Hopping conduction in disordered carbon nanotubes

We report electrical transport measurements on individual disordered multiwalled carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows an exp [ − ( T 0 / T ) 1 / 2 ] dependence on temperature T , suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T 0 . The electric field dependence of low-temperature conductance behaves as exp [ − ( ξ 0 / ξ ) 1 / 2 ] at high electric field ξ at sufficiently low T . Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at T = 1.7 K . Comparison with theory indicates that our data are best explained by Coulomb-gap variable-range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.