Spectral response of dielectric nano-antennas in the far- and near-field regimes

Recent studies show that the spectral behaviour of localized surface plasmon resonances (LPSRs) in metallic nanoparticles su er from both a redshift and a broadening in the transition from the far- to the near-field regimes. An interpretation of this efect was given in terms of the evanescent and propagating components of the angular spectrum representation of the radiated eld. Due to the increasing interest awakened by magnetodielectric materials as a both low-loss material option for nanotechnology applications, and also for their particular scattering properties, here we study the spectral response of a magnetodielectric nanoparticle as a basic element of a dielectric nano-antenna. This study is made by analyzing the changes su ered by the scattered electromagnetic field when propagating from the surface of this dielectric nanostructure to the far-zone in terms of propagating and evanescent plane wave components of the radiated fields.This research was supported by MICINN (Spanish Ministry of Science and Innovation) with project FIS2013- 45854-P

Respuesta espectral de nanoantenas dipolares en campo cercano y lejano

Estudios realizados en nanopartículas metálicas muestran un corrimiento al rojo y ensanchamiento de los picos de las resonancias plasmónicas en la transición del campo lejano al cercano. Este trabajo estudia la respuesta espectral de nanopartículas dieléctricas con alto índice de refracción, las cuales muestran resonancias dipolares eléctricas y magnéticas, y ofrece una interpretación del ensanchamiento y corrimiento al rojo producido en estos materiales en términos de las contribuciones radiativa y no-radiativa al campo electromagnético difundido

CDDA: extension and analysis of the discrete dipole approximation for chiral systems

Discrete dipole approximation (DDA) is a computational method broadly used to solve light scattering problems. In this work, we propose an extension of DDA that we call Chiral-DDA (CDDA), to study light-chiral matter interactions with the capability of describing the underlying physics behind. Here, CDDA is used to solve and analyze the interaction of a nanoantenna (either metallic or dielectric) with a chiral molecule located in its near field at different positions. Our method allowed to relate near field interactions with far field spectral response of the system, elucidating the role that the nanoantenna electric and magnetic polarizabilities play in the coupling with a chiral molecule. In general, this is not straightforward with other methods. We believe that CDDA has the potential to help researchers revealing some of the still unclear mechanisms responsible for the chiral signal enhancements induced by nanoantennas.Ramon y Cajal Fellowship (RYC-2016- 20831); Ministerio de Educación, Cultura y Deporte (PGC2018-096649-B-I); Horizon 2020 Framework Programme (899598)

Sb2S3-based optical switch exploiting the Brewster angle phenomenon [Invited]

Optical switches based on phase change materials (PCMs) hold great promise for various photonic applications such as telecommunications, data communication, optical interconnects, and signal processing. Their non-volatile nature as well as rapid switching speeds make them highly desirable for developing advanced and energy-efficient optical communication technologies. Ongoing research efforts in exploring new PCMs, optimizing device designs, and overcoming existing challenges are driving the development of innovative and high-performance optical switches for the next generation of photonics applications. In this study, we design and experimentally demonstrate a novel optical amplitude switch design incorporating PCM antimony trisulfide (Sb2S3) based on the Brewster angle phenomenon.H2020 Future and Emerging Technologies (899598 – PHEMTRONICS)

Optically addressing interaction of Mg/MgO plasmonic systems with hydrogen

Magnesium-based films and nanostructures are being studied in order to improve hydrogen reversibility, storage capacity, and kinetics, because of their potential in the hydrogen economy. Some challenges with magnesium (Mg) samples are their unavoidable oxidation by air exposure and lack of direct in situ real time measurements of hydrogen interaction with Mg and MgO surfaces and Mg plasmonic nanoparticles. Given these challenges, the present article investigates direct interaction of Mg with hydrogen, as well as implications of its inevitable oxidation by real-time spectroscopic ellipsometry for exploiting the optical properties of Mg, MgH2 and MgO. The direct hydrogenation measurements have been performed in a reactor that combines a remote hydrogen plasma source with an in situ spectroscopic ellipsometer, which allows optical monitoring of the hydrogen interaction and results in optical property modification. The hydrogen plasma dual use is to provide the hydrogen-atoms and to reduce barriers to heterogeneous hydrogen reactions.European Commission under the H2020 grant TWINFUSYON (GA692034). Army Research Laboratory under Cooperative Agreement Number W911NF-17-2-0023. SODERCAN (Sociedad para el Desarrollo de Cantabria) through the Research Vicerrectorate of the University of Cantabria

Analysis of directionality effects in magnetodielectric core-shell nanoparticles by means of polarimetric techniques

The influence of increasing the core size of a Ag-Si core-shell nanoparticle has been investigated by using the values of the linear polarization degree at right angle scattering configuration, PL(90º). Changes in dipolar resonances and Scattering Directionality Conditions as a function of the core radius (Rint) for a fixed shell size (Rext = 230 nm) have been analyzed. An empirical formula to obtain the ratio Rint/Rext by monitoring the influence of the magnetic dipolar resonance in PL(90º) has been found.This research was supported by MICINN (FIS2013-45854-P). Ángela I. Barreda and Y. Gutiérrez want to express their gratitude to the University of Cantabria for their FPU grant

Sustainable and tunable Mg/MgO plasmon-catalytic platform for the grand challenge of SF6 environmental remediation

