Nonlinear behavior in the Thermopower of Doped Carbon Nanotubes Due to   Strong, Localized States
  The temperature dependent thermoelectric power (TEP) of boron and nitrogen doped multi-walled carbon nanotube mats has been measured showing that such dopants can be used to modify the majority conduction from p-type to n-type. The TEP of boron doped nanotubes is positive, indicating hole-like carriers. In contrast, the nitrogen doped material exhibits negative TEP over the same temperature range, suggesting electron-like conduction. Therefore, the TEP distinct nonlinearites are primarily due to the formation of donor and acceptor states in the B- and N- doped materials. The sharply varying density of states used in our model can be directly correlated to the scanning tunneling spectroscopy studies of these materials. 
Y.-M Choi, D.-S. Lee, R. Czerw, P.-W. Chiu, N. Grobert, M. Terrones,   M. Reyes-Reyes, H. Terrones, J.-C. Charlier, P. M. Aj...