Boosting Optical Nanocavity Coupling by Retardation Matching to Dark Modes

Abstract

Plasmonic nanoantennas can focus light at nanometer length scales providing intense field enhancements. For the tightest optical confinements (0.5–5 nm) achieved in plasmonic gaps, the gap spacing, refractive index, and facet width play a dominant role in determining the optical properties making tuning through antenna shape challenging. We show here that controlling the surrounding refractive index instead allows both efficient frequency tuning and enhanced in-/output coupling through retardation matching as this allows dark modes to become optically active, improving widespread functionalities.

Molecular-Induced Chirality Transfer to Plasmonic Lattice Modes

“…A smoother PMMA interface may be obtained from employing a different solvent used for similar coatings. 65,66 The coating with a PMMA film did not disturb the positions of the individual NP in the arrays, as evidenced by the persistence of SLRs with similar quality compared to reference measurements using only indexmatching oils. 62,64 The large area covered by the AuNP array allows us to measure the samples in a commercial CD spectrometer (Jasco J-815a) under normal illumination with a simple, custom-built sample holder (Figure S3).…”

“…All substrate films were covered with immersion oil and a cover slide (Figures S2 and S3) to match the refractive index (RI), and thus, we effectively excite SLRs. − The homogeneous RI environment also prevents scattering, so that the surface roughness of the PMMA film does not compromise the optical properties. A smoother PMMA interface may be obtained from employing a different solvent used for similar coatings. , The coating with a PMMA film did not disturb the positions of the individual NP in the arrays, as evidenced by the persistence of SLRs with similar quality compared to reference measurements using only index-matching oils. , …”

Influence of Quadrupolar Molecular Transitions within Plasmonic Cavities

“…29 The resonant wavelengths of the bright nanocavity modes are experimentally resolved by angularly separating the highangle (θ high ) and low-angle (θ low ) dark-field scattering, for each nanostructure (Figure 1c). 37 Vertical emission (along zdirection) from the (11) mode is captured in low-angle scattering spectra, while (10) and (20) preferentially outcouple at high angles (θ ∼ 60°, defined from the vertical direction), spectrally distinguished from the low-angle component. 23 The experimental mode wavelengths agree with mode positions extracted from finite element method simulations performed with typical parameters for β-carotene nanogaps: D = 80 nm, w = 32 nm, n g = 1.56, and d = 2.4 nm (Figure 1d), where the facet width w has a linear dependence on the particle diameter (w/D = 41%) 35 and n g is defined by βcarotene molecules.…”

Full Control of Plasmonic Nanocavities Using Gold Decahedra‐on‐Mirror Constructs with Monodisperse Facets

“…Embedding NDoMs in a dielectric layer is the most straightforward method and gives a large increase of light in‐coupling for NPoMs. [ 42 ] Here, an 80 nm poly(methyl methacrylate) (PMMA) layer is spin‐coated onto the substrate to fully cover all NDoMs (Figure 6a I). All NDoMs of each size show exactly the same average threefold SERS enhancement for excitation wavelengths of both 633 and 785 nm (see Note S1, Supporting Information).…”