Evidence for active atomic defects in monolayer hexagonal boron nitride: a new mechanism of plasticity in two-dimensional materials.

We report the formation and motion of 4|8 (square-octagon) defects in monolayer hexagonal boron nitride (h-BN). The 4|8 defects, involving less-favorable B-B and N-N bonds, are mobile within the monolayer at high sample temperature (∼ 1000 K) under electron beam irradiation. Gliding of one or two atomic rows along the armchair direction is suggested to be the origin of the defect motion. This represents a completely new mechanism of plasticity in two-dimensional materials.