Plasmonic nanoparticle clusters with tunable plasmonic resonances in the visible spectral region

The seeded growth of poly(ethylene imine)-gold nanoparticle clusters enables the formation of particle assemblies with tunable optical properties. Clusters with increasing particle sizes, filling factors and assemblies consisting of PEI-gold-silver core shell particles can be synthesized in this way. Profound structural characterization is carried out via TEM imaging and FIB milling which allows visualizing the cross-section of the clusters. Determination of the optical properties was performed via UV-Vis spectroscopy and spectral dark field microscopy of individual particles. Additionally, numerical calculations were carried out based on the Mie theory. The results are in good agreement with the experimental findings and reveal the contribution of different multipoles to the spectra which cannot be resolved by UV-Vis spectroscopy in solution. The isotropic nature and adjustable properties of these clusters could render them versatile building blocks for metamaterials.