  This study examines the roughness of mechanically cleaved edges in 2D
crystals and glasses using molecular dynamics simulations with chemically
accurate machine-learning force fields. Our results show that ultra-flat
armchair and zigzag edges can be achieved in graphene by aligning the loading
direction with specific lattice orientations. Deviations from these
orientations create kinks between the atomically smooth armchair and zigzag
segments, with increased irregularities when dynamic effects are considered.
Fracture mechanics analysis highlights the kinetic and dynamic factors
contributing to crack deflection and edge roughening. In three-atom-thick 2D
silica crystals, the relationship between edge morphologies and cleavage
conditions is modified by their bilayer structure and sublattice asymmetry. In
2D silica glasses, this correlation is further disrupted by topological
disorder. These insights are crucial for minimizing edge roughness in 2D
materials, which is essential for their performance in mechanical and
electronic applications.
