Manufacturing of Metal Nanostructures by Tensile Deformation of Liquid Metal Arrays

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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.