Directional Scattering in a Germanium Nanosphere in the Visible Light Region
Directional Scattering in a Germanium Nanosphere in the Visible Light Region
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DOI：
10.1002/adom.201700761
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发表时间：
2017-12-15
影响因子：
9
通讯作者：
Yang, Guowei
中科院分区：
文献类型：
--
作者：
Ma, Churong;Yan, Jiahao;Yang, Guowei
以往设计的光子纳米天线都是基于贵金属等离子体结构，其欧姆损耗大且仅具有偶极等离子体模式。这推动了对贵金属以外的全介电材料（adm）的强烈探索。本文首次证明了锗纳米球在可见光和近红外区域具有很强的散射各向异性。单个锗纳米球（150 nm）的前后散射比在理论上可以达到接近20的最大值，在实验上可以达到接近8的最大值。这种散射行为源于锗折射率特殊的实部和虚部。与其他高折射率的ADMs（如Si和GaAs）不同，由于折射率的虚部不可忽略，Ge纳米球的电偶极子和磁偶极子共振在光谱上更接近彼此。电偶极子和磁偶极子共振的频谱重叠使得锗纳米球在散射峰附近具有高效的定向散射。在锗纳米球二聚体中观察到具有强指向性的范诺共振，这是宽电隙模式与杂化磁模式耦合的结果。这些发现使锗纳米球成为纳米天线、定向源和光开关的有希望的候选者。
Previous designs of photonic nanoantennas are based on noble metal plasmonic structures, suffering from large ohmic loss and only possessing dipolar plasmon modes. This has driven the intense search for all-dielectric materials (ADMs) beyond noble metals. Here, for the first time, a strong scattering anisotropy in a Ge nanosphere is demonstrated in the visible and near-infrared regions. The forward-to-backward scattering ratio for an individual Ge nanosphere (150 nm) can reach a maximum value of approximate to 20 theoretically and approximate to 8 experimentally. This scattering behavior derives from the special real part and imaginary part of refractive index of Ge. Differing form other high-index ADMs such as Si and GaAs, the electric dipole and magnetic dipole resonances of Ge nanospheres are closer to each other in the spectrum due to the non-negligible imaginary part of refractive index. The spectral overlap between electric dipole and magnetic dipole resonances endows Ge nanospheres with efficient directional scattering near the scattering peak. Fano resonances with strong directivity are observed in Ge nanosphere dimers, which is the result of a broad electric gap mode coupled with a hybrid magnetic mode. These findings make Ge nanospheres a promising candidate for nanoantennas, directional sources, and optical switches.