Heat Transport Mechanism And Phonon Regulation Of Graphene And Hexagonal Boron Nitride Heterostructures

Two-dimensional material heterojunction has been a hot research object in recent years,because of its excellent heat transport performance.The two most common materials graphene and hexagonal boron nitride(h-BN)have been widely prepared and studied due to their lattice matching.Quantum size effect leads to the peculiar physical properties of low dimensional materials,which makes them have a broad application prospect in quantum devices.As new materials in optoelectronics,van der waals heterostructures have aroused doubts about the relationship between their stability and structural properties.Under the framework of density functional theory and multi-body perturbation theory,researches on graphene/h-BN heterojunction are more and more frequently,and the two materials are favored by researchers to research.From the perspective of nanomaterials,with the help of Lammps software package,Material Studio modeling,Ovito and other software,the study was carried out based on density functional theory,molecular dynamics and heat transfer theory.In this paper,two different heterojunction models are established based on graphene and hexagonal boron nitride,whose name is asymmetric graphene/h-BN vd W heterojunction.by using 2D atomic layers,it provides possibility to create a framework which has excellent properties and the thermal transport properties of such hybrid heterostructures are crucial for the preparation of functional devices.In the first part,the non-equilibrium molecular dynamics method(NEMD)is used to simulate the heat transfer operation of the model.It is found that for the former model,the heat tends to flow from single layer to multi-layer region,which resulting in a significant thermal rectification(TR)effect.When calculating phonon spectra,it was found that the phonon spectra of AB parts matched well in the high frequency region,but showed significant differences in the low frequency region,which largely depended on the direction of heat flow,especially the out-of-plane phonons below 3.5THz are strongly suppressed in region A(enclosed graphene).The influence of several factors on the thermal rectification phenomenon was investigated such as changing the sample length,asymmetry,ambient temperature of the asymmetric model and the strength of the vd W interaction,the results show that the unexpected increase in TR ratio can attribute to severe changes in the properties of closed graphene phonons resulting from enhanced interlayer coupling.In the second part,the nonlinear heat transport in the asymmetric hBN/graphene vd W heterostructure is studied.It is found that strong interlayer coupling can produce significant negative differential thermal resistance(NDTR)effect at a small temperature deviation ΔT=30K.The system structure and phonon dynamics analysis show that The NDTR effect is attributed to the competition between the out-of-plane vibration mismatch of the wrapped monolayer atomic region and the coupling factor of the in-plane vibration phonon spectrum.This study provides a new idea for thermal design and thermal management of nanodevices.