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

Abstract

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 ($E_{ii}$) and the radial breathing mode frequencies (${\omega }_{\mathrm{R}\mathrm{B}\mathrm{M}}$) 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 $E_{ii}$ versus ${\omega }_{\mathrm{R}\mathrm{B}\mathrm{M}}$ graphs. Only the low energy component of the $E_{11}^M$ 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 $E_{22}^S$ energies are redshifted for $S1$ [$(2n+m)\mathrm{m}\mathrm{o}\mathrm{d}3=1$] nanotubes and blueshifted for $S2$ [$(2n+m)\mathrm{m}\mathrm{o}\mathrm{d}3=2$] nanotubes.