Measuring optical activity in the far-field from a racemic nanomaterial: diffraction spectroscopy from plasmonic nanogratings
Measuring optical activity in the far-field from a racemic nanomaterial: diffraction spectroscopy from plasmonic nanogratings
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DOI：
10.1039/c9nh00067d
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发表时间：
2019-09-01
影响因子：
9.7
通讯作者：
Valev, Ventsislav K.
中科院分区：
文献类型：
--
作者：
Kuppe, Christian;Zheng, Xuezhi;Valev, Ventsislav K.
纳米纤维的最新进展重新划定了手征光学（手征光学）效应适用性的界限。手性通常表示为生物分子中的扭曲，对药物至关重要，它可以导致极其不同的化学性质。由于手性效应在分子中通常非常弱，因此等离子体纳米材料通常被提议作为一种有前途的平台来显著增强这些效应。不幸的是，理想的等离子体纳米材料具有相互矛盾的要求：它的手性应该增强手性分子的手性，但它本身不应该有手性光学响应。在这里，我们提出了一个独特的和解，以满足要求：外消旋等离子体纳米材料，由等量的相反的手性晶胞。我们展示了如何衍射光谱可以用来揭示在远场的这种外消旋纳米光栅的手性的存在。我们的实验得到了数值模拟的支持，并产生了高达15%的圆形强度差。的物理起源证明了全波模拟结合绿色的功能群理论为基础的分析。排除了光电子角分布圆二色性（CDAD）和伪/非本征手性的贡献。我们的研究结果使外消旋纳米材料的远场测量和调谐成为可能，这对于超灵敏的手性分子表征至关重要。
Recent progress in nanofabrication has redrawn the boundaries of the applicability of chiroptical (chiral optical) effects. Chirality, often expressed as a twist in biomolecules, is crucial for pharmaceuticals, where it can result in extremely different chemical properties. Because chiroptical effects are typically very weak in molecules, plasmonic nanomaterials are often proposed as a promising platform to significantly enhance these effects. Unfortunately, the ideal plasmonic nanomaterial has conflicting requirements: its chirality should enhance that of the chiral molecules and yet it should have no chiroptical response on its own. Here, we propose a unique reconciliation to satisfy the requirements: a racemic plasmonic nanomaterial, consisting of equal amounts of opposite chiral unit cells. We show how diffraction spectroscopy can be used to unveil the presence of chirality in such racemic nanogratings in the far-field. Our experiments are supported by numerical simulations and yield a circular intensity difference of up to 15%. The physical origin is demonstrated by full wave simulations in combination with a Green's function -group-theory-based analysis. Contributions from Circular Dichroism in the Angular Distribution of Photoelectrons (CDAD) and pseudo/ extrinsic chirality are ruled out. Our findings enable the far-field measurement and tuning of racemic nanomaterials, which is crucial for hyper-sensitive chiral molecular characterization.