The effect of annealing on the electrical and thermal transport properties of macroscopic bundles of long multi-wall carbon nanotubes

Electrical resistivity, thermal conductivity and thermoelectric power were measured on macroscopic bundles of long multi-wall carbon nanotubes (CNTs) in the temperature range between 2 and 300 K. While the electrical resistivity shows relatively small variation, the thermal conductivity is significantly enhanced and thermoelectric power changes sign from positive to negative after the samples are annealed in Ar at 2800 °C. Although the latter can be attributed to the adsorbed oxygen on the CNTs that is reduced through the annealing process, our results suggest the studied properties, especially thermal conductivity, are sensitive to the sample crystallinity that can be significantly improved by high-temperature annealing as well.