Sulfur hexafluoride (SF₆) is one of the most harmful greenhouse gases producing environmental risks. Therefore, developing ways of degrading SF₆ without forming hazard products is increasingly important. Herein we demonstrate for the first time the plasmon-catalytic heterogeneous degradation of SF₆ into non-hazardous MgF₂ and MgSO₄ products by non-toxic and sustainable plasmonic magnesium/magnesium oxide (Mg/MgO) nanoparticles, which are also effective as a plasmonenhanced SF₆ chemometric sensor. The main product depends on the excitation wavelength; when the localized surface plasmon resonance (LSPR) is in the ultraviolet then MgF₂ forms, while visible light LSPR results in MgSO₄. Furthermore, Mg/MgO platforms can be regenerated in few seconds by hydrogen plasma treatment and can be re-used in a new cycle of air purification. Therefore, this research first demonstrates effectiveness of Mg/MgO plasmoncatalysis enabling environmental remediation with the concurrent functionalities of monitoring, degrading and detecting sulfur- and fluorine- gases in the atmosphere.Y.G., F.G. and F.M. acknowledge MICINN (Spanish Ministry of Science and Innovation) through project PGC2018-096649-B-100. Y.G. thanks the University of Cantabria for her FPU grant

Polymorphic gallium for active resonance tuningin photonic nanostructures: from bulk gallium totwo-dimensional (2D) gallenene

Reconfigurable plasmonics is driving an extensive quest for active materials that can support a controllable modulation of their optical properties for dynamically tunable plasmonic structures. Here, polymorphic gallium (Ga) is demonstrated to be a very promising candidate for adaptive plasmonics and reconfigurable photonics applications. The Ga sp-metal is widely known as a liquid metal at room temperature. In addition to the many other compelling attributes of nanostructured Ga, including minimal oxidation and biocompatibility, its six phases have varying degrees of metallic character, providing a wide gamut of electrical conductivity and optical behavior tunability. Here, the dielectric function of the several Ga phases is introduced and correlated with their respective electronic structures. The key conditions for optimal optical modulation and switching for each Ga phase are evaluated. Additionally, we provide a comparison of Ga with other more common phase-change materials, showing better performance of Ga at optical frequencies. Furthermore, we first report, to the best of our knowledge, the optical properties of liquid Ga in the terahertz (THz) range showing its broad plasmonic tunability from ultraviolet to visible-infrared and down to the THz regime. Finally, we provide both computational and experimental evidence of extension of Ga polymorphism to bidimensional twodimensional (2D) gallenene, paving the way to new bidimensional reconfigurable plasmonic platforms.F.M. acknowledges MICINN (Spanish Ministry of Science and Innovation) through project PGC2018-096649-B-100

Electromagnetic Study of Behaviour of Plasmonic Units

SUMMARY: For any memory or computing device, fast switching speed and low switching energy are most attractive attributes, and approaches by which speed and energy efficiency can be improved are always desirable. Plasmonics offers a way to achieve those attributes of fast switching and low energy consumption: plasmonic resonant structures are inherently capable of harnessing and focusing optical energy on sub-wavelength scales, far beyond the capabilities of conventional optical and photonic elements. Plasmonics can provide us with access to both of these scenarios. Indeed, plasmonics offers additional light manipulation tools, otherwise inaccessible with conventional photonics. The collective oscillation of conduction electrons in a suitably shaped metallic nanoparticle (the so-called localized surface plasmon, LSP) can couple with impinging radiation, which in turn squeezes light into much reduced volumes, and greatly magnifies the local electric field, usually leading to a much reduced (non-diffraction limited) device footprint. This deliverable presents an analysis of the electromagnetic interaction of plasmonic units with phase-change materials (PCMs) as selected in the project PHEMTRONICS. As plasmonic units, we start by considering the common plasmonic metals of gold and silver, analyzing their possibilities and limits. Based on those, we consider the use of metallic nanoantennas made of Ga nanoparticle dimers. Ga has been selected due to its good plasmonic performance, physical and chemical properties and to its polymorphism. We have analyzed the coupling of plasmonic nanoantennas with the PCMs under consideration at the moment in the project, namely, GaS and Sb2S3 in their amorphous and crystalline phases. These two PCMs have been combined with Ga NPs and some gold configurations to make the nanoantenna reconfigurabilty wider and improve its tunability and performance. Further, plasmon coupling to PCM waveguides made of Sb2S3, has been analyzed through metallic grating couplers. Two basic configurations have been selected which could be the base to design a plasmonic enhanced PCM photodetector in collaboration with the PHEMTRONICS partners. Finally, conclusions have been drawn together with the identification of the practical solutions to couple plasmonics with novel PCMs

The UV plasmonic behavior of distorted rhodium nanocubes

For applications of surface-enhanced spectroscopy and photocatalysis, the ultraviolet (UV) plasmonic behavior and charge distribution within rhodium nanocubes is explored by a detailed numerical analysis. The strongest plasmonic hot-spots and charge concentrations are located at the corners and edges of the nanocubes, exactly where they are the most spectroscopically and catalytically active. Because intense catalytic activity at corners and edges will reshape these nanoparticles, distortions of the cubical shape, including surface concavity, surface convexity, and rounded corners and edges, are also explored to quantify how significantly these distortions deteriorate their plasmonic and photocatalytic properties. The fact that the highest fields and highest carrier concentrations occur in the corners and edges of Rh nanocubes (NCs) confirms their tremendous potential for plasmon-enhanced spectroscopy and catalysis. It is shown that this opportunity is fortuitously enhanced by the fact that even higher field and charge concentrations reside at the interface between the metal nanoparticle and a dielectric or semiconductor support, precisely where the most chemically active sites are located.This research has been supported by MICINN (Spanish Ministry of Science and Innovation, project FIS2013-45854-P). Research was sponsored by the Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-17-2-0023. Y.G. wants to thank the University of Cantabria for her FPU (formación del profesorado universitario) gran