Electromagnetic Response of Multiwall Carbon Nanotubes

Abstract

The electromagnetic response of isolated infinitely long multiwall carbon nanotubes (MWCNTs) interacting with electromagnetic waves is analyzed using a semi-classical approach. The electromagnetic scattering and shielding characteristics are investigated using modal expansions to obtain an exact solution for the field expressions, which utilize a quantum mechanical conductivity. The influence of the number of tube walls, the radius of the outermost tube wall, and the presence of a gold core is analyzed. Comparisons between metallic MWCNTs, metallic single wall carbon nanotubes (SWCNTs), and metal wires are analyzed and discussed. The effective conductivity and power dissipation of carbon nanotubes (CNTs) are obtained and discussed. It is found that electromagnetic scattering is strongly dependent on frequency, which is due to the strong frequency dependence of the quantum mechanical conductivity. For metallic MWCNTs there is little shielding due to the presence of the additional tube walls. It is determined that electromagnetic scattering increases as the number of tube walls increase. The same occurs as the outermost tube wall radius increases. For a metallic MWCNT with a gold core, it is found that for small outermost tube wall radii, the electromagnetic response of the structure is commensurate with the electromagnetic response of the MWCNT. For large radii it is commensurate with the electromagnetic response of the gold core. It is determined that for small radii, electromagnetic scattering is greater for SWCNTs and MWCNTs than it is for metal wires. The opposite is the case for large radii. In general, electromagnetic scattering is greater for metallic MWCNTs than it is for metallic SWCNTs. It is found that for up to THz frequencies, the Born approximation can be utilized to obtain an effective conductivity for CNTs. In regards to power dissipation, it is determined that power dissipation is greater for metallic CNTs than for semiconducting CNTs. Also, MWCNTs dissipate more power than SWCNTs.