Dangling bond induced cross-linking model in nanoscratched graphene layers

Dangling bond induced cross-linking in an interlayer graphene during nanoscratch is simulated by molecular dynamics method. The normal stress over 74 GPa leads to a broken hexagonal ring of the intralayer graphene, producing unstable dangling bonds which easily make up sp2 or sp3 between neighbor layers. The cross-linking density increases with increasing scratching depth, causing higher scratch hardness. The maximum scratch hardness is 90 GPa. The cross-linking is reversible after scratch when the normal stress is less than 90 GPa, beyond which the atoms from different graphene layers will be mixed together forming amorphous structure, making the scratch hardness decrease sharply. These results provide insights into the structural and mechanical properties of graphene based materials.