ELECTRICAL TRANSPORT PROPERTIES OF SINGLE-WALLED CARBON NANOTUBE BUNDLES TREATED WITH BORIC ACID

Electric-arc-synthesized single-walled carbon nanotube (SWNT) bundles were sonicated in boric acid, dried and sintered under vacuum at 1200 degrees C using a spark plasma sintering process. The nominal boric acid concentrations were 0%, 2.5%, 5%, 7.5%, 12.5% and 15%. This resulted in a nonmonotonic variation of carrier concentration in the resulting samples. The 7.5% boric acid treated sample showed the least magnitude and weakest temperature-dependence for the thermopower with a distinct phonon-drag peak that was absent in the other samples. These results are discussed within the framework of the doping-induced shift of the Fermi level and changes in the electron-phonon coupling.