Electron Energy Loss Spectroscopy of Bright and Dark Modes in Hyperbolic Metamaterial Nanostructures

in Advanced Optical Materials (2020), 8(13), 2000277

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 ▲]

Bio-assisted tailored synthesis of plasmonic silver nanorings and site-selective deposition on graphene arrays

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 ▲]