High performance ethanol sensing films fabricated from ZnO and In2O3 nanofibers with a double-layer structure

ZnO and In2O3 nanofibers are synthesized via electrospinning methods, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), infrared (IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The nanofibers are deposited on ceramic substrates to form sensing films with various structures (ZnO nanofiber films, ZnO-In2O3 nanofiber films, and ZnO-In2O3-ZnO nanofiber films), and their sensing properties are investigated at different temperatures. Compared with ZnO nanofiber films and ZnO-In2O3-ZnO nanofiber films, the obtained ZnO-In2O3 nanofiber films exhibit improved and excellent sensing properties to ethanol. The highest sensitivity (the ratio of sensor resistance in air to that in target ambience) of 25 is obtained when the ZnO-In2O3 films are exposed to 100 ppm ethanol at 210 °C, while the corresponding values are only 8 for ZnO nanofiber films at 300 °C and 17 for ZnO-In2O3-ZnO nanofiber films at 210 °C. Rapid sensing reactions are also obtained as the response and recovery times of ZnO-In2O3 nanofiber films to 100 ppm ethanol are only about 2 and 1 s, respectively. These high sensing performances are explained by referring the heterocontacts formed by the double-layer structure.