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

Abstract

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 π-π* transitions was found to decrease from Eπ=5.0eV at low nanotube density to Eπ=4.2eV at intermediate densities and increased again at higher densities to Eπ=4.5eV. Furthermore, the Drude background was found only above a critical density (Φo) 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.