Strengthening and Weakening by Dislocations in Monolayer MoS2

TL;DR

This study investigates how dislocations in monolayer MoS2 influence its mechanical strength, revealing that dislocation arrangement and tilt angle can either strengthen or weaken the material, with failure initiating at specific bonds.

Contribution

It introduces a combined atomistic and continuum model to understand dislocation effects on MoS2's mechanical properties, providing insights for dislocation engineering.

Findings

GB strength varies with tilt angle and dislocation arrangement.

Zigzag-tilt GBs show strength increasing with tilt angle.

Failure initiates at bonds shared by 5|7 rings, unlike graphene.

Abstract

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