This Grant Opportunity for Academic Liaison with Industry (GOALI) award provides funding for the development of a novel approach to grow superconducting thin films on metal substrates with prefabricated nanorods. The approach consists of prefabricated nanorod growth on single-crystalline-like buffer film on flexible metal tape followed by epitaxial superconductor film growth by Metal Organic Chemical Vapor Deposition (MOCVD) on the buffer film. Three approaches will be investigated in this program to prefabricate nanostructures on single-crystalline-like buffer templates. The key factors that affect density, dimensions, morphology and orientation of nanorods on the buffer templates will be determined so that the nanorods can be controlled in a predictable manner. The science of epitaxial growth of the superconducting film on an underlying substrate through a maze of nanorods will be studied. The pinning effectiveness of these superconducting films will be evaluated to determine and control the impact of prefabricated nanorod defect structure.
A successful outcome of this program will enable superconducting thin film tapes with significantly improved critical current in high magnetic fields compared to the state-of-the art. Additionally, by separation of nanodefect growth from the epitaxial superconductor growth process, it is expected that growth rate limitation problems that exist in today's technology can be resolved. The expected significance of the program is the creation of a transformative processing science leading to robust manufacturing of superconducting tapes by industry, which in turn would yield a commercial product with much better performance, uniformity and consistency. A successful outcome of this program can result in a broad and positive impact in the field of superconductors which provide solutions to a wide spectrum of problems in energy as well in medicine, transportation, particle physics and chemical research. Furthermore, the program can broadly enable a stronger understanding of nanostructures in thin film materials as well MOCVD process science.
The objective of this program is to develop a new paradigm in superconductor materials processing and manufacturing. The goal is to achieve improved critical current performance in superconductor tapes through flux pinning by prefabricated nanowires embedded in the superconductor film. Three different approaches were developed for growth of prefabricated nanowires on single-crystalline-like buffers on metal substrates. They are Chemical Vapor Deposition (CVD) of oxide nanowires, Ion track-assisted electrodeposition of metallic nanorods, and Focused electron beam deposition of metallic nanorods. The main challenge that had to be overcome was to achieve a controlled growth of out-of-plane nanowires without in-plane nanostructures or any other detrimental modification of the epitaxial film surface on which the superconductor needs to be grown on. Through developing an understanding of the role of the nucleating surface, catalyst size and distribution, gas flow dynamics and the vapor-liquid-solid (VLS) mechanism, a chemical vapor deposition process was successfully developed to achieve a very repeatable growth of tin oxide nanowires with controlled density, size and morphology with nearly no in-plane nanostructures uniformly on long, practical tapes. The influence of post ion bombardment on reorientation of tin oxide nanowires with concomitant removal of in-plane nanostructures with minimal damage to the epitaxial buffer film was discovered. It has been demonstrated for the first time that critical current density in a magnetic field can be increased as much as 50% in superconductor films grown by a vapor-deposition approach on substrates with prefabricated nanowires. The results from this project can lead to superconducting equipment that can strongly impact energy, medical, transportation, and research fields. Cables that can transmit large amounts of power, magnetic energy storage equipment, high power density wind generators, motors, high-field MRI systems and magnetically levitated high speed trains are all potential outcomes of improved superconductors being developed in our research and will all have a tremendous societal impact. The results from this project can be useful not only for superconductor applications but also for other uses such as gas sensors and solar cells. Six graduate students have been trained in this project on nanowire and superconductor materials processing as well as on analytical capabilities using electron microscopy, focused ion beam imaging, atomic force microscopy and X-ray Diffraction and electromagnetic testing at cryogenic temperatures. Two graduate students have been trained by our GOALI industry partner on metal organic chemical vapor deposition of epitaxial superconducting films. Three undergraduate students were trained on electromagnetic testing of superconductors at cryogenic temperatures and four undergraduate students were mentored and trained on design and fabrication of process and test equipment. High school students and teachers have been hosted in the laboratory and were trained on superconducting materials and measurements. The results from this project have been published in two journals and three graduate student theses and dissertation, submitted for publication in a third journal, presented at international conferences and the technology developed was transferred to our GOALI industry partner.
