Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
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DOI：
10.1021/acsnano.9b04530
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发表时间：
2019-08-01
期刊：
影响因子：
17.1
通讯作者：
Suenaga, Kazu
中科院分区：
文献类型：
--
作者：
Gogoi, Pranjal Kumar;Lin, Yung-Chang;Suenaga, Kazu
由货车德瓦耳斯（vdW）堆叠的过渡金属二硫属化物（TMDC）单层构成的异质结构是一类有趣的二维（2D）材料。层间激子的存在，其中电子和空穴由于超快电荷转移而在两层中保持空间分离，是这些异质结构的一个有趣的特征。2D异质结构器件的光电功能主要取决于层的相对旋转角度。然而，组成层的相对旋转角度对层内吸收的作用尚不清楚。在这里，我们调查MoS 2/WSe 2 VDW异质结单色低损耗电子能量损失（EEL）光谱结合像差校正扫描透射电子显微镜和报告，动量守恒是一个关键因素，在层内吸收TMDC VDW异质结。作为旋转角的函数的层内激子低损耗EEL光谱峰加宽的演变揭示了层间电荷转移速率在对准（或反对准）的情况下可以比在未对准的情况下快大约一个数量级。这些结果提供了一个更深入的了解动量守恒的作用，在2D VDW异质结构的电荷转移动力学的基本原则之一。
Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.