Nanoscale optical imaging of excitons in single-walled carbon nanotubes

We present simultaneous near-field photoluminescence (PL) and Raman imaging of single-walled carbon nanotubes (SWNTs) with a spatial resolution better than 15 nm. Highly localized excitation is used to visualize the spatial extent of the contributing excited states. For SWNTs on glass, we typically observe highly confined PL from short segments of about 20 nm in length. The PL from micelle-encapsulated SWNTs on mica is extended along the tube up to several hundreds of nanometers. We find that near-field enhancement is much stronger for photoluminescence than for Raman scattering, an observation that is explained by the low intrinsic quantum yield of SWNTs.