Plasmonic mode interferences and Fano resonances in Metal-Insulator-Metal nanostructured interface OPEN

International audienceMetal-insulator-metal systems exhibit a rich underlying physics leading to a high degree of tunability of their spectral properties. We performed a systematic study on a metal-insulator-nanostructured metal system with a thin 6 nm dielectric spacer and showed how the nanoparticle sizes and excitation conditions lead to the tunability and coupling/decoupling of localized and delocalized plasmonic modes. We also experimentally evidenced a tunable Fano resonance in a broad spectral window 600 to 800 nm resulting from the interference of gap modes with white light broad band transmitted waves at the interface playing the role of the continuum. By varying the incident illumination angle shifts in the resonances give the possibility to couple or decouple the localized and delocalized modes and to induce a strong change of the asymmetric Fano profile. All these results were confirmed with a crossed comparison between experimental and theoretical measurements, confirming the nature of different modes. The high degree of control and tunability of this plasmonically rich system paves the way for designing and engineering of similar systems with numerous applications. In particular, sensing measurements were performed and a figure of merit of 3.8 was recorded ranking this sensor among the highest sensitive in this wavelength range. Surface plasmon polariton (SPP) and Localized surface plasmon (LSP) have attracted numerous researchers due to their high technological potential. SPP's are surface waves confined near a metal dielectric interface that can propagate over large distances 1 , making them appealing for applications in biosens-ing 2,3. On the other hand LSP resonances can be defined as the localized resonance condition that massively enhances the electromagnetic field in the vicinity of a metal nanoparticle (NP), when the NP have dimensions much smaller than the excitation wavelength 4. LSP resonance is very sensitive to changes in the NP's dimensions, the dielectric constant of the surrounding media and the nature of the substrate. Because of intense local electrical field enhancements and sharp resonance excitation peaks, metallic NPs are of great interest for applications in surface enhanced Raman spectroscopy (SERS) 5 , chemical and biological sensors 3,6 , cancer treatment 7 and light harvesting 8–10. Recently, strong attention was paid to the potentials of SPP and LSP combinations by investigating metallic NPs on top of metallic thin films. Several studies on such systems have indeed shown the coupling and hybridization between localized and delocalized modes, and the effect of the thickness of the dielectric spacer. Those works have revealed that such coupled systems exhibit enhanced optical properties and larger tunability of their spectral properties compared to uncoupled systems 1,4,11–2

Lithium Niobate Micro-transducers matrix design

In this work, a two-dimensional (2D) Lithium Niobate (LiNbO3) 36°Y-cut micro-transducers (μTs) matrix design is presented. Two main steps define the fabrication process: electrode deposition and photolithography. These steps are preceded by the optical mask conception, which defines the 2D matrix pattern. In contrary to the one element case, this μTs matrix allows to automatically scan a desired structure in real time. The μTs matrix is characterized using an impedance analyzer. Furthermore, the experimental tests carried out in order to demonstrate the matrix functionality at low frequencies [200 - 800] kHz are presented

Optimization of the PVT process for growth of high quality SiC crystals

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Metamaterial GRIN lens for Infrared applications

International audienceLes propriétés optiques uniques des métamatériaux permettent d’envisager des fonctions optiques complexes sur des dimensions spatiales réduites. récemment, une étude numérique réalisée à l’institut Fresnel a montré qu’une structure « de lentille à gradient d’indice (GRIN) à 10 μm » à gradient d’indice circulaire de quelques λ² seulement, permet une focalisation efficace. De telles structures doivent permettre, à terme, de diminuer le rapport signal à bruit des détecteurs infrarouges. Dans notre travail nous réalisons ces designs sous forme de microstructures 3D, sur deux types de résine positive et négative. Les premières observations ont montré une validation des résultats théoriques des concentrateurs réalisés sur des résines négatives. Parallèlement, nous nous intéressons au remplissage de ces microstructures 3D par des matériaux métalliques ou semi-conducteurs, comme le nickel ou le ZnO, dans le but de réaliser des métamatériaux à indice négatif qui soient fonctionnels à 10 μm

Blocs de construction en métamatériaux pour des applications en infrarouge

International audienceDans ce papier nous présentons nos investigations expérimentales pour réaliser un concentrateur de lumière IR qui correspond à une microstructure polymère 3D à gradient d’indice effectif. Le design proposé par l’Institut Fresnel devrait permettre une focalisation efficace de la lumière à 10μm à proximité immédiat du concentrateur. De telle structure pourra être intégrée sur de détecteurs IR afin de réduire leur volume et d’augmenter ainsi leur rapport signal à bruit. Dans ce travail nous réalisons ces designs sous forme de structures 3D épaisses, sur deux types de résine positive et négative. Les premières observations corroborent avec les simulations théoriques des concentrateurs réalisés sur des résines négatives

New formulation for 2D photolithography with ultra-high resolution for photonic applications

