Plasmonic Au islands on polymer nanopillars

Abstract

The refractive index sensitivity of localized surface plasmon resonance sensors can beimproved by placing the plasmonic metal particles on pillars instead of on a planarsubstrate. In this paper, a simple and versatile colloidal lithography method for thefabrication of plasmonic Au islands on top of polymer nanopillars is described. The pillarheight is controlled by varying the thickness of the initial polymer film. An increased pillarheight results in a blue shift of the absorption spectrum of the Au islands. This is explainedby a decreased effective refractive index around the islands. For pillars higher thanapproximately 40 nm no further blue shift is observed, in agreement with the decaylength of the electromagnetic field around the islands. Pillar-supported Au islandswere also fabricated on a flexible foil, demonstrating the potential of the methoddescribed here for the fabrication of flexible plasmonic substrates. Benefits andlimitations of the method and of using polymers as the pillar material are discussed.