Effects Of Ion Beam Bombardment On Tribological Behaviors Of Graphite And Graphene And Its Mechanism

The layered material represented by graphene has many excellent properties such as good mechanical properties,good electrical conductivity,good thermal conductivity,and the like.Therefore it is considered as a new nano-lubricant material.However,graphene will inevitably be affected by the external environment in the production and application.The surface activity,mechanical properties,electrical properties of graphene will be largely changed,especially under electron,phonon,and ion irradiation conditions.These changes in surface properties will affect the interaction of the system interface,which in turn may affect the tribological behavior of the surface,and may even affect the operation of the system.On the basis of this,the effect of ion bombardment on the tribological behavior of graphite and graphene were studied.The results are as follows.（1）After the low-energy（0⁴00 eV）Ar⁺bombardment of graphite,the basic phenomenon of its surface friction behavior is that the friction first increases,then decreases,and finally tends to be stable.The ion dose was kept 1×10¹⁵ ions/cm².This is because when the ion energy is lower than the penetration threshold E_p（⁴3 eV）and the threshold E_th（⁴7 eV）for vacancy production,it will produce structural protrusions on the graphite surface,so that the friction increases.When the energy is higher than E_th,holes and interstitials are generated on the graphite surface.The existence of holes makes the energy barrier increase,so the friction increases.The reduction of friction is mainly due to partial sputtering of the outmost graphene and the exposure of clean graphene with few of defects.（2）For the treated sample,no damage was found in the graphene when the load was about 20μN.The untreated sample had been damaged when the load was about 18μN.On the one hand,this may be due to the lattice distortion of the modified silica and the increase in hardness due to N⁺implantation.The hardness after treatment was about9.2 GPa and about 8.62 GPa without treatment,as measured by nanoindentation.In-plane distortion of graphene is smaller and carbon-carbon bonds are less stretched,so the graphene is not easy to be destroyed.On the other hand,it may be due to some dangling bonds and chemical bonds on the surface of the substrate after nitrogen ion beam bombardment,such as Si-O-N,N⁺,etc.,which causes certain properties of the surface to change,such as adhesion,etc.,causing the graphene to break.