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Optical versus electron diffraction imaging of Twist-angle in 2D transition metal dichalcogenide bilayers
npj 2D Materials and Applications ( IF 9.7 ) Pub Date : 2021-09-09 , DOI: 10.1038/s41699-021-00258-5
S. Psilodimitrakopoulos 1 , L. Mouchliadis 1, 2 , G. M. Maragkakis 1, 3 , G. Kourmoulakis 1, 2 , G. Kioseoglou 1, 2 , E. Stratakis 1, 3 , A. Orekhov 4, 5 , D. Jannis 4, 5 , N. Gauquelin 4, 5 , J. Verbeeck 4, 5
Affiliation  

Atomically thin two-dimensional (2D) materials can be vertically stacked with van der Waals bonds, which enable interlayer coupling. In the particular case of transition metal dichalcogenide (TMD) bilayers, the relative direction between the two monolayers, coined as twist-angle, modifies the crystal symmetry and creates a superlattice with exciting properties. Here, we demonstrate an all-optical method for pixel-by-pixel mapping of the twist-angle with a resolution of 0.55(°), via polarization-resolved second harmonic generation (P-SHG) microscopy and we compare it with four-dimensional scanning transmission electron microscopy (4D STEM). It is found that the twist-angle imaging of WS2 bilayers, using the P-SHG technique is in excellent agreement with that obtained using electron diffraction. The main advantages of the optical approach are that the characterization is performed on the same substrate that the device is created on and that it is three orders of magnitude faster than the 4D STEM. We envisage that the optical P-SHG imaging could become the gold standard for the quality examination of TMD superlattice-based devices.



中文翻译:

二维过渡金属二硫属化物双层中扭曲角的光学与电子衍射成像

原子级薄的二维 (2D) 材料可以通过范德华键垂直堆叠,从而实现层间耦合。在过渡金属二硫属化物 (TMD) 双层的特殊情况下,两个单层之间的相对方向(称为扭曲角)会改变晶体对称性并创建具有令人兴奋特性的超晶格。在这里,我们展示了一种通过偏振分辨二次谐波产生 (P-SHG) 显微镜以 0.55(°) 的分辨率对扭曲角进行逐像素映射的全光学方法,并将其与四三维扫描透射电子显微镜(4D STEM)。发现WS 2的扭曲角成像双层,使用 P-SHG 技术与使用电子衍射获得的非常一致。光学方法的主要优点是表征是在创建器件的同一衬底上进行的,并且比 4D STEM 快三个数量级。我们设想光学 P-SHG 成像可以成为基于 TMD 超晶格器件质量检查的黄金标准。

更新日期:2021-09-09
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