Mechanical responses of WSe2 monolayers: a molecular dynamics study

The mechanical responses of tungsten diselenide (WSe2) monolayers are systemically investigated using classical molecular dynamics simulation. The tensile behaviors of trigonal prismatic phase (h-phase) and distorted octahedral coordinated phase (t-phase) WSe2 in the armchair and zigzag directions are simulated, and the fracture strain, fracture strength and Young's modulus are calculated under different temperatures, strain rates and vacancy defect ratios. The results show that, at 300 K and a strain rate of 1 x 10(-4) ps(-1), the fracture strength for h-WSe2 is 16.20 GPa under a 0.19 fracture strain in the armchair direction, while it is 15.74 GPa under a 0.21 fracture strain in the zigzag direction. For t-WSe2, the corresponding fracture strengths and strains have much lower values of 3.46 GPa and 0.06 for the armchair direction, and 3.66 GPa and 0.07 for the zigzag direction, respectively. The evaluated Young's moduli in the armchair and zigzag directions are 119.73 GPa and 118.29 GPa for h-WSe2, and 68.57 GPa and 68.03 GPa for t-WSe2, respectively. Also, with the increased temperature, atomic thermal vibrations become stronger, which results in decreased fracture strains, fracture strengths, and Young's moduli in the armchair and zigzag directions for both h-WSe2 and t-WSe2 . When the defect ratio changes from 0% to 5%, the mechanical properties of WSe2 deteriorate due to the stress concentration, increased fracture nucleation and disorder of the W-Se bonds. However, in comparison with temperature and defect effects on mechanical properties, the strain rate effect is less significant.