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 d ifferent classes of SWNT usually included in any staff. This efficient spat ial selection results from the combinaison of confocal microscopy, surfaced -enhanced Raman spectroscopy (SERS) and dilution of the nanotube concentrat ion. In fact, confocal spectroscopy operates a first spatial selection both for the excitation and the collection processes. Because only some nanostr uctures on SERS substrates are efficient to give large Raman signal enhance ments, the SERS process itself plays a major role in spatial selection. Sin gle radial breathing modes have been dearly observed depending on the excit ed location Very short acquisition times associated with high signal to noi se 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 nano tube electronic density of states.