SnO2半导体纳米晶气敏特性尺寸效应与增强机制研究

It is an urgent problem to monitor low concentration toxic gas pollutants in real time precisely. The metal oxide semiconductive nano-grain, such as SnO2, has a small size but large ratio surface area. It has performed the characteristics of high response, low operating temperature and low detection limit in the investigation of gas sensors. However, the mechanism of semiconductor gas sensors is not clear, leaving an important topic in the design and optimization of gas sensors. In the present project, tin oxide nano-grains are selected to be the samples, which are controlled during the preparation process in order to adjust the size, composition and morphology of the grains. The grain size effect and its critical point on gas sensing properties are investigated. The mechanism of the size effect is discussed in the aspect of electron levels, bonds and surface states by using the electrical and optoelectronic in situ characterization. The defect behaviors of formation, distribution and migration are studied by microscopic analysis to conclude controlling techniques. The synergetic and competing mechanisms of acceptors on grain surface are discussed under the volume depletion circumstance. A mathematical model is established for the gas sensing mechanism of semiconductor nano-grains on the basis of the grain size effects. The gas sensing mechanism is interpreted in the aspects of acceptor adsorption, depletion layer and carrier migration, in order to provide guidance for the design, fabrication and optimization of novel gas sensors with excellent performances.

低浓度毒害气体污染物的实时精确监测是当今社会亟待解决的问题。SnO2等金属氧化物半导体纳米晶尺寸小、比表面积高，在气体传感器研究中，已展现出灵敏度高、工作温度低、检测下限低等特点，然而半导体气体传感器的敏感机理仍不明晰，是实现传感器优化设计的关键科学问题。本项目拟采用SnO2纳米晶为研究对象，通过生长条件的控制调节纳米晶的尺寸、组分、形貌和晶面结构等特征，重点研究气敏特性的尺寸效应并探寻尺寸临界点，利用电学、光电原位表征手段，从电子能级、化学键以及表面态等方面讨论尺寸效应的内在机制，采用微观尺度测量方法对晶粒缺陷的产生、分布、迁移等行为模式和调控手段进行研究，尝试探讨尺寸效应下各表面受主种类之间的协同与竞争机制，建立以尺寸效应为基础的半导体纳米晶气敏机理的数学模型，从受主吸附、耗尽区建立和载流子迁移角度定量阐述气敏机理，最终实现指导高性能新型气体传感器件设计、制备和优化的目标。

SnO2等金属氧化物半导体纳米晶由于优异的物化特性和显著的尺寸效应，是研发高性能室温气体传感器的前沿材料，然而它们的气敏机理仍不明晰，是实现传感器优化设计的关键科学问题。本项目实现了SnO2半导体纳米晶（量子点）在水溶液中的尺寸可控合成，系统讨论了从部分耗尽到体耗尽晶粒气敏特性的尺寸效应，建立数学模型探讨半导体纳米薄膜气体传感器的性能增强机制，并完成了SnO2量子点功能材料的应用拓展，取得了一些创新性成果：（1）实现SnO2量子点的水基制备以及尺寸可控生长，制作量子点薄膜气体传感器原型；气敏特性测试表明，当晶粒半径等于耗尽层宽度时，纳米晶对气体的响应达到最高，此晶粒半径即为尺寸效应的临界点，据此从部分耗尽到体耗尽全面阐述纳米半导体气敏特性的尺寸效应。（2）第一性原理计算表明，体耗尽晶粒中的氧空位的形成和表面的氧吸附都具有尺寸效应，表面桥位氧产生概率最高；吸附氧的类型可随晶粒尺寸发生转换，德拜长度的物理内涵为表面吸附氧受主借助晶粒内部原子所束缚电子的最大范围，并建立了基于第一性原理计算的德拜长度测量方法。（3）以尺寸效应为基础，建立涵盖受体功能、转换功能和效用因子的数学模型，以定量方式表述传感器气敏特性与器件参数之间的关系，全面阐述半导体纳米薄膜材料的气敏机理，为气体传感器的设计与优化提供理论依据。（4）完成SnO2量子点功能材料的应用拓展，针对量子点的强量子限域效应带来的宽禁带，利用氧空位在晶粒内部的深能级构建Z型电子跃迁传导通道，实现了在紫外-可见光下油类污染物的高效降解和溢油污染水体的修复。本项目的研究成果以定量方式阐述了尺寸效应的本源和气敏材料关键参数的物理内涵，进一步深化了对SnO2半导体纳米晶的气敏机理认知，并实现了其功能化应用的拓展，完成了项目预定研究目标。