Abstract:

Monolayer Janus transition metal disulfides have low dimension, high mobility, and peculiar electronic structure properties, which have potential applications in electronics and optoelectronic devices. In devices made of monolayer Janus transition metal disulfide and substrate materials,are usually stressed due to lattice mismatch between monolayer Janus transition metal disulfides and substrate, it is significant to study the strain effect on physical properties of monolayer Janus transition metal disulfides through Raman scattering.This paper systematically investigate the biaxial strain effect on the atomic structure, electronic structure and Raman spectra of monolayer Janus MoSSe. The results show that monolayer Janus MoSSe can exhibit a band gap transition from direct to indirect one under biaxial strain, due to both the energy shift of bonding orbitals between the top of the valence band and the bottom of the conduction band and the sensitivity to strain. This paper also thoroughly study the strain effect on the Raman shift and intensity of monolayer Janus MoSSe. It is found that under biaxial strain modulation from decreasing compressive to increasing tensile, for the Raman shift, the three peaks of E¹, E², and A{}_{\mathrm{1}}^{\mathrm{1}} red?shift, while the peak of A{}_{\mathrm{1}}^{\mathrm{2}} blue?shifts abnormally with decreasing compressive strain; for the intensity, the peak intensity of the doubly?degenerate modes (E¹,E²) increases monotonically, while singly?degenerate modes shows the opposite trend, except for the A{}_{\mathrm{1}}^{\mathrm{1}} which intensity decreases with decreasing compressive strain and then increases with tensile strain. This paper propose a simple model to comprehend the strain effect. This theoretical study may supply an effective means to quickly and quantitatively characterize the strain size and type in Janus materials through the frequency difference and intensity ratio between typical Raman peaks.

Key words: Biaxial strain, Raman spectroscopy, Janus monolayer, Strain characterization

摘要：

单层双面神结构过渡金属硫化物具有低维度、高迁移率以及奇特的电子结构性质，因此其在电子学和光电子学器件方面具有潜在的应用前景。由单层双面神结构过渡金属硫化物和基底材料制成的器件，很容易因基底材料和单层双面神结构过渡金属硫化物的晶格失配，导致单层双面神结构过渡金属硫化物受基底材料的应力，因此通过拉曼散射系统研究双轴应变对单层双面神结构MoSSe物性的影响具有重要意义。系统研究了双轴调控下单层双面神结构MoSSe的原子结构、电子结构、声子结构和拉曼散射特性。结果表明，在双轴应变调控下，单层双面神结构MoSSe的电子能带带隙出现了直接与间接的转换；随着压应变的减小和拉应变的增加，3个拉曼特征峰（E¹、E²、A{}_{\mathrm{1}}^{\mathrm{1}}）的频率都发生了单调红移，而A{}_{\mathrm{1}}^{\mathrm{2}}的拉曼特征峰在压应变减小的过程中出现了反常的蓝移；随着压应变的减小和拉应变的增加，双重简并模式（E¹、E²）的拉曼强度单调增加，单重简并模式的拉曼强度单调减小，而A{}_{\mathrm{1}}^{\mathrm{1}}的拉曼强度先减小再增加。针对这些具有普遍性和特殊性的应变效应，通过建模进行了研究。结果表明，基于特征峰频率和强度随应变的变化差异，可以通过特征峰之间的频率差和强度比，快速定量化双面神结构材料的应变类型和大小。

关键词: 双轴应变, 拉曼光谱, 单层双面神结构, 应力表征