Structure and formation of misfit dislocations in an epitaxial fcc film

Three-dimensional molecular dynamics simulation of epitaxial growth of fcc aluminum film with a negative misfit of 0.05, under atomic deposition, has been carried out. An embedded atom method (EAM) potential is employed for computing atomic interaction in aluminum. Formation of misfit dislocation appears in the simulated growth process. Atomistic analysis of the film shows that, in the beginning the misfit dislocation consists of two Shockley partial dislocations with a stacking fault zone between them. The Burgers vectors of the two partial dislocations are of 〈211〉/6 type, and the width of the stacking fault is ～1.8 nm, which agrees well with theoretical calculation. During further deposition growth, the dislocation pair can slide, but their distance remains stable. Further analysis shows that the dislocation pair forms in a local surface disordering-ordering process, like the local melting-crystallization. Atomic scale squeezed-out tetrahedrons are found to form near the surface and soon slide back in the anor of statistical fluctuation. Under some circumstances, however, a squeezed-out tetrahedron causes disorder of its neighboring atoms, and developes into the observed local disorder zone, which later becomes the nucleation site for the formation of the Shockley dislocation pair.