取向生长TiO2纳米薄膜的表面设计及气敏特性研究

Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy source and as a chemical reactant. Oxides-based H2 gas sensors such as SnO2, ZnO, WO3 and TiO2 are cheap,of long service life and easy to be fabricated. Dense TiO2 thin films are more stable and corrosion-resistant than other oxides. Anatase and rutile TiO2 grew along the [001] preferred orientation showed excellent H2 sensing properties in our recent work, with both having room temperature response and the sensitivity being even better under 100 C. The H2 sensor based on anatase TiO2 thin film had shorter response time, while the working temperature needed to be decreased and the sensitivity should be further improved. In this project, firstly, LiF will be incorporated onto the anatase (001) surface to help absorb H2 and to improve the surface conductance of the thin film. Li+ has very high combination energy with H2 and F- is a very effective doping element for the improvement of the electrical conductivity of oxides. DFT calculation could be adopted to calculate the change of surface energy, density of states, energetics of oxygen vacancy after the incorportation of LiF, so that the function of LiF could be clarified. Secondly, we will try to decorate the anatase (001) surface with Au nanoparticles, since Au nanoparticles have been considered as a good catalyst for photocatalysis and gas sensing. The sensitivity of TiO2 thin film is expected to be enhanced after the decoration. The mechanism of the catalystic reaction will be calrified by DFT calculation, testing the change of surface absorption energy, oxygen vacancy density etc. resulted from Au nanoparticles decoration and then followed by the investigation of the effect of those parametors on the sensing properties of TiO2 thin film. Thirdly, multiferroric materials will be used in this project to help improving the H2 sensing property of TiO2 thin film. It is well known that multiferroric materials will be self polarized and this change of charge arrangement in the multiferroric material will affect the surface charge arrangement of TiO2 nano thin film, once these multiferroric nanoparticles are decorated onto anatase (001) surface and thus may result in the improvement of H2 sensing property of the thin film. Furthermore, a heterojunction will be formed between the multiferroric material and TiO2, and the formation of this heterojunction will affect the charge transfer at the interface, where H2 adsorption happens. The barrier height and surface depletion depth at the surface of TiO2 will be investigated. H2 sensor with excellent functionality and ready to scale up commercial potential could be achieved and a detailed sensing mechanism of H2 on the decorated surface of TiO2 thin film will be revealed based on the research results of this project.

氧化物半导体表面与氢气相互作用机理的揭示及其表面修饰导致电子结构改变的深入理解是开发新型高效低成本氢敏器件的根本出发点。针对目前TiO2薄膜氢敏器件表面与氢气相互作用机理不清和气敏效果不够好的问题，本项目在前期自组装取向生长TiO2纳米薄膜氢敏特性的研究基础上，提出采用籽晶层诱导调控取向TiO2纳米阵列薄膜的活性表面面积，并对薄膜进行表面修饰以进一步改善其氢敏特性。结合理论设计和实验验证研究不同修饰方法导致薄膜氢敏特性改善的作用机理：（1）研究Li离子和F离子在TiO2活性表面的嵌入方式对其表面吸氢和导电性的影响；（2）研究金纳米颗粒的表面修饰在TiO2表面氢敏反应中的催化机制；（3）研究多铁纳米颗粒的自发极化和异质结的晶格匹配度对界面电子传输的影响。表面修饰改善TiO2氢敏特性机理的阐明对基于该机理的新型高效、稳定、长寿氢敏器件的研发和推广应用有重要科学意义。

氧化物半导体表面与氢气相互作用及其表面修饰导致气敏性能改善机理的深入理解是开发新型高效低成本氢敏器件的根本出发点。本项目研究了（1）LiF表面修饰对TiO2气敏及光催化活性的影响，发现LiF修饰对TiO2阵列薄膜的气敏性能的影响主要有两方面，一是薄膜的表面电阻下降，二是气敏响应时间变短；经LiF修饰的TiO2具有极强的电负性，F离子以物理吸附、替位掺杂和LiF晶体的形式存在于TiO2中，LiF和TiO2晶体的协同作用，大大增强TiO2表面对染料的吸附作用。（2）籽晶层的引入对TiO2薄膜氢敏器件性能的影响：引入TiO2籽晶层，实现了室温、大气环境、高灵敏度和快速响应的氢气探测。籽晶层的存在对氢敏器件的稳定性有明显改善，气敏响应的温度、浓度都大幅下降。（3）金属纳米颗粒的表面修饰对TiO2表面氢敏性能的影响：用还原法制备了粒径大小为3-7纳米的超细Ag纳米颗粒，室温下18nm的Ag纳米颗粒修饰后的薄膜对氢气的灵敏度增加，响应和恢复时间减小，气敏性能明显优越于修饰前的薄膜；采用磁控溅射法制备了超细Pt颗粒，将其应用于取向生长TiO2阵列薄膜的表面修饰，相比于纯TiO2薄膜，表面溅射10s Pt的氢敏特性有所下降，其主要原因可能是所溅射的Pt氧化严重，从而影响器件性能。（4）多铁纳米颗粒的表面修饰对TiO2薄膜表面气敏性能的影响：采用油酸当分散剂获得了粒径大幅减小，分散性明显改善的BaSrTiO3粉末。将所制备的BaSrTiO3粉末旋涂到TiO2阵列薄膜的表面，薄膜的氢敏性能得到提升。（5）采用DFT计算了LiF的（200）晶面和锐钛矿TiO2（101）晶面的界面相互作用，从理论上解释了TiO2和LiF的混合粉末对染料的吸附作用明显增强的实验现象；采用过渡态探寻的方法，详细描绘了氢分子在金红石（002）高活性表面的分解和氢原子在TiO2晶格中的迁移路径，找到了室温下氢气探测的低反应势垒传输路径，解释了高活性表面高灵敏度氢气探测的机理。