【作者】 张蕊；

【导师】 季惠明；

【作者基本信息】 天津大学 ， 材料学， 2019， 硕士

【摘要】 金属氧化物半导体气体传感器由于其制备简便、成本低廉和性能稳定而被广泛采用。作为气体传感器的主要激发和活化手段,热激发长期以来占据着激发气敏响应的主导地位。随着对传感器的集成化和小型化的要求越来越高,光、磁等多种激发方式逐渐进入研究视野。本课题根据金属氧化物半导体的不同类型,选择了禁带宽度相差较大、电磁极化强度不同的ZnO和BiFeO₃作为气体传感器的核心材料,在热激发的基础上,引入紫外光和磁场辅助激发手段,研究材料的气敏性能和敏感机理。针对禁带宽度较宽、电磁极化较弱的ZnO材料,通过采用第二配体调节Zn-MOF成核生长速率的模板法成功制备了具有不同晶体尺寸和孔径分布的ZnO纳米粉体。热激发时具有组装体结构的ZnO对1ppm正丁醇的响应值高达14,具有较好的灵敏度,并实现了单一材料对不同尺度的气体分子的选择性响应。紫外光的引入能够使带隙较宽的ZnO气体传感器实现室温气敏响应,原因是紫外光能够激发大量价带电子跃迁至导带,使ZnO内部载流子浓度变大,这有利于室温型气体传感器的进一步研究。磁场的引入使极化强度仅为0.02C/m²的ZnO气体传感器的最佳工作温度较原来降低23℃,使ZnO对丁酮产生最高响应,原因是磁场的引入能够改变具有一定极化强度的材料的电子运动状态,降低具有未成对电子的表面吸附氧离子和电子云不对称程度较高的VOCs分子的反应活化能。针对禁带宽度较窄、电磁极化较强的BiFeO₃材料,通过采用水热法和溶胶凝胶法制备了BiFeO₃,并在钙钛矿型BiFeO₃结构A位进行Ba掺杂成功制备了Ba_0.05Bi_0.95Fe O₃。热激发时BiFeO₃气体传感器对1 ppm正丁醇的响应值为1.32,并具有较好的稳定性。紫外光的引入使带隙较窄的钙钛矿型铁氧体BiFeO₃气体传感器的最佳工作温度较原来下降15℃,Ba元素的引入能够使费米能级附近的电子态密度变丰富,导致紫外光激发使Ba_0.05Bi_0.95FeO₃气敏材料的最佳工作温度较原来降低90℃。磁场的引入使极化强度约为1 C/m²的BiFeO₃响应时间缩短将近2倍,但却使其灵敏度有所降低,原因是磁场的引入使多铁性材料BiFeO₃的磁畴转向和净磁矩增大,畴壁聚集效应的减弱导致缺陷含量降低,从而降低了表面吸附氧数量。更多还原

【Abstract】 Metal semiconducting oxide gas sensors have been widely used because of their simplicity,low cost and stable performance.As the main excitation and activation means of such gas sensor,thermal excitation has been playing a leading role in excitation of gas sensitive response for a long time.With the increasing demand for the integration and miniaturization of sensors,various excited methods such as optical and magnetic excitation methods have come into the research vision gradually.According to different types of metal oxide semiconductor,this study chose ZnO and BiFeO₃ as the core gas sensing materials,which have large difference in forbidden band width and electromagnetic polarization intensity.On the basis of thermal excitation,the ultraviolet light and magnetic field were introduced into the gas sensor testing environment to study the sensing performance and various mechanisms.In view of ZnO has wide forbidden band width and weaker electromagnetic polarization,ZnO nanoparticles with different crystal size and pore size distribution were synthesized from Zn-MOF template by second ligand modulating crystal nucleation and growth rates.ZnO sensor with assemble structure has a response value of 14 toward 1 ppm n-butanol,which has good sensing performance.The selective response of gas molecules with different diameters by a single material is realized.The introduction of ultraviolet light excitation can make the ZnO gas sensor with broad band gap realize room-temperature gas sensitive response.The reason is that ultraviolet light excites a large number of valence band electrons to the conduction band,which makes the carrier concentration inside ZnO increase,and that is advantageous for further study of room temperature gas sensor model.The optimal operating temperature of ZnO gas sensor whose polarization intensity is only 0.02C/m² is reduced by 23℃ and ZnO show the highest response to butanone by magnetic excitation.The reason is that introduction of magnetic field can change the electron motion of some materials with certain polarization intensity,and decreases reaction activation energy of the surface adsorption oxygen ion with unpaired electrons and VOCs molecules with high electron cloud asymmetry degree.In view of BiFeO₃ has narrow forbidden band width and stronger electromagnetic polarization,BiFeO₃ samples were prepared through hydrothermal method and sol-gel method,Ba_0.05Bi_0.95Fe O₃ was successfully prepared by doping Ba into A-site of perovskite BiFeO₃ structure.By thermal excitation,BiFeO₃ gas sensor has a value of 1.32 toward 1 ppm n-butanol,and has good stability.After introducing ultraviolet light excitation,perovskite ferrite BiFeO₃ with narrow band gap decreased the optimal working temperature by 15℃,the introduction of Ba element can rich electronic density states near the Fermi level,optimization of working temperature effect of Ba_0.05Bi_0.95Fe O₃gas sensitive material under ultraviolet light excitation is more obvious,which can be decreased by 90℃.After introducing magnetic field,the response time of BiFeO₃ with polarization intensity of 1 C/m² is shorten by nearly 2 times,but the sensitivity became lower.The reason is that the introduction of magnetic field increases the magnetic domain turning and net magnetic moment of BiFeO₃,and the reduction of domain wall aggregation effect leads to the decrease of defect content,thus reducing the amount of surface adsorbed oxygen species.更多还原