Spectral Tuning of High Order Plasmonic Resonances in Multimodal Film‐Coupled Crystalline Cavities

Abstract

allow for a strong confinement and enhancement of the electromagnetic field in subwavelength volumes along with plasmon propagation in structures with low dimensionalities. [2] These appealing properties have triggered the development of biosensing, [3] energy conversion, [4,5] detectors, [6] integrated optical component for information transfer and/or processing, [7] or shaping of the phase front of light. [8,9] Several applications rely on the ability of the plasmonic nanoparticle to efficiently scatter or concentrate the light in a specific region of space at a given energy. As a consequence, a constant effort has been undertaken to control and tune the plasmon resonance of subwavelength plasmonic resonators or antennas from UV to IR. [10,11] Strategies to adjust the conditions of resonance or propagation rely on the static [12,13] or dynamic [14][15][16] modification of the surrounding medium, on the modification of the geometry, [17] the size or the material of the metallic object itself, [12,18,19] or on the modification of the charge carrier density, for instance. [20] A particularly efficient approach exploits the electromagnetic coupling between a plasmonic nanoparticle and a thin metallic film. [21][22][23][24][25][26] The small nanocavity resulting from the metalinsulator-metal (MIM) geometry gives rise to new longitudinal and transverse plasmonic resonances in the gap along with a spectral shift of the native resonance of the nanoparticle. [27][28][29] The adjustment of the coupling strength by varying the distance between nanoparticles and the conductive plasmonic film can be used to tune the surface plasmon (SP) resonance wavelength. [30][31][32] The MIM geometry, which is compatible with operational device configuration, offers therefore a new degree of freedom to control the modal plasmonic landscape and the related scattering properties of the system.While the optical response of subwavelength particles is well defined and usually limited to one or two resonances in the visible, sub-micronic 2D colloidal gold cavities sustain multiple higher order plasmonic resonances that offer a much richer multimodal plasmonic spectrum. Indeed, these highly crystalline and thin metallic cavities exhibit a single transverse mode but several planar resonances of higher order than the dipolar one in the visible and near-infrared. [33][34][35][36] They result from multiple interferences between degenerated high order SP modes and yield optical near-fields that are strongly localized at specific hot spots along the edges and at the center of the Sub-micrometric and ultrathin gold cavities sustain several high order planar plasmon resonances in the visible to near-infrared spectral window that open new perspectives for the realization of self-assembled metasurfaces or integrated components for nano-optics. This article investigates in detail the far-field spectral features of these multimodal crystalline gold nanoprisms, deposited on either dielectric (glass) or metallic substrates (Au, Al) by darkfield scattering s...

Large and Versatile Plasmonic Enhancement of Photoluminescence Using Colloidal Metallic Nanocubes

“…MNPs are actually able to strongly interact with light despite a typical size of a few dozen nanometers, and spreading colloidal MNPs presents the advantage of being a relatively inexpensive technique compared with lithography. In addition, MNPs offer wide a diversity of geometries and sizes, leading to different optical responses. , Metallic nanocubes especially have been proved to be particularly interesting in this context, allowing to fabricate even complex structures, , while being easy to spread quite evenly on a large surface …”

“…In addition, MNPs offer wide a diversity of geometries and sizes, leading to different optical responses. 4,5 Metallic nanocubes especially have been proved to be particularly interesting in this context, allowing to fabricate even complex structures, 6,7 while being easy to spread quite evenly on a large surface. 8 Metallic NPs may enhance the photoluminescence (PL) of a fluorescent layer and thus increase the EQE in two distinct ways.…”