THE STRUCTURE OF EPITAXIALLY GROWN THIN-FILMS - A STUDY OF NIOBIUM ONSAPPHIRE

The x-ray scattering from epitaxially grown films of niobium on sapphi re has been measured as the thickness of niobium was varied. For thick nesses d larger than 80 Angstrom, the mean square displacements perpen dicular to the growth planes increase as d(x) where x = 0.68 +/- 0.08, and the correlation length for these displacements increases as d(y) with y = 0.51 +/- 0.05. A model is put forward to account for these re sults in terms of the strains when the film thickness is larger than t he distance between the misfit dislocations.