Effects of Oxygen Annealing on Gas Sensing Properties of Carbon Nanotube Thin Films

Carbon nanotubes (CNTs) thin films deposited by plasma enhanced chemical vapor deposition have been investigated as resistive gas sensors towards NO2 oxidizing gas. Effects of air oxidative treatment dramatically influence the nanotubes' electrical resistance as determined by volt-amperometric measurements. In particular the electrical measurements show that electrical behavior of the CNT films can be converted from semiconducting to metallic through thermal treatments in oxygen. The electrical response was then measured exposing the films to sub-ppm NO2 concentrations (100 ppb in air) at 165 degreesC. Upon exposure to NO2, the electrical resistance of CNTs was found to decrease. The obtained results demonstrate that nanotubes could find use as a sensitive chemical gas sensor for (a) the fast response accompanied by a high sensitivity to sub-ppm NO2 exposure, and (b) the precise recover of the base resistance value in absence of NO2 at a fixed operating temperature, likewise indicating that intrinsic properties measured on as prepared nanotubes may be severely changed by extrinsic oxidative treatment effects. (C) 2003 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-2010