Part I. Growth and properties of reactively coevaporated superconducting yttrium-barium-copper-oxide thin films. Part II. Amorphous superconducting/normal-metal multilayers in novel geometries

Part I. YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}rm y{rcub}{dollar} thin film growth and film properties were investigated. Films have been made by reactive electron-beam coevaporation using three metal sources. Several anomalous results are presented. In conditions of lower oxygen pressure, films with average composition substantially off the 1:2:3 stoichiometry are found to have more bulk-like properties including higher transition temperatures. Expansion of the c-axis lattice parameter was examined. It is found that films made at lower oxygen pressure have c-axis lattice parameters which are expanded compared to the films made at higher pressures. Such an expanded c-axis cannot be reduced by a low temperature oxygen anneal. The structure of the films thus appears to deviate from the "ideal" YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}rm y{rcub}{dollar} structure. We suggest that cation disorder is present in these films and that this effect is more pronounced at low oxygen pressures during growth. We discuss experimental evidence for a particular Ba for Y substitution model. It is suggested that extended cation solubility in the Y layers at low oxygen growth pressures is the cause of these observations. Consequences on physical properties are also discussed.; Part II. Artificially-structured multilayered films with periodic and fractal structures, consisting of amorphous-MoGe superconducting and normal metal layers were studied. These films are used as a model system to investigate the nature of phase transitions on fractal structures. The structure has been confirmed directly by cross-sectional TEM micrographs of the mutlilayers. The observed upper parallel critical field of the superconducting transition is related to the layering geometry. The interplay of the superconducting coherence length and the physical length scales of the multilayer governs the critical field behavior. A scaling model is presented to explain the experimental results on fractal multilayers.