二维材料摩擦中变形和边界的影响研究

As the size of electronic and mechanical devices shrinking to the nanometer regime, performance begins to be dominated by surface forces. In particular, friction, wear and adhesion are known to be the crucial factors in the designing of reliable micro- and nano-electromechanical systems (MEMS/NEMS). At the nanoscale, the friction law is inconsistent with the macroscale friction law, while new factors that affect the nanoscale friction are continually emerging. Our research group have recently studied the friction behavior of carbon nanotube and graphene, and found that the friction is very sensitive to the substrate stiffness and edge effect. Based on those work, this project aims to investigate the influence of deformation and edge effect on the friction behavior of two-dimensional (2D) materials by using molecular dynamics simulations, and theoretical analysis based on Frenkel-Kontorova model. There are two main themes within this project. The first is to study the effect of stiffness-dependent (including support stiffness of substrate and stiffness of slider) deformation of 2D materials on the friction behavior, and then elucidate the underlying mechanism of friction. The second is to study the influence of the stiffness，the shape and size of the slider on edge effect on friction. In addition, we will study the frictional mechanism by coupling the effect of the stiffness with the edge effect. The expected results may have important scientific values for both promoting the stage of nanotribology, and guiding the designing of nanometer device.

当电子机械系统微型化到纳米尺度时，表面力将变得异常显著，尤其摩擦、磨损、黏附等成为制约开发性能可靠的微纳电子机械系统的关键因素。在纳尺度上，摩擦规律与宏观尺度上的摩擦规律之间差异明显，并出现了许多新的影响摩擦的因素。申请者所在团队近期关于碳纳米管、石墨烯等低维材料的摩擦研究表明，纳米摩擦对刚度和边界效应具有显著依赖性。本项目将延续前期工作，针对二维纳米材料的摩擦开展更系统深入的研究，基于分子动力学模拟着重考察变形和边界效应两个关键因素对摩擦的影响规律，并结合Frenkel-Kontorova理论提出合理的解释机理。具体内容包括：考察依赖于刚度（包括基底支撑刚度和滑块刚度）的接触变形对摩擦行为的影响；分析刚度、边界尺寸及形状决定的边界效应对摩擦的影响机制；还将获得变形及边界效应耦合作用下的一些摩擦规律。预期研究成果对促进纳米摩擦学发展以及对指导纳米器件的研发设计都具有重要的科学意义。

作为当前摩擦学领域的焦点问题之一，纳尺度摩擦行为及其机理研究备受关注。诸多新的纳米摩擦现象、规律和机理被陆续报道。然而，纳米摩擦中许多关键因素的影响及调控机制尚不清楚，还有待于更深入探究。二维材料的摩擦行为研究是促进纳米摩擦学发展的重要突破口，有助于深刻理解摩擦规律及其潜在机理。. 本项目基于分子动力学模拟方法，研究了二维材料（例如石墨烯）的摩擦性能，着力分析了两种关键因素（接触边界，接触变形）对纳米摩擦的影响及作用规律。具体研究内容和结论包括：（1）基于矩形石墨烯薄片与石墨烯基底的滑动接触作用，研究了滑片的长宽比对摩擦的影响。结果表明，当垂直于滑动方向的边界长度增加时，摩擦力显著增大；但摩擦力对平行滑动方向的边界长度的依赖性较小。（2）探究了圆形石墨烯滑片与平整基底表面（金刚石、石墨烯和金）之间的摩擦行为，得到了在高压强情况下摩擦力与接触面积之间的负相关性。（3）分析了面内应变对石墨烯层间摩擦的影响。结果显示，非公度接触时层间的摩擦行为受应变（在小应变情况下）影响微弱；而对于公度接触层间而言，应变引起层间的公度性转变导致摩擦随应变非单调变化。（4）揭示了石墨烯滑片与支撑石墨烯基底之间的摩擦行为的接触变形影响机制，发现压痕深度可用于直接调控摩擦力大小。（5）考察了弯曲石墨滑片在弹簧支撑的石墨烯基底之间的摩擦对滑片曲率的依赖性。结果表明，当滑片曲率减小时，其边界区域原子的摩擦力显着增加，而内部区域原子的摩擦逐渐减小。