多尺度结构下电磁热点的数值模型研究

The project proposes to investigate the influences of morphological details on the near-field enhancement of electromagnetic “hot spots” in the nanoparticle-on-mirror (NPOM) system. 3D electrodynamic calculations are performed using finite element method (FEM) based on COMSOL Multiphysics. Taking advantage of quantum mechanical theory, the modeling is corrected to consider the non-local and quantum tunneling effects. By means of FEM near-field plasmon mapping, properties like the plasmon hybridizations, the local field enhancement and the spectral deviation between near- and far-field resonances are analyzed systematically. As a result, a comprehensive physical image of hot spots can be presented. . Experimentally, the near-field enhancement property is characterized by surface enhanced Raman scattering (SERS) according to the electromagnetic enhancement mechanism. Aimed at active SERS substrates with huge near-field enhancement,the morphological details of hot spots can be modified by appropriate thermal processing or chemical etching. Thus a precise numerical model of hot spots with multi-scale structures can be further established. The study could provide physical insights into the fundamental understanding of hot spots and the role of their morphological details, which benefits greatly both the optimized design and spectroscopy applications of related plasmonic devices.

本项目拟研究电磁“热点”的形貌细节对其近场增强特性的影响，围绕金属镜膜耦合的纳米颗粒体系，首先，结合量子力学理论的修正，考虑非局域效应和量子隧穿效应，运用COMSOL有限元法，系统地模拟热点的局域表面等离子体近场成像，分析其共振模式的耦合、局域电场的强度、近场与远场共振的光谱偏移等性质，给出清晰的物理图像。进而，结合实验，依据表面增强拉曼光谱的电磁增强机理，表征样品的近场增强性质。通过热处理和化学腐蚀工艺来调控热点的形貌细节，制备出具有极大近场增强性质的表面增强拉曼活性基底。最终，建立多尺度结构下的电磁热点数值模型。本项目研究有助于理解电磁热点的物理本质，阐明形貌细节影响热点近场增强性质的物理机制，对相关表面等离子体器件的结构优化设计和光谱学应用具有指导意义。

本项目从现有的大量实验结果出发，提取出典型的热点形貌细节特征，包括粗糙表面和纳米桥接、纳米劈裂、纳米截面，进而建立了一系列具有的多尺度电磁热点几何模型。. 利用COMSOL有限元方法，系统地分析了多尺度结构下热点的局域表面等离激元性质，发现形貌细节极大地影响热点的近场增强性能，但对整个系统的远场光学性质影响较小。原因在于远场光学性质主要由大尺度的初级结构决定，而近场增强性能则取决于小尺度的热点形貌细节次级结构。. 进一步的研究还发现，多尺度结构条件下的热点结构近场增强性能与远场共振光谱的一致性关联存在不确定性，需要结合具体的结构和形貌特征来分析。. 最后，结合电子束刻蚀和倾斜角沉积方法，制备了具有不同结构参数的密排Au纳米结构周期性阵列，用表面增强拉曼散射光谱（SERS）来表征其近场增强性能。理论方面，针对Au纳米结构的粗糙表面，建立了具有粗糙形貌特征的多尺度纳米空腔热点结构的数值模型，证明其近场增强性能和远场光谱具有良好的一致性关联，且粗糙表面有利于进一步提高近场增强性能。. 上述研究结果有助于理解电磁热点的物理本质，为阐明近场和远场光谱的关联提供了新的思路，对相关表面等离激元器件的优化设计和光谱学应用具有一定的指导意义。