Polarized resonant Raman study of isolated single-wall carbon nanotubes: Symmetry selection rules, dipolar and multipolar antenna effects

We studied the polarization dependence of the resonance Raman spectra for several different isolated single-wall carbon nanotubes (SWNTs). One isolated SWNT acts as a dipolar antenna, polarized along the tube axis. For light polarized parallel to the tube axis, the strong resonance-effect breaks the symmetry-selection rules, and symmetry-forbidden modes appear in the Raman spectrum. When the light is not polarized parallel to the tube axis, G-band mode symmetries can be identified. Unusual G-mode intensity behavior is observed when the Raman signal is obtained from more than one SWNT, suggesting a complex multipolar antenna pattern.