Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations

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• 作者：Alexander A. Puretzky ; Liangbo Liang ; Xufan Li ; Kai Xiao ; Kai Wang ; Masoud Mahjouri-Samani ; Leonardo Basile ; Juan Carlos Idrobo ; Bobby G. Sumpter ; Vincent Meunier ; David B. Geohegan
• 刊名：ACS Nano
• 出版年：2015
• 出版时间：June 23, 2015
• 年：2015
• 卷：9
• 期：6
• 页码：6333-6342
• 全文大小：575K
• ISSN：1936-086X

文摘

The tunable optoelectronic properties of stacked two-dimensional (2D) crystal monolayers are determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks; however, fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe₂ and WSe₂ crystals synthesized by chemical vapor deposition, we show that the generally unexplored low frequency (LF) Raman modes (<50 cm^鈥?) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.