The Mechanical Properties Of Graphene,Silicene And Germanene Sheets By Molecular Dynamics Simulation

Since the 2010 Nobel Prize for physics was awarded to Geim and Novoselov for the discovery of graphene,two-dimensional materials have developed rapidly.Because of its good compatibility with crystalline silicon matrix,the applications of graphene,silicene and germanene in transistors have attracted much attention.The manufacture of electronic devices is inseparable from the understanding of the mechanical properties of materials,it is important to understand the mechanical properties of graphene,silicene and germanene.Further study on the mechanical properties of graphene,silicene and germanene can deepen the theoretical understanding of those materials,referring to atomic potential function,molecular dynamics,crystallography and numerical calculation.In this paper,the molecular dynamics simulation method is used to carry out a systematic research.The tensile mechanical properties of chiral graphene,the shear properties of multilayer graphene and the tensile mechanical properties of silicon doped graphene were investigated.The effects of size and temperature on the shear mechanical properties of buckled silicene and the tensile and shear mechanical properties of planar silicene were researched.The effects of size and temperature on the shear mechanical properties of germanene were studied.In addition,the steered molecular dynamics simulation of the mechanical properties of IV pilus was performed for the first time(Appendix).The simulations of the tensile mechanical properties of chiral graphene,the shear properties of multilayer graphene and the tensile mechanical properties of silicon doped graphene were conducted with Tersoff potential.The effect of chiral orientation on tensile mechanical properties of graphene sheets was studied and the stress-strain relationship,and tensile failure morphology of graphene sheets were obtained.The influence of different chiral orientation on the Young's modulus of graphene is not obvious.The relationship of mechanical properties of graphene with the chiral angle is acquired.The effects of the number of layers on the shear mechanical properties of zigzag and armchair graphene sheets were studied and the corresponding stress-strain curves,and shear failure failure morphology were gained.The shear modulus of the armchair and zigzag graphene sheets does not change apparently with the increase of the number of layers.However,the shear strength and ultimate shear strain of the armchair and zigzag graphene sheets decreases gradually.The effect of the ratio of carbon to silicon in the silicon doped graphene on tensile mechanical properties of armchair and zigzag graphene sheets was investigated.The stress-strain relationship and tensile failure morphology were obtained,and the parameters of mechanical properties are fitted by least square method.The influence of silicon substitution rate on the Young's modulus of graphene sheet is evident.The tensile ultimate strain and tensile strength decrease significantly with the increase of the number of silicon atoms.In this paper,the tensile mechanical properties of chiral graphene sheets are first researched,and the relationship between the mechanical properties such as Young's modulus and chiral angle is acquired;The shear failure process of multilayer graphene sheets was first studied;The tensile mechanical properties of silicon doped graphene sheets were got for the first time,and the relationship between the mechanical properties such as Young's modulus and the ratio of carbon to silicon in the silicon doped graphene was gained.The simulations of the shear failure process of buckled silicene sheet were accomplished by using SW potential.In addition to the elastic modulus of armchair buckled silicene sheet,the effect of the silicene size on the elastic modulus of zigzag buckled silicene sheet,shear strength and shear limit strain of both type buckled silicene sheet is obvious.With the increase of temperature,the shear modulus of armchair and zigzag buckled silicene sheets increases at first and then decreases.The shear strength and ultimate shear strain of the armchair buckled silicene decrease distinctly,while those of the zigzag buckled silicene change more gentlely.Under the action of shear loads,the damage of buckled silicene sheet is mainly formed near the edge and extends along the approximate horizontal direction,resulting in the formation of new damage and tetrahedral structure of silicon.In this paper,the mechanical properties,stress-strain curves and shear failure morphology of buckled silicene sheets are first acquied.At the same time,the simulations of the tensile and shear mechanical properties of planar silicene sheets were carried out with Tersoff potential.With the increase of temperature,the shear modulus,shear strength and ultimate shear strain of the armchair and zigzag planar silicene sheets decrease apparently.The effect of the silicene size on the elastic modulus,tensile strength and ultimate strain of the armchair and zigzag planar silicene sheets is not evident.Under the action of shear load,the failure is mainly formed near the edge and extends along the shear horizontal direction until the failure fracture.The simulations of the shear mechanical properties of germanene sheet were performed by using Tersoff potential.The influence of germanene size on elastic modulus,shear strength and shear limit strain of armchair and zigzag germanene sheet is obvious.With the increase of temperature,the shear modulus of armchair and zigzag germanene sheets first increases and then decreases.The shear strength and ultimate shear strain of the armchair germanene sheets decrease distinctly,while the zigzag germanene sheets decrease slightly.Under the action of shear load,the damage of germane sheet is mainly formed near the edge.The damage extends in the approximate horizontal direction for the armchair germanene sheet,and it extends into the middle of sheets for the zigzag germanene.During the shearing process,the hexagonal cells of germanene are gradully destroyed and the tetrahedral structures of germanium are formed.In this paper,the mechanical properties,stress-strain curve and shear failure morphology of germanene sheets are obtained for the first time.