施主缺陷态中空微纳结构半导体涂层制备及室温气敏机理研究

Hollow micro-nanostructure can effectively enhance the specific surface area and porosity of gas sensing materials while the donor defects at the surface can increase the reaction activity of the materials. How to prepare semiconductor gas sensing layers which own these features is a difficult problem. This project proposes a new composite soft template-liquid plasma spray (CST-LPS) method: The stable composite soft template will be fabricated firstly to gather/fix metal ions, then synthesize the hollow structured precursor with controllable morphology and size by using alkali source as precipitant. After that, the sensing layers with high specific surface area, high porosity and high donor defect concentration will be deposited on the surface of electrodes via liquid plasma spray. The construction and synthesis of composite soft template will be studied firstly, clarifying how those key factors affect the arrangement of nanoparticles and the combination at the interfaces; secondly, the deposition characteristic of plasma sprayed hollow materials will be investigated and the regulatory mechanism of the coating structures will be illuminated; thirdly, the gas sensing properties of the coatings at room temperature will be studied, establishing and completing the correlative mechanism between the morphology, microstructure, donor defect concentration of the coatings and its gas sensing properties. The illumination of the deposition mechanism and room-temperature gas sensing mechanism of CST-LPS coatings will not only be of importance to the research and development of room-temperature gas sensing layers with high performance, but also can provide new ideas for the design and fabrication of other functional coatings.

中空微纳结构可有效提高气敏材料的比表面积与孔隙率，表面施主缺陷可增强材料的反应活性，而如何制备同时具有这些特征的半导体气敏层是一个难题。本项目提出复合软模板—液料等离子喷涂（CST-LPS）新方法：首先构筑稳定复合软模板以富集/固定金属离子，然后通过碱源作沉淀剂制备形貌和尺寸可控的中空微纳结构前驱体液料，接着利用液料等离子喷涂技术将前驱体液料沉积在电极表面获得具有高比表面积、高孔隙率、高表面施主缺陷浓度的气敏层。首先研究复合软模板的构建与合成，阐明关键因素对纳米粒子排列和界面结合的影响规律；其次研究等离子喷涂中空微纳结构材料的沉积特性，阐明涂层结构的调控机制；最后研究该涂层的室温气敏特性，建立并完善涂层形貌、微观结构及施主缺陷与气敏性能的关联机制。阐明CST-LPS的涂层沉积机制及室温气敏机理，不仅对研发高性能室温气敏层具有重要意义，也为其它功能涂层的设计和制备提供新思路。

项目在国内外研究基础上，针对低工作温度下响应值低、响应和恢复速率慢的突出问题，以In2O3和ZnO为研究对象，利用复合软模版法合成具有中空结构的金属氧化物，采用液料等离子喷涂工艺制备了富含缺陷结构金属氧化物气敏涂层的可控制备，提高气体传感器在室温下的气敏性能。主要研究内容包括：（1）通过改进的复合软模版法制备了具有中空球形貌且结构更加稳定的氢氧化铟（In(OH)3）前驱体悬浮液，以等离子生成辅助气体H2流量为变量，制备了富含氧缺陷的中空结构In2O3气敏涂层。以三种不同H2流量为变量制备得到的气体传感器的最佳工作温度均为100oC，但H2流量为2 L/min时，涂层对NO2的气敏性能最佳，对100 ppb NO2的响应值达到了4.7，响应/恢复时间仅为475/770 s，且具有良好的稳定性。（2）采用大气等离子喷涂法制备了氧缺陷自掺杂ZnO1-x气敏材料。一是利用等离子焰流的还原性使ZnO部分还原，形成氧缺陷。二是利用大气等离子喷涂的特点，使ZnO在极高温度下发生原子逸散，由于Zn和O的逸散速度不同，使得ZnO化学计量比失衡，并在快速冷却后保留这种失衡的化学计量比，形成氧缺陷。气敏性能测试结果表明，氢气流量为7 L/min时传感器气敏性能最佳，其在蓝光照射下对500 ppb NO2的响应为3.3。（3）采用溶液等离子喷涂技术（SPPS）直接制备了多孔纳米结构高浓度氧缺陷ZnO1-x传感器，高浓度氧缺陷的引入主要源于SPPS的三个工艺特征：超高焰流温度（10000 K以上）、极快冷却速度（105-107 K/s）和还原性气氛。其中，可见光的波长对ZnO1-x传感器的NO2气敏响应有明显的影响，当波长减小时，基准电阻降低，响应值增大，响应和恢复时间缩短，蓝光为最佳照射波长。蓝光照射下，传感器具有良好的线性度、稳定性和选择性，传感器室温NO2气敏性能的提高可归因于高浓度氧缺陷的引入、多孔纳米结构和异质结的构筑。