Effect of point and grain boundary defects on the mechanical behavior of monolayer MoS_2 under tension via atomistic simulations

摘要

Atomistic simulation is used to study the structure and energy of defects in monolayer MoS_2 and the role of defects on the mechanical properties of monolayer MoS_2. First, energy minimization is used to study the structure and energy of monosulfur vacancies positioned within the bottom S layer of the MoS_2 lattice, and 60° symmetric tilt grain boundaries along the zigzag and armchair directions, with comparison to experimental observations and density functional theory calculations. Second, molecular dynamics simulations are used to subject suspended defect-containing MoS_2 membranes to a state of multiaxial tension. A phase transformation is observed in the defect-containing membranes, similar to prior work in the literature. For monolayer MoS_2 membranes with point defects, groups of monosulfur vacancies promote stress-concentration points, allowing failure to initiate away from the center of the membrane. For monolayer MoS_2 membranes with grain boundaries, failure initiates at the grain boundary and it is found that the breaking force for the membrane is independent of grain boundary energy.