表面等离激元“热点”的可控激发及近场增强光谱学

Surface plasmon resonance “hot spots” and near-field enhanced spectroscopy at interfaces

金属纳米结构中特定表面等离激元模式的光学激发及其相互作用是发展高分辨、高灵敏、高精度界面光谱学的物理基础.本文综述了我们研究组近期在表面等离激元共振的光学激发、分类识别、近场增强及在界面光谱学中的应用等方面的进展,主要内容包括:1)利用时域有限差分法,分析了金属粒子-基底体系中SPR"热点"产生的物理机制及影响因素,讨论了电模式和磁模式下界面"热点"的可控激发及"热点"转移的影响因素;2)利用粒子-金膜体系,实现了可见光频率的表面等离激元磁共振,并利用其形成的"热点"进行了表面增强拉曼光谱实验,获得了比常规电模式更高的拉曼增强;3)通过界面SPR"热点"增强二次谐波的实验和理论研究,提出并实现了空间分辨率达到1 nm的等离激元增强二次谐波纳米尺;4)讨论了针尖增强拉曼光谱及针尖增强荧光体系中的空间分辨率、定向发射等关键共性问题的解决方案.相关研究成果可为界面SPR"热点"的可控激发及进一步发展表面增强拉曼、针尖增强拉曼、表面等离激元增强二次谐波等各类高灵敏度,高空间分辨率的界面光谱学方法提供新的思路.

Optical excitations and mutual couplings of surface plasmons with specific modes in metal nanostructures are the physical basis for developing the high spatial resolution, high sensitivity, and high precision spectroscopy. Here, we systematically review latest advances in optical excitations, classifications and identifications of surface plasmon resonance modes and their typical applications in several typical interfaces.We discuss several aspects below. First, the intrinsic mechanism of creating "hot spots" in metal particle-film systems is elucidated by the finite-difference time-domain numerical method. Spatial transfers and influence factors of the "hot spots" under plasmon-induced electric-resonance and plasmon-induced magnetic-resonance conditions are discussed. Second, the plasmon-induced magnetic-resonance in the visible-light region is successfully realized in a gold nanoparticle-film system. Meanwhile, experimental results of surface-enhanced Raman spectroscopy show that the "hot spots" in the magnetic-resonance mode can output Raman scattering with a much higher enhancement factor than that in the conventional electric-resonance mode. Third, we design nonlinear nanorulers that can reach approximately 1-nm resolution by utilizing the mechanism of plasmonenhanced second-harmonic generation(PESHG). Through introducing Au@SiO2(core@shell) shell isolated nanoparticles, we strive to maneuver electric-field-related gap modes such that a reliable relationship between PESHG responses and gap sizes, represented by " PESHG nanoruler equation", can be obtained. Fourth, a critical and general solution is proposed to quantitatively describe the spatial resolution and directional emission in tip-enhanced Raman spectroscopy and tip-enhanced fluorescence. These results may help enhance our understanding of the intrinsic physical mechanism of the surface plasmon resonance, and offer opportunities for potential applications in surface-enhanced Raman spectroscopy, tip-enhanced Raman spectroscopy, second harmonic generation, and other plasmon-enhanced spectroscopy.