Fabrication and characterization of inkjet-printed carbon nanotube electrode patterns on paper

An aqueous conductive ink of multi-walled carbon nanotubes (MWCNTs) for inkjet printing was formulated. To prepare the homogeneous MWCNT ink in a size small enough not to block a commercial inkjet printer nozzle, we used a kinetic ball-milling process to disperse the MWCNTs in an aqueous suspension with naphthyl-group-based non-ionic surfactants. When a patterned electrode was overlaid by repeated inkjet printings of the ink on various types of paper, the sheet resistance decreased rapidly following a power law, reaching approximately 760 Ω/sq, which is the lowest value ever for a dozen printings. Hall effect measurements at various magnetic fields and temperatures showed that the printed MWCNT paper electrode exhibited excellent semi-metallic conductivity with a p -type extrinsic semiconductive behavior such that the temperature-dependent resistivity was dominantly affected not by the lattice phonon scattering related to the mobility but by the charge impurity scattering related to the concentration of doped impurities. The Raman and Fourier transform infrared spectra revealed that the oxidation of the MWCNTs was the source of the doped impurities.