Optical near-field investigations of individual single-walled carbon nanotubes*

Optical excitation of semiconducting nanotubes creates excitons that determine nearly all light-based applications. Near-field photoluminescence (PL) and Raman imaging with a spatial resolution better than 15 nm was used to probe the spectroscopic properties of excitonic states along single nanotubes on substrates [1,2]. The PL intensity was found to decrease towards the nanotube ends on a length scale of few 10 nm probably caused by exciton transport to localized end states followed by efficient non-radiative recombination. DNA-wrapping of nanotubes results in pronounced emission energy variations on a length scale of few 10 nm indicating the potential of the material for nanoscale sensing applications [3]. Inter-nanotube energy transfer was studied for different pairs of semiconducting nanotubes forming bundles and crossings [4]. Efficient transfer is found to be limited to a few nanometres because of competing fast non-radiative relaxation and can be explained in terms of electromagnetic near-field coupling. We also report on our recent experimental results on time-resolved near-field PL measurements, electrically gated nanotubes and the PL of nanotubes on metal surfaces. \\[4pt] References: \\[0pt] [1] A. Hartschuh, Angew. Chem. Int. Ed. 47, 8178 (2008). \\[0pt] [2] I. O. Maciel et. al, Nature Mat. 7, 878 (2008). \\[0pt] [3] H. Qian et. al, Nano Lett. 8, 2706 (2008). \\[0pt] [4] H. Qian et. al, Nano Lett. 8, 1363 (2008).