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 atomic-scale 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.