Chemical sensing with multiwalled carbon nanotube

The fundamental contributions of junction resistances in mutli-walled carbon nanotube (MWCNT) mats, namely the resistances between the tubes, play a key role in allowing these nanostructures to be utilized as sensors via affecting their sensitivity to external gas environments and water vapours. In this work, we use MWCNTs functionalized in acetone (on a glass substrate) by pulse valve deposition to investigate their potential as chemical sensors. In a series of experiments we have grown and characterised samples in various chemical environments (cycling water vapour in a vacuum environment) and report that the MWCNT mats exhibit fast and high-quality responses. We examine in some detail the parameters affecting the chemical-sensing responses, such as the thickness of the films, heat treatment (temperature) and residual solvents. We find that by increasing the thickness of the films, the ratio of the junction resistance to the tube resistance (the resistance along the tube) decreased, owing to the parallel arrangement of tubes. Concomitant with this effect was a decrease in the samples' responses due to lower current diffusion and the role of junction resistance in thicker films.