Effect Of Commensurability Between Graphene And Substrate On The Friction Properties Of Graphene

Graphene exhibits exceptional mechanical properties and chemically stable structures and therefore is commonly used as one of the most popular materials for understanding fundamental mechanisms of nanoscale friction.The research on the friction behavior of graphene is a core issue,which is often a problem shared by the friction behavior of two-dimensional materials and nanotribology,so it has become the focus of many scholars.The study of friction behavior and dissipation mechanism of graphene is helpful to understand the characteristics and mechanism of nanoscale friction,and has important scientific research value and practical significance for improving the reliability of equipment,innovative design of new devices,and efficient utilization of energy.In both experimental tests and numerical simulations,the frictional property of graphene is generally measured as that of a graphene sheet on a substrate.In potential device applications,a graphene sheet is expected to work on a supporting material.Graphene has the high surface area to volume ratio and its various properties strongly depend on the choice of the substrate.However,in both experimental tests and numerical simulations,the stacking(mismatch)angle between graphene and substrate cannot be precisely controlled.Whether the friction performance of graphene depends on the contact commensurability between the graphene and the substrate.Based on the situations,we investigated the dependence of the frictional properties of graphene on the contact commensurability between the graphene and the substrate.The main conclusions and achievements are as follows:(1)The friction properties of graphene depends on the commensurability between graphene and substrate,which means that even on the substrate with the same medium,the mismatch angle between graphene and substrate is a non-negligible factor in measuring the friction properties of graphene.Molecular dynamics simulation results show that the main factor affecting the friction properties of graphene is the interlaminar shear strength between the graphene and the substrate.The friction force between the probe and the graphene decreases gradually,as the interlaminar shear strength between the graphene and the substrate increases.In addition,it is found that the influence of factors such as normal load,probe sliding speed,and boundary spring stiffness on the frictional force depends on the interlaminar shear strength between the graphene and the substrate.When the interlaminar shear strength is greater,these factors have a weaker influence on the friction.We revealed the friction dissipation mechanisms associated with the mismatch angle between the graphene and the substrate by the in-plane deformation and stick-slip motion of the graphene sheet.(2)During the simulation,we counted the changes in the position of the atoms in the graphene plane,the changes in the position of the graphene sheet relative to the substrate,and the sliding trajectory of the probe on the graphene sheet from a microscopic point of view.The statistics and records of the above data facilitate our in-depth understanding of the molecular dynamics simulation process,the relative motion between the probe-graphene-substrate,and the basic mechanism of friction dissipation.(3)The contribution of the in-plane deformation of the graphene sheet to the friction dissipation is considered.The graphene sheet produces local in-plane deformation,due to the interaction between the probe and the graphene sheet and the lattice structure between the probe-graphene-substrate when the probe is loaded or sliding on the graphene sheet.As the probe slides,the elastic deformation energy generated by the deformation is continuously accumulated and released,causing irreversible energy loss,and the contribution of this part of the energy to friction dissipation is not negligible.(4)Use an equivalent spring to simulate the size of graphene.In the experimental measurements,the size of the graphene sheet is on the order of nanometers.However,in the simulation,it is generally within 100 nm.In this article,we use an equivalent spring to simulate the size of graphene to make it close to the size used in actual applications and experiments,thereby eliminating the influence of the boundary effects on the simulation results.