Plasmon Resonance Hybridization of Gold Nanospheres and Palladium Nanoshells Combined in a Rattle Structure

Gold and palladium nanopartides are characterized by their localized surface plasmon resonance (LSPR). In contrast with the sharp LSPR spectrum of gold nanopartides, palladium nanoparticles had a broad LSPR spectrum. Palladium-gold nanorattles (PdAuNRT) are an ideal system with optical properties that are a hybrid of gold and palladium nanopartides. The PdAuNRTs consisted of small gold nanospheres (AuNSs) located inside hollow palladium nanospheres (PdHNSs) of larger sizes without touching each other. PdAuNRTs of various sizes were synthesized by systematic variation of the experimental parameters. Interestingly, for the PdAuNRTs, where PdHNSs and AuNSs are separated by a distance, it was found that the broad plasmon resonance band of the PdHNSs hybridizes with the sharp plasmon resonance of the AuNSs located in its center. This was further confirmed experimentally by optical absorption measurements and theoretically using discrete dipole approximation technique. The plasmon resonance hybridization resulted in broadening of the LSPR spectrum of the PdAuNRTs and the appearance of a dip due to a Fano resonance.