Study On Preparation And Gas Sensitivity Of Doped Zinc Oxide Nanomaterials

Zinc oxide（ZnO） is a groupⅡ-Ⅵ semiconductor with a wide and direct band gap.It is widely favored by scholars for its unique advantages in the fields of piezoelectric,photoelectric,gas sensing,and SAW.It is found that the ZnO gas sensor,as a surface resistance-controlled functional device,depends mainly on its microstructure.In addition,doping some metal elements can not only accelerate the transport of ZnO carriers,enhance the gas adsorption capacity and related reaction speeds,but also cause lattice defects,grain size refinement,lattice distortion,oxygen vacancies and zinc vacancies and other structural changes,thereby changing the physical and chemical properties of the original ZnO lattice,so that the doped nanomaterials show excellent gas-sensitive properties.The main research contents of this topic are as follows:We used magnetron sputtering to prepare pure ZnO thin films and Ta-doped ZnO thin films（Ta-ZnO） on Al₂O₃ ceramic tubes,and then tested the gas sensitivity of the two kinds of thin film sensors.It was found that the Ta-ZnO gas sensor’s average sensitivity was 9.8 to 100 ppm ethanol,and its response time and recovery time was 12.4s and 11.8s,respectively,it also showed good selectivity and repeatability for ethanol.Besides,its long-term effectiveness was up to 30 days.The improvement in the gas-sensitivity characteristics of the Ta-ZnO sensor could be attributed to 3 factors:the introduction of Ta impurities,which reduced the grain size of ZnO and increased its specific surface area;generated quantities of excess electrons on the surface of the thin film,resulting in stronger adsorption capacity;increased grain boundaries,causing more surface defects.We deposited different types of metal intermediate layers on Al₂O₃ ceramic tubes by magnetron sputtering,and then we prepared the corresponding ZnO nanostructures on the surface by hydrothermal method.We found that the Al intermediate layer could be doped into the ZnO nanostructures as impurities to obtain two-dimensional ZnO nanosheets（ZnO/Al）,and ZnO nanostructures with different doping amounts could be obtained by controlling the thickness of Al transition layer,then we investigated the relationship between Al doping amount and ZnO nanostructures and gas sensing properties.According to the detection of ethanol,it was found that the sensitivity gradually increased with the increase of the Al content.When the growth time of the Al transition layer was 1 min,the optimal doping concentration was reached.At that doping concentration,the average sensitivity to 100ppm ethanol was 78.9,and the response time and recovery time of ZnO/Al were 17s and 13s,respectively,it also showed good selectivity and repeatability to ethanol.Besides,its long-term effectiveness was 7 days.The improvement of the ZnO/Al sensor’s gas-sensing properties could be attributed to the introduction of a suitable amount of Al impurity to make the ZnO nanosheets have a large specific surface area,inherent defects and higher surface energy.We used magnetron sputtering method and hydrothermal method to prepare flaky ZnO nanosheets on Al₂O₃ ceramic tube,then obtained Au modified ZnO nanosheet material（Au-ZnO）by light reduction method,and tested its gas sensitivity.It was found that the Au-ZnO gas sensor’s sensitivity was 101.8 to 100ppm ethanol,and its response/recovery times were 21s and 10s,respectively,it also showed excellent selectivity and repeatability for ethanol.Besides,its long-term effectiveness was up to7 days.The improvement of the gas-sensitivity characteristics of the Au-ZnO sensor could be attributed to the unique electron-capturing ability of Au nanoparticles and efficient surface catalytic activity.