Polarized Raman spectroscopy on isolated single-wall carbon nanotubes

Polarized micro-Raman spectroscopy has been performed on spatially separate d single-wall carbon nanotubes (SWNTs) in the form of individual. nanotubes or thin ropes of only a few SWNTs. Different from bulk samples, the Raman spectra are composed of well-resolved peaks which allow a direct comparison of experimental data with theoretical calculations. Orientation-dependent measurements reveal maximum intensity of all Raman modes when the nanotubes art: aligned parallel to the polarization of the incident laser light. The angular dependences clearly deviate from the selection rules predicted by theoretical studies. These differences are attributed to depolarization eff ects caused by the strongly anisotropic geometry of the nanotubes and to el ectronic resonance effects for excitation at 633 nm.