Effects Of Doping And Heterojunction On Gas Sensing Properties Of Metal Oxide Semiconductors

With the development of society and science,environmental pollution is becoming more and more serious,and air pollution is particularly serious.Air pollution not only destroys nature but also threatens people's health and safety.It is often reported in news that the explosion caused by flammable or injuries and deaths caused by leakage of hazardous gas.Therefore,it is necessary to monitor the quality of the air and prevent in time.Semiconductor gas sensor has many advantages,such as high response,simple operation,small size and low cost.And many researchers ate committed to prepare better gas sensors.Since 1962 T Seiyama et al successfully manufactured semiconductor gas sensor with Zn O and Sn O2 thin films,metal oxide semiconductor sensor has become an important branch of semiconductor gas sensor.There are many methods for preparing nanomaterials,such as liquid deposition method,hydrothermal method,water bath method and electrostatic spinning method.Hydrothermal method has advantages of high purity of product,controlling the ratio and morphology of products,and low reaction temperature,so it is widely used in the preparation of nanomaterials.In this paper,the gas sensing material was prepared by hydrothermal method and the performance of gas sensor was improved by doping and constructing heterojunction.The main contents of this paper are as follows:Firstly,?-MoO₃ and Ni-doped ?-MoO₃ were prepared through a simple solvothermal method and samples were characterized by a variety of methods to investigate the phase an morphological properties.The gas sensing measurements revealed that Ni-doped ?-MoO₃ had superior formaldehyde sensing capability as compared to pure ?-MoO₃.The degree of improvement was not directly proportion to the amount of dopant.When the doping concentration was 5mol%,the response was the highest.And the response was ten times of that pure ?-MoO₃ at the operating temperature.The mechanism involved in gas sensing performance of Ni-doped ?-MoO₃ was also discussed.Secondly,In₂O₃ and Al-doped In₂O₃ were prepared through a simple hydrothermal method and gas sensor was used to test the gas sensitivity of ethyl acetate.The gas sensing measurement showed that 5at% Al-doped In₂O₃ had superior ethyl acetate sensing capability compared with pure In₂O₃.The maximum response value approached 56.3-100 ppm ethyl acetate at 184 °C and the response of pure In₂O₃ was 24.1.The excellent gas sensing performance of Al-doped In₂O₃ gas sensor might be attributed to the larger chemical potential gradient caused more electrons transfer and grain size decreased.Thirdly,pure In₂O₃ and Zn O/In₂O₃ composites were prepared through a facile hydrothermal method and gas sensor was used to test the gas sensitivity of triethylamine.The operating temperature of the pure In₂O₃ and Zn O/In₂O₃ composites gas sensors was 206 °C and 184 °C respectively and the response to 100 ppm triethylamine was 14.5 and 53.5 respectively.Zn O/In₂O₃ composites gas sensor had lower operating temperature,higher response and lower detection limit.If the detection limit set the response value equal to 2,the detection limit of the Zn O/In₂O₃ gas sensor was 3 ppm.