Robust Fano-like Antiresonances in Large-Area Au-coated Ag-Nanoisland Ensembles

We investigate plasmonic resonances and Fano-like interference in Au-coated Ag nanoislands fabricated by solid-state dewetting followed by Au overgrowth. By combining electrostatic spectral analysis, full-wave simulations, and linear transmission spectroscopy, we show that the optical response is governed by hybridization between plasmonic modes supported by the Ag-island and the Au-coating. Increasing the Au-coating thickness red-shifts the low-energy resonance and transfers spectral weight from high-energy to low-energy resonances, while a pronounced anti-resonant dip remains nearly fixed. The eigenmode analysis identifies this dip as the signature of destructive interference between super-radiant and sub-radiant hybridized modes. These results establish coated bimetallic nanoislands as promising platforms for tunable Fano-like optical responses accessible through standard far-field spectroscopy, using a fabrication route that requires no lithographic patterning and is compatible with large-area, low-cost production.