Anisotropic Failure of sp2-Hybrid Bonds in Graphene Sheets

A combined atomic force microscopy and theoretical study reveals preferred fracture directions in the topmost graphene sheets of mechanically exfoliated graphite. Fractures in the basal plane of single-crystal grains are found to depend on the applied stress direction and crystallographic orientation. Interatomic bonds that are aligned with the applied stress direction exhibit the largest resistance against fracture. The findings are modeled through an angle-dependent failure of sp(2)-hybrid bonds, which results from a larger interatomic energy dispersion of sheared C-C bonds