Department of Chemistry and The Photonics Center, Boston University, Boston, Massachusetts 02215, USA.
ACS Nano. 2012 Jan 24;6(1):951-60. doi: 10.1021/nn204577v. Epub 2011 Dec 19.
We investigate photonic-plasmonic mode coupling in a new class of optoplasmonic materials that comprise dielectric microspheres and noble metal nanostructures in a morphologically well-defined on-chip platform. Discrete networks of optoplasmonic elements, referred to as optoplasmonic molecules, were generated through a combination of top-down fabrication and template-guided self-assembly. This approach facilitated a precise and controllable vertical and horizontal positioning of the plasmonic elements relative to the whispering gallery mode (WGM) microspheres. The plasmonic nanostructures were positioned in or close to the equatorial plane of the dielectric microspheres where the fields associated with the plasmonic modes can synergistically interact with the evanescent fields of the WGMs. We characterized the far-field scattering spectra of discrete optoplasmonic molecules that comprised two coupled 2.048 μm diameter polystyrene microspheres each encircled by four 148 nm diameter Au nanoparticles (NPs), through far-field scattering spectroscopy. We observed a broadening of the TE and TM modes in the scattering spectra of the optoplasmonic dimers indicative of an efficient photonic-plasmonic mode coupling between the coupled photonic modes of the WGM resonators and the localized surface plasmon modes of the NPs. Our experimental findings are supported by generalized multiple particle Mie theory simulations, which provide additional information about the spatial distributions of the near fields associated with the photonic-plasmonic hybrid modes in the investigated optoplasmonic molecules. The simulations reveal partial localization of the spectrally sharp hybrid modes outside of the WGM microspheres on the Au NPs where the local E-field intensity is enhanced by approximately 2 orders of magnitude over that of an individual Au NP.
我们研究了一类新的光等离子体材料中的光子-等离子体模式耦合，这类材料由介电微球和贵金属纳米结构组成，位于形态上定义明确的片上平台中。通过自上而下的制造和模板引导的自组装相结合，产生了离散的光等离子体元件网络，称为光等离子体分子。这种方法便于相对 whispering gallery 模式（WGM）微球精确和可控地垂直和水平定位等离子体元件。等离子体纳米结构被定位在介电微球的赤道平面内或附近，其中与等离子体模式相关的场可以与 WGM 的消逝场协同相互作用。我们通过远场散射光谱学，对包含两个耦合的 2.048μm 直径聚苯乙烯微球的离散光等离子体分子的远场散射光谱进行了表征，每个微球都被四个 148nm 直径的 Au 纳米粒子（NPs）包围。我们观察到光等离子体二聚体散射光谱中 TE 和 TM 模式的展宽，表明 WGM 谐振器的耦合光子模式和 NPs 的局域表面等离子体模式之间存在有效的光子-等离子体模式耦合。我们的实验结果得到了广义多粒子 Mie 理论模拟的支持，该模拟提供了有关在研究的光等离子体分子中与光等离子体混合模式相关的近场空间分布的附加信息。模拟揭示了混合模式的部分局域化，其位于 WGM 微球外部的 Au NPs 上，局部 E 场强度比单个 Au NP 增强了约 2 个数量级。
