WO3外延薄膜的气敏性能研究

The crystalline phase, exposed lattice plane and vertical grain size of epitaxial WO3 thin films are precisely controllable. The films exhibit the advantages of having large specific surface areas and high thermal stability, and hence are considered to be promising candidates for gas sensing applications. This proposed project is aimed at studying epitaxial WO3 films, with the focus putting on the following aspects:(1) using laser molecular beam epitaxy to grow epitaxial WO3 films of specific crystalline phases and preferred crystal orientations deposited on single crystal LaAlO3, SrTiO3 and Al2O3 substrates of different crystal orientations; and combining the results of structural characterization, material property measurements, first principle calculation and gas sensing property measurements to investigate the influences of crystalline phase, exposed lattice plane and film thickness on the gas sensing properties of the films,(2) adding decorative materials, like NiO, SnO2 and Pd, on the epitaxial WO3 film surfaces to see how the gas sensing properties of the films are modulated by the formation of the p-n, n-n and metal-oxide heterojunctions,(3) carrying out long-term gas sensing stability tests of the film samples in order to reveal how the results are associated with the change in the microstructure of the films, and hence to seek possible solution for improving the gas sensing stability. This project, primarily using epitaxial WO3 films as the object for investigating the modulation effects of crystalline phase, lattice plane and heterostructure on their gas sensing properties, will provide new ideas for oxide-based gas sensor research. In addition, the study on gas sensing stability will provide references for pursing practically useable oxide-based gas sensors.

WO3外延薄膜的晶相、外露晶面及纵向晶粒尺寸可精确控制，且具有比表面积大、热稳定性好等优点，是极具潜力的气敏材料。本项目拟针对WO3外延薄膜开展如下研究：（1）用激光分子束外延在不同取向的LaAlO3、SrTiO3、Al2O3单晶衬底上制备具有特定晶相和晶面的WO3外延薄膜，结合结构表征、物性测量、第一性原理计算以及气敏性能测试，研究晶相、外露晶面及膜厚等参数对气敏性能的影响，（2）在WO3外延薄膜表面修饰NiO、SnO2、Pd等材料，探究p-n、n-n及金属-氧化物异质结对气敏性能的调控作用，（3）开展气敏性能长期稳定性测试，利用结构表征手段，揭示薄膜微结构变化与传感器稳定性的关联，探索提高稳定性的方法。本项目以WO3外延薄膜为研究对象，探究晶相、晶面及异质结对气敏性能的调控作用，为氧化物气敏材料的研究工作提供了新思路。此外，气敏性能稳定性研究也可为开发实用的氧化物气敏元件提供借鉴。

本项目以氧化物气敏薄膜为核心，系统开展薄膜结构调控及气敏性能研究，微纳气体传感器研制及稳定性研究，以及传感器测试系统开发等工作，主要研究成果有：（1）系统研究WO3薄膜结构参数对其氢敏性能影响，基于光、电响应的互补性开发出光电耦合氢气传感器。（2）利用SCBD技术制备出兼具小晶粒尺寸和高疏松度的ZnO薄膜，其在室温下对氢气的响应时间小于1 s；提出紫外辅助氢敏机理模型，对氢敏性能的紫外抑制效应进行定性解释。（3）系统研究ZnO薄膜在紫外照射下对气态氧和溶解氧的响应行为，提出ZnO薄膜氧敏机理模型，实现溶解氧浓度的快速检测。（4）利用脉冲激光沉积实现WO3气敏材料的大范围结构调控；在不同氧化物单晶衬底上制备出WO3外延薄膜，发现衬底晶格常数对WO3外延薄膜气敏性能的巨大调控作用。（5）采用第一性原理平面波超软赝势方法对单斜WO3的晶体结构、表面结构、表面能量及吸附构型开展理论计算，定性解释了WO3外延薄膜对氢气和二氧化氮响应行为的差异。（6）在氧化物异质结界面观察到持久光电导效应，揭示了氧化物异质结界面处金属区和近藤区光致电阻变化机制。（7）基于Si基微加工技术设计和制备出三种不同类型的钯纳米间隙型氢气传感器，实现传感器性能的精确调控。（8）研制基于WO3和ZnO纳米薄膜的微纳氢气传感器并开展器件稳定性研究，发现传感器性能漂移主要发生在老化测试初期，主要原因是Pd催化剂的形变。（9）基于真空技术设计并搭建用于高精度测试的准静态自动化测试系统，以及用于批量VOC传感器检测的静态测试系统，目前已为多个课题组开展测试服务。上述结果发表在Sensors and Actuators B: Chemical, Applied Physics Letters等期刊。