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. Model ing the diffraction intensities through application of simulated annealing techniques, together with least-squares refinement, has led to a crystallog raphic description of this structure in terms of a set of three-dimensional modulation functions. We find that the reconstruction persists through bot h 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.