Owing to their one-dimensionality, single-walled carbon nanotubes (SWNTs) demonstrate electronic and optical properties that make them exciting candidates for incorporation into nanoscale devices. For example, nanotubes emit in the near-infrared (NIR) region of the electromagnetic spectrum, an area that is relevant to applications in telecommunications and biological sensing. Isolated SWNTs are also extremely photostable and so they could be useful as possible components for biological sensing, displays, solar cells, and quantum cryptography. One significant consideration for their use in such devices is the extremely low ensemble fluorescence quantum yield of these materials (~0.1%). Current synthesis methods result in heterogeneous mixtures of nanotubes with assorted diameters and chiralities. Therefore, single molecule studies are useful for unmasking the contributions from different nanotube structures and the individual molecules that comprise an ensemble spectrum.
(a) Ensemble SWNT fluorescence spectrum. (b) Fluorescence from four individual SWNTs that make up an ensemble
Through the use of epifluorescence confocal microscopy, our goal is to characterize the fluorescence quantum yield of individual carbon nanotubes via direct comparison with CdTe/ZnS quantum dots whose quantum yield is known. Using this idea, we will be able to clarify whether all nanotubes are weak emitters or if their emissive efficiency is influenced by their structure, processing defects, or inter-tube interactions.
Confocal Microscope Setup
