Woo-Jae Kim, Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, building 66-580, Cambridge, MA 02139 and Michael S. Strano, 66-566 Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139.
We carried out annealing studies on transparent thin films made with functionalized metallic single-walled carbon nanotubes (SWNT), and also investigated the effect of functional groups on the conductivity of SWNT thin films. Metallic SWNT films were prepared by selective functionalization using 4-hydroxybenzene diazonium salts followed by density-induced centrifugation, as reported in our previous work. Sheet resistance of functionalized metallic SWNT film is extremely high (23,564 kŮ/sq at 75% transmittance); however it reduces down to 1.2kŮ/sq, i.e., 5% of the un-annealed value, when the film is annealed at above 400oC in N2 flow, because all the functional groups are completely removed as confirmed by Raman and FT-IR experiment. Furthermore, this value is lower by 20% than that of un-separated SWNT film, indicating that metallic SWNT film shows higher conductivity than un-separated SWNT film. However, when the metallic SWNT film is annealed at higher temperature (600oC), the transparency of the film is increased, resulting in the increase of sheet resistance, due to the strong bundling of the SWNT, and the sheet resistance further increases due to the isolation of metallic SWNT from the network. We also demonstrated the effect of surfactant impurities on the conductivity of SWNT films.