Carbon Nanotubes and Nanophotonics

Carbon nanotubes (CNTs) have been demonstrated to be suitable for an array of potential applications ranging from field emitters for displays to field-effect transistors and light-emitting diodes to chemical and mechanical sensors.19 All types of nanotube growth rely explicitly on catalysis.

The challenges for catalytic growth reflect the fact that a very high degree of control is essential for the development of new nanotechnologies supported by optimized carbon nanotubes. Control of a range of nanotube diameters or chiral indices (n,m) still remains challenging. 

A factor typically overlooked in current discussions within the growth community is the importance of the quality of the nanotubes produced by catalytic growth.  Many applications have stringent constraints on the defect density, which can determine electrical doping. Moreover, essentially all advanced applications require the absence of dislocations in the growth of the nanotube crystal, since such dislocations can induce changes in the chirality and, hence, in the electronic properties.

We address synthetic issues by a range of materials chemistry techniques that have already proven the possibility for systematic improvement of nanotube growth which in turn has permitted identification and electronic characterization of carbon nanotubes of defined (n,m). Semiconducting single-walled nanotubes have been shown to have exciton lifetimes sufficient to permit transport of excitons over distances of microns.  We consequently wish to explore whether we can construct a model photo-catalyst in which excitation is collected at one site by an appropriate nanostructure and delivered to the photo-reaction center by means of a nanotube.  While this prospect may sound somewhat improbable, as noted above, many of the key ingredients are currently in place, including knowledge of excitation dynamics in nanotubes and the ability to functionalize nanotubes with metallic and semiconducting structures.

Analysis and characterization of nanotube/particle nanostructures are possible using a range of optical probes. Heinz and collaborators have proposed to study exciton generation in which recent research has provided a basis to expect that excitation with light well above the band gap may produce multiple excitons directly in carbon nanotubes, in a manner analogous to that already observed for appropriate semiconductor nanoparticles. It has been found that Confocal Raman microscopy is a powerful combined spectroscopic/structural probe with which to image and record the Raman spectra of individual single-wall carbon nanotubes (SWNTs) and single-layer graphene on silicon substrates at both room and low temperatures.

Orientation control over carbon nanotubes.