Periodic Arrays of Dewetted Silver Nanostructures on Sapphire and Quartz: Effect of Substrate Truncation on the Localized Surface Plasmon Resonance and Near-Field Enhancement

Substrate-supported plasmonic nanostructures are distinct from their colloidal counterparts, in that they are surrounded by an asymmetric dielectric environment composed of the substrate material and the surrounding ambient. Such environments inevitably lead to plasmonic resonances and near-fields that differ from those of solution-dispersed structures. The most straightforward method for fabricating substrate-based plasmonic nanostructures is through the solid-state dewetting of ultrathin films. This process typically leads to nanostructures with an asymmetric geometry due to an apparent truncation by the substrate to an otherwise symmetric structure. While changes to the plasmonic properties resulting from the substrate- imposed dielectric environment are well studied, a comprehensive understanding of the effect of substrate truncation is lacking. Here, a study of the plasmonic properties of substrate-truncated Ag nanospheres is presented, where, through experiment and simulation, the influence of substrate truncation on plasmonic resonances and the associated near-fields are elucidated. It is shown that increases to the degree of truncation give rise to a substantial red shift and strengthening of the dipole resonance, a weakening of the quadrupole resonance, and a strengthening of the near-field intensities near the nanostructure−substrate interface. The study contributes to the understanding needed to rationally design nanostructure−substrate systems for on-chip plasmonic devices. ■