Brittle and ductile behavior in monolayer MoS2

Abstract

Using first-principles calculations, we study the response of monolayer MoS2 with pentagon–heptagon (5|7) pair defect-dominated grain boundary (GB) to an in-plane tension. Brittle or ductile behaviors can occur depending on the GB tilt angle (θ). Brittle failure is dominated by step-by-step dissociation of bonds at GBs, while ductile failure is characterized by a series of reaction and glide events of dislocations. Surprisingly, as θ = 9.40°, 5|7 dislocation defects are annihilated by stretching to form defect-free MoS2. Moreover, the failure strength increases with increasing 5|7 dislocation defect and can be explained by the continuum disclination dipole theory.