Atomic structures of dislocation intersections at (001) low-angle twist and shear boundaries in silicon

The first atomistic simulations of orthogonal networks of screw dislocations in silicon have been performed to investigate the core structures of dislocation intersections. Structural models for the dislocation intersections are proposed and examined by the classical molecular dynamics method with the empirical interatomic potential of Tersoff. The screw dislocations (b = (a/2)[110]) are assumed to be undissociated, according to experimental data on atomic structures of the synthetic low-angle Si/Si(001) twist boundaries. It is found that cores of the dislocation intersections are formed by closed characteristic groups of atoms (extended point defects). The structure of these defects depends on the fact whether the screw dislocation arrays generate a twist or a shear boundary. The former has a well-defined energy minimum, with the characteristic groups having the point-group symmetry 222 (D-2). The latter is found to exhibit a degeneracy in the number of local energy minima, corresponding to non-symmetrical characteristic groups with a different coordination of atoms.