Manufacturing of Metal Nanostructures by Tensile Deformation of Liquid Metal Arrays

金属纳米结构对于能量转换和存储、传感器、等离子体、水净化和生物医学应用至关重要。尽管对这些技术的需求不断增长，但金属纳米结构的制造方法仍然很少，而且往往很复杂。聚合物纳米结构可以通过纳米印迹、模板渗透和静电纺丝等方法大规模制备。为了满足微电子工业的需要，已经开发了大量的自顶向下（蚀刻）和自底向上（定向或自组装）的半导体纳米结构技术。相比之下，金属纳米结构仍然需要多个光刻和薄膜沉积步骤，这些步骤缓慢且昂贵。该奖项支持液态金属流变学的基础研究，以推进一种涉及液态金属阵列拉伸变形和破裂的新型纳米制造技术。该研究使得在金属、玻璃、聚合物和半导体等各种衬底上组装可控金属纳米结构的纳米光刻制造成为可能。该项目为本科生和研究生提供金属纳米制造方面的教育和实践培训，并为少数民族学生和残疾学生提供工程方面的机会。聚合物液体的变形可以产生各种形状，如液滴、薄膜、串珠、锥形结构和长纤维。这是通过调整聚合物溶液的流变学和界面特性来实现的。然而，类似的方法不适用于液态金属，因为它们的粘度低，表面张力高，缺乏粘弹性。传统金属的这些挑战可以通过使用非晶金属或玻璃成形金属合金来克服，这些金属合金表现出亚稳态过冷液态，模仿热塑性塑料的流变学。系统地研究了粘度、表面张力和应变速率对金属过冷液体流动行为的影响。这些知识被用于通过机械手段操纵过冷液体状态以实现高通量金属纳米结构的制造。研究工作涉及液态金属阵列的拉伸或拉伸变形，以创建高纵横比和空心金属纳米结构，这是现有压花方法无法实现的。玻璃状或非晶状纳米结构随后被反氮化或结晶化，用于需要结晶金属纳米结构的应用。除了带来新的应用之外，这个纳米制造项目通过对纳米尺度样品进行热、电和机械测试，使金属玻璃尺寸效应的基础研究成为可能。

Metal nanostructures are essential for energy conversion and storage, sensors, plasmonics, water purification, and biomedical applications. Despite growing demand in these technologies, the manufacturing methods for metal nanostructures have remained few and often complex. Polymer nanostructures can be massively fabricated by nanoimprinting, template infiltration, and electrospinning. A plethora of top-down (etching) and bottom-up (directed- or self-assembly) techniques have been developed for semiconductor nanostructures to meet the needs of microelectronics industry. In contrast, metal nanostructures still require multiple lithographic and thin film deposition steps which are slow and expensive. This award supports fundamental research in the rheology of liquid metals to advance a new nanomanufacturing technique involving tensile deformation and rupture of arrays of liquid metal. The research enables nanolithography-free fabrication of controllable metal nanostructures assembled on various substrates such as metals, glasses, polymers, and semiconductors. The project provides education and hands-on training in metal nanomanufacturing to undergraduate and graduate students and opportunities in engineering to minority students and students with disability. A variety of shapes such as droplets, thin films, beads-on-a-string, conical structures, and long fibers can be created by deformation of polymer liquids. This is enabled by tuning rheological and interfacial properties of polymer solutions. However, a similar approach is not applicable to liquid metals because of their low viscosity, high surface tension, and lack of viscoelasticity. These challenges of conventional metals are overcome by using amorphous metals or glass forming metal alloys which exhibit a metastable supercooled liquid state that mimics the rheology of thermoplastics. Effects of viscosity, surface tension, and strain-rate on flow behavior of metallic supercooled liquids are systematically studied. Such knowledge is used to manipulate the supercooled liquid state for high-throughput manufacturing of metal nanostructures by mechanical means. The research work involves extensional or tensile deformation of liquid metal arrays to create high-aspect-ratio and hollow metal nanostructures which are not feasible by existing embossing methods. The glassy or amorphous nanostructures are subsequently devitrified or crystallized for applications which require crystalline metal nanostructures. Besides leading to new applications, this nanomanufacturing project enables fundamental studies on size effects in metallic glasses through performance of thermal, electrical, and mechanical tests on nanoscale specimens.