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 ( ) occurring in low frequency modes in graphene, positive in the whole Brillouin zone is demonstrated in monolayer MoS 2 with much larger 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 result obtained by fitting the dielectric oscillators with the infrared reflectivity spectrum. The lifetime of Raman A 1 ′ mode (38.36 ps) is about 7 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 Wm -1 K -1 , two orders of magnitude lower than that of graphene.

We study interface thermal resistance (ITR) in a system consisting of two dissimilar anharmonic lattices exemplified by the Fermi-Pasta-Ulam and Frenkel-Kontorova models. It is found that the ITR is asymmetric; namely, it depends on how the temperature gradient is applied. The dependence of the ITR on the coupling constant, temperature, temperature difference, and system size is studied. Possible applications in nanoscale heat management and control are discussed.

Thermal conductivity of graphene nanoribbons (GNR) with length 106Å and width 4.92Å after isotopic doping is investigated by molecular dynamics with quantum correction. Two interesting phenomena are found: (1) isotopic doping reduces thermal conductivity effectively in low doping region, and the reduction slows down in high doping region; (2) thermal conductivity increases with increasing temperature in both pure and doped GNR; but the increasing behavior is much more slowly in the doped GNR than that in pure ones. Further studies reveal that the physics of these two phenomena is related to the localized phonon modes, whose number increases quickly (slowly) with increasing isotopic doping in low (high) isotopic doping region.

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