基于局域和传播型表面等离激元长程耦合的新型表面/针尖增强拉曼光谱和传感基底

The surface plasmon based on metal nanostructures has attracted plenty of attention due to its capability of confining lights in nanoscale and providing enhanced electric field. The key issue in applying surface plasmon is how to effectively combine the advantages of localized surface plasmon (LSP) with strongly enhanced electric field and propagated surface plasmon (PSP) with low loss and ultrahigh sensitivity to the change of surface refractive index. In this project, we try to systematically investigate the coupling of LSP and PSP of nanoparticle-metal film, tip-metal film and periodical array-metal film systems，which can be conveniently fabricated with low cost, with electromagnetic field simulation and experiments with separating excitation and collection paths. We aim to propose the physical model to understand the long-range and collective coupling of LSP of multiple metal nanoparticles through PSP that is a standing wave. Then we will develop new substrates for surface and tip enhanced Raman spectroscopy with purely near-field excitation from PSP based on the understanding. Furthermore, periodical structure will be fabricated on the metal film with holographic method to increase the modes of coupling LSP and PSP and improve the flexibility of optical properties of the surface. Then we expect to realize a new type of sensor that is able to simultaneously provide fingerprint information based on the near-field enhancement of LSP and ultrahigh sensitivity of refractive index change based on the narrow band of PSP.

基于金属纳米结构的表面等离激元由于能将光局域在表面纳米级的范围内，并得到强的电场增强，因此受到越来越多的关注。而如何将具有高增强的局域表面等离激元（LSP）与低损耗，对表面折射率改变高敏感的传播型表面等离激元（PSP）有效耦合，同时发挥两者的优势成为其应用的关键。本项目拟通过电磁场理论模拟，采用激发光路和收集光路分离的方法，系统研究能够低成本大批量制备的金属粒子与金属膜、针尖与金属膜以及周期阵列与金属膜中LSP和PSP耦合的光学模式和效率，提出远距离的多个金属纳米粒子LSP通过驻波场的PSP实现长程和群体耦合的物理模型。进一步发展基于金属膜PSP的纯粹近场激发的表面增强拉曼和针尖增强拉曼光谱基底。通过全息光刻引入周期结构，丰富金属纳米结构LSP和PSP耦合的光学模式并大大提高表面光学性质的可调性，从而实现同时利用LSP的近场增强提供指纹信息和窄带PSP的高灵敏度折射率传感的新型检测基底。

基于金属纳米结构的表面等离激元由于能将光局域在表面纳米级的范围内，并得到强的电场增强，因此在表面增强拉曼光谱（SERS）和针尖增强拉曼光谱（TERS）得到广泛的关注和应用。而如何将具有高增强的局域表面等离激元（LSP）与低损耗，对表面折射率改变高敏感的传播型表面等离激元（PSP）有效耦合，同时发挥两者的优势成为其应用的关键。为此，本项目搭建了基于三束光的全息干涉曝光系统，能保证在高功率情况下快速制备周期性纳米结构，避免因长时间曝光时基底的振动、漂移等对制备结构造成的影响，从而稳定制备具有PSP模式的金属周期结构。制备了传播表面等离激元（PSP）和局域表面等离激元（LSP）耦合的具有高增强效应的表面增强拉曼光谱（SERS）基底。并进一步结合电化学沉积和原位暗场观察，减少纳米结构间隙，在提高增强因子的同时保持高的均匀性。发展了电化学沉积方法制备AFM的针尖增强拉曼光谱（TERS）针尖，所制备镀银针尖增强因子达到10^5，高于目前AFM-TERS针尖的平均增强因子，而且具有长的使用寿命（19天）。通过制备的TERS针尖，我们首先对二维材料边缘缺陷的电子性质和晶格性格进行高空间分辨研究，定量检测了边缘缺陷所引起的电子和晶格重构长度；深入研究了表面等离激元热载流子催化反应过程，测量出热空穴的扩散长度。