Conductance in multiwall carbon nanotubes and semiconductor nanowires

Electronic transport in an ensemble of multiwall carbon nanotubes and semiconductor nanowires was compared. The nanotubes and nanowires are obtained by template synthesis and are contacted in a current perpendicular to the plane geometry by using different methods. In all cases, the nonohmic behavior of the conductance, the so-called zero-bias anomaly, shows a temperature dependence that scales with the voltage dependence. This robust scaling law describes the conductance G(V,T) by a single coefficient alpha. A universal behavior as a function of alpha is found for all samples. Magnetoconductance measurements furthermore show that the conduction regime is weak localization. The observed behavior can be understood in terms of the Coulomb blockade theory, providing that a single tunnel barrier is present. This hypothetical tunnel barrier would have a resistance of the order of 2500 Omega and a typical energy of about 40 meV for all samples.