Optical and electrical properties of preferentially anisotropic single-walled carbon-nanotube films in terahertz region

The absorption and dispersion of aligned single-walled carbon-nanotube films were measured from 0.2 to 2.0 THz using a source of freely propagating subpicosecond pulses of THz electromagnetic radiation. The real conductivity increased rapidly with increasing frequency up to 0.45 THz and decreased at a high-frequency range. The Maxwell-Garnett model, where the nanotubes were embedded in a dielectric host, fit the results of this study with the Drude-Lorentz model for nanotube network. We have observed the transverse phonon mode of 2.4 THz propagating along the c direction. This suggested that the carbon nanotube network is composed of metallic and semiconducting nanotubes embedded in an air dielectric host. (C) 2004 American Institute of Physics.