GROWTH AND X-RAY CHARACTERIZATION OF THIN EPITAXIAL CR(110) FILMS ON NB(110)

We have grown by molecular-beam-epitaxy thin Cr(110) films on Nb(110) buffer layers on sapphire Substrates. Films ranging from 50 Angstrom to 1100 Angstrom in thickness exhibit a single-domain structure. Using extensive x-ray characterization methods, we find a pronounced in-plane expansion of the Cr layers which relaxes as the film thickness increases, while the out-of-plane lattice spacing remains constant and bulklike over the entire thickness range. The in-plane lattice relaxation can be described by an isotropic strain relaxation model. In contrast, the out-of-plane behavior is highly anomalous, which may be due to strain density waves.