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 °C was employed for detection ammonia (NH₃) in 500 sccm nitrogen (N₂) 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.