Second harmonic generation from aluminum plasmonic nanocavities: from scanning to imaging.

Metamaterials and plasmonic structures made from aluminum (Al) have attracted significant interest due to their low cost, long-term stability, and the relative abundance of aluminum compared to the rare metals. Also, aluminum displays distinct dielectric properties allowing for the excitation of surface plasmons in the ultraviolet region with minimal non-radiative losses. Despite these clear advantages, most of the research has been focused on either gold or silver, probably due to difficulties in forming smooth thin films of aluminum.

Strong coupling between an inverse bowtie Nano-Antenna and a J-aggregate.

We demonstrate strong coupling between a single or few J-aggregates and an inverse bowtie plasmonic structure, when the J-aggregate is located at a specific axial distance from the metallic surface. Three hybrid modes are clearly observed, witnessing a strong interaction, with a Rabi splitting of up to 290 meV, the precise value of which significantly depends on the orientation of the J-aggregate with respect to the symmetry axis of the plasmonic structure. We repeated our experiments with a set of triangular hole arrays, showing consistent formation of three or more hybrid modes, in good agreement with numerical simulations.

Optimization of Gold Nanorod Features for the Enhanced Performance of Plasmonic Nanocavity Arrays.

Nanoplasmonic biosensors incorporating noble metal nanocavity arrays are widely used for the detection of various biomarkers. Gold nanorods (GNRs) have unique properties that can enhance spectroscopic detection capabilities of such nanocavity-based biosensors. However, the contribution of the physical properties of multiple GNRs to resonance enhancement of gold nanocavity arrays requires further characterization and elucidation.

Second harmonic generation by strongly coupled exciton-plasmons: The role of polaritonic states in nonlinear dynamics.

We investigate second harmonic generation (SHG) from hexagonal periodic arrays of triangular nano-holes of aluminum using a self-consistent methodology based on the hydrodynamics-Maxwell-Bloch approach. It is shown that angular polarization patterns of the far-field second harmonic response abide to threefold symmetry constraints on tensors. When a molecular layer is added to the system and its parameters are adjusted to achieve the strong coupling regime between a localized plasmon mode and molecular excitons, Rabi splitting is observed from the occurrence of both single- and two-photon transition peaks within the SHG power spectrum.

A simple, inexpensive and multi-scale 3-D fluorescent test sample for optical sectioning microscopies.

Fluorescence standards allow for quality control and for the comparison of data sets across instruments and laboratories in applications of quantitative fluorescence. For example, users of microscopy core facilities can expect a homogenous and time-invariant illumination and an uniform detection sensitivity, which are prerequisites for imaging analysis, tracking or fluorimetric pH or Ca -concentration measurements. Similarly, confirming the three-dimensional (3-D) resolution of optical sectioning microscopes calls for a regular calibration with a standardized point source.

Cathodoluminescence Nanoscopy of 3D Plasmonic Networks.

Nanoporous metallic networks are endowed with the distinctive optical properties of strong field enhancement and spatial localization, raising the necessity to map the optical eigenmodes with high spatial resolution. In this work, we used cathodoluminescence (CL) to map the local electric fields of a three-dimensional (3D) silver network made of nanosized ligaments and holes over a broad spectral range. A multitude of neighboring hotspots at different frequencies and intensities are observed at subwavelength distances over the network.

Supercritical Angle Fluorescence Microscopy and Spectroscopy.

Fluorescence detection, either involving propagating or near-field emission, is widely being used in spectroscopy, sensing, and microscopy. Total internal reflection fluorescence (TIRF) confines fluorescence excitation by an evanescent (near) field, and it is a popular contrast generator for surface-selective fluorescence assays. Its emission equivalent, supercritical angle fluorescence (SAF), is comparably less established, although it achieves a similar optical sectioning as TIRF does.

Polyhedral Water Droplets: Shape Transitions and Mechanism.

While classical liquid droplets are rounded, transitions have recently been discovered which render polyhedral water-suspended droplets of several oils. Yet, the mechanism of these transitions and the role of the droplets' interfacial curvature in inducing these transitions remain controversial. In particular, one of the two mechanisms suggested mandates a convex interface, in a view from the oil side.

Fabrication of Dipole-Aligned Thin Films of Porphyrin J-Aggregates over Large Surfaces.

We report a new approach for large-scale alignment of micron-sized J-aggregates of a derivative of porphyrin onto planar glass substrates. We applied a unidirectional nitrogen flow to an aqueous dye drop deposited onto a glass substrate to form an about 5 nm thick film of aligned J-aggregates over macroscopic surface areas up to several millimeters. The inter-aggregate distance is ∼500 nm, and it scales with the nitrogen pressure.

Second Harmonic Generation for Moisture Monitoring in Dimethoxyethane at a Gold-Solvent Interface Using Plasmonic Structures.

