 whereas a metallic tube of the same diameter is at about 1510 cm À1 . 71,72 The resonance window for G bands is broader than for RBMs (about 300 meV compared to about 100 meV), 70 meaning that resonance conditions are not as strict for G bands.…”

Wall-to-wall stress induced in (6,5) semiconducting nanotubes by encapsulation in metallic outer tubes of different diameters: A resonance Raman study of individual C60-derived double-wall carbon nanotubes

“…For semiconducting nanotubes, the LO mode (G + band) is a bond stretching mode with little diameter dependence and the TO mode is a bond bending mode whose frequency decreases with decreasing nanotube diameter (G − band) [21]. Also, the G − band of isolated semiconducting tubes (S-SWNTs) generally has a smaller FWHM linewidth than that of metallic tubes [22]. Since the inner tubes of our DWNTs are semiconducting, their spectra show sharp G − features that are easy to fit unambiguously with a Lorentzian lineshape.…”

Resonance Raman spectroscopy in one-dimensional carbon materials

“…In graphite the feature has a single peak, since in-plane tangential vibrations are degenerate in the hexagonal sheet. In nanotubes this feature splits into up to 6 peaks due to the curvature of the graphene sheet and the quantum confinement along the tube circumference (Jorio et al 2000(Jorio et al , 2002a(Jorio et al , b, 2003b.…”