Department of Physics, The Chinese University of Hong Kong , Shatin, Hong Kong SAR China.
Department of Electronic Engineering, The Chinese University of Hong Kong , Shatin, Hong Kong SAR China.
ACS Nano. 2018 Feb 27;12(2):1720-1731. doi: 10.1021/acsnano.7b08423. Epub 2018 Feb 8.
Directional optical nanoantennas are often realized by nanostructured systems with ingenious or complex designs. Herein we report on the realization of directional scattering of visible light from a simple configuration made of single Ag nanorods supported on Si substrates, where the incident light can be routed toward the two flanks of each nanorod. Such an intriguing far-field scattering behavior, which has not been investigated so far, is proved to result from the near-field coupling between high-aspect-ratio Ag nanorods and high-refractive-index Si substrates. A simple and intuitive model is proposed, where the complicated plasmon resonance is found to be equivalent to several vertically aligned electric dipoles oscillating in phase, to understand the far-field properties of the system. The interference among the electric dipoles results in wavefront reshaping and sidewise light routing in a similar manner to the broadside antenna described in the traditional antenna theory, allowing for the naming of these Si-supported Ag nanorods as "broadside nanoantennas". We have carried out comprehensive experiments to understand the physical origins behind and the affecting factors on the directional scattering behavior of such broadside nanoantennas.
定向光学纳米天线通常通过具有巧妙或复杂设计的纳米结构系统来实现。在这里，我们报告了一种简单配置的可见光定向散射的实现，该配置由支撑在 Si 衬底上的单个 Ag 纳米棒组成，其中入射光可以被引导到每个纳米棒的两个侧翼。这种有趣的远场散射行为迄今尚未得到研究，被证明是由于高纵横比 Ag 纳米棒和高折射率 Si 衬底之间的近场耦合引起的。提出了一个简单直观的模型，其中复杂的等离子体共振被发现等效于几个垂直排列的电偶极子以相同的相位振荡，以理解系统的远场特性。电偶极子之间的干涉导致波前整形和侧向光路由，类似于传统天线理论中描述的宽边天线，因此可以将这些 Si 支撑的 Ag 纳米棒命名为“宽边纳米天线”。我们进行了全面的实验，以了解这种宽边纳米天线的定向散射行为背后的物理起源和影响因素。
