Unified Description of the Optical Phonon Modes in N-Layer MoTe2
Unified Description of the Optical Phonon Modes in N-Layer MoTe2
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DOI：
10.1021/acs.nanolett.5b02683
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发表时间：
2015-10-01
期刊：
影响因子：
10.8
通讯作者：
Berciaud, Stephane
中科院分区：
文献类型：
--
作者：
Froehlicher, Guillaume;Lorchat, Etienne;Berciaud, Stephane
n层过渡金属二硫化物提供了一个独特的平台来研究体（三维）和单层（准二维）极限之间物理性质的演变。在这里，我们使用高分辨率微罗曼光谱，报告了n层2h -二碲化钼（MoTe2）中f点光学声子的统一实验描述。我们观察到一系列与n相关的低频层间剪切和呼吸模式（低于40 cm(-1)，记为LSM和LBM）和中频模式（在100-200 cm（-1）范围内，记为iX和oX）的明确Davydov分裂，这些模式仅涉及硫原子的位移。相比之下，由金属和硫原子的位移引起的高频模式（在200-300 cm（-1）范围内，表示为iMX和oMX）表现出明显减少的分裂。声子模式的流形与面内和面外位移相关，通过力常数模型定量描述，包括到第二近邻的相互作用和表面效应作为拟合参数。在n层晶体中观察到的iX和oX模式的分裂分别与E-2u/E-1g和B-1u/A（1g）模式之间相应的体Davydov分裂直接相关，并提供了体沉默E-2u和B-1u光学声子模式频率的测量。我们的分析可以很容易地推广到其他层状晶体。
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 microRaman spectroscopy, we report a unified experimental description of the F-point optical phonons in N-layer 2H-molybdenum ditelluride (MoTe2). We observe series of N-dependent lowfrequency interlayer shear and breathing modes (below 40 cm(-1), denoted LSM and LBM) and well-defined Davydov splittings of the mid-frequency modes (in the range 100-200 cm(-1), denoted iX and oX), which solely involve displacements of the chalcogen atoms. In contrast, the high-frequency modes (in the range 200-300 cm(-1), 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.