Nowadays, the origination of the broad THz conductivity peak (TCP) of thin single-wall carbon nanotube (SWNT) film is under debate. As shown in paper [1], the main contribution to TCP formation at room temperature comes from finite-length effect in SWNTs. In present report, we experimentally demonstrate the dependence of the frequency of TCP on the length of SWNTs. The non-aggressive acid cutting approach was developed to obtain SWNTs with different length distribution and weak sidewall degradation. Thin SWNTs films with different average tube lengths were prepared on silicon substrate. The FIR spectra of prepared samples demonstrate the TCP blue shift with decreasing of SWNT length. The experimental study of the influence of acid doping on the TCP in SWNTs film was presented. The experimental results are well described by the theory of localized plasmon resonance in SWNTs.
The electromagnetic response of multiwall carbon nanotubes (MWNTs) of small cross-sectional radius and finite length was theoretically studied in the terahertz and sub-terahertz regimes, by solving an integral equation. The polarizability of the MWNT peaks in the terahertz regime, depending on the length and the number of metallic shells. At lower frequencies, a strong depolarizing field creates a shielding effect: the penetration depth of the axial component of incident field depends on the frequency, the length, and the electron relaxation time. The screening effect makes MWNTs suitable as interconnects.
[1] G.Ya. Slepyan, M.V. Shuba, S.A. Maksimenko, C. Thomsen, and A. Lakhtakia, “Terahertz conductivity peak in composite materials containing carbon nanotubes: Theory and interpretation of experiment”. - Phys. Rev. B 81, 205423 (2010).
