Direct Growth Of Heterostructural Chemiresistive Gas Sensors And Their Sensing Performances

Metal oxide semiconductor gas sensors have developed quickly for several years in the field of sensors,due to their simple preparation,low cost,and high performance.However,metal oxide semiconductor gas sensors still have some disadvantages,such as low sensitivity and stability,high working temperature,and so on.One-dimensional nanostructures exhibit good gas sensing properties due to their lager surface-to-volume ratio and less agglomeration.The fabrication of heterojunction can significantly enhance the gas sensing performance of pristine materials.These thesis take the ZnO andα-Fe₂O₃ as the main object of study.The gas sensor fabricate on the flat Al₂O₃ substrate by introducing the seed layer and in-situ growth method.Many efforts have also been done to improve their sensing properties by the form of PN and NN heterojunction.The main results are as follows:1.ZnO nanorods array have been grown directly on the flat Al₂O₃ substrate by introducing the seed layer and hydrothermal method.CuO,as typical p-type semiconductor,is selected to fabricate PN heterojunction sensor via wet chemical method.It indicated that the responseof CuO/ZnO PN heterojunction nanorods to 50 ppm trimethylamine（TEA）at 40^oC is 8,which is 2³ times than pure ZnO nanorod.CuO/ZnO sensors also exhibit good selectivity.In order to further verify that the formation of PN heterojunction can improve the gas sensing performance,we prepared NiO/ZnO nanorods and Co₃O₄/ZnO nanorods gas sensors.2.It proposed that the gas sensing properties of porousα-Fe₂O₃ nanorod can be greatly improved by optimizing the p-type shell thickness based on the Debye length.When the shell thickness is optimized to Debye length（λ_d）of p-type semiconductor shell,theα-Fe₂O₃@NiO（CuO）core-shell PN heterojunction sensors exhibit the best gas sensing performance.By theoretic calculation and energy-band structure,the improved gas sensing performance of such core-shell heterostructural sensor is attributed to the great change in initial resistance caused by optimizing the p-type shell thickness based on the Debye length.3.Based on the synergistic working principle of NN heterojunction,we design a TEA gas sensor by constructingα-Fe₂O₃/ZnO nanorods and investigated their sensing properties.At the optimum operating temperature（325^oC）,the response ofα-Fe₂O₃/ZnO nanorods to 50ppm TEA is 39,which is higher than pristine ZnO nanorods.The enhanced sensing performance is explained via theoretic calculation and energy-band structure of NN heterojunction in detail.