Adsorption Principle Of Charge Layer At The Interface Of P-n Metal Oxides And Gas Sensing Selectivity Regulation

CO and H₂are two kinds of gases that often exist in secondary gas.These two gases are not only flammable and explosive,CO is also toxic,therefore,leakage of these two gases into the air during industrial production must be monitored in real time.Although the metal oxide semiconductor sensor has the advantages of high sensitivity,low cost and portability to become the best choice for gas detection.Unfortunately,it is difficult to use a metal oxide semiconductor material for accurate selective detection of these two gases with similar properties.The poor selectivity seriously restricts the development of metal oxide semiconductor sensing technology.This work aimed at the the restriction factor of promoting the development of gas sensors,on the basis of the discovery of the different adsorption activities of CO and H₂on the surface of n-type and p-type metal oxide semiconductor,the adsorption principle of charge layer at the interface of p-n metal oxides was proposed to accurately identify CO and H₂.Based on this mechanism,the concentrations of p-type materials and n-type materials in the p-n heterostructures of different p-n systems are modulated to regulate the concentrations of electrons and holes,the height of the potential barrier and the thickness of the interfacial charge layer,so as to improve the gas sensing selectivity of the p-n heterostructures sensor to CO,and even to accurately identify CO and H₂.The detailed research content and results are as follows:(1)The gas sensing properties of two n-type materials(ZnO and SnO₂)were studied.Firstly,the preparation process and operating conditions of ZnO and SnO₂were optimized,which laid a foundation for the follow-up study of the gas sensing properties of ZnO and SnO₂based p-n heterostructure composites.In addition,the gas sensing response of both ZnO and SnO₂to H₂are greater than that to CO,which proves that the adsorption activity of H₂on the surface of ZnO and SnO₂are greater than that of CO.Since the adsorption mechanism of the interface charge layer proposed in this paper is based on the different adsorption activities of CO and H₂on the surface of n-type material and p-type material,the work in this part also proves the reliability of the proposed mechanism.(2)The gas sensing properties of n-SnO₂/p-x CuO and n-ZnO/p-x CuO nanocomposites with different compositions were studied by modulating the concentration of n-type semiconductors and p-type semiconductors to control the concentration of electrons and holes in the composites.With the increase of x value in the composite,the gas sensing properties of the composites to CO and H₂change from n-type to p-type.The composites at the p-n transformation(n-SnO₂/p-2.78CuO and n-ZnO/p-0.429CuO)have higher gas sensing selectivity to CO than those composed of other composites.The above research results prove the feasibility of the strategy proposed in this paper,and the gas sensing selectivity of CO can be improved by modulating the composition of p-n composites.(3)The n-ZnO/p-xNiO composites were constructed and the gas sensing properties of the composites to CO and H₂are studied.With the increase of x value in the composites,the gas sensing response of the composites to CO and H₂changes from n-type to p-type.The n-ZnO/p-0.425NiO composite at the critical point of p-n conversion shows p-type response to CO and n-type response to H₂,and this material can accurately identify CO and H₂.The above phenomena are analyzed by the mechanism of charge layer at the interface of p-n type metal oxides.The above work verifies the feasibility of our proposed mechanism and the effectiveness of the strategy,and provides a new idea and a new method for realizing the selective identification of two gases with similar properties(CO and H₂).