Carbon nanotubes consist of a hexagonal network of carbon atoms rolled up into a cylinder. The length of these cylinders is typically a few microns, while the diameter is usually a few nanometers. The confinement of electrons in the radial direction of a nanotube results in unexpected electronic properties. For example, nanotubes surprisingly can be either metallic or semiconducting, depending on the diameter and helicity of the carbon lattice. We are concerned with determining the fundamental electronic and optical characteristics of individual carbon nanotubes. These investigations are carried out using atomic force microscopic in conjunction with optical spectroscopic methods.
Materials possessing large optical nonlinearities are desirable for important future applications such as all-optical switching. However, the optical nonlinearities of most materials are much smaller than that needed for practical devices, motivating the search for new materials. Inorganic semiconductor particles containing a few thousand atoms, known as semiconductor nanocrystals, as well as carbon nanotubes, are predicted to have greatly enhanced nonlinear optical properties compared to their bulk counterparts. We are using state of the art ultrafast optical techniques to probe the magnitude and dynamics of the nonlinear optical response in these materials.
A significant remaining challenge for materials science is to connect nanometer-sized materials to the macroscopic world. To that end, we are also developing simple synthetic methods to make nanocrystals and nanotubes, and are exploring chemical modification of their surfaces. Our eventual goal is to build integrated optical devices and biological sensors using nanomaterials as building blocks.
