Abstract: Gallium?magnesium (Ga-Mg) core-shell nanoparticles were synthesized by sequential evaporation of gallium and magnesium molecular beams on sapphire substrates. The surface plasmon resonance properties of this novel bimetallic system are demonstrated and investigated in a broad spectral range, from the near-UV to the visible and to the near-IR by in situ real-time spectroscopic ellipsometry. Both the mean NP ensemble diameter and the relative core-shell radii affect the resultant plasmon resonance, and this study shows that the resonance can be red-shifted and tuned into the near-IR by increasing the extent of the Mg-shell, while limiting the overall nanoparticle size, promoting this novel, nanomaterials system for applications of bifunctional plasmonic-catalytic nanoparticles with optical properties tunable across a broad spectral range. Experimental real-time plasmonic results are corroborated by discrete dipole approximation calculations applied to core?shell nanoparticles supported on the substrate, which rationalize the red-shift of the Ga-Mg core-shell structure with the increase of the Mg shell relative volume.

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