Lattice vibrational modes and phonon thermal conductivity of monolayer MoS2

The anharmonic behavior of phonons and intrinsic thermal conductivity associated with the umklapp scattering in monolayer MoS2 sheet are investigated via first-principles calculations within the framework of density functional perturbation theory. In contrast to the negative Gruneissen parameter (gamma) occurring in low-frequency modes in graphene, positive gamma in the whole Brillouin zone is demonstrated in monolayer MoS2 with much larger gamma for acoustic modes than that for the optical modes, suggesting that monolayer MoS2 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 MoS2 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 MoS2 is found to be around 23.2 Wm(-1) K-1, two orders of magnitude lower than that of graphene.