Plasmonic coupling in single flower-like gold nanoparticle assemblies

Localized surface plasmon resonance(LSPR) arises when light interacts with metallic nanoparticles(NPs).When nanoparticles(NPs) assemble together, the plasmon coupling effect between the NPs often leads to new features in the LSPR of the assembled structure. Understanding the plasmon coupling in the complex assemblies will greatly benefit the development of new plasmonic devices. Here we demonstrate the fabrication of a 3D structure using two different sized Au NPs as building blocks. This 3D structure was achieved by manipulating the binding efficiency of ligands linking the NPs, and proper choice of the NP size. The assembled structure is flower-like structure, with one 130 nm Au NP in the center, and several 40 nm Au NPs attaching as"petals". Single particle dark-field scattering measurements of the individual assemblies were performed,together with electrodynamics simulations. The experimental and theoretical studies show that, the plasmonic coupling lead to broadening of the LSPR and additional peaks, depending on the number and 3D arrangement of the 40 nm NPs around the center 130 nm NP.