Chirality (C) is a fundamental property of objects, in terms of symmetry. It is extremely important to sense and distinguish chiral molecules in the fields of biochemistry, science, and medicine. Vibrational circular dichroism (VCD) spectroscopy, obtained from the differential absorption of left- and right- circularly polarized light (CPL) in the infrared range, is a promising technique for enantiomeric detection and separation. However, VCD signals are typically very weak for most small molecules. Dielectric metasurfaces are an emerging platform to enhance the sensitivity of VCD spectroscopy of chiral molecules via superchiral field manipulation. Here, we demonstrate a dielectric metasurface consisting of achiral germanium (Ge) tetramer nanoresonators that provide a proper and accessible high C enhancement (C_E). We realize a maximum C enhancement (C_{E_max}) with respect to the incident CPL (C_{E_max} = C_max/C_RCP) of more than 750. The volume-averaged C enhancement (C_{E_ave} = C_ave/C_RCP) is 148 in the 50 nm thick region above the sample surface and 215 in the central region of the structure. Especially, the corresponding C_{E_ave} values are more than 89 and 183 even when a 50 nm thick chiral lossy molecular layer is coated on the metasurface. The metasurface benefits from geometrically achiral nanostructure design to eliminate intrinsic background chiral-optical signal from the substrate, which is useful in chiral sensing, enantioselectivity, and VCD spectroscopy applications in the mid-infrared range.

中文翻译：

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支持振动圆二色光谱强超手性场的介电四聚体纳米谐振器


就对称性而言，手性 ( C ) 是物体的基本属性。感知和区分手性分子在生物化学、科学和医学领域极其重要。振动圆二色性 (VCD) 光谱是通过红外范围内左旋和右旋圆偏振光 (CPL) 的差异吸收获得的，是一种有前途的对映体检测和分离技术。然而，对于大多数小分子来说，VCD 信号通常非常弱。介电超表面是一个新兴平台，可通过超手性场操纵来增强手性分子 VCD 光谱的灵敏度。在这里，我们展示了一种由非手性锗 (Ge) 四聚体纳米谐振器组成的介电超_表面，可提供适当且可实现的高C增强 ( CE )。我们实现了相对于入射 CPL ( C _{E_max} = C _max /C _RCP ) 的最大C增强 ( C _{E_max} ) 超过 750。体积平均C增强 ( C _{E_ave} = C _ave /C _RCP ) 为 148样品表面上方 50 nm 厚的区域和结构中心区域的 215 nm 厚的区域。特别是，即使在超表面上涂覆50 nm厚的手性有损分子层，相应的C _{E_ave}值也大于89和183。 超表面受益于几何非手性纳米结构设计，可消除基底的固有背景手性光学信号，这在中红外范围内的手性传感、对映选择性和 VCD 光谱应用中非常有用。