Ultra-thin sodium films offer low-cost alternative to gold and silver in optical technologies

From solar panels to next-generation medical devices, many emerging technologies rely on materials that can manipulate light with extreme precision. These materials—called plasmonic materials—are typically made from expensive metals like gold or silver. But what if a cheaper, more abundant metal could do the job just as well or better?

That’s the question a team of researchers set out to explore. The challenge? While sodium is abundant and lightweight, it’s also notoriously unstable and difficult to work with in the presence of air or moisture—two unavoidable parts of real-world conditions. Until now, this has kept it off the table for practical optical applications.

Researchers from Yale University, Oakland University, and Cornell University have teamed up to change that. By developing a new technique for structuring sodium into ultra-thin, precisely patterned films, they found a way to stabilize the metal and make it perform exceptionally well in light-based applications.

Their approach, published in the journal ACS Nano, involved combining thermally-assisted spin coating with phase-shift photolithography—essentially using heat and light to craft nanoscopic surface patterns that trap and guide light in powerful ways.

Even more impressively, the team used ultrafast laser spectroscopy to observe what happens when these sodium surfaces interact with light on time scales measured in trillionths of a second. The results were surprising: sodium’s electrons responded in ways that differ from traditional metals, suggesting it could offer new advantages for light-based technologies like photocatalysis, sensing, and energy conversion.

The study was led by Conrad A. Kocoj, Shunran Li, and Peijun Guo at Yale Engineering (Guo is also a member of the Yale Energy Sciences Institute); Xinran Xie, Honyu Jiang, and Ankun Yang at Oakland University; and Suchismita Sarker at Cornell University.

Their collaboration brought together expertise in nanofabrication, ultrafast optics, and materials science.