Plasmonic Properties of Silver Nanoparticle Clusters Prepared by AFM Manipulation

The plasmonic resonance of nanostructures is extremely sensitive to the size and shape of the constituting nanoparticles, geometric configuration, inter-particle separation, and the dielectric property of the medium. While there has been much theoretical advancement in the plasmonic properties of ensembles of noble metal nanoparticles, practical realization of such ensembles has been challenging. Here, we present a versatile method for fabricating plasmonic nano-assemblies using atomic force microscope (AFM) manipulation, which allows precise fabrication of well-defined ensembles of single crystalline nanoparticles, and to some extent the control of inter-particle separations as well. Polyhedral single crystalline AgNPs were prepared via the hydrogen reduction method with a uniform diameter of ~110 nm. Combined with dark-field microscopy and spectroscopy, our method also enables the collection of the scattering spectrum for each ensemble with excellent signal-to-noise ratio. We manipulated chemically synthesized high purity AgNPs into linear chains, rings, dimers, trimers and other various geometries. The scattering spectra of these ensembles will be presented within the framework of plasmonic hybridization.