复杂环境下石墨烯表面纳米摩擦行为调控及机理研究

Reducing friction and wear-related mechanical failures in moving Micro/Nano-electromechanical systems (MEMS/NEMS) has gained increased attention due to their adverse impacts on efficiency, durability, and environmental compatibility. Since the atomically thin structure, well friction-reduction and incredible mechanical, electronic properties, graphene has tremendous potential for applications in a wide range of MEMS/NEMS. In order to ensure efficient and reliable utilization of graphene into MEMS/NEMS, it is meaningful to study the nanotribological properties and mechanism of graphene surface comprehensively and uniformly under complicated environments..Firstly, the normal spring constant and lateral sensitivity of the Si cantilever of atomic force microscopy (AFM) will be calibrated with the thermal noise and improved wedge calibration method，respectively．The graphene with controllable surface wettability and structural defects will be achieved by plasma treatment and thermal reduction. Secondly, the nanotribological properties including adhesion and nanofriction of graphene on silicon oxide substrate will be investigated using calibrated AFM tip as function of load and scanning velocity. The nanofriction on graphene will be studied and compared according to the difference of the surface structure and properties. The effect and mechanism of structure and surface properties on nanotribological behaviors will be clarified. Thirdly, the effect of complex environment including gas, humidity and temperature on the nanotribological properties of graphene with controllable surface properties and structure will be conducted. The possible mechanisms will be proposed for this based on the abundant experiments. Finally, the key load for wear of graphene will be found out by scanning the graphene with different surface properties and structure defects. Additionally, effects and mechanisms of the anti-wear properties of graphene under complicated environments such as temperature, different gas and relative humidity will be studied further. Also the anti-wear properties of graphene will be assessed and compared. The nano-wear mechanism of graphene sheets will be proposed．.The fulfillment of this project will result in a better understanding and enriching nanotribological fundamentals. Also a systematic evaluation for regulating nanoscale friction of graphene will be established by controlling structure and surface properties. In addition, this project will provide insights in the use of graphene as solid lubricants in MEMS/NEMS applications under complicated environments, such as nanolubricants, nanomotors, and movable components.

石墨烯超薄厚度、优异机械、电学和润滑性能，在微/纳机电系统（MEMS/NEMS）中广泛应用，其纳米摩擦行为成为影响性能与寿命关键。项目引入等离子体处理和热还原工艺对石墨烯表面性质和结构有效调控，基于标定原子力显微镜（AFM）探针，对比研究不同表面性质与结构的石墨烯表面纳米摩擦性能，揭示石墨烯表面性质与结构对表面纳米摩擦行为调控及机制；基于AFM的环境控制腔体设计不同湿度、温度和含氧气体保护等复杂环境，深入研究复杂环境下不同表面性质与结构石墨烯的纳米摩擦行为，揭示石墨烯表面性质与结构和各种环境耦合下的纳米摩擦调控机制；最后寻求石墨烯表面纳米磨损的临界载荷，探索湿度、气体保护和温度对纳米磨损临界载荷的影响，揭示复杂环境下石墨烯纳米磨损机理；项目将丰富和扩展石墨烯纳米摩擦基础理论，为石墨烯在MEMS/NEMS复杂环境应用摩擦学设计与调控提供科学依据，从而提高可靠性，延长使用寿命。

石墨烯因其独特的机械和物理化学性能，可作为纳米润滑薄膜用于微/纳机电系统（MEMS/NEMS）活动构件的纳米间隙表面，减小界面摩擦磨损和降低系统能耗。本文首先通过等离子体处理对石墨烯的表面性质和结构缺陷进行调控，进而分别研究了表面性质和结构缺陷在石墨烯表面纳米摩擦中的作用。研究发现石墨烯表面的粘附力和摩擦力均随表面亲水性增强而单调增加。摩擦力的层数依赖性随着表面亲水性加强而逐渐消失。表面粘附力对结构缺陷不敏感，但表面摩擦力随结构缺陷程度增加而单调增大。增强表面亲水性通过增加针尖-石墨烯界面粘附作用而增大界面滑动势垒，并通过石墨烯发生更大程度的面外变形而增加摩擦力。石墨烯表面在动态摩擦过程中产生了粘附增强效应，且其程度随表面亲水性增强而增大。氧化石墨烯因为表面强亲水特性使得摩擦力随载荷非线性变化，并产生了更大程度的粘附增强效应。氟化石墨烯因表面强疏水特性没有产生粘附增强效应。. 机械剥离的原始石墨烯的抗磨损性能最好，CVD生长的石墨烯其次，而还原氧化石墨烯和氧化石墨烯的抗磨损性能相差不大并且远远差于前两者。还原氧化石墨烯和氧化石墨烯中缺陷的存在被认为是影响其磨损性质的最主要因素。此外，研究还发现氧化石墨烯的抗磨损性能随着其厚度的增加而大幅度增强，这是由于厚度的增加导致氧化石墨烯薄片弯曲刚度的增加。项目研究了不同石墨烯的纳米摩擦性能，丰富了石墨烯的纳米摩擦机理，为石墨烯在MEMS/NEMS复杂环境应用摩擦学设计与调控提供科学依据，从而提高可靠性，延长使用寿命。