Enhanced thermal conductivity and isotope effect in single-layer hexagonal boron nitride

The thermal conductivity, κ, of single layers of hexagonal boron nitride (h-BN), as well as that of bulk h-BN have been calculated utilizing an exact numerical solution of the phonon Boltzmann transport equation. The stronger phonon-phonon scattering in h-BN is revealed as the cause for its lower κ compared with graphite. A reduction in such scattering in the single layer arising mainly from a symmetry-based selection rule leads to a substantial increase in κ, with calculated room temperature values of more than 600 Wm^-1K^-1. Isotopic enrichment further increases κ, with the calculated enhancement exhibiting a peak with temperature, whose magnitude shows a dramatic sensitivity to crystallite size.