Thermal Transport In Two-dimensional Transitional Metal Dichalcogenides:A Molecular Dynamics And First Principles Study

Two-dimensional transition metal dichalcogenides?TMDs?have received great attention due to their unique optical,electrical and thermal properties and their broad application prospects in the field of optoelectronic devices.Due to the complexity of thermal measurement experiments,the study of the thermal transport properties of TMDs lags far behind the study of their optoelectronic properties.The study of the thermal transport properties of TMDs has important scientific significance for understanding the physical properties and energy transport processes at the micro-nano scale,and could provide physical basis for applications of new two-dimensional materials in?opto?electronic devices.In this thesis,the in-plane thermal conductivity,size effect and temperature effect of single-layer 1T-ReS₂ and MoS₂ are calculated by molecular dynamics.The thermal conductivity of single-layer 1T-ReS₂ at room temperature is calculated to be about 29 W/m K.The single layer MoS₂ is 92 W/m K,and they do not exhibit anisotropy in both the Zigzag and Armchair directions.The phonon group velocity and phonon relaxation time are obtained by analyzing the phonon dispersion relationship of the single layer 1T-ReS₂ and MoS₂,which yields the phonon mean free path.The difference in the in-plane thermal conductivity of the two materials is due to that the phonon group velocity and the phonon mean free path of the single layer 1T-ReS₂ each are about 40% smaller than the single layer MoS₂.The thermal transport properties of the 1T-ReS₂ /MoS₂ heterojunction are also studied by molecular dynamics.The in-plane thermal conductivity of the monolayer 1T-ReS₂ /MoS₂ heterojunction at room temperature is 57.7 W/m K,which is slightly lower than 62.3 W/m K,the average value of the in-plane thermal conductivity of MoS₂ and 1T-ReS₂.Part of the reason for the decrease in thermal conductivity may be that the coupling between the heterojunction interfaces blocks the transport of phonons in the in-plane direction,while the molecules The kinetic calculation shows that the interface thermal conductance of 1T-ReS₂ /MoS₂ is about 243 MW/m² K.In addition,the phonon thermal transport of 1T'-ReS₂?1T distorted phase?is studied by the first-principles calculation method,and the thermal conductivity in the direction of the Re-chain and the thermal conductivity in the direction of the vertical Re-chain are obtained by the SLACK empirical formula.The anisotropy ratio between the two is 1.3,which is similar to the reported experimental measurements.And the accuracy of the calculation of SLACK formula is verified by the calculation of thermal conductivity of black phosphorus.In terms of the computational methods,molecular dynamics calculations rely on empirical potential energy,and their absolute values are often not accurate enough.They are generally used to explore the trend of the thermal transport properties of materials varying with a certain parameter.First-principles calculations are more accurate than the Boltzmann transport equations,but the computational cost of calculating low-symmetric two-dimensional materials is high.The calculation of SLACK formula depends on the subtle changes of the lattice with temperature.The temperature is very sensitive and is more suitable for qualitative analysis or semi-quantitative analysis of heat transport properties.In this paper,the thermal conductivity of two-dimensional TMDs materials is calculated by these methods.The results provide insights for the theoretical study of anisotropic thermal transport of low-symmetry two-dimensional materials,and also provide a critical physical basis for energy transport and thermal management of the new two-dimensional TMDs materials?optical?electronic devices.