Confocal observation of individual classes of single wall nanotubes by surface-enhanced Raman spectroscopy

In this paper, we demonstrate that single classes of single wall nanotubes (SWNT) can be observed by Raman spectroscopy, despite the large number of different classes of SWNT usually included in any staff. This efficient spatial selection results from the combinaison of confocal microscopy, surfaced-enhanced Raman spectroscopy (SERS) and dilution of the nanotube concentration. In fact, confocal spectroscopy operates a first spatial selection both for the excitation and the collection processes. Because only some nanostructures on SERS substrates are efficient to give large Raman signal enhancements, the SERS process itself plays a major role in spatial selection. Single radial breathing modes have been dearly observed depending on the excited location Very short acquisition times associated with high signal to noise ratios have been obtained at such locations. This experimental procedure opens the way to fine study of the evolution of the Raman signals of SWNT as a function of the excitation energy in order to get investigate the nanotube electronic density of states.