Anisotropic phonon transport in van der Waals nanostructures

Phonon transport in van der Waals materials behaves strong anisotropic and size-dependent properties. With the help of molecular dynamics simulation, nonequilibrium Green's function, and Monte Carlo simulation methods, it is demonstrated that when the structure size is smaller than the phonon mean free paths, the thermal conductivity cannot be simply predicted by the classical anisotropic model. For thin van der Waals nanowires, the cross-plane phonon modes dominate heat transfer process along arbitrary crystalline directions except the in-plane direction, which makes phonons transport in zigzag way. Increasing the structure size, the in-plane phonon modes gradually dominate heat transfer process along arbitrary crystalline directions except the cross-plane direction. A phenomenological model based on the modified Boltzmann transport equation is put forward to describe anisotropic phonon transport in the van der Waals nanostructures when the structure size is smaller than the phonon mean free paths, which fits well with the molecular dynamics results.

Automated summary

Phonon transport in van der Waals materials exhibits strong anisotropic and size-dependent properties, especially for van der Waals nanowires. A phenomenological model has been proposed to describe the anisotropic phonon transport behavior, which deviates from classical predictions when the structure size is small.