石墨烯在金刚石基体表面的纳米摩擦学行为研究

采用热化学气相沉积法(Thermal Chemical Vapor Deposition，TCVD)和机械剥离法分别制备了单层和少层石墨烯并转移至MPCVD制备的多晶金刚石基体表面，利用原子力显微镜研究了大气环境下石墨烯在金刚石基体上的纳米摩擦和磨损性能. 研究结果表明:单层和少层石墨烯在金刚石基体上具有良好的减摩作用，摩擦系数分别为0.03和0.014. 然而，由于石墨烯和金刚石表面之间的物理吸附作用较弱，其摩擦力会略高于SiO₂/Si基体表面石墨烯的摩擦力. 随扫描速度升高，金刚石表面的单层与少层石墨烯的摩擦力的变化可以分为自然对数正比上升，基本保持不变以及黏性阻尼增加三个阶段. 在磨损试验中，TCVD法制备和转移石墨烯的过程中产生的缺陷和污染物降低了单层石墨烯的耐磨性能，而机械剥离的少层石墨烯因为无缺陷的石墨烯晶体结构在金刚石基体上展现了优异的耐磨特性. 本研究可为以金刚石为基体的石墨烯固体润滑剂使用提供理论基础. 

Nanoscale Tribological Behavior of Graphene on Diamond Substrates

In present study, the nanoscale tribological behaviors of graphene on the diamond substrate surface were investigated using atomic force microscopy (AFM) in ambient air condition. Single-layer (SLG) and few-layer graphene (FLG) sheets were fabricated by thermal chemical vapor deposition and mechanical exfoliation method respectively and then transferred onto the surface of a polycrystalline diamond substrate, which was fabricated by microwave plasma chemical vapor deposition (MPCVD). The AFM results show that both SLG and FLG nanosheets remarkably reduced the nanoscale friction of the diamond substrate and exhibited extremely low coefficients of friction around 0.03 and 0.014, respectively. However, the friction of graphene on diamond surface was always higher than that on SiO₂/Si substrates due to their relatively weaker interaction on the diamond surface. Regarding to the influence of sliding velocity, under the normal loads of 0, 20 and 40 nN, the friction force evolution of graphene nanosheets on diamond substrates could be divided into three stages as the increasing sliding velocity. In the first stage, a roughly logarithmic increasing trend was observed for the sliding velocity up to 3 μm/s. The second stage saw a plateau as the sliding velocity increased from 3 μm/s to 10 μm/s. In the third stage, an increasing trend was dominated by the viscous damping term at the sliding velocity higher than 10 μm/s. Besides, the FLG sheets exhibited better wear resistance than the SLG sheets in a long-duration friction test under high normal load, which was supposed to be attributed to defects formed in SLG sheets and contaminants produced during the transfer process.