Lattice thermal conductivity of β 12 and χ 3 borophene* *Project supported in part by the National Key Research and Development Program of China (Grant No. 2016YFA0200901), the National Natural Science Foundation of China (Grant No. 11890703), the Science and Technology Commission of Shanghai Municipality, China (Grant Nos. 19ZR1478600 and 18JC1410900), the Fundamental Research Funds for the Central Universities, China

Abstract

Borophene allotropes have many unique physical properties due to their polymorphism and similarity between boron and carbon. In this work, based on the density functional theory and phonon Boltzmann transport equation, we investigate the lattice thermal conductivity κ of both β 12 and χ 3 borophene. Interestingly, these two allotropes with similar lattice structures have completely different thermal transport properties. β 12 borophene has almost isotropic κ around 90 W/(m⋅K) at 300 K, while κ of χ 3 borophene is much larger and highly anisotropic. The room temperature κ of χ 3 borophene along the armchair direction is 512 W/(m⋅K), which is comparable to that of hexagonal boron nitride but much higher than most of the two-dimensional materials. The physical mechanisms responsible for such distinct thermal transport behavior are discussed based on the spectral phonon analysis. More interestingly, we uncover a unique one-dimensional transport feature of transverse acoustic phonon in χ 3 borophene along the armchair direction, which results in a boost of phonon relaxation time and thus leads to the significant anisotropy and ultrahigh thermal conductivity in χ 3 borophene. Our study suggests that χ 3 borophene may have promising application in heat dissipation, and also provides novel insights for enhancing the thermal transport in two-dimensional systems.