Study On The Influence Mechanism Of Annealing Temperature On Wear Of Graphene Step

Graphene has outstanding mechanical,electrical and optical properties,so it is widely used in many fields,especially in microelectronic devices and lubrication protection.However,the commonly used oxygen-assisted rapid chemical vapor deposition(CVD)preparation of graphene and the annealing process to regulate its mechanical properties may affect its mechanical stability and lubrication performance,which are also the prerequisites for its application in micro-nano mechatronic devices and lubrication protection materials.Because step edge of graphene is the most vulnerable and sensitive area to external factors,it is necessary to study the wear mechanism of the step to find a solution to improve the lubrication performance of graphene.Therefore,it is very necessary to explore the wear mechanism of step edge of graphene in different environments and the influence mechanism of annealing treatment at different temperatures on its wear performance.Moreover,the cumulative damage of step edge of graphene at micro-nano scale will make its lubrication characteristics fail quickly at macro scale,so it is of great significance to find out the influence of annealing temperature on the lubrication performance of graphene at macro scale to realize the lubrication performance of graphene at multi-scale.The main research contents and conclusions of this thesis are as follows:(1)The microscopic wear mechanism on the step edge of graphene is revealed,involving atomic exfoliation dominated by tribochemical action and cut-like scratches,local tears and folding dominated by mechanical action.And the remarkable wear resistance of step edge of graphene under oxygen is clarified,i.e.,the large number of epoxy groups are generated after the oxygen dissociative adsorption of the step edge and its surrounding plane,and the ether bond functional groups are easy to break the C-C bond and C-O bond on the step edge and surrounding plane of graphene under the induction of large stress.(2)The effect mechanism of annealing temperature on the microscopic wear of edges of graphene is revealed.Based on the wear results of edges of graphene annealed at different temperatures by active silicon probes and inert diamond probes,combined with friction force test and Raman detection,it was found that higher annealing temperatures would promote the transformation of zigzag step edges into armchair step edges.Since zigzag step edges have higher chemical activity and mechanical stiffness than armchair step edges,the tribochemical wear of step edge is suppressed to a certain extent with the increased annealing temperature,while mechanical wear is more likely to occur.(3)An optimization scheme based on annealing treatment to improve the macroscopic lubricating properties of graphene is proposed.The effect of annealing temperature on the lubrication characteristics of graphene coating on macro scale was studied by means of friction and wear tester.The morphology,elemental composition and defect density of wear debris before and after annealing were analyzed by scanning electron microscope-energy dispersive spectrometer and Raman detection.It was found that annealing treatment could drastically reduce the oxidation degree and defect density of graphene coating surface.This is mainly due to the transformation of the atomic structure of the microscopic step edge of graphene coating by annealing treatment,which significantly reduces the chemical activity of the microscopic step edges,making it more difficult to generate microcracks due to friction and chemical wear.Therefore,the graphene coating has not been annealed is easily torn and rolled into powder,and the lubrication effect is not good.However,the annealed coating can still remain flaky after tearing,and the silicon dioxide abrasive particles are wrapped in the process of wear,thus achieving excellent lubrication effect.