Phonon Transport In Anharmonic Interfacial Systems And Regulating Thermal Conductivity Of Layered Materials

The interfacial thermal transport process has been one of the most challenging problems in heat transfer process.On the one hand,the research on phonon transport process in interfacial systems is insufficient.On the other hand,the existence of interfacial thermal resistance does provide a new direction for the design of materials with lower thermal conductivity.In this paper,we first adopt the self-consistent anharmonic phonon concept for nonlinear lattices to investigate the phonon propagation within the materials as well as across interfaces based on equilibrium molecular dynamics simulations.Based on linear response theory,we propose an efficient method to calculate the frequency dependent transmission coefficient in a nonlinear lattice.By this method,phonon renormalization at finite temperature can be easily handled.Compared with other methods for calculating the frequency dependent transmission coefficient,our method is no longer limited to harmonic systems or periodic structures.The results are consistent with atomistic Green function method at the limit of weak anharmonicity.For nonlinear lattices under high temperatures,the anharmonicity is found to increase the cut-off frequency of transmission coefficient due to phonon renormalization.Further analysis shows that the anharmonicity also promotes the interfacial thermal conductance by causing the redistribution of the spectral flux of the excited vibrational waves during their propagation.Due to the existence of interlayer phonon mismatch,layered materials have shown great potential in thermal conductivity regulation.For example,the thermal conductivity of multilayer transition metal dichalcogenides does have huge potential to be regulated.Atomistic green function method is introduced in detailed analysis for designing multilayer transition metal dichalcogenides materials with ultralow thermal conductivities.The anisotropic contributions of phonon branches are examined and a huge mid-frequency-gap is found.For reducing the phonon conductance,alloys and nanodomains are also introduced into multilayered transition metal dichalcogenides.The result shows that alloys show stronger effect than nanodomains in reducing thermal conductance because of the coherent transport of low-frequency phonons.Besides,a 75% drop in thermal conductance by introducing alloys is checked.At last,the influence of period thickness on thermal conductance of multilayered transition metal dichalcogenides is analyzed.As the period thickness increases,a typical competing regime between the decrease of group velocity and the interface density dependent phonon-alloy scattering effect is examined.This competition will ultimately determine the specific thermal conductivity of multilayer transition metal dichalcogenides materials.