Metallic–nonmetallic transition on the conductivity temperature dependence of multiwall carbon nanotubes

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Abstract
We applied a noncontacting surface acoustic wave technique to measure the conductivity of aligned multiwall carbon nanotube films. By changing intensities of the parallel and perpendicular electric field components at the surface of the film sample, we observed different temperature dependencies of the conductivity. It was found that the temperature dependence of the conductivity parallel to the tube axis is comparable to that of a single-wall carbon nanotube, namely, there is a metallic–nonmetallic transition at temperature of 280 K. On the other hand, the temperature dependence of the conductivity perpendicular to the tube axis is similar to that of a graphene sheet.