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首页> 外文学位 >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.
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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.

机译：第一部分：反应共蒸发的超导钇钡钡铜氧化物薄膜的生长和性能。第二部分新型几何形状的非晶态超导/标准金属多层。

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摘要

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.
机译：第一部分，研究了YBa {sal} sb2 {dollar} Cu {dollar} sb3 {oll} O {dollarssb {lcub} rm y {rcub} {dollar}的薄膜生长和薄膜性能。使用三种金属源通过反应性电子束共蒸发制得了薄膜。提出了几个异常结果。在较低的氧气压力条件下，发现平均组成基本上偏离化学计量比为1：2：3的薄膜具有更多的块状特性，包括更高的转变温度。检查了c轴晶格参数的扩展。发现在较低氧气压力下制备的膜具有与在较高压力下制备的膜相比扩大的c轴晶格参数。不能通过低温氧退火来减小这种扩展的c轴。因此，膜的结构似乎偏离“理想的” YBa {dollar} sb2 {dollar} Cu {dollar} sb3 {dollar} O {dollar} sb {lcub} rm y {rcub} {dollar}结构。我们建议在这些薄膜中存在阳离子紊乱，并且这种效应在生长过程中的低氧气压力下更为明显。我们讨论了针对Y替代模型的特定Ba的实验证据。提示在低氧气生长压力下Y层中阳离子溶解度的延长是这些发现的原因。还讨论了物理性质的后果。第二部分研究了由非晶态的MoGe超导层和正常金属层组成的具有周期性和分形结构的人工结构多层膜。这些薄膜用作模型系统，以研究分形结构上的相变性质。该结构已通过多层膜的截面TEM显微照片直接确认。观察到的超导过渡的上平行临界场与分层几何形状有关。多层的超导相干长度和物理长度尺度之间的相互作用决定了临界场的行为。提出了比例模型来解释分形多层的实验结果。

著录项

  • 作者

    Matijasevic, Vladimir Cort.;

  • 作者单位

    Stanford University.;

  • 授予单位 Stanford University.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 1991
  • 页码 203 p.
  • 总页数 203
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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