无序工程黑色二氧化钛表面壳层中缺陷对激发态载流子动力学影响研究

Disorder-engineering was demonstrated to be a conceptually new approach to engineer the band structures of wide-bandgap oxide semiconductors by introducing disorder in the surface layers of the nanocrystals, the black resultants possess substantial solar-driven photocatalytic activities and strong microwave absorption properties. Although great effort has been devoted to develop this technique, a deeper understanding of the functions of defects in the black samples responsible for the disorder-engineering and resultant enhanced photocatalytic efficiency and strong microwave absoption is still lacking. In this project, We will study the influence of different defects in the surface disordered titanium dioxide on the dynamic process of excited state carriers, and analyze the regulatory mechanism of different defects on the photoelectric properties of materials. In experiment, the selective control of the defects in the disordered shell is achieved by high-pressure hydrogenation or chemical reduction. The carrier relaxation process of excited states with different defects will be investigated by femtosecond laser pump-probe technique. Theoretically，First principles calculations are used to simulate the role of hydrogen impurity and oxygen vacancy related defects in lattice disorder and the influence of band gap structure, then we will study the carrier relaxation process of excited states based on time-dependent density functional theory. Combining theory with experiment, we can determine the corresponding paths of relaxation process at different time scales, clarify the physical mechanisms of different defects in improving the photocatalytic and microwave absorption of disordered-engineered oxide, and provide physical basics for the optimization of material preparation strategy.

无序工程技术是利用表面晶格无序化调节宽禁带氧化物半导体能带结构，获取具有高效光催化、强微波吸收等多功能性材料的新技术。虽然国内外对该技术开展了大量研究，但无序化处理引入的缺陷在材料光催化及电磁特性调控方面的作用机制尚存争议。本课题将通过研究表面无序二氧化钛中不同缺陷对激发态载流子动力学过程影响，解析不同缺陷对材料光电特性的调节机制。实验上，通过高压氢化及化学还原实现纳米二氧化钛无序化壳层中缺陷的选择性调控，利用飞秒激光泵浦-探测技术研究含不同缺陷材料的激发态载流子弛豫过程。理论上，运用第一性原理计算模拟氢杂质及氧空位相关缺陷在晶格无序化中的作用及对能带结构的影响，进而采用基于含时密度泛函的分子动力学计算研究激发态载流子弛豫过程。理论结合实验确定不同时间尺度动力学过程的对应弛豫路径，厘清不同缺陷对改善无序工程氧化物光催化及微波吸收的物理机制，为材料制备策略的优化提供物理基础。

纳米尺度半导体光电材料高效性及先进功能的开发主要依赖于材料结构、杂质缺陷、表面界面的准确调控。无序工程技术是一种新型能带调控技术，其利用氧化物纳米材料表面晶格无序化实现了光催化性能及微波吸收能力的大幅提升，在能源及军事应用领域具有重大应用前景。本项目针对无序工程氧化物半导体制备方法的革新及表面无序二氧化钛中不同缺陷对激发态载流子动力学过程影响开展系统研究工作，期望在厘清缺陷及结构调控实现二氧化钛材料光催化及微波吸收性能增强的物理机制。此外，在Ⅲ-Ⅴ族纳米线材料的晶型控制与掺杂方面开展系统研究工作，为纳米线器件性能提升提供优质材料基础。国家自然科学青年基金资助三年期间，课题研究达到既定目标，取得如下成果：1) 开发了安全高效的无序工程黑色二氧化钛纳米材料制备方法，利用瞬态吸收光谱确定了无序工程材料光催化增强的缺陷来源，2）构建了黑磷/二氧化钛复合异质结催化剂，实现光催化性能2.4倍提升，通过时间分辨光谱，紫外光电子能谱与第一性原理计算结合，证实了异质结构促进激子分离及载流子传输，实现光催化增强的物理机制，为富激子型材料光催化系统设计及在光催化产氢领域的应用提供新策略，3）分子束外延制备高质量GaAs纳米线及Be, Si掺杂调控GaAs纳米线结构相变及光学特性研究，提出了不同Ⅴ/Ⅲ比例对Si掺杂纳米线结晶与导电性调控作用指导方案4）仿真设计了任意偏振多焦点超透镜，获得了多通道、多功能和可控能量比的优越性能超透镜，在偏振成像，多路复用通信和多维全息图等领域具有重要应用。