The properties of single-walled carbon nanotubes (SWNTs) make them ideal for developing and improving electronic, optoelectronic, medical, biotechnology, and energy applications. However, integrating individual SWNTs into commercial products and devices remains a challenge. SWNTs can be coated with surfactants or polymers to aid dispersion but bundled nanotubes remain due to large van der Waals attractions. Conventional dispersion processes use high-shear homogenization, ultrasonication, and ultracentrifugation to remove nanotube bundles. Integrating SWNTs into large-scale processes, therefore, requires alternative routes to remove SWNT bundles from suspensions. Our group is working on developing models that describe experimentally observed dispersion and aggregation rates so new covalent and non-covalent functionalization schemes can be developed. These models will also help support experiments which aim to improve the removal of bundles from aqueous surfactant dispersions.

A significant obstacle to the widespread use of SWNTs in many applications is the formation of both metallic and semiconducting SWNTs in all nanotube synthesis techniques. These metallic and semiconducting SWNTs only vary by small changes in the crystallinity of the SWNT or the angle (chirality) by which the graphene layer is wrapped into a seamless nanotube. The small differences in the physical properties of the nanotubes make separating these mixtures difficult. Our group is investigating both large-scale and high-purity approaches to separating metallic from semiconducting nanotubes. We are using type-dependent reactivity differences as well as differences in the physical properties (e.g. permittivity, conductivity) to separate nanotubes by their electrical properties.

Nanowires are expected to play a role in future integrated circuits as both devices and interconnects. Our group is using multiple techniques to synthesize these materials including both the vapor-liquid-solid and templated growth processes. Supercritical fluids have been instrumental in the synthesis of nanowires with uniform diameters. The ability to control the mass-transfer properties of a supercritical fluid is particularly important for the nucleation and growth of crystals or the synthesis of nanowire arrays. These nanowire and nanotube structures are being used for catalytic applications, transport studies through porous membranes, integrated circuits, LEDs, solar cells, thermoelectrics, biosensors, and nanoelectromechanical systems.