Dislocation Formation during Vapor Deposition of Epitaxial Multilayers

A molecular dynamics method has been used to study the formation of dislocations during the vapor deposition of NiFe/Au/NiFe/Au and CoFe/NiFe/CoFe/Cu multilayers. We observed the direct nucleation of misfit dislocations (with zero critical thickness) at (111) interfaces in the NiFe/Au/NiFe/Au system. Both the dislocation configuration and density observed in the simulations were similar to those reported in HRTEM experiments. A misfit energy increasing dislocation structure was found in simulated CoFe/NiFe/CoFe/Cu multilayers. These dislocations were formed during deposition on the (111) surface of the f.c.c. lattice. Deposited adatoms were able to either occupy f.c.c. or h.c.p. sites if the energy difference between these sites were minor (e.g., ~ 2meV). This resulted in islands with h.c.p. stacking and the creation of partial dislocations at the f.c.c and h.c.p. domain boundaries. Since these boundaries were filled the last and tended to have missing atoms, the surface layer tended to have less planes compared to the underlayer even the surface atoms were slightly smaller. This phenomenon is negligible for large lattice mismatch interfaces such as NiFe/Au where the lattice mismatch dominates the dislocation nucleation, but is relatively significant for small lattice mismatch interfaces such as CoFe/Cu.