Theoretical Study On The Effects Of Surface Grain Boundary On Mechanical Properties Of Two-dimensional Materials

With the discovery of graphene,people pay more and more attention to twodimensional materials.However,in the process of growth or synthesis,defects will inevitably occur on the surface of the material,which will affect the physical and chemical properties of the material.Both experimental and theoretical studies have found that there are certain grain boundaries(GBs)on the surface of monolayer molybdenum disulfide(MoS2),and its GBs profoundly affect the electronic properties and mechanical properties of MoS2 materials.However,the GBs of the surface of bilayer MoS2 have been relatively few,and how the GBs affect the mechanical properties of the material is unclear.Biphenylene,as a new two-dimensional,has not yet been reported on the structure types and properties effects of defects.Therefore,the study of surface defects and GBs of twodimensional materials and the in-depth understanding of the effects of defects on the electronic and mechanical properties of materials will be helpful for better regulation and further application of these two-dimensional materials.In this paper,different types of GBs are constructed in bilayer MoS2 and biphenylene,and the structural stability and mechanical properties of the material under uniaxial tensile strain are studied by first-principles calculation method,and the research content and conclusions are summarized as follows:(1)The structure stability of different stacking registries and different GBs of bilayer MoS2 containing GBs were systematically studied,and the electronic properties of bilayer MoS2 under the influence of GBs were discussed.The calculation results show that the 2H stacking registry is more advantageous in terms of energy.Among the four GBs,the binding energy between the bilayer MoS2 containing 4|4 GB is the strongest.In addition,the existence of GBs allows defective states to be introduced near the Fermi level,enhancing the conductivity of the material.(2)The influence of GBs on the mechanical properties of bilayer MoS2 was systematically studied,and the fracture process of bilayer MoS2 containing GBs under external strain was revealed.The calculation results show that the bilayer MoS2 has better tensile resistance than the monolayer MoS2.In the four GBs,the 55|8 GB has the largest Young’s modulus,while the 4|4 GB has the smallest Young’s modulus.Four-membered rings in GBs are more prone to fracture,while eight-membered rings are more resistant to external stretching.In addition,the increase in GB density further reduces the mechanical properties of bilayer MoS2.(3)The possible GBs and point defects in the biphenylene were systematically studied,and the stability of the defects and the mechanical behavior under tensile strain were discussed.The calculation results show that among the three point defects considered,the rigidity of the double vacancy is the be st,the hardness of the bond rotation is the highest,and the stiffness and hardness of the single vacancy are the worst.Among the GBs on the biphenylene surface,the GB composed of five-membered rings has the largest Young’s modulus,and the GB composed of six-membered rings has a relatively large shear modulus.In addition,as the density of surface defects decreases,material rigidity decreases.