When bilayer films of Co and Ag were melted by a nanosecond pulsed laser, the dewetting self-organization spontaneously produced arrays of nanoparticles with a narrow size distribution. By varying the individual film thickness, the scientists were able to vary the particle size by one order of magnitude, while independently controlling the composition of the sample over a large range.

Since Co and Ag are immiscible, the nanoparticles consisted of segregated regions of the metals. As a consequence, the team was able to tune the localized surface plasmon resonance (LSPR) to change by one order of magnitude in wavelength compared with pure Ag, by varying either the size and/or composition of the particles. The group also discovered that the sensitivity of the bimetallic nanoparticles to detecting local dielectric change, which is central to LSPR sensing, was as good as that of pure Ag.

Another interesting discovery was that the Co-Ag material appears to have much higher environmental stability compared with the pure Ag, an effect that is currently being investigated. In the near future, the researchers also plan to study the magneto-optical properties of the arrays, which have applications in optical communication and sensing.

This inter-disciplinary research was supported by the US National Science Foundation (NSF) and the Department of Energy (DOE) as well as the US NSF-supported TN-SCORE programme. The study was led by researchers at the University of Tennessee-Knoxville, US, and was a collaboration between Oak Ridge National Laboratory and other academic institutions (Southern Illinois University in Edwardsville and Washington University in St. Louis).

A full description of study can be found in the journal Nanotechnology.