单层二硫化钼纳米带弛豫性能的分子动力学研究

Molecular dynamics study on relaxation properties of monolayer MoS_2 nanoribbons

采用分子动力学方法,基于REBO势函数研究了不同长宽比的单层二硫化钼纳米带在不同热力学温度(0.01—1600 K)条件下的弛豫性能.对弛豫过程中纳米带的能量变化和表面起伏程度进行了分析对比,研究了单层二硫化钼纳米带自由弛豫的动态平衡过程.仿真结果显示:理想温度(0.01 K)条件下,分子动能较低,振动振幅较小,并不足以使纳米带产生起伏现象;但在室温或高温条件下时,纳米带的边缘及内部均会出现一定程度的起伏;随着体系温度的升高以及纳米带长宽比的增加,起伏程度也会增大.最后,讨论了不同热力学温度条件下,手性对纳米带驰豫性能的影响.研究结果表明,不同于扶手椅型纳米带,锯齿型纳米带不仅会出现垂直于纳米带表面的起伏和弯曲,同时还会在纳米带面内出现明显的沿着宽度方向的弯曲现象.

In order to study the essential structural characteristics of monolayer MoS2 nanoribbons in natural state, and also the effects of the aspect ratio and the ambient temperature on the relaxation properties of the nanoribbons, the relaxation properties of monolayer MoS2 nanoribbons with different aspect ratios are simulated by molecular dynamics （MD） method based on REBO potential functions at different thermodynamic temperatures from 0.01 K to 1500 K. The energy curves and surface morphologies of monolayer MoS2 nanoribbon are obtained, and the dynamic equilibrium process of the monolayer MoS2 nanoribbons is also discussed in all the simulation process. The simulation results show that the monolayer MoS2 nanoribbons do not generate a fluctuation at the ideal temperature （0.01 K） for the reason that the kinetic energy of the monolayer MoS2 nanoribbons is almost zero and the vibration amplitude is small. However, a certain degree of fluctuations occurs at the edges and inside of the monolayer MoS2 nanoribbons at the room temperature or high temperature. The fluctuation height and the fluctuation degree also increase with increasing the ambient temperature and the aspect ratio of the MoS2 nanoribbon, even a high aspect ratio monolayer MoS2 nanoribbon exhibits a surface curved fluctuation, which is perpendicular to the surface of the MoS2 nanoribbons under high temperature condition. Finally, the influences of chirality on relaxation property under different temperature conditions are studied in this paper further, the results show that unlike the armchair structure, the zigzag monolayer MoS2 nanoribbons not only present a surface fluctuation, but also exhibit an obvious bending phenomenon along the width direction simultaneously. Like the armchair nanoribbons, the surface fluctuation height and the surface fluctuation degree of the zigzag nanoribbons also increase with increasing both the ambient temperature and the aspect ratio of the MoS2 nanoribbons. It is also observed that the armchair and zigzag monolayer MoS2 nanoribbons with a similar aspect ratio have a similar surface fluctuation degree at the same ambient temperature. Unlike the armchair nanoribbons, the bending phenomenon along the width direction of the zigzag nanoribbons is more significant, and the bending width and the bending degree increase with increasing the ambient temperature and the aspect ratio of the MoS2 nanoribbons. Although the bending degree of the zigzag nanoribbons becomes larger with the increase of temperature, the increasing rate of the bending degree will become smaller and smaller until the bending degree reaches a maximum value.