MSE Seminar Series: Jan Schroers (Yale)

Description

Nanomolding for Nanofabrication and as a Microstructure Characterization Tool

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 respects 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 T M 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 manner with a special resolution of ~10 nm over the entire microstructure(cm2 ). Hence, TMNM may help decode the deformation behavior of microstructures understand complex properties including creep, fatigue, and aspects of corrosion.
 

Bio:
Jan Schroers, an internationally recognized leader in the rapidly developing field of bulk metallic glasses, was recently appointed the Robert Higgin Professor of Mechanical Engineering and Materials Science, effective immediately.

He is a faculty member at the Yale School of Engineering & Applied Science (SEAS).

Schroers joined the Yale faculty in the Department of Mechanical Engineering in 2006, following a postdoctoral fellowship at the California Institute of Technology and working as director of research at Liquidmetal Technologies. At Yale, his research has focused on the study of bulk metallic glasses, a relatively new class of materials made from complex, multicomponent alloys that have the moldable pliability of plastics, but the strength of metals. Some of his many contributions to the field include the discovery and explanation of ductility in metallic glasses, the development of bulk glasses based on gold, and the introduction of high temperature metallic glasses.

For his work, Schroers received the 2017 Lee Hsun Award from the Chinese Academy of Sciences. He has also led the organization of numerous international symposia and served as scientific advisor to commercial companies, including Liquidmetal Technologies, Desktop Metals, and Supercool Metals.