Beckman Institute, University of Illinois, 405 North Mathews Avenue, Urbana, Illinois 61801, United States.
Nano Lett. 2012 Jun 13;12(6):2817-21. doi: 10.1021/nl300160y. Epub 2012 May 2.
The spectroscopic characterization of individual nanostructures is of fundamental importance to understanding a broad range of physical and chemical processes. One general and powerful technique that addresses this aim is dark-field microscopy, with which the scattered light from an individual structure can be analyzed with minimal background noise. We present the spectroscopic analysis of individual plasmonic nanostructures using dark-field illumination with incidence nearly normal to the substrate. We show that, compared to large incidence angle approaches, the near-normal incidence approach provides significantly higher signal-to-background ratios and reduced retardation field effects. To demonstrate the utility of this technique, we characterize an individual chemically synthesized gold nanoshell and a lithographically defined heptamer exhibiting a pronounced Fano-like resonance. We show that the line shape of the latter strongly depends on the incidence angle. Near-normal incidence dark-field microscopy can be used to characterize a broad range of molecules and nanostructures and can be adapted to most microscopy setups.
对单个纳米结构的光谱特性进行描述对于理解广泛的物理和化学过程至关重要。一种通用且强大的技术可以实现这一目标，即暗场显微镜，通过该技术可以最小化背景噪声来分析单个结构的散射光。我们使用几乎垂直于基底的暗场照明来进行单个等离子体纳米结构的光谱分析。我们表明，与大入射角方法相比，近垂直入射方法提供了高得多的信号与背景比，并减少了延迟场效应。为了展示该技术的实用性，我们对单个化学合成的金纳米壳和一个具有明显类福照共振的光刻定义的七聚体进行了特征描述。我们表明，后者的线形状强烈依赖于入射角。近垂直入射暗场显微镜可用于对广泛的分子和纳米结构进行特征描述，并且可以适应大多数显微镜设置。
