Interfacial strain accommodation in thin metal films

We report a surface x-ray scattering study of surface alloying as a mechanism for interfacial strain accommodation at bimetallic interfaces. Specifically, thin Cu or Ag films grow strained on a Ru(0001) surface due to a lattice mismatch accompanying their epitaxy with a 5.8% tensile stress for Cu and a 6.3% compressive strain for Ag. Cu and Ag do not form bulk alloys but mix in a single layer on Ru(0001) which allows the lattice misfit to be compensated. We grew single layer films by co-depositing various Ag/Cu compositions at 690 K on Ru(0001). To monitor the strain relief at this interface during alloying, we studied the diffraction pattern of the Ag_xCu_1-x film. Our results give evidence that the interfacial misfit between the Cu/Ag alloy and the Ru substrate reduces continuously as more Cu is added. For Ag_50Cu_50 mixtures the alloy reflection coincides with the Ru CTR suggesting that the two phases have the same lattice constant along [100]. This observation is consistent with the Ag and Cu lattice misfits compensating each other at this composition leading to a strain free interface. Work performed at BNL is supported by the US DOE, under contract DE-AC02-98CH10886. UT-Battelle, LLC manages ORNL for the US DOE under contract DE-AC05-00OR22725.