A Gas Sensor Using a Multi-Walled Carbon Nanotube Sheet to Detect Oxygen Molecules

A gas sensor using a multi-walled carbon nanotube (MWCNT) sheet, which can detect oxygen (O-2) gas, is presented and its output characteristics are evaluated in this study. A simple, cost effective and novel fabrication technique is described compared to dispersing CNTs into a liquid or polymer. The sheets are spun from a MWCNT forest grown on a silicon substrate; its electrical resistance decreases linearly with O2 exposure. The MWCNT sheet has a large surface area and many individual MWCNT contact points; this leads to a linear sensitivity, a fast response time, repeatability, and stability. It is well known that the surface distribution and areal density of MWCNTs have a significantly affect on their sensing characteristics. The sensors fabricated using dispersed CNTs on a substrate, either with separated CNTs of low density or with overlapping CNTs of low resistance, reveal much lower sensitivities. The large surface area and uniform distribution of the gas sensor, however, allow for the higher interaction of the MWCNTs with the O-2 molecules, increasing the sensor's characteristics. Moreover, the MWCNT sheet does not need purification or a complex transfer process to be used as a sensor, making it suitable for practical applications.