Optoelectronic properties of transparent and conducting single-wall carbon nanotube thin films

Optoelectronic characterization of transparent and conducting single-wall carbon nanotube thin films is reported. By eliminating the influence of voids and bundle-bundle interactions within the effective medium theory, we show that the complex dielectric response of the individual nanotube varies with its density in the film. Specifically, the absorption peak assigned to the maximum intensity of pi-pi(*) transitions was found to decrease from E-pi=5.0 eV at low nanotube density to E-pi=4.2 eV at intermediate densities and increased again at higher densities to E-pi=4.5 eV. Furthermore, the Drude background was found only above a critical density (Phi(o)) of nanotubes. These results unequivocally demonstrate that the optical processes are not confined only to in-tube transitions and that the absence of confinement in nanotube networks profoundly affects the electronic behavior of the individual tube. (c) 2006 American Institute of Physics.