Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea.
Nano Lett. 2020 Nov 11;20(11):8096-8101. doi: 10.1021/acs.nanolett.0c03089. Epub 2020 Oct 15.
Optical metamaterials, engineered to exhibit electromagnetic properties not found in natural materials, may enable new light-based applications including cloaking and optical computing. While there have been significant advances in the fabrication of two-dimensional metasurfaces, planar structures create nontrivial angular and polarization sensitivities, making omnidirectional operation impossible. Although three-dimensional (3D) metamaterials have been proposed, their fabrication remains challenging. Here, we use colloidal crystal engineering with DNA to prepare isotropic 3D metacrystals from Au nanocubes. We show that such structures can exhibit refractive indices as large as ∼8 in the mid-infrared, far greater than that of common high-index dielectrics. Additionally, we report the first observation of multipolar Mie resonances in metacrystals with well-formed habits, occurring in the mid-infrared for submicrometer metacrystals, which we measured using synchrotron infrared microspectroscopy. Finally, we predict that arrays of metacrystals could exhibit negative refraction. The results present a promising platform for engineering devices with unnatural optical properties.
光学超材料经过设计可具有自然界材料所不具备的电磁特性，有望催生包括隐身和光计算等新的基于光的应用。虽然二维超表面的制造已经取得了重大进展，但平面结构会产生非平凡的角度和偏振灵敏度，使得全方位运作成为不可能。虽然已经提出了三维（3D）超材料，但它们的制造仍然具有挑战性。在这里，我们使用胶体晶体工程和 DNA 从 Au 纳米立方体制备各向同性的 3D 金属晶体。我们表明，这种结构在中红外波段的折射率可高达约 8，远大于常见的高折射率电介质。此外，我们报告了在具有良好形态的金属晶体中首次观察到多极 Mie 共振，对于亚微米金属晶体，这些共振出现在中红外波段，我们使用同步辐射红外微光谱进行了测量。最后，我们预测金属晶体阵列可能会表现出负折射。这些结果为具有非自然光学特性的器件工程提供了一个很有前景的平台。
