Synthesis and characterization of new Au-Ag plasmonic alloy materials

Confining the delocalized fields of electromagnetic waves to the nanometer scale of metallic surface regions by exciting surface plasmons enables new methods of information transfer, energy conversion, red-ox chemistry and catalysis. Currently, Ag and Au are the most commonly used plasmonic materials, but neither is ideal. The goal of this work is to synthesize and characterize new Au- and Ag-based alloy materials with improved plasmonic response, low optical losses and high chemical stability by employing an electroless reduction method to deposit the alloys through co-deposition of silver and gold ions. The deposition kinetics of the ions in solution have been examined, followed by characterization of the resulting films to assess their quality, crystallinity and physical and chemical properties. We have employed spectroscopic ellipsometry (SE) to assess the optical and plasmonic properties, X-ray photoelectron spectroscopy (XPS) for film composition and electronic structure, X-ray diffraction (XRD) for film crystallinity, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) for their crystalline structure and morphology. The chemical stabilities of the alloy films have also been addressed by examining their stability upon exposure to various oxidants. Nanostructured alloy films deposited using the same chemistry on films patterned by electron beam lithography (EBL) yield large area, high quality, crystalline nanopillar arrays. These metamaterial arrays demonstrate plasmonic response which is determined by pillar diameter, periodicity and composition. The development of new high quality, crystalline, plasmonic alloy materials will enable new and improved performance in plasmonic and metamaterial research and application.