Dependence of Raman spectraG′band intensity on metallicity of single-wall carbon nanotubes

Abstract

We report the peculiar behavior of the $G^{\prime }$ band Raman intensity, which is dependent on the metallicity of single-wall carbon nanotubes (SWCNTs). In the metallic SWCNTs, the $G^{\prime }$ band intensity was enhanced relative to the $G$ band intensity, while the $G^{\prime }$ band intensity was suppressed in the semiconducting SWCNTs. Resonance Raman spectroscopy (using laser energies of $E_{\mathit{\text{laser}}}=2.41$, 1.96, 1.58, and $1.165\mathrm{eV}$) showed these features on the metal-enriched and semiconducting-enriched SWCNT samples that had been selectively separated by the nitronium ions. The metallicity dependence was explained theoretically by calculating the resonance Raman intensity within the extended tight-binding calculations. The calculated results confirm that the $G^{\prime }$ band intensity of the metallic SWCNTs is stronger than that for the semiconducting SWCNTs because the electron-phonon matrix elements for the TO phonon at the $K$ point is larger for metallic SWCNTs and the resonance window for $E_{33}^S$ is larger than that for $E_{11}^M$.