Atomic-scale Theoretical Investigation On The Adhesion And Mechanical Properties Of Graphene

Graphene,as a new carbon nanomaterial,because of its unique physical,chemical,biological and other disciplines superior performance,has highly potential applications in the high-sensitivity sensor,drug delivery systems,rechargeable lithium-ion battery technology,and many other high-tech products.The adhesion and adsorption mechanical properties of graphene possess important implications for graphene-based high-sensitivity sensor overall performance,drug delivery systems carrying transmission efficiency,and lithium-ion battery charge and discharge rate and so on.Therefore,studying the adhesion and adsorption mechanical properties of graphene is very important.Based on the Lennard-Jones potential,a theoretical model of atom/ion adsorption and diffusion on graphene surface was promoted,and different atoms and ions adsorption and diffusion on graphene surface were studied and analyzed.At the same time,based on the theoretical model,using numerical analysis method,by discussing and analyzing the dynamic process of a microscope probe scanning on the graphene surface,the adhesion and adsorption mechanical properties of graphene was further revealed.Firstly,by analyzing the atomic structure of infinite graphene,the interaction potential between atom/ion and graphene could be expanded by Fourier series,then an approximate expression of the interaction potential was obtained.And then several typical metal atoms and ions were selected,and their migration along the graphene surface normally and tangentially were studied.The equilibrium height,adsorption energy of each atom and ion in a few special positions were calculated,and the stability and diffusion barrier differences among different equilibrium positions were discussed.As an example,lithium-ion was selected diffusion along x-axis,y-axis,and the directions with different angles with x-axis,the interaction potential and the tangential force of lithium-ion suffered were studied.In addition,the adsorption and migration of lithium-ion on several finite sizes of graphene,and a graphene which has two kind of vacancy defects were studied.It found that the adsorption and migration of lithium-ion on the different sizes of graphene surface showed a significant dependence on the size of graphene and a significant edge effect.Furtherly,by analyzing the energy barriers of lithium-ion migration in different directions,it was found that the lithium ion would only diffuse on graphene surface,rather than penetrate through the graphene carbon ring to the other side.Meanwhile,a single carbon atom vacancy defect and a carbon ring vacancy defect were studied.It was found that a defect can increase the energy barrier.And,if the defect is large enough,the lithium ion can easily penetrate through the defective area to the other side.Finally,based on the theoretical model,it was extended to research static and dynamic interactions between microscope probe and graphene.In addition to obtaining similar results as a single atom/ion adsorption and migration on graphene surface,based on the Tomlinson model of tip scanning on graphene surface,using numerical analysis method,the variations of static and dynamic friction,displacement and velocity of probe were studied in different scanning velocities,damping and vertical distance of tip and graphene.It also considered the effects of different vertical distance between the tip and graphene and damping.These work will help to study the high-sensitivity sensor,drug delivery systems,rechargeable lithium-ion battery,carbon material based energy storage and so on.