Thermoelectric power properties of graphitic nanotubule bundles

Thermoelectric power (TEP) properties of graphite nanotubule bundles were measured in the range 80–280 K. It was found that the TEP is positive and the magnitude at 280 K reaches about an order of +15 μV/K, far larger than that in highly oriented pyrolytic graphite. Moreover, in the studied range, the TEP can be approximately described by the formula S(μV)=0.167T−(70.2+0.085T)e−302.5/T derived based on a two-band model. The experimental results support such an idea that in the buckybundles both kinds of nanotubes, i.e., metallic tubes with a highly mobile velocity and semiconductive tubes with a narrow energy gap are included. The Fermi energy of the valence band for the metallic tubes is about −0.22 eV, and the average effective energy gap of the semiconductive tubes is estimated at about 52.2 meV. This conclusion is in good agreement with the theoretical predictions.