Nanoscale Imaging of Plasmonic Hot Spots and Dark Modes with the Photothermal-Induced Resonance Technique

Abstract 

The collective oscillation of conduction electrons, responsible for the localized surface plasmon resonances, enables engineering nanomaterials by tuning their optical response from the visible to terahertz as a function of nanostructure size, shape, and environment. In this work, the photothermal-induced resonance (PTIR) technique is applied for the first time to image the dark plasmonic resonance of gold asymmetric split ring resonators (A-SRRs) in the mid-infrared spectral region with nanoscale resolution. Additionally, the PTIR is used to map the local absorption enhancement of poly(methyl methacrylate) coated on A-SRRs. We argue that PTIR nanoscale characterization will facilitate the engineering and application of plasmonic nanomaterials for mid-IR applications.