Second harmonic generation (SHG) is forbidden from most bulk metals because metals are characterized by centrosymmetric symmetry. Adsorption or desorption of molecules at the metal interface can break the symmetry and lead to SHG responses. Yet, the response is relatively low, and minute changes occurring at the interface, especially at solid/liquid interfaces, like in battery electrodes are difficult to assess.

Calibrating Evanescent-Wave Penetration Depths for Biological TIRF Microscopy.

Roughly half of a cell's proteins are located at or near the plasma membrane. In this restricted space, the cell senses its environment, signals to its neighbors, and exchanges cargo through exo- and endocytotic mechanisms. Ligands bind to receptors, ions flow across channel pores, and transmitters and metabolites are transported against concentration gradients.

Decoding the Information Contained in Fluorophore Radiation Patterns.

Dipole radiation patterns change when a fluorescent molecule comes close to the boundary between media of different refractive indices. Near-interface molecules emit mostly into the higher-index medium, predominantly around the critical angle. The radiation pattern encodes information about the emitter distance, orientation, and the refractive index of the embedding medium.

Second harmonic generation hotspot on a centrosymmetric smooth silver surface.

Second harmonic generation (SHG) is forbidden for materials with inversion symmetry, such as bulk metals. Symmetry can be broken by morphological or dielectric discontinuities, yet SHG from a smooth continuous metallic surface is negligible. Using non-linear microscopy, we experimentally demonstrate enhanced SHG within an area of smooth silver film surrounded by nanocavities.

Nanoporous Metallic Networks: Fabrication, Optical Properties, and Applications.

Nanoporous metallic networks are a group of porous materials made of solid metals with suboptical wavelength sizes of both particles and voids. They are characterized by unique optical properties, as well as high surface area and permeability of guest materials. As such, they attract a great focus as novel materials for photonics, catalysis, sensing, and renewable energy.

Bio-inspired Photocatalytic Ruthenium Complexes: Synthesis, Optical Properties, and Solvatochromic Effect.

We report the synthesis, characterization, and photo-physical properties of two new ruthenium -phenol-imidazole complexes. These bio-mimetic complexes have potential as photocatalysts for water splitting. Owing to their multiple phenol-imidazole groups, they have a higher probability of light-induced radical formation than existing complexes.

Carbon Dots-Plasmonics Coupling Enables Energy Transfer and Provides Unique Chemical Signatures.

Plasmonic nanostructures and carbon dots (C-dots) are fascinating optical materials, utilized in imaging, sensing, and color generation. Interaction between plasmonic materials and C-dots may lead to new hybrid materials with controllable optical properties. Herein, we demonstrate for the first time coupling between plasmonic modes and C-dots deposited upon a plasmonic silver hole array.

Secondary Electron Cloaking with Broadband Plasmonic Resonant Absorbers.

Scanning electron microscopy (SEM) is one of the most powerful tools for nanoscale inspection and imaging. It is broadly used for biomedicine, materials science, and nanotechnology, enabling spatial resolution beyond the optical diffraction limit. In SEM, a high-energy electron beam illuminates a specimen, and the emitted secondary electrons are routed to a positively biased, synchronized detector for image creation.

Hybridization between nanocavities for a polarimetric color sorter at the sub-micron scale.

Metallic hole arrays have been recently used for color generation and filtering due to their reliability and color tunability. However, color generation is still limited to several microns. Understanding the interaction between the individual elements of the whole nanostructure may push the resolution to the sub-micron level.

Ultrafast energy transfer between molecular assemblies and surface plasmons in the strong coupling regime.

The nonlinear optical dynamics of nanomaterials comprised of plasmons interacting with quantum emitters is investigated by a self-consistent model based on the coupled Maxwell-Liouville-von Neumann equations. It is shown that ultrashort resonant laser pulses significantly modify the optical properties of such hybrid systems. It is further demonstrated that the energy transfer between interacting molecules and plasmons occurs on a femtosecond time scale and can be controlled with both material and laser parameters.

Strong light-molecule coupling on plasmonic arrays of different symmetry.

The strong coupling of porphyrin J-aggregates to plasmonic nanostructures of different symmetry is investigated. The nanostructures of higher symmetry show the strongest interaction with the molecular layer, suggesting that surface plasmon mode degeneracy plays an important role in the coupling efficiency. At high coupling strengths a new, weakly dispersive mode appears which has recently been predicted theoretically to be due to long-range energy transfer between molecules mediated by surface plasmons.

Strong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal film.

We demonstrate strong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal film. The coupling manifests itself as an anticrossing behavior of the two newly formed polaritons. As the coupling strength grows, a new mode emerges, which is attributed to long-range molecular interactions mediated by the plasmonic field.

Molecules on si: electronics with chemistry.

Basic scientific interest in using a semiconducting electrode in molecule-based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics.