Nucleation and growth of DyBa2Cu307_x thin films on SrTi03 substrates studied by transmission electron microscopy and atomic force microscopy

The microstructure of superconducting films influence their properties, requiring optimization of processing conditions. The early stages of nucleation and growth determine the final microstructure of the film. We report our studies of the initial stages of epitaxial growth of DyBa2Cu3O7 _x films on SrTiO3 substrates by transmission electron microscopy (TEM), atomic force microscopy (AFM), and reflection high energy electron diffraction (RHEED). Prethinned, electron transparent, reconstructed (100) and (110) SrTiO3 substrates were used to deposit 40-, 100-, and 1000-A-thick DBCO films by ozone-assisted molecular beam epitaxy (MBE). The reconstructed substrates have a stepped surface and the film nucleates preferentially at the steps giving rise to an interconnected network of islands. The growth mechanism appears to be nucleation at the step edges and propagation of these steps. In situ reflection high energy electron diffraction yielded identical conclusions. Islands saturate at a certain size and further coverage merely increases tne number of islands. This has significance in the application of ultrathin DyBa2Cu307 _xfilms to devices and their use as a model systems to study superconductivity. Factors other than the substrate temperature, such as substrate surface morphology are found to influence the epitaxial relationship.