Monolayer MoS2 Sheet Research Articles

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 occurring in low frequency modes in graphene, positive Gruneissen parameter in the whole Brillouin zone is demonstrated in monolayer MoS2 with much larger Gruneissen parameter 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 A2'' respectively, in good agreement with experimental result obtained by fitting the dielectric oscillators with the infrared reflectivity spectrum. The lifetime of Raman A1' mode (38.36 ps) is about 7 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 non-equilibrium Green's function calculations, the room temperature thermal conductivity of monolayer MoS2 is found to be around 23.2 Wm-1K-1, two orders of magnitude lower than that of graphene.

Phonon thermal conductivity of monolayer MoS2 sheet and nanoribbons

We investigated the thermal conduction of monolayer MoS2 sheet and nanoribbons using molecular dynamics simulations. Room temperature thermal conductivity of monolayer MoS2 is found to be 1.35 W/mK, which is three orders of magnitude lower than that of graphene. In contrast to the remarkable size effect observed in graphene nanoribbons, the thermal conductivity of MoS2 nanoribbons is insensitive to width (3–16 nm), length (4–111 nm), and the type of edge, which are explained by the local heat flux analysis and phonon scattering mechanisms. The low thermal conductivity together with reported high Seebeck coefficient opens up the possibility to realize MoS2-based two-dimensional thermoelectric devices.

Density functional theory study of Fe adatoms adsorbed monolayer and bilayer MoS2 sheets

Functionalization of MoS2 sheet (monolayer and bilayer) by the adsorption of transition metal Fe adatom to its surface and interlayer has been investigated computationally using first-principles calculations based on the density functional theory. We found that the systems with absorption of Fe adatoms on the surfaces of both monolayer and bilayer MoS2 sheets are still semiconductors, without spin polarization at the Fermi level. However, for the system with absorption of Fe adatom in the interlayer of bilayer MoS2 sheet, its electronic structure exhibits half-metal behavior, with 100% spin polarization at the Femi level, which provides a promising material for spintronic devices.