复合纳米晶的灵活构筑及其光电性能的精准调控特性研究

Plasmonic nanoparticles can manipulate the micro-and nanospatial energy field flexibly on the basis of the coupling mechanism between surface free electrons and electromagnetic fields, which is expected to play a significant role in pushing developments of a variety of technologies, such as breaking through the diffraction limit of optical imaging, enhancing optical nonlinearity, controlling chemical reactions, studying pathology at the level of single cell. However, for more than decades, the development of plasmonic nanomaterials in practicality is very slow. A key problem is that for pure nanomaterials it is difficult to improve the material performance due to the limitation of free carrier concentration and lifetime. Specifically, noble metals rich in free electrons have strong plasmon resonance effect, whereas have serious optical loss caused by free electron with high concentration. On the other hand, the plasmon resonance effect of semiconductors and oxide materials with low optical loss is difficult to be improved owing to the low free carrier concentration and poor stability. In this project, a preparation technology of composite nanocrystals is proposed to build excellent plasmonic nanoparticles by precisely controlling the concentration and stability of free carriers. Herein we choose nanocomposite noble metal/molybdenum oxide as a main research subject. Combining experimental and theoretical research, we focus on the following work: 1) quantitative analysis and mechanism investigation of the influence of decisive factors on the plasmon resonance effect, including carrier concentration, carrier mobility, materials parameters, nanostructure parameters, and plasmon resonance coupling; 2) the intensity, stability and optical loss of plasmon resonance in the constructed composite nanomaterials, and the intrinsic relationship between plasmon resonance and the local energy field; 3) coupling characteristics between light field, electric field and heat field at interfaces of composite nanomaterials, as well as quantum dynamical properties of electron transition, electron transport and electron interface transfer; 4) the influence of local fields on optical absorption, light radiation, photoelectric conversion and photochemical properties of the nanomaterials. On the basis of above research, an optimization strategy for the local energy field manipulating the optoelectronic properties of nanomaterials will be suggested, which can provide basic supports for the development of nanomaterials with excellent photoelectric properties. Under the current international situation in the field of nanomaterials, it is particularly urgent to develop flexible fabrication technology of plasmonic composite nanocrystals to greatly improve the photoelectric properties of nanomaterials. The plasmonic composite nanocrystals will be developed and in Raman signal detection, the Raman enhancement factor will increase nearly two orders of magnitude that of the current non-metallic plasmonic nanocrystals. We will publish 2~4 articles.

等离子体纳米粒子基于表面自由电子与电磁场的耦合作用机制，可灵活操控微纳空间能量场，从而有望在许多学科发展中起到巨大推进作用，如突破光学成像的衍射极限、增强光学非线性效应、控制化学反应、实现单细胞内病理研究等等。然而经过十几年的研究，等离子体纳米材料的实用化进程缓慢。关键问题在于，单质纳米材料受自由载流子浓度和寿命的限制，难以突破其性能局限性。具体而言，富含自由电子的贵金属拥有强等离子体共振效应，但高自由电子浓度也造成了严重的光损耗；而光损耗低的半导体和氧化物材料，却因自由载流子浓度低、稳定性差等因素，无法提高等离子体共振效应。本项目提出灵活构筑复合纳米晶技术，通过不同材料之间能量场相互作用，控制复合体系的自由载流子浓度和寿命，从而获得性能优异的等离子体纳米材料。基于前期研究，本项目选择贵金属/二氧化钼复合纳米体系为主要研究对象，通过精确调控等离子体共振性能的决定因素，突破现有等离子体纳米材料的局限性。重点开展以下实验和理论研究：1）量化分析贵金属/二氧化钼复合纳米晶的等离子体共振效应的决定因素及其作用机制，包括载流子浓度和迁移率的作用、材料和结构参数的作用、以及等离子体共振耦合作用；2）研究复合纳米晶的等离子体共振强度、稳定性、光损耗，及其与局域能量场的内在关系；3）研究复合材料界面处光、电、热场之间的耦合特性，和电子跃迁、传输以及界面转移的量子动力学特性；4）探索局域场对材料光学特性、电学特性以及光化学特性的作用机制。在此基础上获得性能优异的等离子体纳米材料，并用于拉曼检测、荧光和光电催化等领域。在当前世界各国竞相发展性能优异的功能纳米材料的背景下，研发等离子体复合纳米晶的灵活构筑技术，大幅度提升纳米材料光电性能显得尤为迫切。本项目将研发出高性能的等离子体复合纳米晶，在拉曼信号检测中，与当前非金属等离子体纳米材料相比，拉曼增强因子提高近两个数量级。发表学术论文2~4篇。

本项目的开展紧密围绕灵活构筑等离子体纳米晶、性能表征和用途开发的主要研究内容。重要结果包括：1）探索了复合纳米晶的表面等离子体共振特性，首次发现等离子体MoO2纳米晶和TiO2纳米晶复合物（MoO2/TiO2）具有良好的昼夜光催化能力。另外，该材料用于光伏电池，开发出昼夜发电的太阳电池器件。2）研究了Au/TiO2阵列薄膜的等离子体共振增强效应，开发出基于同心套管阵列的等离子体共振增强衬底。由于同心套管之间的狭缝和相邻纳米管间狭缝皆小于10 nm，并且均匀分布在阵列薄膜中，从而获得大面积局域能量场的均匀增强，成为增强弱拉曼信号的良好衬底。3）利用精确构筑纳米晶的方法，合成出尺寸、形貌、成分比例都高度均匀的纳米材料，并进而获得精确的实验测量光谱数据。基于实验数据，修正和改善理论算法，开发出了精确计算纳米材料光学性能的仿真平台。依托该项目已发表SCI论文3篇，正在投专利3项。