Intermediate states and structure evolution in the free-falling process of the dislocation in graphene

This paper investigated the intermediate states and the structure evolution of the dislocation in graphene when it falls freely from the saddle point of the energy landscape. The <i>O</i>-type dislocation, an unstable equilibrium structure located at the saddle point, is obtained from the lattice theory of the dislocation structure and improved by the <i>ab</i> <i>initio</i> calculation to take the buckling into account. Intermediate states along the kinetics path in the falling process are obtained from the <i>ab</i> <i>initio</i> simulation. Once the dislocation falls from the saddle point to the energy valley, this <i>O</i>-type dislocation transforms into the stable structure that is referred to as the <i>B</i>-type dislocation, and in the meantime, it moves a distance that equals half a Burgers vector. The structure evolution and the energy variation in the free-falling process are revealed explicitly. It is observed that rather than smooth change, a platform manifests itself in the energy curve. The unusual behaviour in the energy curve is mainly originated from symmetry breaking and bond formation in the dislocation core. The results can provide deep insight in the mechanism of the brittle feature of covalent materials.