外诱表面态对3D间隔结构TiO2气敏响应时间的调制机理研究

Response time is a key parameter of fast-response type gas sensor used for automatic combustion control, however, the mechanisms during response time and interface charge transfer speed between gas and sensitive material remains unclear. Our pre-feasibility study together with related reports indicate that the surface state and work function of sensing-material are the key points in regulating charge transfer process. The purpose of this project is to regulate the surface state and work function of sensing material by building external induced surface. A 3D space fabric type TiO2 gas sensor is proposed as research object. Based on the first-principles calculations, the outlook of the tendency of chemical properties, band structure and energy change are discussed, and a coupling model is designed to simulate the gas adsorption configurations and charge transfer. From the aspects of experimental studies, the surface defect, charge distribution and the electrical properties (work function, contact potential barrier, et al) of sensing material before and after gas adsorbing are researched. A new model for the relationship between microscopic chemical state, electrical characteristics and macroscopic gas response rate is presented firstly, and the sensitive activation properties of the model are analyzed. This subject will be helpful to understand the scientific connotation of the energy change and charge transfer process on sensing material surface, and conduce to improvement the methods on construction and characterization for surface state. This research will also possess an important meaning for the manufacture of fast-response type gas sensor.

响应时间是应用于控制领域快速响应型气敏传感器的核心参数，但气体-敏感材料界面电荷转移速度对响应时间的影响机制尚不明确。文献和我们的研究表明，敏感材料表面状态和电学参量是影响气-固界面电荷转移的关键。本课题以3D间隔结构TiO2气敏传感器为研究载体，通过构筑外诱表面态调节材料表面物理化学状态和电学参量。基于第一性原理，计算研究外诱表面态的化学特性、能带结构和能量变化趋势，构建典型气体的吸附构型和电荷转移模型；结合实验研究，分析外诱表面原子的缺陷状态和电荷分布状态，揭示气体吸附前后材料功函数和接触势垒等半导体电学特性的演变规律，建立外诱表面态微观化学状态、电学特性和宏观气敏响应速率的关联模型，阐明材料对气体敏感活化的速度机制。本项目研究，有助于深入认识气敏材料界面能量变化和电荷转移速度的科学内涵，丰富表面态的可控构筑方法和表征手段，对气敏材料响应速率的性能调控具有重要理论意义。

本项目拟通过研究气体-敏感材料界面电荷转移速度对响应时间的影响机制，揭示气体吸附前后材料功函数和接触势垒等半导体电学特性的演变规律，建立表面态微观化学状态、电学特性和宏观气敏响应速率的关联模型，阐明材料对气体敏感活化的速度机制。本项目在执行过程中，通过阳极氧化法，研究了关键工艺参数与TiO2纳米管阵列形貌的内在联系，实现TiO2纳米管阵列长度、形貌、均匀性的可控制备和几何结构优化。将所制备TiO2纳米管阵列转移到具有电极的基体上，构建了TiO2气敏传感器。通过第一性原理密度泛函理论的计算研究，模拟了不同气体吸附过程中键序、电荷转移值和吸附振动频率的变化过程，计算研究了气体分子在外诱表面态的吸附构型演变趋势，进而从理论上建立外诱表面态对TiO2表面化学特性的影响机制及气体在表面的反应机理模型。通过构建含S表面态，研究了以S为代表的非金属元素表面态对TiO2和Pt/TiO2的影响机制，并提出了影响传感器气敏特性的表面状态影响模型。通过构建含Mn表面态，研究了以Mn为代表的的金属元素表面态对TiO2表面状态和气敏特性的影响机制，提出了影响气敏特性的能带模型和电阻模型。项目的实施过程中，获得了400-600℃温度范围内响应时间180-20ms的快速响应型TiO2气敏传感器。本项目的顺利实施为空/燃比控制用氧传感器的抗劣化抗污染以及延长使用寿命提供了理论基础和改性方向，对气敏材料响应速率的性能调控具有重要理论意义。