Atomistic characterization of three-dimensional lattice trapping barriers to brittle fracture

We present a detailed account of an atomistic study of three-dimensional lattice trapping barriers to brittle fracture in Si. By means of a prototypical interatomic potential model, we map out the molecular details of the evolution of atomically sharp cracks in the (111) cleavage plane with straight crack fronts along the 1⁄21 10 and 1⁄211 2 directions, respectively. The thermally activated processes of bond rupturing along the crack front are quantitatively characterized using a reaction pathway sampling scheme. The calculated minimum energy paths reveal a mechanism of kink-pair formation and migration in facilitating the crack front advancement. We show that the physical origin of directional anisotropy in cleavage crack propagation can be attributed to a difference in the kink-pair formation energy for different crack orientations. The effects of interatomic potentials are delineated by comparing the Stillinger–Weber model with an environment-dependent model.