Theory of multiwall carbon nanotubes as waveguides and antennas in the infrared and the visible regimes

The propagation of azimuthally symmetric guided waves in multiwalled carbon nanotubes (MWCNTs) was analyzed theoretically in the midinfrared and the visible regimes. The MWCNTs were modeled as ensembles of concentric, cylindrical, conducting shells. The influence of intershell electron tunneling on the optical properties of MWCNTs was examined by focusing on a double-walled carbon nanotube (DWCNT). Longitudinal electrostatic waves exist in DWCNTs due to intershell tunneling. Conditions for weak influence of intershell tunneling in DWCNTs were identified, and an integral-equation approach for scattering by an MWCNT was formulated when those conditions prevail. Slightly attenuated guided waves and antenna resonances due to the edge effect exist for not-too-thick MWCNTs in the far-infrared and the midinfrared regimes. Interband transitions retard the propagation of guided waves and have a deleterious effect on the performance of a finite-length MWCNT as a nanoantenna. Propagation of surface-plasmon waves along an MWCNT with a gold core was also analyzed. In the near-infrared and the visible regimes, the shells behave effectively as lossy dielectrics to suppress surface-plasmon-wave propagation along the gold core.