Transparent conductive carbon nanotube films

Abstract

This work presents the results of a study of the fabrication of multiwall carbon nanotubes (MWCNTs) by chemical vapour deposition (CVD), the purification and the development of transparent conductors films (TCFs) using these nanotubes. The as produced MWCNTs had some impurities due the CVD method including small amounts of the iron catalyst, amorphous carbon and hydrocarbon residues from the organic precursors. These impurities have been reported to be detrimental to both the electrical and optical properties of the TCFs. For this reason the purification of the nanotubes was studied using 3 different techniques. The three methods involved; A) selective oxidation in air of the MWCNTs followed by a hydrochloric acid solution etch to remove the iron, B) a selective oxidation using H$_2$O$_2$ followed by the hydrochloric acid etch treatment, and C) an oxidation-etch procedure using a mixture of H$_2$O$_2$ and hydrochloric acid. The best result results were obtained using the combined H$_2$O$_2$ and hydrochloric acid treatment. With this method MWCNTs were obtained with a purity of up to 94%. The purified MWCNTs were dispersed in solutions of different solvents without surfactant. Thin films of MWCNT were fabricated using a combined spray and spin coating technique, which produced a uniform deposit of controllable thickness. Either a transparent nitrocellulose-based varnish or acrylic was used to fix the film to the glass substrate. Both the optical transparency and the electrical square resistivity of the samples were measured by spectrophotometry and standard electrical techniques, respectively. Our results were similar to those of other groups in that the transparency was almost inversely proportional to the resistivity.