提出了一种可用于表面增强拉曼测量的基于金属纳米圆盘上方放置金属纳米球颗粒构成的金属纳米结构, 其在径向偏振光束激发下, 由于金属纳米圆盘的呼吸模式表面等离激元共振的作用, 可以形成纵向电场有效增强的间隙模式等离激元共振。 对此进行了有限元模拟计算研究, 计算结果证明该间隙模式的纵向电场分量相对于径向偏振入射光的有效激发横向电场分量增强了100倍以上。 为了更清晰地展现这种新型纳米结构的光谱特性以及表面电场分布特征, 同时对单个金属纳米圆盘, 单个金属纳米球, 金属薄膜, 金属纳米球-金属薄膜这几种纳米结构在同一个模拟计算框架下进行了计算以及比较分析。 由于可以把金属纳米球类比为金属探针的尖端, 所提出的新型间隙模式也有望在针尖型拉曼增强中得到应用。

This proposesa metal nanostructure composed of a metal nanodisc and a metal nanosphereon top of it, which canbe applied for surface enhanced Raman scattering. Due to the excitation of the breathing mode surface plasmon resonance of the nanodisc, this nanostructure can form a gap mode with efficient longitudinal electric field enhancement under the illumination of a radially polarized vector beam. The simulation based on finite element method is carried out to investigate this gap mode and an electrical filed enhancement of 100 times relative to the valid transverse electrical field is demonstrated. In order to present more clearly the spectrum characteristic and the surface electric field distribution of this new nanostructure, the other structures including a single metal nanodisc, a single metal nanosphere, metal film and a metal nanosphere-on the metal film-are also studied under the same simulation configuration. Since the metal nanosphere can be regarded as the tip of a metal probe, the gap mode proposed here is expected to find application in tip enhanced Raman scattering.