Single Crystal Metal Nanorods by Thermomechanical Nanomolding

Yale University, New Haven CT

Investigators

Abstract

Making very small things is very hard to do. Think of nanoscale devices ??these are devices that are smaller in size than the width of a human hair (a human hair is about 80,000 nanometers wide) ? that need to be manufactured in large numbers, how can it be done?. This project supports research in the mass manufacture of nanostructures for nanoscale devices and systems though a manufacturing process known as nanomolding. Molding, at any scale, places a soft, liquid-like state of a material into a mold to solidify. Crystalline metals, despite their wide range of potential applications in nano and quantum devices, are currently unsuited for nanomolding. However, technologies such as energy, environment, and information hinge on the effective, precise, and versatile nanofabrication of metals. A recent, potential solution to the limited nanomoldability of metals is thermomechanical nanomolding and it has been used to fabricate gold and copper nanorods that are up to a thousand times longer than their diameter. The process, based on atomic diffusion, enables nanomolding with essentially all metals and alloys. This project explores the nanomolding process and its scalability and determines nanomoldability of different classes of metals and alloys. Technologically, the ability to fabricate very large surface area nanostructures, such as, high aspect ratio single crystal nanorods, of a broad range of metals and alloys impacts several technologies, for example, catalysis, photovoltaics, plasmonics, and tunable material cell interaction for implants and sensors. Therefore, results from this research benefits national health, prosperity, and defense, and hence, have a broad impact on U.S. economy and society. This project exposes students to state-of-the-art nanofabrication techniques, thus contributing to the training of the next generation of scientists and engineers. This project investigates the thermomechanical nanomolding process to form an array of high aspect ratio metallic nanorods over a large area. It studies deformation based on atomic diffusion as the underlying mechanism. The research involves determining processing parameters, such as time, temperature and pressure, on the nano-scale moldability of various metals and alloys, such as FCC and BCC metals and solid-solution and intermetallic alloys. Metal nanorod arrays are characterized in terms of their length and length uniformity over macroscopic dimensions. Furthermore, crystallographic orientation and potential grain boundaries are identified as a function of processing conditions and mold diameter to explore possibilities of the formation of single crystal nanorods with preferred orientation. A theoretical understanding of thermomechanical nanomolding is used to explore novel nanofabrication methods. These include the potential to add an additional dimension to nanomolding by using a multi-layered feedstock with combinations of miscible and immiscible metals. This allows for the possibility of varying, controlling, and manipulating the crystal structure and composition within one nanorod over the smallest dimensions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.