Thermoelectric power of aligned and randomly oriented carbon nanotubes

Thermoelectric power was used to elucidate the electrical transport properties of aligned and randomly oriented carbon nanotube systems in the temperature range 77--450 K. A weakly negative thermoelectric power, comparable with that of a graphite flake, was observed for a macroscopic bundle of multiwall carbon nanotubes with individual axes aligned parallel to the main axis. However, mats of randomly oriented multiwall carbon nanotubes gave a strongly positive thermoelectric power, as did mats of single-wall nanotubes. This is evidence of the importance of intertube contacts in the interpretation of the thermoelectric power data for carbon nanotube systems. Models for thermoelectric power behavior incorporating contact effects are described.