Layer-number dependent high-frequency vibration modes in few....

Two-dimensional transition metal dichalcogenides (TMDs) have attracted extensive attention due to their many novel properties. The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds, while van der Waals interactions combine the layers together. This makes its lattice dynamics layer-number dependent. The evolutions of ultralow frequency (<50 cm^-1) modes, such as shear and layer-breathing modes have been well-established. Here, we review the layer-number dependent high-frequency (>50 cm^-1) vibration modes in few-layer TMDs and demonstrate how the interlayer coupling leads to the splitting of high-frequency vibration modes, known as Davydov splitting. Such Davydov splitting can be well described by a van der Waals model, which directly links the splitting with the interlayer coupling. Our review expands the understanding on the effect of interlayer coupling on the high-frequency vibration modes in TMDs and other two-dimensional materials.

通信作者：谭平恒，中国科学院半导体研究所，Email：[e-mail]

Cite this article：Qing-Hai Tan, Xin Zhang, Xiang-Dong Luo, Jun Zhang and Ping-Heng Tan. Layer-number dependent high-frequency vibration modes in few-layer transition metal dichalcogenides induced by interlayer couplings. Journal of Semiconductors, 2017, 38(3): 031006

Fig. 3. (a) Atomic displacements of LB and A₁^'-like modes in 4L MX₂^[]. (b) The experimental (Exp) frequency (solid red circles) and the calculated one based on the vdW model for the A₁^'-like modes in 1-6L MoTe₂ flakes^[]. (c) The experimental (Exp) frequency (solid red circles) and the calculated one based on the vdW model for the A₁^'-like modes in 1-6L MoSe₂ flakes^[]. The solid line is a guide for the eye.

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