Excellent Room-Temperature NO₂ Gas-Sensing Properties of TiO₂-SnO₂ Composite Thin Films Under Light Activation

Thin TiO₂-SnO₂ nanocomposite films with high gas sensitivity to NO₂ were synthesized by oxidative pyrolysis and comprehensively studied. The composite structure and quantitative composition of the obtained film nanomaterials have been confirmed by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy, which causes the presence of n-n heterojunctions and provides improved gas-sensitive properties. The sensor based on the 3TiO₂-97SnO₂ film has the maximum responses, which is explained by the existence of a strong surface electric field formed by large surface potentials in the region of TiO₂-SnO₂ heterojunctions detected by the Kelvin probe force microscopy method. Exposure to low-intensity radiation (no higher than 0.2 mW/cm², radiation wavelength-400 nm) leads to a 30% increase in the sensor response relative to 7.7 ppm NO₂ at an operating temperature of 200 °C and a humidity of 60% RH. At room temperature (20 °C), under humidity conditions, the response is 1.8 when exposed to 0.2 ppm NO₂ and 85 when exposed to 7.7 ppm. The lower sensitivity limit is 0.2 ppm NO₂. The temporal stability of the proposed sensors has been experimentally confirmed.