Localization Of Electromagnetic Energy Research Articles

(Invited) Optical Properties and Active Plasmon Excitations in Nanocrystals and 2D Materials

The control and tuning of the optical properties of materials and the localization of electromagnetic energy are long standing quests for scientists. Not only it allows to design new classes of adaptive devices such as smart windows but also to perform surface enhanced vibrational spectroscopies such a SERS. Behind all these applications, fundamental questions are still debated : what is the role of electron correlation in the optical response ? How to include to contribution of crystal field in the dielectric response of complex system ? How the local electro-magnetic field influence the optical absorption and the SERS activity ?For metallic nanostructured systems, the optical properties are directly related to collective electronic excitation (plasmons) and they depend mainly on the composition, shape and size of the system. Doped semiconductors such as Indium Tin Oxide have been also shown to display active plasmon, i.e., optical excitations that can be controlled by an external stimulus such as static electric potential [1].In 2D materials like graphene, the electrostatic doping is a commonly used to modify the optical response due to the low density of state at the Fermi energy. Moreover, topological corrugation, anisotropy [2], chemical doping [3] and electrostatic coupling in vanderwaals heterostructures plays very specific roles on the optical responses. Graphene nanodots and molecular PAH also supported plasmon excitation and electrochromic behavior.In this presentation, based on numerical simulations, we analyze the optical properties of these compounds and we discuss the influence of electrostatic coupling and charging effects. We emphasized the role of the electron correlation and of the local field in classical, semi-empirical and ab-initio methods.[1] A. Maho et al. Solar Energy Materials and Solar Cells 200 (2019) 110014[2] B. Majerus et al. Phys. Rev. B 98 (2018) 125419[3] F. Joucken et al. Phys. Rev. Mat. 3 (2019) 110301

(Invited) Optical Properties and Active Plasmon Excitations in 2D Materials

The control and tuning of the optical properties of materials and the localization of electromagnetic energy are long standing quests for scientists. Not only it allows to design new classes of adaptive devices such as smart windows but also to perform surface enhanced vibrational spectroscopies such a SERS.For metallic nanostructured systems, the optical properties are directly related to collective electronic excitation (plasmons) and they depend mainly on the composition, shape and size of the system. Doped semiconductors such as Indium Tin Oxide have been also shown to display active plasmon, i.e., optical excitations that can be easily controlled by an external stimulus, e.g. a static electric potential [1].In 2D materials, an electrostatic doping is common due to the low density of state at the Fermi energy. Moreover, anisotropy plays a very specific role [2] and surface plasmon became 1D plasmon. In this presentation, based on numerical simulations, we analyze the plasmon excitation associated to edge of 2D materials or to metallic mirror twin boundaries in Transition Metal Dichalcogenide [3]. Doped graphene [4] nanodots or shape engineering in wrinkled structures will also be discussed.[1] A. Maho et al. Solar Energy Materials and Solar Cells 200 (2019) 110014[2] B. Majerus et al. Phys. Rev. B 98 (2018) 125419[3] A. A. Koos et al. J. Phys. Chem 123 (2019) 24855[4] F. Joucken et al. Phys. Rev. Mat. 3 (2019) 110301

Toroidal Dipole Resonances in All‐Dielectric Oligomer Metasurfaces

AbstractDynamic toroidal multipoles have been attracting an increasing amount of attention, thanks to their unique electromagnetic properties. The concept bears great promises in the field of optical sensing as well as electromagnetic energy localization. Metal‐based structures with specific designs have been widely adopted to obtain toroidal responses. However, applications for such structures are often hindered by the significant intrinsic loss when it comes to optical frequencies. Here, several configurations of all‐dielectric metasurfaces, in which the meta‐molecules are composed of disk oligomers (trimer, quadrumer, pentamer, and hexamer), are proposed to support toroidal dipole resonances in the near‐infrared waveband when the polarization of the normally incident excitation plane wave is directed to one of the symmetry axes of the oligomers. Multipole expansion including the toroidal dipole term along with near‐field electromagnetic patterns confirms the existence of strong toroidal dipolar responses within certain wavelength ranges. This work would enrich the diversity of the all‐dielectric optical systems with toroidal dipole resonances.

Silver Nanoparticles Added Polymer Film Prepared by Electrochemical Route for Surface Enhanced Raman Scattering Applications

A simple method for the fabrication of stable and highly active surface enhanced Raman scattering (SERS) substrate by exploiting the optical properties of the silver nanoparticles (AgNPs) and organizational characteristics of the polymer is presented. Homogeneous distribution of AgNPs is achieved with the usage of poly (4,7-di-2,3-dihydrothieno [3,4-b] [1,4] dioxin-5-yl-2,1,3 benzoselena diazole) (PESeE) film coated on the indium tin oxide glass (ITO) surface. The obtained structure ensured the emergence of a large number of hot spots where the localization of electromagnetic energy can result in enhancement of the Raman signal. The effect of the PESeE film thickness, the density of AgNPs added to the polymer film, and the concentration of silver ion solution on the morphology of the substrate and the enhancement of the SERS signal was revealed by using field emission scanning electron microscopy (FE-SEM) and SERS measurements. Enhancement power, homogeneity, and stability of the PESeE-AgNPs substrate were also investigated with measurement of the Raman probe. Spot-to-spot and batch-to-batch reproducibilities of the prepared substrate were calculated as 8.4%, and 10.2% (RSD %) respectively. Due to these properties, PESeE-AgNPs SERS substrate can be a good candidate for the detection and sensor application of various biological and chemical analytes.

Localization of electromagnetic energy by a pair of parallel waveguides with contradirectional coupling

The contradirectional coupling between a pair of planar dielectric waveguides, whose guiding layers are respectively a negative index medium and a positive index medium (PIM, i.e., the conventional medium), is theoretically investigated using the coupled mode theory. It is shown that, by tapering the middle segment of the PIM guiding layer to introduce a certain phase shift, the energy flow circulation can be established based on the contradirectional coupling effect, and, thus, the electromagnetic energy is localized in the waveguide system. This phenomenon is further verified numerically with the finite-difference time domain method. The quality factor of this open waveguide cavity is also discussed.

Tailored polymer–metal fractal nanocomposites: an approach to highly active surfaceenhanced Raman scattering substrates

An important design approach for sensitive and robust surface enhanced Ramanscattering (SERS) substrates is the use of metal nanoparticle aggregates withnanometer tailored interstitial distances between their surfaces, in order to confine theelectromagnetic energy. The nanostructural instability of the aggregates to agglomerationdue to their strong van der Waals force poses a challenge for the preparation oflarge-scale, reliable SERS substrates. We present a novel route for preparing stable andhighly active SERS substrates using polymer–metal fractal nanocomposites. Thismethodology is based on the unique morphology of fractal nanocomposite structuresformed just below the percolation threshold that consists of extremely narrow (∼0.8 nm)interstitial polymer junctions between the Ag nanoparticle aggregates along with the appropriate nanoscale(<100 nm) surface roughness. Such nanomorphology allows the formation of well-defined andlarge numbers of hot spots where the localization of electromagnetic energy can result invery large enhancement of the Raman signal. We applied a simple plasma etching processto remove the polymer structures that allowed the formation of Ag structures with veryuniform and controllable inter-particle gaps that were proved to provide significant SERSenhancement of typical biological systems such as double-stranded deoxyribonucleic acid(dsDNA). These advanced nanocomposite films could be used for the development oflarge-scale spectroscopy-based sensors for direct detection and analysis of various biologicaland chemical samples.