Anisotropic thermal transport in phosphorene: effects of crystal orientation.

As an intrinsic thermally anisotropic material, the thermal properties of phosphorene must vary with respect to the crystal chirality. Nevertheless, previous studies of heat transfer in phosphorene have been limited to the 0.0° (zigzag, ZZ) and 90.0° (armchair, AC) chiralities. In this study, we investigate the orientation-dependent thermal transport in phosphorene sheets with a complete set of crystal chirality ranging from 0.0° to 90.0° using the Boltzmann transport equation (BTE) associated with the first-principles calculations. It was found that in the phosphorene sheets, the intrinsic thermal conductivity is a smooth monotonic decreasing function of the crystal chirality, which exhibits sinusoidal behavior bounded by the two terminated values 48.9 (0.0°) and 27.8 (90.0°) W m(-1) K(-1). The optical modes have unusually large contributions to heat transfer, which account for almost 30% of the total thermal conductivity of phosphorene sheets. This is because the optical phonons have comparable group velocities and relaxation times to the acoustic phonons.