Lu Yang, Chen Jun, Coupin Matthew J, Sinha Sapna, Warner Jamie H
Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
Material Sciences and Engineering Program, Texas Materials Institute, The University of Texas at Austin, Austin, Texas, 78712, USA.
Adv Mater. 2022 Oct;34(43):e2205403. doi: 10.1002/adma.202205403. Epub 2022 Sep 25.
Artificially introduced small twist angles at the interfaces of vertical layered heterostructures (VLHs) have allowed deterministic tuning of electronic and optical properties such as strongly correlated electronic phases and Moiré excitons. But creating a Moiré twist in van der Waals (vdWs) systems by manual stacking is challenging in reproducibility, uniformity, and accuracy of the twist angle, which hinders future studies. Here, it is demonstrated that contrary to the commonly believed 0°-orientation in vdWs epitaxy, these VLHs show small twist angles controlled by the low-order commensurate phase with low energy and local atomic relaxation. A commensurate multilevel map is proposed to predict possible orientations. Remarkably, high-mismatch VLHs show discrete and sometimes non-zero twist angles dependent on their natural mismatch value. Such framework is experimentally confirmed in five epitaxially grown VLHs under high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and can provide significant insights for large-scale engineering of twist angle in VLHs.
在垂直层状异质结构（VLHs）的界面处人工引入小的扭转角，可以对电子和光学性质进行确定性调控，如强关联电子相和莫尔激子。但是，通过手动堆叠在范德华（vdW）系统中创建莫尔扭转，在扭转角的可重复性、均匀性和准确性方面具有挑战性，这阻碍了未来的研究。在此，研究表明，与vdW外延中通常认为的0°取向相反，这些VLHs显示出由低能量和局部原子弛豫的低阶共格相控制的小扭转角。提出了一个共格多级图来预测可能的取向。值得注意的是，高失配的VLHs显示出离散的、有时非零的扭转角，这取决于它们的自然失配值。这种框架在高角度环形暗场扫描透射电子显微镜（HAADF-STEM）下对五个外延生长的VLHs进行了实验验证，并可为VLHs中扭转角的大规模工程提供重要见解。
