On the formation of ternary metallic-dielectric multicore-shell nanoparticles by inert-gas condensation method

Magneto-plasmonic hybrid nanoparticles (HNPs) are promising for a large number for dual magneto-optical bioapplications. Gas-phase techniques offer a good alternative to chemical routes for the generation of tailored HNPs. Here, we present a novel method to synthesize ternary HNPs composed of multiple dumbbell-like FeAg cores encapsulated by an amorphous Si shell. The method involves a simultaneous sputtering of Fe, Ag and Si targets under controlled conditions. We demonstrate that the morphology and the size of the HNPs can be modulated by tuning experimental parameters such as the energy and the cooling rate, or the collision and coalescence processes experienced by the HNPs during their formation. We find that by increasing the residence time of the HNPs in the aggregation zone, we increase both the size of the HNPs, and the thickness of the Si shell. HNPs exhibit ferromagnetic behavior and show an enhanced, red-shifted, light absorption band due to the strong near-field coupling between the Ag cores and the Si shell. A mechanism of formation of these HNPs is suggested, combining the physico-chemical properties of the materials (Fe, Ag, Si) with the experimental conditions.