Comparison on thermal transport properties of graphene and phosphorene nanoribbons

Remarkable Role of Grain Boundaries in the Thermal Transport Properties of Phosphorene

In this work, we study the effect of grain boundary (GB) on the thermal transport of phosphorene by using molecular dynamics simulations. By exploring a total of 19 GBs with different GB defect types and densities, we find that there is a relatively high Kapitza thermal boundary resistance at these boundaries. By analyzing the spatial distributions of the heat flux, we find that this high thermal boundary resistance can be attributed to the strong phonon-boundary scattering at the GBs. With the same type of defect, the thermal boundary resistance is found to increase with the increase of the defect density along the GBs, which can be attributed to the nonuniform distribution of stress and lattice distortion. Finally, we investigate the anisotropy in the thermal conductivity of phosphorene with GBs and reveal a strikingly high anisotropy ratio of thermal conductivities, which is found to arise from the different influences of boundaries on the thermal transport along the zigzag and armchair directions. Our results highlight the importance of GBs in the transport behavior of phosphorene and the need to include their effects in the thermal management of phosphorene-based electronic devices.

Design of phosphorene/graphene heterojunctions for high and tunable interfacial thermal conductance

Using density functional theory calculations and molecular dynamics simulations, we systematically explore various possible atomic structures of phosphorene/graphene in-plane heterojunctions and their effects on interfacial thermal conductance (ITC). Unlike the remarkable orientation-dependence of thermal conductivity in pure phosphorene, the ITC is much less orientation-dependent. In addition, the ITC is found to be high, comparable to those of graphene-MoS2 in-plane heterojunctions and chemically-bonded graphene-metal heterojunctions. Moreover, the ITC of armchair heterojunctions abnormally increases with tensile strain, while the zigzag heterojunctions simply follow the normal trend. To gain an in-depth understanding of these interesting observations, we further analyze the atomic topology and phonon vibrational spectrum and examine the nonlinear interfacial coupling in the heat transport, ITC anisotropy, and temperature effect on the ITC. Our findings suggest that phonon anharmonicity plays a critical role in the thermal transport behavior of two-dimensional in-plane heterojunctions.

Large diffusion anisotropy and orientation sorting of phosphorene nanoflakes under a temperature gradient

We perform molecular dynamics simulations to investigate the motion of phosphorene nanoflakes on a large graphene substrate under a thermal gradient. It is found that the atomic interaction between the graphene substrate and the phosphorene nanoflake generates distinct rates of motion for phosphorene nanoflakes with different orientations. Remarkably, for square phosphorene nanoflakes, the motion of zigzag-oriented nanoflakes is 2-fold faster than those of armchair-oriented and randomly-oriented nanoflakes. This large diffusion anisotropy suggests that sorting of phosphorene nanoflakes into specific orientations can be realized by a temperature gradient. The findings here provide interesting insights into strong molecular diffusion anisotropy and offer a novel route for manipulating two-dimensional materials.