Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS2

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• 作者：Shengxi Huang ; Liangbo Liang ; Xi Ling ; Alexander A. Puretzky ; David B. Geohegan ; Bobby G. Sumpter ; Jing Kong ; Vincent Meunier ; Mildred S. Dresselhaus
• 刊名：Nano Letters
• 出版年：2016
• 出版时间：February 10, 2016
• 年：2016
• 卷：16
• 期：2
• 页码：1435-1444
• 全文大小：563K
• ISSN：1530-6992

文摘

van der Waals homo- and heterostructures assembled by stamping monolayers together present optoelectronic properties suitable for diverse applications. Understanding the details of the interlayer stacking and resulting coupling is crucial for tuning these properties. We investigated the low-frequency interlayer shear and breathing Raman modes (<50 cm<sup>–1sup>) in twisted bilayer MoS<sub>2sub> by Raman spectroscopy and first-principles modeling. Twisting significantly alters the interlayer stacking and coupling, leading to notable frequency and intensity changes of low-frequency modes. The frequency variation can be up to 8 cm<sup>–1sup> and the intensity can vary by a factor of ～5 for twisting angles near 0° and 60°, where the stacking is a mixture of high-symmetry stacking patterns and is thus sensitive to twisting. For twisting angles between 20° and 40°, the interlayer coupling is nearly constant because the stacking results in mismatched lattices over the entire sample. It follows that the Raman signature is relatively uniform. Note that for some samples, multiple breathing mode peaks appear, indicating nonuniform coupling across the interface. In contrast to the low-frequency interlayer modes, high-frequency intralayer Raman modes are much less sensitive to interlayer stacking and coupling. This research demonstrates the effectiveness of low-frequency Raman modes for probing the interfacial coupling and environment of twisted bilayer MoS<sub>2sub> and potentially other two-dimensional materials and heterostructures.