Design and Synthesis of p-n Conversion Indium-Oxide-Based Gas Sensor with High Sensitivity to NO_x at Room-Temperature

摘要

Indium oxide (In2O3) nanoparticles with internal porous structure were obtained through thermal treatment of the hydrothermally synthesized indium hydroxide (In(OH)3) nanocubes precursor. The structure and morphology of In2O3 were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). The fresh In2O3 exhibits p-type conductivity according to gas response testing. However, the fresh In2O3 allowed switchable p- to n- conductivity after it was induced by high concentration NO_x and the induced In2O3 sensor (IIS) exhibited excellent sensing performances in terms of high response, enhanced selectivity and good stability to NO_x at room temperature. From the characterization of XPS, it was found that a large amount of oxygen adsorbed on the surface of indium oxide, which led to the n-p type surface conductivity conversion of In2O3. The formation of adsorbed species of high concentration NO_x induced In2O3 transition from p- to n- type surface conduction was investigated by in situ Diffuse Reflectance Infrared Transform Spectroscopy (DRIFT). The present work not only offers a strategy to change the type of electrical conductivity of the material, but also offers an opportunity to deeply understand the mechanism of n-p-n type electrical surface conductivity conversion.