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

9901460wu本项目研究了一种新型阳离子交换工艺中汞基高tc超导体（Hg-HTS）薄膜的生长机理，旨在开发技术上可行的大规模高质量高温超导薄膜外延技术。高温高温超导的高挥发性限制了传统热反应处理在大范围内的使用。提出的关于阳离子交换过程的研究使用一种方法解决了挥发性化合物外延中的这个问题，在这种方法中，通过用所需的挥发性阳离子取代前驱体晶格中的弱键阳离子形成高挥发性化合物。挥发性化合物的外延直接继承自外延前驱体基质。通过选择具有预先设计的晶体结构和化学成分的前驱体基质，阳离子交换过程允许许多现有挥发性化合物的高质量外延，以及寻找新的挥发性化合物。主要研究四个方面：(1)确定阳离子交换过程的特征参数及其对阳离子交换机理的影响；(2)大面积外延（直径2英寸）三区阳离子交换工艺的开发；(3)技术相容衬底上阳离子交换处理的Hg-HTS薄膜的表面形貌和膜/衬底-界面微观结构研究；(4) Tl-HTS器件直接转换为Hg-HTS器件。该项目涉及具有高潜在技术相关性的材料科学主题领域的基础研究问题。这项研究的成功可能会导致商业上可行的高温超导薄膜应用技术的发展，包括微波元件/系统、红外探测器和大电流超导带，并有望建立具有预先设计的晶体结构和化学成分的挥发性化合物的合成新方法。该研究将在基础层面上为电子器件的新方面贡献基础材料科学知识。各种各样的基本问题将在这些研究中得到解决，并且提出的实验也将开发一种技术上重要的超导材料。该计划的一个重要特点是通过在基础和技术重要领域培养学生，将研究和教育相结合

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.***