NanoBiophotonics Group, Institute of Physics, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149, Münster, Germany.
Organic Chemistry Institute, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149, Münster, Germany.
Small. 2016 Mar 23;12(12):1667-75. doi: 10.1002/smll.201503536. Epub 2016 Feb 5.
Coupling of plasmon resonances in metallic gap antennas is of interest for a wide range of applications due to the highly localized strong electric fields supported by these structures, and their high sensitivity to alterations of their structure, geometry, and environment. Morphological alterations of asymmetric nanoparticle dimer antennas with (sub)-nanometer size gaps are assigned to changes of their optical response in correlative dark-field spectroscopy and high-resolution transmission electron microscopy (HR-TEM) investigations. This multimodal approach to investigate individual dimer structures clearly demonstrates that the coupling of the plasmon modes, in addition to well-known parameters such as the particle geometry and the gap size, is also affected by the relative alignment of both nanoparticles. The investigations corroborate that the alignment of the gap forming facets, and with that the gap area, is crucial for their scattering properties. The impact of a flat versus a rounded gap structure on the optical properties of equivalent dimers becomes stronger with decreasing gap size. These results hint at a higher confinement of the electric field in the gap and possibly a different onset of quantum transport effects for flat and rounded gap antennas in corresponding structures for very narrow gaps.
金属间隙天线中等离子体共振的耦合由于这些结构所支持的高度局域强电场及其对结构、几何形状和环境变化的高灵敏度，在广泛的应用中引起了关注。具有（亚）纳米级间隙的不对称纳米粒子二聚体天线的形态改变归因于它们在相关暗场光谱学和高分辨率透射电子显微镜 (HR-TEM) 研究中的光学响应变化。这种对单个二聚体结构进行多模态研究的方法清楚地表明，除了众所周知的参数（如粒子几何形状和间隙大小）之外，等离子体模式的耦合还受到两个纳米粒子相对取向的影响。研究证实，形成间隙的面的取向以及由此产生的间隙面积对于它们的散射特性至关重要。对于等效二聚体，与圆形间隙结构相比，平坦间隙结构对光学性质的影响更强。这些结果表明，在相应的非常窄间隙结构中，对于平坦和圆形间隙天线，电场的限制更高，并且可能出现不同的量子输运效应的起始。
