Molecular Dynamics Study Of Thermal Conductivity Of 2D Heterojunction And Thermal Resistance At 2D Material/Substrate Interface

The appearance of graphene opens the way to explore two-dimensional materials.Compared with graphene with zero band gap,two-dimensional transition metal dichalcogenides(TMDs)with 1?2V band width are widely used in electronic and photoluminescence devices.However,the heat dissipation of these devices may be the bottleneck of their performance and reliability,so it becomes more and more important to understand the thermal transport in nanostructures.Compared with single-layer two-dimensional materials,the van der Waals heterostructure formed by stacking different TMDs shows unusual performance,and has a good application prospect in optics and electronics.At present,there are two main methods to fabricate heterostructures:direct-growth bottom-up processes and mechanical top-down(exfoliation and restacking)approaches.Different synthesis processes may lead to lattice mismatch,interlayer rotation and species intermixing.In this paper,We adopt non-equilibrium molecular dynamics simulations to explore the influence of these factors on the thermal conductivity of bilayer heterostructures that are formed by single-layer MoS₂ and MoSe₂.The results show that the thermal conductivity of the bilayer made up of unstrained MoS₂ and MoSe₂ layers is 121%larger than the AB stacked one.Detailed phonon scattering analysis reveals that the tensile strain-induced enhancement of anharmonicity is the main reason.The study of the twisted bilayer structure shows that the interlayer rotation considerably alters the phonon band structure but has little impact on the thermal conductivity.We also find that thermal conductivity varies inversely with the species intermixing ratio due to the increase of localized phonon modes.Two dimensional materials with substrates,such as MoS₂/SiO₂,are widely used in photodetectors and field effect transistors.When the two-dimensional material is placed on the substrate,there are two main ways to radiate heat to the environment:one is along the plane direction of the two-dimensional material,the other is through the interface between the two-dimensional material and the support material.When the contact area between the two-dimensional material and the substrate is much larger than the heat dissipation area along the two-dimensional material,most of the waste heat is dissipated through the interface between the two-dimensional material and the substrate.Therefore,in order to obtain two-dimensional device with reliable life and performance,the interfacial thermal resistance(ITR)between two-dimensional material and support material must be fully considered.In this paper,We adopt non-equilibrium molecular dynamics simulations to explore the influence of mass,interlayer force,potential energy,and temperature on the interfacial thermal resistance of MoS₂/SiO₂.Besides,a simple method by calculating the phonon density of state(PDOS)is proposed to qualitatively analyze the interfacial thermal resistance.The results show that the potential energy and atomic mass are the main reasons for the difference of interfacial thermal resistance between MoS₂/SiO₂ and MoSe₂/SiO₂.By changing the molecular weight of S atom,it is found that the interfacial thermal resistance decreases first and then increases with the increase of S atom mass.We also found that the interfacial thermal resistance decreases with the increase of interming rate by changing the average mass of atoms.In addition,the interfacial thermal resistance decreases with the increase of temperature and LJ potential energy intensity.The predicted value of the theoretical model of interfacial thermal resistance based on PDOS proposed in this paper is consistent with the calculated value,and it can compare the interfacial thermal resistance qualitatively.