Polarization effects in surface-enhanced resonant Raman scattering of single-wall carbon nanotubes on colloidal silver clusters

Polarization effects are studied in surface-enhanced resonant Raman scattering (SERRS) experiments on single-wall carbon nanotubes (SWNT’s) in contact with silver colloidal clusters. For metallic SWNT’s the very low depolarization ratio of the G band observed in normal resonant Raman scattering (RRS) is nearly completely preserved in SERRS, and this is ascribed to the strong antenna effect of metallic carbon nanotubes. For semiconducting SWNT’s, the depolarization ratio is a factor of 2 larger in SERRS compared to RRS. This is attributed to a lowering of symmetry for the resonant Raman scattering properties of the SWNT’s arising from the very large field gradients on the metal colloidal clusters. The polarization directions of the local optical fields, as seen by the SWNT’s on metallic clusters, are preserved.