悬浮石墨烯摩擦特性

石墨烯作为固体润滑剂在微/纳米机电系统中具有巨大的应用潜力.本文在SiO_2/Si基底上制备了微孔阵列,将石墨烯剥离在微孔上,形成悬浮结构.使用原子力显微镜研究悬浮石墨烯和支撑石墨烯的摩擦特性,结果表明:悬浮石墨烯表面摩擦力比基底支撑石墨烯明显减小,同时在支撑石墨烯上出现的摩擦增强效应也消失.随着石墨烯厚度的增大,面外刚度逐渐增大,悬浮石墨烯与支撑石墨烯的摩擦力差异逐渐减小.此外,使用预磨损探针时,悬浮石墨烯和支撑石墨烯的摩擦力都显著增大,且悬浮石墨烯的摩擦力依然比支撑石墨烯小.通过对比不同厚度石墨烯,不同针尖半径时悬浮石墨烯与支撑石墨烯表面摩擦力的变化,揭示了面外变形对石墨烯摩擦力的影响,为有效提高石墨烯固体润滑剂的摩擦性能提供了理论指导.

Friction properties of suspended graphene

Minimizing friction is a goal that has long been pursued in history.The role of micro-electromechanical system and nano-electromechanical system(MEMS/NEMS)in electronic devices is becoming more and more important.Due to the increasingly small size of the device,large surface-to-volume ratio leads to severe friction and wear problems of the device,thus limiting its performance.Graphene is considered as a good lubricating material in MEMS/NEMS due to its extremely thin size and excellent anti-friction effect.The study of nanofriction properties of graphene is of great significance in further developing the MEMS/NEMS.In this work,microporous arrays are prepared on a SiO2/Si substrate,and graphene is stripped on the micropores to form a suspension structure.The friction properties of suspended graphene and supported graphene are measured by using atomic force microscope.The results show that the nanofriction on suspended graphene is significantly reduced compared with that on supported graphene.The supported graphene experiences a frictional enhancement effect because of the puckering effect,while the friction enhancing effect disappears in the suspended graphene.With the increase of graphene thickness,the out-of-plane stiffness increases gradually,and the friction difference between suspended graphene and supported graphene decreases gradually.In addition,the nanofriction properties of suspended graphene under new tip and pretreated tip are also different.The friction between the pretreated tip and graphene is significantly higher than that between the new tip and graphene.The surface friction difference between the suspended graphene and the supported graphene decreases when the pretreated tip is used compared with the new tip.This work demonstrates that the deformability of atomicscale structures can provide an additional channel of regulating the friction of contact interfaces.By comparing the changes of surface friction between the suspended graphene and the supported graphene with different thickness and tip sizes,the influence of out-of-surface deformation on the friction of graphene is revealed,thus providing theoretical guidance for effectively improving the friction performance of graphene solid lubricant.