NSF/ONR: Advanced Processing, Characterization and Properties of Epitaxial Multilayer Superconductor Heterostructures and Devices

[421718] Narayan高温超导体、金属和电介质之间的界面结构和特性的理解是薄膜外延结构特性的关键。界面的结构和化学成分决定了薄膜外延生长的性质和缺陷，直接影响传输性能和器件特性。本提案的目的是：先进超导体器件所需的多层异质结构的原位加工。主要的焦点将放在钇、氧化钡和氧化铜超导材料系统上。薄膜多层异质结构将通过脉冲激光沉积处理，使用多目标支架，其中多达五种不同的薄膜可以在一个单独的腔室中生长。通过用激光反射镜取代其中一个目标，可以在衬底上引导激光能量并实现原位原子级清洁。对应力和应变进行建模，以了解薄膜外延生长和缺陷含量的性质。这些结果将与薄膜中界面的原子结构和化学组成以及缺陷的性质有关。薄膜的外延质量和缺陷含量将得到优化，以达到最高理论超导温度Tc（约94开尔文）和临界电流密度Jc大于500万安培。每平方厘米77开尔文)的高性能器件。优化后的薄膜将用于制造一些高性能（高响应性或高速度）的测热计。超导材料提供了一种极具吸引力的低损耗节能输电方式。然而，为了充分利用这种超导特性，材料必须经过超冷处理。此外，为了实际应用，这些超导体必须被内置到设备中。为了使应用最大化，人们需要在最低冷却程度下操作这些设备。通过对多层超导器件制备过程的了解，预计该技术在新型电子器件中的广泛应用将成为可能。＊＊＊

9421718 Narayan Understanding of the structure and properties of interfaces between high-temperature superconductors, metals and dielectrics holds key to the properties of thin film epitaxial structures. The structure and chemical composition of interfaces determines the nature of epitaxial growth and defects in thin films which directly affect transport properties and device characteristics. The objective of this proposal is: In-situ processing of multilayer heterostructures needed for advanced superconductor devices. The primary focus will be on yittria, barium oxide, and copper oxide superconducting materials systems. Thin film multilayer heterostructures will be processed by pulsed laser deposition using a multitarget holder where up to five different films can be grown in a single chamber. By replacing one of the targets with a laser mirror it is possible to channel the laser energy on the substrate and achieve in-situ atomic level cleaning. Modeling of stresses and strains will be carried out to understand the nature of epitaxial growth and defect content in thin films. These results will be correlated with atomic structure and chemical composition of interfaces and nature of defects in thin films. Epitaxial quality and defect content of thin films will be optimized to achieve highest theoretical superconducting temperature Tc (about 94 Kelvin) and critical current density (Jc greater than 5.0 million amps. per square cm at 77 Kelvin) for high performance devices. The optimized thin films will be used to fabricate a few high-performance bolometers (high responsivity or high speed). Superconducting materials offer an attractive energy conserving way of transmitting electricity with very low losses. However, in order to capitalize on this superconducting property, the material has to be super cooled. Further, for practical applications these superconductors have to be built into devices. In order to maximize the application, one needs to operate these devices with m inimum degree of cooling. By understanding the process of multilayer superconducting devices, it is anticipated that a broader application of this technology may become possible into new electronic devices. ***