Lattice vibrational modes and phonon thermal conductivity of monolayer MoS${}_{2}$

Lattice vibrational modes and phonon thermal conductivity of monolayer MoS $_{2}$

Yongqing Cai, Jinghua Lan, Gang Zhang, and Yong-Wei Zhang

Phys. Rev. B 89, 035438 – Published 31 January 2014

Abstract

The anharmonic behavior of phonons and intrinsic thermal conductivity associated with the umklapp scattering in monolayer MoS $_{2}$ sheet are investigated via first-principles calculations within the framework of density functional perturbation theory. In contrast to the negative Grüneissen parameter ( $γ$ ) occurring in low-frequency modes in graphene, positive $γ$ in the whole Brillouin zone is demonstrated in monolayer MoS $_{2}$ with much larger $γ$ for acoustic modes than that for the optical modes, suggesting that monolayer MoS $_{2}$ sheet possesses a positive coefficient of thermal expansion. The calculated phonon lifetimes of the infrared active modes are 5.50 and 5.72 ps for $E^{'}$ and $A_{2}^{''}$ , respectively, in good agreement with experimental results obtained by fitting the dielectric oscillators with the infrared reflectivity spectrum. The lifetime of the Raman $A_{1}^{'}$ mode (38.36 ps) is about seven times longer than those of the infrared modes. The dominated phonon mean free path of monolayer MoS $_{2}$ is less than 20 nm, about 30-fold smaller than that of graphene. Combined with the nonequilibrium Green's function calculations, the room temperature thermal conductivity of monolayer MoS $_{2}$ is found to be around 23.2 W m $^{- 1}$ K $^{- 1}$ , two orders of magnitude lower than that of graphene.