Optical Response of Nanostructures: From Pure to Alloyed Metals

In this chapter, we review the near- and far-field optical responses of metallic nanostructures, ranging from pure metals, heterometallic systems, and metallic alloys. We utilize numerical simulations to discuss the near- and far-field optical properties of self-assembled Au and Ag-Au heterometallic nanostructures with geometries that mimic molecules such as CH₄ and WCl₆. We discuss the unique, polarization-independent response for structures containing at least threefold rotational symmetry. We quantify the absorption characteristics of Au and Au/Ag metasurfaces formed by ordered arrays of linear trimers and show that by modifying the arrangement and relative spacing between the nanoparticles, the absorption is reversibly switched between high and low within the visible range of the spectrum. Further, we present alloyed metallic nanoparticles of Au and Ag and map their optical response at the nanoscale using near-field scanning optical microscopy. We spatially resolve high transmittance centered directly beneath the nanoparticles at resonance, which is in excellent agreement with our numerical simulations. Overall, this study demonstrates alternative materials with on-demand optical properties for applications in photonics such as waveguides, sensors, polarization converters, and color displays.