Unified Description of the Optical Phonon Modes in N-Layer MoTe2

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• 作者：Guillaume Froehlicher ; Etienne Lorchat ; Fran莽ois Fernique ; Chaitanya Joshi ; Alejandro Molina-S谩nchez ; Ludger Wirtz ; St茅phane Berciaud
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：October 14, 2015
• 年：2015
• 卷：15
• 期：10
• 页码：6481-6489
• 全文大小：781K
• ISSN：1530-6992

文摘

N-layer transition metal dichalcogenides provide a unique platform to investigate the evolution of the physical properties between the bulk (three-dimensional) and monolayer (quasi-two-dimensional) limits. Here, using high-resolution micro-Raman spectroscopy, we report a unified experimental description of the 螕-point optical phonons in N-layer 2H-molybdenum ditelluride (MoTe₂). We observe series of N-dependent low-frequency interlayer shear and breathing modes (below 40 cm^鈥?, denoted LSM and LBM) and well-defined Davydov splittings of the mid-frequency modes (in the range 100鈥?00 cm^鈥?, denoted iX and oX), which solely involve displacements of the chalcogen atoms. In contrast, the high-frequency modes (in the range 200鈥?00 cm^鈥?, denoted iMX and oMX), arising from displacements of both the metal and chalcogen atoms, exhibit considerably reduced splittings. The manifold of phonon modes associated with the in-plane and out-of-plane displacements are quantitatively described by a force constant model, including interactions up to the second nearest neighbor and surface effects as fitting parameters. The splittings for the iX and oX modes observed in N-layer crystals are directly correlated to the corresponding bulk Davydov splittings between the E_2u/E_1g and B_1u/A_1g modes, respectively, and provide a measurement of the frequencies of the bulk silent E_2u and B_1u optical phonon modes. Our analysis could readily be generalized to other layered crystals.