Study of Grain Boundaries in Superconducting YBCO Thin Films: Correlation Between Critical Current Densities and Boundary Geometry/Structure/Chemistry

9803212陈这个项目将对高温超导体YBa2Cu307-x(YBCO)的晶界进行全面的研究。PI将研究在织构镍/铜带上生长的织构薄膜中经常出现的001倾斜边界，以及在单晶衬底上生长的YBCO薄膜中的某些特殊边界。一些YBCO倾斜边界将通过使用高度特定的双晶、三晶、n-晶体作为薄膜生长的模板来制备。在这些模板衬底中将设计低折射率平面作为边界平面，以避免在YBCO薄膜中出现刻面。单个边界上的临界电流密度将通过对边界约瑟夫森涡旋成像来测量(这些涡旋的宽度与局部临界电流密度直接相关)。用扫描超导量子干涉显微镜(SSM)进行磁通量子成像。同样的边界将用扫描电子显微镜(SEM)和背散射沟道菊池图案进行研究，以确定每个边界的5个几何参数。边界的临界电流密度将作为几何参数的函数绘制出来。将记录任何方向错误的平面外组件或错误方向轴不是100的组件。在SSM和SEM中观察到的单个边界将与样品上的基准点相匹配。重要边界的特殊区域将被制备成平面视图样本，用于在透射电子显微镜中观察，使用衍射对比显微镜、电子衍射、高分辨率电子显微镜、使用能量色散X射线分析绘制边界成分图以及使用电子能量损失谱绘制化学图。将检测到晶界偏析和晶间薄膜。除了完全化学计量比的靶材外，略微偏离化学计量比的靶材还将用于制备YBCO薄膜。这些非化学计量比薄膜可以用来评估不同边界偏析的敏感性程度。来自显微镜的这001个倾斜边界的几何规格将与它们的结构、成分图谱、它们的局部约瑟夫森穿透长度、它们的临界电流密度以及整个薄膜的成分有关。材质中的颗粒边界通常控制该材质的属性。这在高温超导体中尤其如此，并限制了由这些材料制成的设备在商业和军事应用中的用途。了解晶界对超导性能的影响将使设备工程师能够利用这些材料开发更好的设备。***

9803212 Chan This project will perform a comprehensive study of the grain boundaries in the high-temperature superconductor YBa2Cu307- x (YBCO). The PI will study 001 tilt boundaries that often occur in textured films grown on textured Ni/Cu tapes as well as certain special boundaries in YBCO films on single crystal substrates. Some YBCO tilt boundaries will be prepared by using highly specific bicrystals, tricrystals, n-crystals as templates for film growth. Low indices planes as boundary planes will be engineered in these template substrates to avoid faceting in the YBCO films. Critical current densities on individual boundaries will be measured by imaging the boundary Josephson vortices (the widths of these vortices are directly related to the local critical current density). The magnetic flux quantum imaging is performed by scanning superconducting quantum interference device microscopy (SSM). The same boundaries will be studied by scanning electron microscopy (SEM) with back-scattering channeling Kikuchi patterns to identify the 5 geometric parameters of each boundary. Critical current densities of boundaries will be plotted as a function of the geometric parameters. Any out of plane component of misorientation or with a misorientation axis other than 100 will be noted and recorded. Individual boundaries observed in SSM and SEM will be matched by fiducial points on the samples. Special areas of important boundaries will be prepared into planar view samples for observation in transmission electron microscopes employing diffraction contrast microscopy, electron diffraction, high resolution electron microscopy, boundary composition mapping with energy dispersive x-ray analysis, and chemical mapping with electron energy-loss spectroscopy. Boundary segregation and intergranular films will be detected. In addition to perfectly stoichiometric targets, slightly off-stoichiometric targets will be used to make YBCO films. These off stoichiometric films can be used to assess the degree of susceptibility to segregation of different boundaries. The geometric specifications of these 001 tilt boundaries from microscopy will be related to their structure, their composition mapping, their local Josephson penetration lengths, their critical current densities, and the overall film compositions. %%% Grain boundaries in materials often control the properties of that material. This is especially true in high- temperature superconductors, and limits the usefulness of devices made from these materials in commercial and military applications. An understanding of the grain boundary effect on the superconducting properties will enable device engineers to develop better devices from these materials. ***