Large Scale Epitaxy of Mercury-Based High-Temperature Superconducting Thin Films in Cation-Exchange Process

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9901460WuThis project addresses the growth mechanism of thin films of Hg-based high-Tc superconductors (Hg-HTSs) in a novel cation exchange process, and aims at developing technologically feasible techniques for high-quality epitaxy of Hg-HTS thin films over large scales. The high volatility of the Hg-HTSs limits use of conventional thermal-reaction processing over large areas. The proposed research on the cation-exchange process addresses this problem in epitaxy of volatile compounds using an approach, in which a highly volatile compound is formed by replacing a weakly bonded cation in a precursor lattice with the desired volatile cation. The epitaxy of the volatile compound is directly inherited from the epitaxial precursor matrix. By choosing precursor matrices with pre-designed crystalline structures and chemical compositions, the cation-exchange process allows high-quality epitaxy of many existing volatile compounds as well as a search for new volatile compounds. Four topics to be addressed include: (1) Identification of characteristic parameters in the cation-exchange process and study of their effects on the cation-exchange mechanism; (2) Development of a three-zone cation exchange process for large-area epitaxy ( 2 inches in diameter); (3) Study of surface morphology and film/substrate-interface microstructures of cation-exchange processed Hg-HTS thin films on technologically compatible substrates; and (4) Direct conversion of Tl-HTS devices to Hg-HTS devices.%%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The success of this research may lead to development of commercially viable technologies for Hg-HTS film-based applications including microwave components/systems, infrared detectors, and high-current superconducting tapes, and is expected to allow establishment of novel methods for synthesis of volatile compounds with pre-designed crystalline structures and chemical compositions. The research will contribute basic materials science knowledge at a fundamental level to new aspects of electronic devices. A variety of fundamental issues are to be addressed in these investigations, and the proposed experiments will also develop a technologically important superconducting material. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area.***