Plasmonics aims to exploit the unique optical properties of metallic nanostructures to enable the routing and the active manipulation of light at the nanoscale. However, the broad plasmon resonance of individual NPs limits the potential applications. A promising way to improve the quality of the LSPRs in to create Fano resonaces. When light is incident on an array of NPs, it is scattered by different elements in the structure. The presence of order in the system enables the appearance of coherent effects among the various scattered waves. These new modes are called lattice surface modes (LSMs) and are characterized by very narrow symmetric and asymmetric (Fano) peaks. The LSMs modes represent a new decay channel for emitters and offer new routes for the design of nano-structured surfaces that enable a control of the spontaneous emission. Fano resonances possess an inherent sensitivity to changes in geometry or in the local environment: small perturbations can induce dramatic shifts in the resonance or line shape and exceptionally large field enhancements. These properties render Fano resonant media particularly attractive for a range of applications spanning from plasmonic photovoltaics, to bio-sensing, SERS and SEIRA spectroscopies.

The objective of this study is to investigate how both the pattern of the array (unit cell, motif, period and dimensionality) and the specific properties of the NPs (size, shape, plasmon coupling) modify the spectral line shape of the plasmonic crystal. Samples are fabricated using electron beam lithography. Three different experimental configurations have been investigated: a) Array of Au nanopillars at Air/SiO2 interface, b) Array of Au nanopillars embedded within an homogeneous dielectric medium (SiO2) and c) Array of Au nanospheres embedded within an homogeneous dielectric medium (SiO2). For each configuration, Fano resonances have been investigated as a function of the NP size (20-100nm) and the array pitch (200-600nm).