A transmission electron microscopy study, using weak-beam imaging, was made of the interface dislocation arrays that initially formed at the (001)Ni/Cu interface during coherency loss. Interface dislocations were absent from 2.5nm-Ni/100nm-Cu bilayers, but were present in 3.0nm Ni samples; thus indicating that the critical Ni film thickness for coherency loss was between 2.5 and 3nm. The key features of the interface dislocation structure at the onset of coherency loss were that the majority of interface dislocations were 60° dislocations which presumably formed via the glide of threading dislocations in the coherently stressed Ni layer and had a Burgers vector in the {111} glide plane. The interface contained approximately 5% Lomer edge dislocations, with a Burgers vector in the {001} interface plane, and occasional Shockley partial dislocations. Isolated segments of interface dislocation, terminating at the surface, were regularly observed. This experimental study showed that, near to the critical thickness, the accumulation of interface dislocations occurred in a somewhat stochastic fashion, with favourable regions where coherency was first lost.

Interface Dislocation Structures at the Onset of Coherency Loss in Nanoscale Ni–Cu Bilayer Films. D.Mitlin, A.Misra, T.E.Mitchell, J.P.Hirth, R.G.Hoagland: Philosophical Magazine, 2005, 85[28], 3379-92