Substitutional doping of carbon nanotubes to control their electromagnetic characteristics

Substitutional doping of bundles and composite materials, containing a mixture of semiconducting and metallic single-wall carbon nanotubes (SWNTs), by either nitrogen or boron atoms substantially alters their electromagnetic characteristics in the terahertz and the far-infrared regimes. Metallization of semiconducting SWNTs caused by doping exclusively by either boron or nitrogen increases the axial polarizability, the antenna efficiency, and the intensity enhancement factor of SWNT bundles; likewise, the conductivity of SWNT-based composite materials is enhanced by substitutional doping. The frequencies of the antenna resonances in the axial-polarizability spectra of the doped bundles are blueshifted in comparison with the resonance frequencies in the undoped ones. The doping-caused enhancement of the effective conductivity of SWNT-based composite materials in the far-infrared regime may occur not only due to the enhancement of conductivities of single SWNTs but also due to the decrease in the depolarizing field.