title: 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. While theoretical calculations helped tremendously in understanding plasmonic nanomaterials and optimizing their light matter interaction, only a few experimental techniques are available to study these materials with high spatial resolution. 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 (IR) spectral region with nanoscale resolution. Additionally, the chemically specific PTIR signal is used to map the local absorption enhancement of poly(methyl methacrylate) coated on A-SRRs, revealing hot spots with local enhancement factors up to ≈30 at 100 nm lateral resolution. We argue that PTIR nanoscale characterization will facilitate the engineering and application of plasmonic nanomaterials for mid-IR applications.
authors.affiliation: Center for Nanoscale Science and Technology, National Institute Standards and Technology , Gaithersburg, 100 Bureau Drive, Maryland 20899, United States.
authors.forename: Basudev
authors.initials: B
authors.lastname: Lahiri
authors.forename: Glenn
authors.initials: G
authors.lastname: Holland
authors.forename: Vladimir
authors.initials: V
authors.lastname: Aksyuk
authors.forename: Andrea
authors.initials: A
authors.lastname: Centrone