ITO-film gas sensor for measuring photodecomposition of NO2 gas

ITO-film NO2 gas sensors (thickness=15 nm) were prepared by DC magnetron sputtering. The highest sensitivity was obtained at the sensor temperature of 523 K. When the NO2 gas flow in a measurement tube was terminated, the as-prepared ITO-film sensor showed a gradual decrease of NO2 concentration without NO2 gas leak. We attribute this phenomenon to the desorption of decomposed NO2 from the sensor surface. By annealing the sensor in NO2 gas at 573 K, the sensor showed no decrease of the concentration and could be used for detecting the photodecomposition of NO2. XPS revealed that annealing in NO2 gas for 0.5 h caused a CO-like bond to be formed on the sensor surface. This may become a stable adsorption site for NO2, thus inhibiting decomposition.