Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, China.
ACS Nano. 2017 Oct 24;11(10):10366-10372. doi: 10.1021/acsnano.7b05321. Epub 2017 Oct 13.
The Raman tensor of a crystal is the derivative of its polarizability tensor and is dependent on the symmetries of the crystal and the Raman-active vibrational mode. The intensity of a particular mode is determined by the Raman selection rule, which involves the Raman tensor and the polarization configurations. For anisotropic two-dimensional (2D) layered crystals, polarized Raman scattering has been used to reveal the crystalline orientations. However, due to its complicated Raman tensors and optical birefringence, the polarized Raman scattering of triclinic 2D crystals has not been well studied yet. Herein, we report the anomalous polarized Raman scattering of 2D layered triclinic rhenium disulfide (ReS) and show a large circular intensity differential (CID) of Raman scattering in ReS of different thicknesses. The origin of CID and the anomalous behavior in polarized Raman scattering were attributed to the appearance of nonzero off-diagonal Raman tensor elements and the phase factor owing to optical birefringence. This can provide a method to identify the vertical orientation of triclinic layered materials. These findings may help to further understand the Raman scattering process in 2D materials of low symmetry and may indicate important applications in chiral recognition by using 2D materials.
晶体的拉曼张量是极化率张量的导数，取决于晶体的对称性和拉曼活性振动模式。特定模式的强度由拉曼选择定则决定，该定则涉及拉曼张量和偏振配置。对于各向异性二维（2D）层状晶体，偏振拉曼散射已被用于揭示晶体取向。然而，由于其复杂的拉曼张量和光学双折射，三方 2D 晶体的偏振拉曼散射尚未得到很好的研究。在此，我们报告了二维层状三方二硫化铼（ReS）的异常偏振拉曼散射，并展示了不同厚度 ReS 中拉曼散射的大圆形强度差（CID）。CID 的起源和偏振拉曼散射中的异常行为归因于非零对角拉曼张量元素和由于光学双折射出现的相位因子。这可以提供一种识别三方层状材料垂直取向的方法。这些发现可能有助于进一步理解低对称性 2D 材料中的拉曼散射过程，并可能表明在使用 2D 材料进行手性识别方面的重要应用。
