(n, m) structural assignments and chirality dependence in single-wall carbon nanotube Raman scattering

Raman spectra were obtained from thin bundles containing just a few single- wall carbon nanotubes (SWNTs). These spectra exhibit new characteristics ab sent in the ensemble Raman measurements. A large variation in the radial br eathing mode (RBM) Stokes to anti-Stokes Raman intensity ratio was observed for different metallic tubes and can be understood with a simple resonant Raman analysis. An (n, m) structural assignment for many tubes at 632 nm la ser excitation was tentatively achieved on the basis of the RBM frequency a nd the Stokes to anti-Stokes Raman ratio. The (9, 9) armchair tube fits the simple model poorly. The varying relative intensities of different compone nts observed in the tangential G-band Raman modes provide convincing eviden ce for a recently predicted chirality dependence of Raman scattering. A new Raman feature at 1417 cm(-1) was assigned to achiral tubes.