The Influence Of Free Edges And Interface On Mechanical Properties Of Two-dimentional Materials

Two-dimensional(2D)nanomaterials are a class of materials with atomic thickness,where the edge effect plays an important role for their mechanical properties.We perform both molecular dynamics simulations and theoretical analysis to study the two types for edges:the free edges of graphene and the spread(grad)interfaces of in-plane heterostructure.For the The main works are as follows:(1)We derive analytic expressions for the Young 's modulus and the Poisson's ratio of the graphene nanoribbon,in which free edges are warped by the compressive edge stress.Our analytic formulas explicitly illustrate the reduction of the Young's modulus by the warped free edges,leading to the obvious width dependence for the Young's modulus of the graphene nanoribbon.The Poisson's ratio is also reduced by the warped free edges,and negative Poisson's ratio can be achieved in the graphene nanoribbon with ultra-narrow width.These results are comparable with previous theoretical works.(2)Both molecular dynamics simulations and theoretical analysis are performed to study the sensitivity of the mass sensor based on graphene nanomechanical resonators,which are actuated following the global extended mode or the localized edge mode.We find that the mass detection sensitivity corresponding to the edge mode is about three times higher than that corresponding to the extended mode.Our analytic derivations reveal that the enhancement of the sensitivity originates in the reduction of the effective mass for the edge mode due to its localizing feature.Our findings shed light on improving the sensitivity of the graphene based mass spectrometry by utilizing the localized edge mode.(3)The motion of graphene on the substrate of MoS2-WSe2 heterostructure with spread edge(graded edge)is studied by molecular dynamics simulations and theoretical analysis.The MD results review that the direction for the diffusion is sensitive to the graphene sheet's initial location,which is in two different regions.The graphene sheet diffuses in opposite directions for the initial location that falls in different regions.We derive an analytic formula for the interlayer coupling potential,which discloses the underlying mechanism for the dependence of the directional motion on the initial location of the graphene sheet.The highlights of this thesis are as follows.First,for the influence of graphene's free edges on mechanism,the former's task are mainly based on the numerical simula-tions,while we obtain theoretical expressions.Second,we discuss the possibility of the applications of edge mode on the detection of micro-mass,and propose a new approach of enhancement of sensitivity for mass detection.Third,we reveal a novel mechanism for the directional motion and which may be valuable for the application of the transition metal dichalcolegides graded lateral heterostructure in practical electronic devices.