Attracted by their desired functional properties, significant effort has been taken during the last two decades in the development of nano fabrication techniques for metals. A wide range of bottom-up and top-down techniques have been developed. Those techniques, however, are generally limited in some critical aspects such as material choice, geometry, and/or scalability. A highly versatile and widely used fabrication method is molding, which is generally associated with a soft state of a material. Nanomolding has been realized for polymers, gels, and some glasses that soften at elevated temperatures, but is limited for crystalline metals, that remain hard in their crystalline state. The supercooled liquid state in metallic glasses had enabled nanomolding metallic glasses with exciting electrochemical, optical, and cell response properties. However, as the formation of metallic glasses is limited to a small number of alloys, broad utilization of alloy chemistry to optimize functional properties has been limited with thermoplastic nanomolding of metallic glasses. Recently, we discovered that nanomolding is possible with crystalline metals. Scaling considerations suggest that the underlying process is based on atomic diffusion and the driving force is realized by a pressure gradient between the top of the feedstock material and the tip of the nanorod. Most effective, at ~0.5 TM such thermomechanical nanomolding (TMNM) results in single crystal nanowires of very high aspect ratio of up to ~1000 and as small as 5 nm in diameter. As the underlying diffusion process is present in all metals and alloys, TMNM offers itself as a versatile nanomolding technique. In some cases, TMNM results in the formation of nanorods of the same composition than the feedstock, and in other cases into drastic composition changes. For example, intermetallic phases can be precisely molded resulting into single crystal intermetallic nanorods whereas some solid solutions result in essentially elemental nanorods. TMNM can be essentially used to fabricate nanowires from all metals and most alloys (solid solutions, intermetallic, and eutectics). In addition to the use of TMNM as a versatile nanofabrication method, it can also be explored to characterize the deformation behavior of microstructures. Here local mechanism can be revealed in a massively parallel fashion with a special resolution of ~10 nm over the entire microstructure (cm2). Hence, TMNM may help decode the deformation behavior of microstructures.
Jan Schroers is a professor in the Department of Mechanical Engineering and Materials Science at Yale University. He received his Ph.D. in Physics from the RWTH Aachen. He spent three years at Caltech as a post-doc before joining Liquidmetal Technologies for three years as a Director of Research where he developed processing methods for bulk metallic glasses. He is the founder of Supercool Metals and helped develop additive manufacturing methods for metals at Desktop Metals. His research focuses on structure-property-processing relationships in metals. For this he uses combinatorial material science, machine learning, artificial microstructures, and nanomolding methods and has focused on various material classes such as metallic glasses, foams and composites, high-entropy alloys, and nanocrystalline alloys. His research has resulted in over 234 journal publications and 13 patents and patent applications.