Fabrication Of Metal Oxide Semiconductor Based On Micro-nano Structure And Gas Sensing Properties

With the acceleration of social science and technology, and the improvement of the living quality today, the requirements of the health and living environment around are increasing day by day. Especially, for the detection of harmful gases from the air polluting and the indoor decoration become more urgent. Chemical sensors, as devices or systems of information access, have become a major industry of modern technology. Sensing material is a core part of the gas sensor, and the research and development of novel and efficient sensitive materials is one way to develop a high-performance gas sensor. For decades of research and development,metal-oxide-semiconductor gas sensors have been widely applied due to their advantages of simple structure, low cost and high sensitivity. Development of nanotechnology injects new power for research of metal-oxide-semiconductor and the design of material microstructure. Preparation of gas-sensitive materials using nanotechnology is an important way to improve the performance of gas sensor. This paper mainly focuses on the problems of metal-oxide-semiconductor gas sensor in the detection to design and develop efficient and green synthetic strategies for the preparation of micro-nanostructure metal-oxide-semiconductor sensitive material. It is of great importance to regulate the surface structure, hetero-junction interface and element composition to improve the performance of sensor, such as sensitivity, time of response and reply, selectivity, stability and other indicators. Study the roles of micro-nanostructures and phase system components in gas sensing performance to provide a large number of experimental data for the research on gas sensing mechanism of metal-oxide-semiconductor. The main contents are as follows:(1) Use a simple, efficient and environmentally friendly method to prepare a sensitive material with mesoporous structure. Combine solvent evaporation and inter-molecular force to guide the nanocrystalline self-assemble into a mesoporous structure Sn O2. This work resolved the problem of agglomeration of irregular nanoparticles due to the van der Waals force, increased the surface area of the material, and analyzed the performance of mesoporous and non-mesoporous Sn O2 sensitive material to highly toxic NO. By comparison, we can confirm the conclusion that uniform mesoporous structure can not only encourage more gas adsorption on the material, but also increase the diffusion rate of gas to enhance the response.(2) By using hydrothermal synthesis strategy to prepare Ni O doped Sn O2 porous hollow spheres. We previously synthesized a long-chain-nickel nitrilotriacetic acid(NTA) polymer, which was added into sodium stannate solution, and then NTA was dissolved in stannate sodium. After hydrothermal reaction and calcination treatment,the Ni O particles were implanted in Sn O2 porous hollow spheres. On the one hand, the combination of a loose shell and a hollow structure contributes to the transmission action of gas molecules, increasing the amount of target gas molecules adsorbed on the surface of the sensitive body; on the other hand, the introduction of Ni O may promote the migration of electrons, thereby enhancing the sensitivity characteristics.Also, a sensing mechanism model was established.(3) Through a simple two-hydrolysis reaction to obtain a white precipitate, which was treated by directly hydrothermal treatment to form Zn Sn O3 ternary metal oxide nanosheets turned from dimensional face-centered cubic structure to a two-dimensional rhombic structure. The sensor shows high sensitivity and fast response-recover, particularly in response time of less than 1s. It is responsible for the thickness of the nanosheet(in the 10-15 nm range) which is about twice the Debye length. Combine the sensitivity formula with the Debye length to explain the advantages of the sheet structure in response. Based on the results, we analyze and explain the reason of the ultra-high gas sensing characteristics. The sensor has similar sensitivity between alcohol and acetone, but the response speed to acetone is quicker than that to ethanol. This is related to the chemical reactions of the two gases with oxygen adsorption.(4) We anchored two-dimensional Ni Co2O4 nanosheets on reduced graphene oxide(RGO) by hydrothermal synthesis techniques to research RGO improving performance of lithium ion battery. And this composite material was used to test a reducing gas, showing p-type response. At the optimum temperature of 280 oC, the sensor shows a sensitivity of 4.47 to 500 ppm alcohol gas, which is about 4 times sensitivity of Ni Co2O4 based sensor at this temperature. The response and recovery time Ni Co2O4 based sensor were 21 s and 32 s, respectively; and after the introduction of RGO, the response and recovery time were reduced to 9 s and 12 s, respectively.Although the gas sensing performance is not very good, the results tell us the introduction of RGO can significantly improve the sensor response to alcohol gas. We compared and analyzed the role of p-type RGO in improving gas sensing performance.This work provides a new direction for the development of new materials and expansion of the range in applications of gas sensors.