Short-length carbon nanotubes as building blocks for high dielectric constant materials in the terahertz range

Abstract

Due to the high polarizability of finite-length carbon nanotubes (CNTs) in the quasi-static regime, they can be considered as building blocks for the fabrication of high dielectric constant material. Our theoretical estimations, based on an effective medium approach and solutions of a boundary value problem for individual CNT, predict that composite materials comprising short-length CNTs can have very high dielectric constants (up to 300) and low dielectric loss tangents (below 0.03) in the terahertz range. In order to prove this, 500-1000 nm thick films comprising single- and multi-walled CNTs of both long (0.5-2 μm) and short (0.1-0.4 μm) lengths have been fabricated. The analysis, based on the time-domain terahertz spectroscopy in the range 0.2-1.0 THz, demonstrated a decrease in the dielectric loss tangents of the CNT-based materials with a reduction in CNT length. In the terahertz range, the films comprising short-length CNTs had a relative effective permittivity with a large real part (25-136) and dielectric loss tangent (0.35-0.60).