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Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
ACS Nano ( IF 15.8 ) Pub Date : 2019-07-25 00:00:00 , DOI: 10.1021/acsnano.9b04530 Pranjal Kumar Gogoi 1 , Yung-Chang Lin 1 , Ryosuke Senga 1 , Hannu-Pekka Komsa 2 , Swee Liang Wong 3 , Dongzhi Chi 3 , Arkady V. Krasheninnikov 2, 4 , Lain-Jong Li 5 , Mark B. H. Breese 6, 7 , Stephen J. Pennycook 8 , Andrew T. S. Wee 6 , Kazu Suenaga 1
ACS Nano ( IF 15.8 ) Pub Date : 2019-07-25 00:00:00 , DOI: 10.1021/acsnano.9b04530 Pranjal Kumar Gogoi 1 , Yung-Chang Lin 1 , Ryosuke Senga 1 , Hannu-Pekka Komsa 2 , Swee Liang Wong 3 , Dongzhi Chi 3 , Arkady V. Krasheninnikov 2, 4 , Lain-Jong Li 5 , Mark B. H. Breese 6, 7 , Stephen J. Pennycook 8 , Andrew T. S. Wee 6 , Kazu Suenaga 1
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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.
中文翻译：
电子能量损失谱揭示的范德华异质结构中层旋转角依赖的激子吸收
包含范德华（vdW）堆叠的过渡金属二卤化硅（TMDC）单层的异质结构是一类引人入胜的二维（2D）材料。这些异质结构的一个吸引人的特征是层间激子的存在，其中电子和空穴由于超快的电荷转移而在两层中保持空间分隔。2D异质结构器件的光电功能严格取决于层的相对旋转角度。但是，构成层的相对旋转角对层内吸收的作用尚不清楚。在这里，我们研究MoS 2 / WSe 2使用单色低损耗电子能量损失（EEL）光谱结合像差校正的扫描透射电子显微镜观察vdW异质结构，并发现动量守恒是TMDC vdW异质结构层内吸收的关键因素。层内激子低损耗EEL谱峰展宽随旋转角的变化表明，在对准（或反对准）的情况下，层间电荷转移速率比未对准的情况快约一个数量级。 。这些结果使人们对动量守恒的作用有了更深入的了解，动量守恒是控制二维vdW异质结构中电荷转移动力学的基本原理之一。
更新日期：2019-07-25
中文翻译：
电子能量损失谱揭示的范德华异质结构中层旋转角依赖的激子吸收
包含范德华（vdW）堆叠的过渡金属二卤化硅（TMDC）单层的异质结构是一类引人入胜的二维（2D）材料。这些异质结构的一个吸引人的特征是层间激子的存在，其中电子和空穴由于超快的电荷转移而在两层中保持空间分隔。2D异质结构器件的光电功能严格取决于层的相对旋转角度。但是，构成层的相对旋转角对层内吸收的作用尚不清楚。在这里，我们研究MoS 2 / WSe 2使用单色低损耗电子能量损失（EEL）光谱结合像差校正的扫描透射电子显微镜观察vdW异质结构，并发现动量守恒是TMDC vdW异质结构层内吸收的关键因素。层内激子低损耗EEL谱峰展宽随旋转角的变化表明，在对准（或反对准）的情况下，层间电荷转移速率比未对准的情况快约一个数量级。 。这些结果使人们对动量守恒的作用有了更深入的了解，动量守恒是控制二维vdW异质结构中电荷转移动力学的基本原理之一。
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