Behavior of single-walled carbon nanotube-based gas sensors at various temperatures of treatment and operation

The behavior of single-walled carbon nanotube (SWNT)-based gas sensors at various conditions of operation was reported. The sensors were fabricated from SWNT powder by the screen-printing method, followed by an annealing pretreatment in open-air for 2 h at various temperatures to enhance the sensor characteristics. It was found that, the annealing at a suitable temperature not only removed the residual solvent and amorphous impurities from the SWNTs, but also opened the nanotube-caps, resulting in enhancement the sensor sensitivity. Subsequently, the sensor annealed at 200 degrees C was employed for detection ammonia (NH3) in 500 sccm nitrogen (N-2) flowing. After 10 min exposing to 5 ppm NH3 at room temperature, the resistance of the sensor increased up to 8% in comparison with its initial value. The sensitivity increased as the NH3 concentration increased but was diminished when NH3 concentration reached to 40 ppm. The sensor recovery was amended either by increasing the carrier gas flux or by heating in desorption time. By choosing a suitable regime of operation, in which the carrier gas flux, the heating duration and temperature were appropriately controlled, the characteristics of the SWNT-based sensor such as recovery and reproducibility were significantly improved. (c) 2005 Elsevier B.V. All rights reserved.