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See detailPlasmon Hybridization in Compressible Metal-Insulator-Metal Nano-Cavities: an Optical Approach for Sensing Deep Sub-Wavelength Deformation
Carrara, Angelica; Maccaferri, Nicolò UL; Cerea, Andrea et al

in Advanced Optical Materials (2020)

We present a pressure-induced deformation-sensitive device based on 2D matrices of plasmonic gold nanodisks coupled to a metal thin layer through a compressible dielectric spacer, namely a deformable ... [more ▼]

We present a pressure-induced deformation-sensitive device based on 2D matrices of plasmonic gold nanodisks coupled to a metal thin layer through a compressible dielectric spacer, namely a deformable metal-insulator-metal (MIM) nanocavity, to report deep sub-wavelength size variations (< λ/200). The system is characterized by two hybrid branches, which are resonant in the visible/near infrared spectral region. The fundamental mode, owing to the near-field interaction between the plasmonic nanostructures and the metal film, exhibits a remarkable sensitivity to the gap size, exceeding that of a planar “macroscopic” optical cavity and extending its operational domain to the sub-wavelength range, where excellent opportunities towards truly multiscale MIMs-based pressure sensors can be envisioned. Concurrently, its intrinsic plasmonic nature synergistically combines into a single platform multi-purpose functionalities, such as ultrasensitive detection, remote temperature readout etc., with practical perspectives in ultra-compact inspection tools for structural and functional information at the nanoscale. [less ▲]

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See detailBio-assisted tailored synthesis of plasmonic silver nanorings and site-selective deposition on graphene arrays
Giovannini, Giorgia; Ardini, Matteo; Maccaferri, Nicolò UL et al

in Advanced Optical Materials (2020), 8(4), 1901583

The spontaneous interaction between noble metals and biological scaffolds enables simple and cost‐effective synthesis of nanomaterials with unique features. Here, plasmonic silver nanorings are ... [more ▼]

The spontaneous interaction between noble metals and biological scaffolds enables simple and cost‐effective synthesis of nanomaterials with unique features. Here, plasmonic silver nanorings are synthesized on a ring‐like protein, i.e., a peroxiredoxin (PRX), and used to assemble large arrays of functional nanostructures. The PRX drives the seeding growth of metal silver under wet reducing conditions, yielding nanorings with outer and inner diameters down to 28 and 3 nm, respectively. The obtained hybrid nanostructures are selectively deposited onto a solid‐state 2D membrane made of graphene in order to prepare plasmonic nanopores. In particular, the interaction between the graphene and the PRX allows for the simple preparation of ordered arrays of plasmonic nanorings on a 2D‐material membrane. This fabrication process can be finalized by drilling a nanometer scale pore in the middle of the ring. Fluorescence spectroscopic measurements in combination with numerical simulations demonstrate the plasmonic effects induced in the metallic nanoring cavity. The prepared nanopores represent one of the first examples of hybrid plasmonic nanopore structures integrated on a 2D‐material membrane. The diameter of the nanopore and the atomically thick substrate make this proof‐of‐concept approach particularly interesting for nanopore‐based technologies and applications such as next‐generation sequencing and single‐molecule detection. [less ▲]

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See detailElectron Energy Loss Spectroscopy of Bright and Dark Modes in Hyperbolic Metamaterial Nanostructures
Isoniemi, Tommi; Maccaferri, Nicolò UL; Ramasse, Quentin M. et al

in Advanced Optical Materials (2020)

Layered metal/dielectric hyperbolic metamaterials (HMMs) support a wide landscape of plasmon polariton excitations. In addition to surface plasmon polaritons, coupled Bloch-like gap-plasmon polaritons ... [more ▼]

Layered metal/dielectric hyperbolic metamaterials (HMMs) support a wide landscape of plasmon polariton excitations. In addition to surface plasmon polaritons, coupled Bloch-like gap-plasmon polaritons with high modal confinement inside the multilayer are supported. Photons can excite only a subset of these polaritonic modes, typically with a limited energy and momentum range in respect to the wide set of high-K modes supported by hyperbolic dispersion media, and coupling with gratings or local excitation is necessary. Strikingly, electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope allows nm-scale local excitation and mapping of the spatial field distribution of all the modes supported by a photonic or plasmonic structure, both bright and dark, and also all other inelastic interactions of the beam, including phonons and interband transitions. Herein, experimental evidence of the spatial distribution of plasmon polaritons in multilayered type II HMM nanostructures is acquired with an aloof electron beam adjacent to structures of current interest. HMM pillars are useful for their separation and adjustability of optical scattering and absorption, while HMM slot cavities can be used as waveguides with high field confinement. The nature of the modes is confirmed with corresponding simulations of EEL and optical spectra and near-field intensities. [less ▲]

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See detailThrough the Spherical Looking-Glass: Asymmetry Enables Multicolored Internal Reflection in Cholesteric Liquid Crystal Shells
Geng, Yong UL; Jang, Ju-Hyun; Noh, Kyung-Gyu et al

in Advanced Optical Materials (2017), 6(1), 1700923

Spheres of cholesteric liquid crystal generate dynamic patterns due to selec- tive reflection from a helical structure subject to continuously curved bounda- ries. So far the patterns are investigated ... [more ▼]

Spheres of cholesteric liquid crystal generate dynamic patterns due to selec- tive reflection from a helical structure subject to continuously curved bounda- ries. So far the patterns are investigated exclusively as function of reflections at the sphere exterior. Here it is shown that the cholesteric shells in a microfluidics produced double emulsion enable also a sequence of internal reflections if the shells have sufficiently thin top and thick bottom. While such asymmetry is promoted by buoyancy when the internal droplet has lower density than the liquid crystal, the elasticity of the cholesteric helix prefers a symmetric shell geometry, acting against gravity. This subtle balance can hide the internal reflections for long time. Eventually, however, the asymmetry is established, revealing a new class of photonic patterns characterized by colored sharp concentric rings. With the complete knowledge of the diverse light-reflecting behavior of cholesteric liquid crystal shells, and utilizing the tunability of the structure period by, e.g., temperature, electric field, or expo- sure to various chemical species as well as polymer stabilization for making the shells long-term stable, they may be developed into remarkable new optical elements for photonics, sensing, or security pattern generation. [less ▲]

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