(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 absent in the ensemble Raman measurements. A large variation in the radial breathing 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 laser excitation was tentatively achieved on the basis of the RBM frequency and the Stokes to anti-Stokes Raman ratio. The (9, 9) armchair tube fits the simple model poorly. The varying relative intensities of different components observed in the tangential G-band Raman modes provide convincing evidence for a recently predicted chirality dependence of Raman scattering. A new Raman feature at 1417 cm -1 was assigned to achiral tubes.