Abstract
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 VMoS3 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 VMoS3 point defects on the elastic properties of monolayer MoS2 sheets. Under the constrained uniaxial tensile test, the elastic properties of monolayer MoS2 sheets containing VMoS3 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 VMoS3 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 % VMoS3 vacancies. However, an anomalous parabolic relationship between the elastic modulus and the temperature is found in the monolayer MoS2 containing 0.1 % VMoS3 vacancy, bringing a crucial and fundamental issue to the application of monolayer MoS2 with defects.
Highlights
The monolayer molybdenum disulfide (MoS2) is a graphene-like crystal with quasi-two-dimensional (2D) honeycomb lattice, consisting of a monatomic Mo-layer sandwiched between two monatomic S-layers
The pristine monolayer MoS2 holds many remarkable physical and chemical properties for its intrinsic direct bandgap of 1.8 eV [1] and high elastic modulus of ~0.2 TPa, which strongly promises for burgeoning 2D nanodevices, including transistor [2], field-effect transistor [3], phototransistors [4], nanomechanical resonator [5], and photodetector [6]
Besides VS, VMoS3 is another type of defect preferentially generated by the extended electron irradiation [7]
Summary
The monolayer molybdenum disulfide (MoS2) is a graphene-like crystal with quasi-two-dimensional (2D) honeycomb lattice, consisting of a monatomic Mo-layer sandwiched between two monatomic S-layers. The structural defects can be commonly observed [7, 8] or deliberately introduced [9] in the monolayer MoS2, which have significant influence on its electrical conductivity [10], electrical contacts [11], band-to-band tunneling [12], catalytic [13], photoluminescence [14], magnetism [15], and thermal conductivity [16]. Dang and Spearot [17] conducted molecular dynamics (MD) nanoindentation simulations to investigate the VS effect on the mechanical behavior of monolayer MoS2. They revealed that the VS defects weaken the breaking force and induce displacive phase transformations under indentation.
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