TiO2/SnO2 and TiO2/CuO thin film nano-heterostructures as gas sensors

The nano-heterostructures of TiO2/SnO2 and TiO2/CuO thin films have been investigated towards NO2 detection. Thin films have been deposited by reactive magnetron sputtering of metallic targets in Ar + O-2 atmosphere. The properties of samples have been characterized by means of X-ray diffraction in grazing incidence GIXRD, X-ray reflectivity XRR, scanning electron microscopy SEM, optical methods and X-ray photoelectron spectroscopy XPS. It has been shown the SnO2 and CuO surface is well developed, with uniformly dispersed polycrystalline nanoparticles of TiO2. The addition of TiO2 thin layer increased the response of SnO2 nanostructure towards NO2. A very high resistance change similar to 4500 has been demonstrated for TiO2/SnO2 at 150 degrees C for 4 ppm of NO2, while for the SnO2 sensor the resistance change has been similar to 2300. The TiO2/SnO2 sensor responses to CO and H-2 reducing gases were significantly lower. Such extremely good sensing properties of the n-n heterostructure to NO2 may be assigned to the formed interfaces and higher surface-to-volume ratio. However, TiO2/CuO n-p heterostructures reveal much smaller responses to NO2, what may be attributed to the effect of charge compensation.