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    陆海林, 段芳莉

    Motion behavior of graphene sheets and friction characteristics between the interfaces of silicon-based materials

    Lu Hai-Lin, Duan Fang-Li
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    • 应用从头算分子动力学方法, 模拟了在挤压剪切作用下石墨烯片层作为润滑剂添加于硅基材料界面的摩擦过程, 研究了水分子和石墨烯表面氧化对石墨烯片层运动行为的影响. 干燥环境下, 压强较大时单纯石墨烯片层才会出现滑移, 而氧化石墨烯片层在低压强下就开始滑移. 潮湿环境下, 界面结构影响水分子的整体分布和运动状态, 而水分子的运动状态又影响氧化石墨烯片层的运动行为. 由于二氧化硅表面羟基取向角较大, 使得水分子在挤压剪切作用下偶极矩角变大, 从而导致其与氧化石墨烯片层之间的结合强度削弱, 二者之间出现相对滑移. 石墨烯片层运动行为的改变引起了剪切面的转变. 通过对石墨烯片层沿滑移方向上的速度波动幅度的分析, 发现其与摩擦系数之间存在正相关性.
      The ab initiomolecular dynamics method is used to simulate the friction process of the graphene sheet as lubricant added to the silicon-based material interface under the action of compression and shear, and the influence of water molecules and oxidation of graphene surface on the movement behavior of graphene sheet are studied. In a dry environment, the pristine graphene (PG) sheet will slip only when the pressure is high. Owing to the presence of surface functional groups, a strong force is formed between the graphene oxide (GO) sheet and the substrate. The direction of the hydroxyl groups on the surface of the upper slab is consistent as the upper slab moves at a constant speed, resulting in the fact that the force between the GO sheet and the upper slab is greater and the GO sheet slides forward with the upper slab. Owing to the formation of mechanical interlock between the GO sheet and the lower slab surface, the GO sheet no longer slips when the pressure is high. In a humid environment, the interface structure affects the overall distribution and movement state of water molecules. The water molecules between the PG sheet and the upper slab are adsorbed only on the surface of the upper slab and always remain in a “flat” state, and their motion behavior is consistent with the upper slab’s. Comparing with a dry environment, the PG sheet starts to slip only when the pressure is high. Since the hydroxyl orientation angle on the surface of the upper slab is greater than the hydroxyl orientation angle on the surface of the GO sheet, the water molecules gradually change from the "flat" state to the slightly “upright” state as the pressure increases. The change of the orientation of water molecules makes the bonding strength between water molecules and the GO sheet gradually decrease, leading to a relative slip between them. The change in the movement behavior of the graphene sheet causes the shear plane to change. There is a positive correlation between the velocity fluctuation mean square error of the graphene sheet and the friction coefficient as the oxidation rate of graphene sheet increases under different coverages of water molecules, indicating that the motion behavior of the lubricant affects the interface friction characteristics.
          通信作者:段芳莉,flduan@cqu.edu.cn
        • 基金项目:国家自然科学基金(批准号: 51775066)资助的课题
          Corresponding author:Duan Fang-Li,flduan@cqu.edu.cn
        • Funds:Project supported by the National Natural Science Foundation of China (Grant No. 51775066)
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      出版历程
      • 收稿日期:2021-01-14
      • 修回日期:2021-02-21
      • 上网日期:2021-07-13
      • 刊出日期:2021-07-20

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