Molecular Dynamics Simulations On The Thermal And Mechanical Properties Of In-plane Graphene/h-BN Heterostructure

Hexagonal boron nitride(h-BN)and graphene have similar honeycomb-lattice topological structure,with only 2.44%difference in lattice constant.In-plane graphene/h-BN heterostructure is widely used in nanoscale integrated circuits and electronic devices because of its outstanding electric properties.As the size of electronic components continuously decreases,the energy density dramatically increases and the heat transport and dissipation of in-plane graphene/h-BN heterostructure have received more and more attention.In-plane graphene/h-BN heterostructure is usually generated by two-step chemical vapor deposition method,with dislocations,holes,cracks and other topological defects along the grain boundaries.These defects may influence the mechanical and thermal properties of in-plane graphene/h-BN heterostructure.The experiments to measure the mechanical and thermal properties of in-plane glraphene/h-BN heterostructure are difficult and expensive.In comparison,molecular dynamics simulations can not only accurately predict the mechanical and thermal properties of in-plane graphene/h-BN heterostructure but observe the evolutionary process from atomic scale.Nowadays,molecular dynamics simulations are a common approach to investigate the mechanical and thermal properties of 2D materials.In this thesis,we use molecular dynamics methods to study the mechanical and thermal properties of in-plane graphene/h-BN heterostructure.The first chapter introduces the main properties of graphene,boron nitride and in-plane graphene/h-BN heterostructure;the second chapter outlines the basic numerical methods to calculate the thermal and mechanical properties from the simulations of in-plane graphene/h-BN heterostructure.The simulation results on the thermal and mechanical properties of in-plane graphene/h-BN heterostructure with different topological defects will be presented in chapter 3 and 4,respectively.The third chapter focuses on the thermal properties of in-plane graphene/h-BN heterostructure.The temperature field of the system is created by adding heat flux in a hot bath and siphoning the same heat flux in cold bath.Thermal conductance of grain boundaries and polycrystalline structures is obtained on the basis of the temperature field and heat flux.The present study investigates the effects of applied tension/torsion,temperature and grain size on the thermal conductivity of grain boundaries in polycrystalline structures.The fourth chapter mainly studies the effects of topological defects and temperature on the mechanical properties of in-plane graphene/h-BN heterostructure.Tensile stress-strain curves are obtained from the simulations by applying uniaxial tension which is perpendicular to the direction of grain boundaries.We also discuss ultimate strength and ultimate strain of the nanostructures which are strongly influenced by the tilt angle and temperature.