石墨烯表面纳米摩擦精准调控研究

Nanofriction can be used as a driving force for the devices in Micro/Nano electromechanical systems (MEMS/NEMS), where the precise control of the friction is needed. Since the atomically thin structure, well friction-reduction and incredible mechanical, electronic properties, as well as the ability for friction control by surface treatment, graphene has tremendous potential for applications in MEMS/NEMS to realize precise regulation of nanofriction. Graphene with controllable surface wettability and topography will be achieved by local anodic oxidation based on atomic force microscopy. The correlation between surface wettability and structural characteristics of functionalized graphene and the nanotribological behaviors are investigated systematically. Based on which, multi-factor coupling nanotribological mechanism of nanoscale functionalized graphene is revealed combining with the law of external parameters. Then, the influence of heterogeneous surface characteristics of the nanoscale functionalized graphene on the adhesion and friction behaviors are explored theoretically and experimentally, since the meniscus serves as a bridge between the tip and the functionalized graphene. Finally, nanofriction model coupling multiple factors will be completed, which provides the key theoretical support for the accurate nanoscale manipulation of surface nanotribological behavior of graphene..The fulfillment of this project will result in a better understanding and enriching in nanotribological fundamentals. Furthermore, this project will provide scientific basis and theoretical guidance for the use of graphene in MEMS/NEMS applications.

随着微/纳机电系统（MEMS/NEMS）中器件特征尺寸的不断降低，以摩擦力为驱动力的MEMS/NEMS器件需要摩擦力在纳米尺度精确可控。石墨烯因具有超薄的厚度，优异的机械、电学和摩擦性能，并可通过表面改性处理进行摩擦调控，成为MEMS/NEMS中实现纳米摩擦精准调控的理想材料。本项目引入基于原子力显微镜的局部阳极氧化法对石墨烯表面性质与结构进行有效调节；揭示石墨烯表面性质与结构对表面纳米摩擦行为的调控机制；基于外在参数影响规律，阐明纳米尺度功能化石墨烯表面多因素耦合摩擦机理；重点以针尖-石墨烯间纳米液桥为桥梁，揭示各影响因素对液桥动态特性影响机制，阐明纳米尺度功能化石墨烯表面性质结构与纳米摩擦性能间精准映射关系，构建纳米尺度功能化石墨烯表面多因素耦合摩擦力模型，实现石墨烯表面纳米摩擦精准调控。项目将丰富石墨烯纳米摩擦基础理论，为石墨烯在MEMS/NEMS中的摩擦学设计和调控提供理论依据。

微/纳机电系统（MEMS/NEMS）在纳米尺度下因表面积增大而具有很强的表面效应，导致以粘附力和摩擦力为代表的表面力远大于以惯性力和电磁力为代表的体积力，摩擦、磨损问题成为制约MEMS/NEMS性能与寿命的关键。然而在某些场合，由于空间限制和结构特点，MEMS/NEMS器件需要利用摩擦作为驱动力和牵引力，此时要求接触面间的摩擦力精确可控。本项目首先研究了石墨烯表面的性质与结构特征对摩擦行为的影响机制，通过AFM局部阳极氧化方法调节石墨烯表面性质，指出双亲水界面间毛细力为主导作用力，若至少一个界面疏水则毛细凝聚被抑制；同时探究了石墨烯表面不同台阶结构，以及石墨烯样本在支撑及悬空状态下的摩擦响应特性，构建了表面性质结构特征与纳米摩擦行为间的关联，为后续的研究奠定基础。其次，在获得石墨烯表面摩擦行为对表面性质和结构特征的依赖关系后，进一步引入环境湿度、电场等外在因素，调节毛细力以及静电力，阐明外在影响因素与石墨烯表面性质和结构特征的耦合作用机制；并通过自制的多尺寸微球探针，与商业探针相结合，实现针尖尺寸在纳米、亚微米和微米尺度下的覆盖，探究尺度效应对石墨烯表面摩擦行为的作用机制。最后，基于以上结果，获得基于AFM局部阳极氧化的石墨烯表面纳米摩擦精准调控方法，可以实现从分辨率、频率及幅值三个方面对石墨烯表面摩擦性能进行调控。此外，将研究结果进一步拓展到同为二维材料的六方氮化硼表面，通过电场的调控，获得六方氮化硼上纳米摩擦的实时动态、可逆的调节。项目的实施将有助于丰富二维材料纳米摩擦学理论基础，为石墨烯在MEMS/NEMS中的摩擦学设计和调控提供理论指导与依据。