Structure of pseudomorphic and reconstructed thin Cu films on Ru(0001)

The structure of strained Cu films deposited on Ru(0001) surfaces at 720 K was investigated by x-ray diffraction techniques. Our analysis shows that a single Cu monolayer adopts a pseudomorphic structure with the first three interlayer spacings significantly relaxed. The two-layer structure consists of a commensurate, uniaxially modulated stripe-phase reconstruction. Modeling the diffraction intensities through application of simulated annealing techniques, together with least-squares refinement, has led to a crystallographic description of this structure in terms of a set of three-dimensional modulation functions. We find that the reconstruction persists through both Cu layers, and leads to relaxation of the Cu and Ru interlayer spacings. We also calculate the average strain distribution as a function of position across the unit cell.