Since the discovery of single-walled carbon nanotubes (SWNTs) they have attracted much attention due to their unique electronic and mechanical properties. Before these properties can be manipulated for materials science applications and electronic devices, however, several technical hurdles must be overcome. The biggest hurdle to their widespread use in electronic and energy applications is the random formation of both metallic and semiconducting SWNTs in all 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 nanotube often designated by the indices n and m. These small changes in chirality induce different electrical properties for each nanotube yielding both metal and semiconducting nanotubes. The metallic and semimetallic nanotubes are described by the indices | n – m | = 3q where q is an integer. The remaining species are semiconducting nanotubes with geometry-dependent bandgaps. Here we are investigating approaches that will achieve SWNTs of a specific (n,m) type.

Another problem that must be overcome is the ability to control the length of the nanotubes. Nanotubes are typically synthesized with polydisperse micrometer lengths where they are bound into macroscopic entangled ropes. Many applications, however, will require short undamaged individual nanotubes 20 – 100 nm in length. The availability of single-walled carbon nanotube samples of uniform length is essential to many specialized applications. One such application is molecular electronics, in which a nanotube of precise length and specific band gap will need to be placed in a well-defined location. Specific length nanotubes are also essential for biological imaging and sensing where shorter nanotube lengths will be required to penetrate cells and to serve as biological markers.

To achieve these short length nanotubes, cutting strategies have been developed. These processes can be viewed as a two-step process: (i) introduction of sidewall damage; and (ii) consumption of damaged sites. Room temperature piranha solutions (sulphuric acid/hydrogen peroxide) have recently been shown to cut nanotubes with minimal carbon loss and little sidewall damage. While these processes yield shorter length SWNTs they often still have significant polydispersity. Therefore, bulk-scale length-based separation processes are being explored that will yield monodisperse nanotube length fractions.