First-principles study on phonon transport properties of MoTe 2 and WTe 2 monolayers in different phases

Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDC) monolayer is a key method for manipulating the lattice thermal conductivity. In this paper, we investigate the phonon thermal transport properties of MoTe 2 and WTe 2 monolayers with H and T′ phases (H-TMDC and T′-TMDC) via first-principles calculations. H-MoTe 2 and H-WTe 2 monolayers have isotropic lattice thermal conductivities, whereas the lattice thermal conductivities of T′-MoTe 2 and T′-WTe 2 monolayers are highly anisotropic. Meanwhile, in comparison with the H phase, the maximal lattice thermal conductivity in T′ phase has a reduction of 83.85% and 77.92% at 300 K for MoTe 2 and WTe 2 monolayers, respectively. Furthermore, we observe that phonon heat capacities and phonon lifetimes of T′-TMDC monolayers are lower than those of H-TMDC monolayers, while the phonon group velocities of T′-TMDC monolayers are larger. Hence, the competitive relationship among these parameters leads to a lower lattice thermal conductivity of the T′-TMDC monolayer. In addition, lower critical phonon MFPs (mean free path) of T′-TMDC monolayers prove that the lattice thermal conductivity has a weaker size dependence. These findings demonstrate that MoTe 2 and WTe 2 monolayers with different phases have a great potential in 2D nanoelectronic devices.