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Structural defects in monolayer molybdenum disulfide (MoS2) have significant influence on the electric, optical, thermal, chemical, and mechanical properties of the material. Among all the types of structural defects of the chemical vapor phase-grown monolayer MoS2, the V point defect (a vacancy complex of Mo and three nearby S atoms) is another type of defect preferentially generated by the extended electron irradiation. Here, using the classical molecular dynamics simulation with reactive empirical bond-order (REBO) potential, we first investigate the effect of V point defects on the elastic properties of monolayer MoS2 sheets. Under the constrained uniaxial tensile test, the elastic properties of monolayer MoS2 sheets containing V vacancies with defect fraction varying from 0.01 to 0.1 are obtained based on the plane anisotropic constitutive relations of the material. It is found that the increase of V vacancy concentration leads to the noticeable decrease in the elastic modulus but has a slight effect on Poisson's ratio. The maximum decrease of the elastic modulus is up to 25 %. Increasing the ambient temperature from 10 K to 500 K has trivial influences on the elastic modulus and Poisson's ratio for the monolayer MoS2 without defect and with 5 % V vacancies. However, an anomalous parabolic relationship between the elastic modulus and the temperature is found in the monolayer MoS2 containing 0.1 % V vacancy, bringing a crucial and fundamental issue to the application of monolayer MoS2 with defects. [ABSTRACT FROM AUTHOR]

The single-layer molybdenum disulfide (SLMoS2) nanosheets have been experimentally discovered to exist in two different polymorphs, which exhibit different electrical properties, metallic or semiconducting. Herein, molecular dynamics (MD) simulations of nanoindentation and uniaxial compression were conducted to investigate the phase transition of SLMoS2 nanosheets. Typical load–deflection curves, stress–strain curves, and local atomic structures were obtained. The loading force decreases sharply and then increases again at a critical deflection under the nanoindentation, which is inferred to the phase transition. In addition to the layer thickness, some related bond lengths and bond angles were also found to suddenly change as the phase transition occurs. A bell-like hollow, so-called residual deformation, was found to form, mainly due to the lattice distortion around the waist of the bell. The effect of indenter size on the residual hollow was also analyzed. Under the uniaxial compression along the armchair direction, a different phase transition, a uniformly quadrilateral structure, was observed when the strain is greater than 27.7%. The quadrilateral structure was found to be stable and exhibit metallic conductivity in view of the first-principle calculation. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations based on reactive empirical bond order potentials are performed to investigate the attributes of the thermally agitated ripples in single-layer molybdenum disulfide (SLMoS 2 ) membranes, including the vibrational mode and the height fluctuation. The effects of aspect ratio, type and shape of boundary conditions, and chirality, on the attributes of the ripples are mainly concerned. The aspect ratio has a major influence on the vibrational mode of the ripples for rectangular SLMoS 2 membranes. Most of the effect of chirality is concentrated on the height fluctuation for the slender SLMoS 2 nanoribbons due to inducing different number of ripples. The types of boundary conditions is shown to have minor influence on the vibrational mode and height fluctuation for the rectangular SLMoS 2 membranes. Only high-order resonant mode is thermally agitated in SLMoS 2 nanosheets with circular boundary conditions. The height fluctuation in most of SLMoS 2 membranes increases with increasing the temperature, which is consistent with the elastic theory of membrane. The work can be useful for the application of strain engineering in SLMoS 2 nanodevices. [ABSTRACT FROM AUTHOR]