Fig. 4
a Dynamic electrical resistance variation curves of the Sn2S3 thin film on exposure to various NO2 gas concentrations (0.2–2.5 ppm) under light irradiation. b Dynamic electrical resistance variation curves of the Sn2S3–SnO2 thin film on exposure to various NO2 gas concentrations (0.2–2.5 ppm) under light irradiation. c Schematics of the Sn2S3–SnO2 thin film surface reaction with NO2 gas molecules and gas sensor device. d Cyclic gas-sensing response curves of the Sn2S3–SnO2 thin film on exposure to 0.2 ppm NO2 gas under light irradiation. e The gas-sensing responses of the Sn2S3–SnO2 thin film on exposure to various test gases