Zhan Yaohui, Lei Dang Yuan, Li Xiaofeng, Maier Stefan A
Institute of Modern Optical Technologies & Collaborative Innovation Center of Suzhou Nano Science and Technology, Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province & Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou 215006, China.
Nanoscale. 2014 May 7;6(9):4705-15. doi: 10.1039/c3nr06024a.
Plasmonic Fano resonances arising from electromagnetic interactions in metallic nanostructures exhibit spectral characteristics analogous to those from the electron waves in oligomer molecules. Though a great deal of research interest has been attracted to study the optical properties and explore the associated applications of metallic nanoparticle oligomers, the plasmonic response of their complementary structures--nanohole clusters--remains largely unexplored. Here we show numerically by a full-wave finite element method that a nanohole quadrumer can sustain two Fano resonances when the incident electric field is oriented along the long-axis of the quadrumer system. The underlying physical mechanisms responsible for the Fano resonance formation are revealed explicitly by spectrally deconstructing the Fano lineshape, spatially decomposing the structure configuration and mapping the electric field profile and charge distribution, which collectively demonstrate a strong mode coupling between either two antiparallel dipolar modes or dipole-quadruple modes in the nanohole quadrumer. We further show that the spectral profile of the Fano resonance including the resonance linewidth and spectral contrast can be engineered flexibly by adjusting the geometrical parameters of the nanohole cluster, including the nanohole diameter, film thickness and interhole distance. With an optimized and realistic geometrical configuration, the nanohole quadrumer system exhibits an overall sensing figure of merit up to 14.25, far surpassing the value reported for conventional nanoparticle oligomers.
金属纳米结构中电磁相互作用产生的表面等离子体激元法诺共振表现出与低聚物分子中电子波类似的光谱特征。尽管金属纳米粒子低聚物的光学性质研究及其相关应用探索已经吸引了大量的研究兴趣，但其互补结构——纳米孔簇——的表面等离子体激元响应在很大程度上仍未被探索。在这里，我们通过全波有限元方法进行数值模拟表明，当入射电场沿四聚体系统的长轴方向时，纳米孔四聚体可以支持两种法诺共振。通过对法诺线形进行光谱解构、对结构构型进行空间分解以及绘制电场分布和电荷分布，明确揭示了形成法诺共振的潜在物理机制，这些共同证明了纳米孔四聚体中两个反平行偶极模式或偶极 - 四极模式之间存在强模式耦合。我们进一步表明，通过调整纳米孔簇的几何参数，包括纳米孔直径、膜厚度和孔间距，可以灵活地设计法诺共振的光谱轮廓，包括共振线宽和光谱对比度。具有优化且现实的几何构型时，纳米孔四聚体系统展现出高达14.25的整体传感品质因数，远远超过传统纳米粒子低聚物报道的值。
