Preparation Of Two-dimensional Sn-based Semiconductor Materials And Research On Their Gas Sensitivity

With the development of industry,the massive combustion of fossil fuels such as coal and petroleum and the emission of automobile exhaust have caused serious air pollution problems.In order to accurately detect polluted gases,gas sensors was developed.Among them,semiconductor gas sensors have received widespread attention due small size,high sensitivity,and low cost.Traditional semiconductor oxide-based gas sensors usually need to be heated,which not only causes high power consumption,but also is not conducive to integrate.In addition,there is a risk of explosion while detecting flammable gas.Therefore,it is very important to invent a gas sensor that can operate at room temperature.Affected by the size effect,two-dimensional semiconductor materials show excellent properties compared with bulk materials,and have been widely used in the fields of optoelectronic devices,energy storage,catalysis,and gas sensors.As two typies of Sn-based sulfides,SnS and SnS₂ can used as gas sensitive materials to achieve room temperature operation.Moreover,Sn and S have many advantages,such as,abundant in nature,safe and non-toxic,suitable for practical production and application.Therefore,this thesis takes SnS and SnS₂ as materials for gas sensors operated at room temperature.The main research contents are as follows:Firstly,the bulk SnS material was synthesized by hydrothermal method,and the influence of reaction time on the morphology of the material was explored.The obtained SnS material was coated into a sensitive film after annealed controlled in air and nitrogen atmosphere,respectively.The effect of annealing conditions on the performance of the gas sensor were explored in detail.The results show that both SnS annealed in nitrogen and that in air have sensitive response to NO₂,but the SnS after annealled in air shows better gas sensitivity than else.The reason maybe that part of SnS was oxidized to SnS₂ after annealing in air,which has good gas sensitivity to NO₂.Therefore,the follow-up focus on SnS₂ nanomaterials.Secondly,a corrugated SnS₂ material was synthesized by hydrothermal method,and the obtained material was coated onto ceramic wafer substrate with electrodes to test its gas sensitivity.The results show that the corrugated SnS₂material has poor gas sensitivity to NO₂at room temperature but shows good performance under heating at 140℃.The reason for heating maybe that corrugated SnS₂material cannot react with NO₂at room temperature and require external heating to activate.Thirdly,a layered SnS₂ nanosheet material was synthesized by hydrothermal method,and the prepared material was used as sensitive film.The room temperature detection of NO₂was realized under the irradiation of white light LED.The response to 1 ppm NO₂was 4.39,with good selectivity and repeatability.The reason was supposed that the energy of white light matches the band gap of SnS₂,which leads to the transition of electrons and increases the electron concentration in the conduction band,thereby improving the gas sensitivity of the SnS₂material.Finally,a flower-like SnS₂ nanosheet material was synthesized by a hydrothermal method,and the material was made into sensitive films and annealed in the range from 100 to 500℃.It was found that the SnS₂material annealed at 300℃ can detect NO₂at room temperature,and the response to 400 ppb NO₂is as high as 37.The results show that the annealing temperature has an important effect on the sensing performance,the annealed material has good crystallinity and purity as well as the ultra-thin SnS₂ morphology is conducive to the adsorption and desorption of NO₂ at room temperature.Therefore,this SnS₂ material shows a high gas sensitivity to NO₂.