International audienceIn this paper, we report on the development of a high resolution negative photoresist for 2D nanolithography. The formulation which is based on PMMA as polymer matrix contains a mixture of triacrylic monomer and a photoinitiator sensitive at both one and two photon activation. Thanks to PMMA, the liquid mixture thoroughly wet out the Silicon or glass substrate and make it possible the fabrication of ultrathin photopolymerizable films (50 – 1000 nm) with good surface roughness and high spatial resolution. During the writing process, continuous diffusion of oxygen at the interface of the ultrathin photopolymer film seems to play a determinant role in the control of polymerization growth. Surface relief gratings were generated using far and near field irradiation set-ups at different wavelengths (442 and 780 nm). The patterned polymer films were characterized by AFM and SEM. The influence of the mixture composition, the exposure time, the laser intensity and the spatial frequency was investigated. The material shows high resolution (up to 6000 t/mm) with polymer line-widths smaller than 60 nm corresponding to writing wavelength/13. The photopatterned polymer can be used as a mask for etching of Silicon or ZnO surfaces. Based on this study, 2D thick metamaterial structures that focalize light in the infrared domain (5-10 µm) are fabricated by Two Photon Polymerization and characterized at 5.64 µm using QCL (Quantum Cascade Laser) source and IR CCD Camera

High resolution patterning using photoresist based PMMA for photonic applications

International audienceThe control of spatial resolution of photopolymers is one of the most important issue needed for their successful use in many nanoscale applications. Despite the rapid and impressive advances of lasers and the use of 2-Photon lithography, feature sizes and spatial resolution are still limited by the diffraction. Breaking this diffraction barrier is a great challenge in many fields of nanotechnology. This challenge has spurred a great number of effort aiming towards usage of shorter wavelengths or some original phenomena such as stimulated emission depletion, confining light to deep subwavelength using photochromes or confining the polymerization reaction to smaller volumes using new highly efficient photoinitiators, oxygen or inhibitors, so that smaller light/matter interaction volume is defined. In this paper, we report on the development of a high resolution negative photoresist for 2D nanolithography. The formulation which is based on PMMA as polymer matrix contains a mixture of triacrylic monomer and a photoinitiator sensitive at both one and two photon activation. Thanks to PMMA, the liquid mixture thoroughly wet out the Silicon or glass substrate and make possible the fabrication of ultrathin photopolymerizable films (50 – 1000 nm) with good surface roughness and high spatial resolution. During the writing process, continuous diffusion of oxygen at the interface of the ultrathin photopolymer film seems to play a crucial role in the control of polymerization growth. Surface relief gratings are generated using far and near field irradiation set-ups at different wavelengths (442 and 780 nm). The patterned polymer films are characterized by AFM and SEM. The influence of the mixture composition, the exposure time, the laser intensity and the spatial frequency is investigated. The material shows high resolution (up to 6000 t/mm) with polymer line-widths smaller than 60 nm corresponding to writing wavelength/13. The photopatterned polymer can be used as a mask for etching of Silicon or ZnO surfaces. Based on this study, 2D thick metamaterial structures that focalize light in the infrared domain (5-10 μm) are fabricated by Two Photon Polymerization and characterized at 5.64 μm using QCL source and IR CCD Camera

Self-Limited Grafting of Sub-Monolayers via Diels–Alder Reaction on Glassy Carbon Electrodes: An Electrochemical Insight

The grafting of molecular monolayers is critical for the functionalization of surfaces. In molecular electrochemistry, the surface modification of electrodes and the way molecules are attached to the electrode surface are highly critical to electron transfers and electrochemical reactions. In this paper, sub-monolayers were covalently grafted onto glassy carbon (GC) electrodes via Diels−Alder cycloaddition with two soluble dienophiles, that is, propargyl bromide and ethynyl ferrocene. Such an approach is clean (no by-product, no catalyst/additive) and occurs under mild conditions by heating at 50°C in toluene for few hours. The as-modified electrodes were thoroughly characterized by FTIR, XPS, and cyclic voltammetry using both millimetric GC electrodes and ultra-microelectrodes. Cyclic voltammetry gave access to surface coverage and clearly evidenced the covalent grafting of sub-monolayers. The grafting of functional sub-monolayers via Diels− Alder cycloaddition could be easily extended to various functionalities and carbons to prepare electrochemical sensors or electrocatalytic surfaces

Lithium Niobate Micro-transducers matrix design

In this work, a two-dimensional (2D) Lithium Niobate (LiNbO3) 36°Y-cut micro-transducers (μTs) matrix design is presented. Two main steps define the fabrication process: electrode deposition and photolithography. These steps are preceded by the optical mask conception, which defines the 2D matrix pattern. In contrary to the one element case, this μTs matrix allows to automatically scan a desired structure in real time. The μTs matrix is characterized using an impedance analyzer. Furthermore, the experimental tests carried out in order to demonstrate the matrix functionality at low frequencies [200 - 800] kHz are presented

Enhanced gold film coupled graphene based plasmonic nanosensors

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