Fracture toughness enhancement of h-BN monolayers via hydrogen passivation of a crack edge

Molecular dynamics-based simulations were performed in conjunction with reactive force-field potential parameters to investigate the effect of crack-edge passivation via hydrogenation on the fracture properties of h-BN nanosheets. In semi-hydrogenated (H is attached to either B or N) and fully hydrogenated (H is attached to both B and N) crack-edge atoms, three hybridisation states - sp², sp³ and sp² + sp³ - were considered in the simulations. Significant improvement in the fracture toughness of h-BN nanosheets was predicted with semi- and fully hydrogenated crack-edge atoms. An overall improvement in fracture toughness of h-BN in the range of 16%-23% was estimated with the sp³ or sp² + sp³ hybridisation state of crack-edge atoms. This significant shift in the fracture toughness of h-BN nanosheets was attributed to lowered crack-edge energy, a stress-relieving mechanism and blunting of the crack tip. Semi-hydrogenated crack-edge atoms with hydrogen attached only to N atoms have shown a negative response in terms of fracture toughness.