NSF/ONR: In-Plane Aligned Buffer-Layer Interfaces for High Temperature Superconductors

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9421911 Shaw This three-year study of high temperature oxide superconductor (HTS) thin-film growth on polycrystalline and amorphous substrates will further understanding of the biaxial alignment of a-b planes and the related nucleation and growth mechanisms in two HTS thin films, Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O (1223 phase), selected for this study. Two methods, ion-beam assisted deposition and graphoepitaxial growth, will be used to fabricate integrated film-buffer-substrate composite systems. The ultimate goal of this project is to develop and optimize processing techniques for the fabrication of long HTS thin films with high critical current densities on both metallic and glass substrates using ion-beam assisted deposition. Initially, biaxially aligned buffer layers of yttrium-stabilized zirconia (YSZ) will be deposited on Hastelloy. The orientation of the YSZ film will then be studied as a function of ion-beam angle, ion/atom flux ratio, ion-beam energy and chamber pressure. The effect of ion-beam assisted deposition on alignment and etching will be investigated: and scanning and transmission electron microscopy will be used to establish the relationship between the deposition conditions and the film-growth mechanism. Graphoepitaxial methods will also be employed to produce biaxially aligned HTS films on Hastelloy. As critical length is a crucial parameter of biaxial alignment, the relationship between critical length and interfacial shear strength, surface film thickness, and fracture strength will also be addressed. Results will be compared to theoretical prediction. Improvements in crystalline growth and alignment resulting from this work are expected to significantly improve the electric and magnetic properties of high temperature superconductor thin films. Further, by gaining better insight into the physical processes and by optimizing the deposition parameters, this work should foster the development of practical applications. Discovery of high temperature superconductors years ago promised major commercial applications in electrical machineries and electronic devices due to enormous increase in the efficiency of transmission of electricity. However, progress has been hampered by two features: (1) superconducting temperatures are still well below room temperature and (2) processing of practical devices remain relatively slow and its impact on properties are not fully understood. This research offers the opportunity to bring the technology a little closer to larger scale commercialization of superconductors. ***