Micro-Raman investigation of aligned single-wall carbon nanotubes

Polarized micro-Raman experiments were performed on samples of aligned single-wall carbon nanotubes (SWNTs) previously characterized by scanning electron microscopy. The analysis of the different spectral shapes of the tangential G band, when the position of the laser beam changes from spot to spot on the sample, allows us to distinguish the contribution from metallic and semiconducting nanotubes. The angular dependence of the polarized spectra reveals that the line around $\sim 1580\hspace{0.5em}{\mathrm{cm}}^{-1}$ is an intrinsic feature of metallic SWNTs. Moreover, it is shown that the “antenna” effect for the Raman scattering in SWNTs is stronger for metallic than for semiconducting nanotubes.