Optical properties of bilayer systems of gold and silver

The optical properties of metallic materials change abruptly when at least one of their dimensions is reduced to the nanometric scale. Metallic nanostructures exhibit the phenomenon of surface plasmon resonance, which corresponds to the coherent and collective oscillation of free electrons under the excitation of electromagnetic radiation. In thin films nanostructures, surface plasmons are propagative waves along the metal-dielectric interface and their resonance frequency depends on the type of metal and the surrounding dielectric. One of the most studied plasmonic systems is nanometric thin films of gold and silver due to their noble properties, which is a great advantage for sensor applications. This work aims to prepare more complex systems (bilayers) of gold on silver and silver on gold to understand how the plasmonic response is enhanced or affected depending on the thickness ratio and how it differs from traditional single-metal systems. Experimental measurements were performed by measuring reflectance as a function of the incidence angle using the Kretschmann configuration and numerical simulations were performed to interpret the data using the Pyllama Python library based on the transfer matrix method. The main results show that for the gold-on-silver (Au/Ag) system the best plasmonic response is obtained for the Au-34nm/Ag-24nm sample and for the silver-on-gold (Ag/Au) system the best response is obtained for the Ag-38nm/Au-23nm sample.