Thermoelectric power properties of graphitic nanotubule bundles

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Abstract
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.