Interface structure and misfit dislocations in thin Cu films on Ru(0001)

We show, from scanning tunneling microscopy measurements, that the strain at the interface between Cu films and a Ru(0001) substrate is reduced by a structural transformation from a more tightly bound, strained pseudomorphic first Cu layer to a unidirectionally contracted second Cu layer with periodic partial misfit dislocations. These results for a two-dimensional structure confirm the mechanism of stress accommodation in strained layers predicted in the one-dimensional dislocation model of Frank and ven der Merwe.