We describe the modulation of localized surface plasmons in gold nanodumbbells through stepwise silver coating, along with a detailed discussion regarding the experimental parameters affecting the final core shell morphology. Interestingly, whereas conformal growth was observed for thin coatings, for intermediate and high silver salt concentrations, the final nanoparticles end up with either rod-like or irregular faceted morphologies as a consequence of anisotropic silver growth. Upon silver reduction, pronounced changes in the optical properties were observed, which could be modeled using the boundary element method (BEM), which also allowed the assignment of different plasmon modes. Such core shell Au@Ag nanoparticles are expected to serve as excellent SERS substrates, as significantly higher enhancement factors are expected for silver as compared to gold. Optical enhancing properties for SERS were tested with two laser lines, evidencing significantly larger enhancement factors for the bimetallic nanoparticles, as compared to those of gold.
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