Ab initio investigation of single-layer high thermal conductivity boron compounds

Abstract

The discovery and design of materials with large thermal conductivities (${\ensuremath{\kappa}}_{L}$) is critical to address future heat management challenges, particularly as devices shrink to the nanoscale. This requires developing novel physical insights into the microscropic interactions and behaviors of lattice vibrations. Here, we use ab initio phonon Boltzmann transport calculations to derive fundamental understanding of lattice thermal transport in two-dimensional (2D) monolayer hexagonal boron-based compounds, h-BX ($X=\mathrm{N}$, P, As, Sb). Monolayer h-BAs, in particular, possesses structural and dispersion features similar to bulk cubic BAs and 2D graphene, which govern their ultrahigh room temperature ${\ensuremath{\kappa}}_{L}$ (1300 W/m K and 2000--4000 W/m K, respectively), yet here combine to give significantly lower ${\ensuremath{\kappa}}_{L}$ for monolayer h-BAs (400 W/m K at room temperature). This work explores this discrepancy, and thermal transport in the monolayer h-BX systems in general, via comparison of the microscopic mechanisms that govern phonon transport. In particular, we present calculations of phonon dispersions, velocities, scattering phase space and rates, and ${\ensuremath{\kappa}}_{L}$ of h-BX monolayers as a function of temperature, size, defects, and other fundamental parameters. From these calculations, we make predictions of the thermal conductivities of h-BX monolayers, and more generally develop deeper fundamental understanding of phonon thermal transport in 2D and bulk materials.