Strengthening and Weakening by Dislocations in Monolayer MoS2

Dislocations govern the properties of crystals. Yet, how pentagon-heptagon (5 vertical bar 7) pairs in grain boundaries (GBs) affect the mechanical properties of MoS2 remains poorly known. Using atomistic simulations and the continuum disclination dipole model, we show that depending on the tilt angle and 5 vertical bar 7 dislocation arrangement, MoS2 GB strength can be enhanced or reduced with the tilt angle. For zigzag-tilt GBs primarily composed of Mo5 vertical bar 7 + S5 vertical bar 7 dislocations, GB strength monotonically increases as the square of the tilt angle. For armchair-tilt GBs with Mo5|7 or S5 vertical bar 7 dislocations, however, the trend of GB strength breaks down, as dislocations are unevenly spaced. Moreover, mechanical failure initiates at the bond shared by 5 vertical bar 7 rings, in contrast to graphene in which failure occurs at the bond shared by 6 vertical bar 7 rings. This work provides new insights into the mechanical design of synthetic transition metal dichalcogenide crystals via dislocation engineering.