Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
Nano Lett. 2012 Mar 14;12(3):1660-7. doi: 10.1021/nl3000453. Epub 2012 Feb 23.
While the far field properties of Fano resonances are well-known, clusters of plasmonic nanoparticles also possess Fano resonances with unique and spatially complex near field properties. Here we examine the near field properties of individual Fano resonant plasmonic clusters using surface-enhanced Raman scattering (SERS) both from molecules distributed randomly on the structure and from dielectric nanoparticles deposited at specific locations within the cluster. Cluster size, geometry, and interparticle spacing all modify the near field properties of the Fano resonance. For molecules, the spatially dependent SERS response obtained from near field calculations correlates well with the relative SERS intensities observed for individual clusters and for specific Stokes modes of a para-mercaptoaniline adsorbate. In all cases, the largest SERS enhancement is found when both the excitation and the Stokes shifted wavelengths overlap the Fano resonances. In contrast, for SERS from carbon nanoparticles we find that the dielectric screening introduced by the nanoparticle can drastically redistribute the field enhancement associated with the Fano resonance and lead to a significantly modified SERS response compared to what would be anticipated from the bare nanocluster.
虽然 Fano 共振的远场性质是众所周知的，但等离子体纳米粒子簇也具有独特的空间复杂近场性质的 Fano 共振。在这里，我们使用表面增强拉曼散射 (SERS) 研究了单个 Fano 共振等离子体簇的近场性质，包括随机分布在结构上的分子和沉积在簇内特定位置的介电纳米粒子。簇的大小、形状和粒子间的间距都会改变 Fano 共振的近场性质。对于分子，从近场计算得到的空间相关 SERS 响应与单个簇和对苯硫酚吸附物的特定斯托克斯模式的相对 SERS 强度很好地相关。在所有情况下，当激发和斯托克斯位移波长都与 Fano 共振重叠时，SERS 增强最大。相比之下，对于来自碳纳米粒子的 SERS，我们发现纳米粒子的介电屏蔽可以极大地重新分配与 Fano 共振相关的场增强，并导致与从裸纳米团簇预期的相比，显著修改的 SERS 响应。
