Ultrathin Films of Single-Walled Carbon Nanotubes: A Potential Methane Gas Sensor

Abstract

Due to unique electrical, mechanical and optical properties of carbon nanotubes (CNTs), they find huge industrial application. For some device applications, CNTs need preferential alignment onto the solid substrates. Here we demonstrate a control over alignment of bundles of single-walled carbon nanotubes (SWCNTs) during the ultrathin film fabrication on the solid substrates by Langmuir–Blodgett (LB) technique. During the LB film deposition process, the long axis of the SWCNTs are made to align either parallel or perpendicular to the direction of the electric field applied by a patterned interdigitated electrode (IDE). The current–voltage characterization of such films indicated a strong evidence of the parallel and perpendicular alignments of the SWCNTs between the IDE. The LB film of SWCNTs on the oxidized silicon substrate is employed to sense the methane (CH4) gas in dry and humid environments at the room temperature. The sensing capability of highly organized SWCNTs in the LB films is compared with that of randomly oriented SWCNTs in the drop cast film. The LB films of the SWCNTs show a step like response (contact potential difference) due to a change in the concentration of the CH4 gas molecules. Interestingly, the sensitivity in the humid condition was found to be significantly larger as compared to that in dry environment. The enhanced capability of LB film for sensing CH4 gas can be attributed to the aligned SWCNTs which may provide aligned adsorption sites for the gas molecules.