Morphology-induced plasmonic resonances in silver-aluminum alloy thin films

We have investigated the optical properties of sputter-deposited silver-aluminum alloy thin films on silicon substrates at room temperature. In addition to the primary feature that corresponds to the bulk plasma resonance, a secondary dip appears in the optical reflectance spectra, which shifts and diminishes with thermal annealing. Careful structural characterization of both the as-deposited and annealed films suggests that the resonant feature originates from the surface plasmon resonances, which are localized in the dielectric gap between grains. This result indicates that the morphology of metal alloys could have a significant effect on their optical properties. VC 2011 American Institute of Physics. [doi:10.1063/1.3619840]