金纳米结构的光频磁性共振及其对磁偶极辐射的调控机制

Magnetic resonances are required for the realization of electromagnetic metamaterials. They also provide an effective way to enhance the interaction between matters and magnetic field of light. However, the realization of magnetic resonances in optical range requires to artificially design nanostructures with special symmetry. In this proposal, we will develop wet-chemistry method for the preparation of nanoparticles that can support magnetic resonance in individual nanoparticles. The magnetic resonances of the nanoparticles, the coupling of the magnetic resonance and between magnetic and electric resonances will be systematically studied. We will also study the control of magnetic resonance on the emission of magnetic dipole. We will develop a facile wet-chemistry preparation method for Au nanocups and split nanorings by the control of the nucleation and growth kinetics and thermodynamics. The evolution of magnetics resonances with the morphologies and structures of Au nanocups and nanorings will be systematically studied. We will also unraveling the magnetic resonance-based coupling of nanostructure dimers with various configurations. Finally, by choosing rare-earth nanoparticles, we will study the control of magnetic resonances on the emission of magnetic dipole. We foresee that the success of this project will lead to the production of high-quality colloidal Au nanocups and nanorings supporting strong and energy-variable magnetic plasmon resonance at low cost. Moreover, the unique geometries of Au nanocups and nanorings will offer unprecedented opportunities for studying the interactions of magnetic plasmon resonance with other optical processes, which will greatly contribute to the understanding of magnetic plasmon resonances and their interactions at the nanoscale.

磁性共振是实现电磁超材料的必要条件，且是一种有效增强物质和磁场作用的方法，然而光频波段磁性共振只能通过人为设计具有特殊对称性的纳米结构来实现。本项目拟开发能够在单个颗粒中产生磁性共振的纳米结构的湿化学制备方法，并研究其磁性共振性质、磁性共振耦合、磁性与电性共振耦合、以及其对磁偶极辐射的调控作用。通过研究金的成核和生长动力学与热力学，开发金纳米杯和缺口金纳米环的可控湿化学制备方法；通过研究不同形貌与结构的金纳米杯和缺口金纳米环中的磁性共振性质，阐明磁性共振随形貌和结构的演变规律；采用不同构型的二聚体，研究磁性共振之间以及磁性共振与电性共振之间的耦合随二聚体构型的变化规律；以稀土纳米颗粒中磁偶极辐射为代表，研究磁性共振调控前后磁偶极辐射的强度、方向、偏振及谱形的变化，揭示磁性共振对磁偶极辐射的增强和调控机制。本项目开发的制备方法及磁性共振性质研究，为基于磁性共振的应用提供理论依据和技术积累。

光频磁性共振是实现电磁超材料的必要条件，且是增强物质和电磁波中磁场相互作用的有效途径。然而由于自然界中缺少磁单极子，普通材料无法实现光频波段磁性共振，磁性只能通过一些特殊的纳米结构才能实现。尽管开口金纳米环和纳米颗粒低聚体已在光频波段实现了磁性共振，但是依然存在光频磁性共振很难在单个贵金属纳米颗粒中实现、很难将磁性共振频率调控到可见光波段、复杂的结构不利于研究磁性共振和其它光学物质的相互作用等不足。由于磁性共振纳米结构在制备上的困难，致使到目前为止关于磁性共振之间的耦合、磁性共振和电性共振之间的耦合、以及磁性共振对电偶极和磁偶极的增强和调控机制不清楚。围绕这些关键科学问题，本项目开发了能够在单颗粒中产生光频磁性共振金纳米结构的高效低成本湿化学合成方法，解决了磁性共振纳米结构大批量、低成本制备的难题。揭示了金纳米结构中磁性共振—磁性共振、磁性共振—电性共振的耦合规律，为磁性共振纳米结构在电磁超材料、负折射率材料、超透镜等领域的应用奠定了理论基础。通过利用双官能团表面活性剂对稀土纳米颗粒进行表面修饰，成功实现了磁性金纳米结构和稀土纳米颗粒的组装，为在单颗粒水平精准研究纳米结构中的电性共振和磁性共振对电偶极和磁偶极辐射奠定了实验基础。揭示了磁性共振对电偶极和磁偶极辐射的增强规律，明确了磁性共振对电偶极和磁偶极远场辐射能量空间分布的调控作用；磁性共振不仅可以增强磁偶极辐射，也可增强电偶极辐射，磁性共振对磁偶极的辐射方向有强的调控作用，可以实现磁偶极的定向辐射，但是磁性共振对电偶极的辐射调控作用较弱；该结果为纳米光学芯片的设计提供了理论基础。目前，该项目资助的研究成果已在Journal of the American Chemical Society、Advanced Materials、Advanced Optical Materials、Nanoscale、Optics Express等国际著名期刊发表论文25篇。综上所述，本项目达到了预期研究目标。