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 (Eᵢᵢ) and the radial breathing mode frequencies (ωRBM) 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 Eᵢᵢ versus ωRBM graphs. Only the low energy component of the E₁₁M 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 E₂₂S energies are redshifted for $S1$ [(2n+m) mod 3=1] nanotubes and blueshifted for $S2$ [(2n+m) mod 3=2] nanotubes.