Optical Transition Energies for Carbon Nanotubes from Resonant Raman Spectroscopy: Environment and Temperature Effects

This Letter reports the laser energy dependence of the Stokes and anti-Stokes Raman spectra of carbon nanotubes dispersed in aqueous solution and within solid bundles, in the energy range 1. 52--2. 71 eV. The electronic transition energies (E₈₈) and the radial breathing mode frequencies (ₑ₁₌) are obtained for 46 different (18 metallic and 28 semiconducting) nanotubes, and the (n, m) assignment is discussed based on the observation of geometrical patterns for E₈₈ versus ₑ₁₌ graphs. Only the low energy component of the E₁₁^M value is observed from each metallic nanotube. For a given nanotube, the resonant window is broadened and down-shifted for single wall carbon nanotube (SWNT) bundles compared to SWNTs in solution, while by increasing the temperature, the E₂₂^S energies are redshifted for S1 (2n+m) mod 3=1 nanotubes and blueshifted for S2 (2n+m) mod 3=2 nanotubes.