Department of Materials Science and Engineering, ‡Department of Electrical Engineering, and §Stanford Nanocharacterization Laboratory, Stanford University, Stanford, California 94305, United States.
Nano Lett. 2013 Sep 11;13(9):4137-41. doi: 10.1021/nl401642z. Epub 2013 Aug 13.
Advances in the field of metamaterials have enabled unprecedented control of light-matter interactions. Metamaterial constituents support high-frequency electric and magnetic dipoles, which can be used as building blocks for new materials capable of negative refraction, electromagnetic cloaking, strong visible-frequency circular dichroism, and enhancing magnetic or chiral transitions in ions and molecules. While all metamaterials to date have existed in the solid-state, considerable interest has emerged in designing a colloidal metamaterial or "metafluid". Such metafluids would combine the advantages of solution-based processing with facile integration into conventional optical components. Here we demonstrate the colloidal synthesis of an isotropic metafluid that exhibits a strong magnetic response at visible frequencies. Protein-antibody interactions are used to direct the solution-phase self-assembly of discrete metamolecules comprised of silver nanoparticles tightly packed around a single dielectric core. The electric and magnetic response of individual metamolecules and the bulk metamaterial solution are directly probed with optical scattering and spectroscopy. Effective medium calculations indicate that the bulk metamaterial exhibits a negative effective permeability and a negative refractive index at modest fill factors. This metafluid can be synthesized in large-quantity and high-quality and may accelerate development of advanced nanophotonic and metamaterial devices.
超材料领域的进展使得对光物质相互作用的控制达到了前所未有的水平。超材料的组成部分支持高频电偶极子和磁偶极子，它们可以用作构建新材料的基础，这些新材料能够实现负折射、电磁隐身、强可见光圆二色性以及增强离子和分子中的磁或手性跃迁。虽然迄今为止所有的超材料都存在于固态中，但人们对设计胶体超材料或“元流体”产生了浓厚的兴趣。这种元流体将结合基于溶液的处理的优势，以及易于集成到传统光学组件中。在这里，我们展示了各向同性元流体的胶体合成，该元流体在可见光频率下表现出很强的磁响应。蛋白质-抗体相互作用用于指导离散超分子在溶液相中自组装，这些超分子由紧密包裹在单个介电核周围的银纳米颗粒组成。单个超分子和整体超材料溶液的电和磁响应通过光学散射和光谱学直接探测。有效媒质计算表明，在适度的填充因子下，整体超材料表现出负有效磁导率和负折射率。这种元流体可以大量高质量地合成，并且可能会加速先进的纳米光子学和超材料器件的发展。
