Anisotropic Electrical Transport Properties of Aligned Carbon Nanotube Films

We report a large scale synthesis of well-aligned carbon nanotube films with controllable diameter and length. A simple technique has been developed to measure anisotropic electrical transport properties of as-aligned carbon nanotube films. The temperature dependence of relative electrical resistances suggests that most of the well-aligned carbon nanotubes are semiconductive in both directions parallel and perpendicular to the tube axis. The anisotropy (R⊥/R∥) of electrical resistances increases with decreasing temperature T, reflecting difference in the longitudinal and transverse hopping rates. The differences of the electrical properties in both directions could be explained by a difference in the degree of localization of charge carries. The plot of the logarithm of relative resistance against powers of the reciprocal temperature 1/T is closely fitted by three-dimensional variable range conduction. After annealing and Br2-doping treatments, the resistivities of the aligned carbon nanotube films decreased by 2 orders of magnitude, which resulted from fewer defects and more carries density, respectively.