Band gap engineering in simultaneous phononic and photonic crystal slabs

We discuss the simultaneous existence of phononic and photonic band gaps in two types of phononic crystals slabs, namely periodic arrays of nanoholes in a Si membrane and of Si nanodots on a SiO2 membrane. In the former geometry, we investigate in detail both the boron nitride lattice and the square lattice with two atoms per unit cell (these include the square, triangular and honeycomb lattices as particular cases). In the latter geometry, some preliminary results are reported for a square lattice

Resonant states in GaAs/Ga1-xAlxAs Multi-Quantum-Wells

The effect of buffer layers on resonant states in a Multi-Quantum-Well (MQW) sandwiched between two substrates is investigated here theoretically. These resonances appear as well-defined peaks in the density of states (DOS). The local and total densities of states are obtained from an analytical determination of the Green functions. Due to the substrate/buffer layer/ MQW /substrate interaction, different kinds of resonant states are found and their properties are investigated. We show in particular that an incident electron in the left-hand side substrate is transmitted in the right hand side substrate of the structure with large time delays in the phase time. The peaks in the phase time associated with the transmission coefficient are found to be similar to those corresponding to the DOS. The intensity of these peaks associated with extended states in MQW’s and Tamm like states lying at the MQW/buffer layer interface, strongly depends on the width of the buffer layer.The effect of buffer layers on resonant states in a Multi-Quantum-Well (MQW) sandwiched between two substrates is investigated here theoretically. These resonances appear as well-defined peaks in the density of states (DOS). The local and total densities of states are obtained from an analytical determination of the Green functions. Due to the substrate/buffer layer/ MQW /substrate interaction, different kinds of resonant states are found and their properties are investigated. We show in particular that an incident electron in the left-hand side substrate is transmitted in the right hand side substrate of the structure with large time delays in the phase time. The peaks in the phase time associated with the transmission coefficient are found to be similar to those corresponding to the DOS. The intensity of these peaks associated with extended states in MQW’s and Tamm like states lying at the MQW/buffer layer interface, strongly depends on the width of the buffer layer

Evolution of LSPR of gold nanowire chain embedded in dielectric multilayers

International audienceThe objective of this paper is to improve the sensitivity and the performance of nano-sensors by using the simulation, which was done by finite element method in 2D plasmonic nanostructures. Meanwhile, the effects of geometric parameters of a hexagonal gold nanostructure, and the influence of two dielectrics Si3N4 and SiOx were treated. In order to have better sensitivity, the nature and the thickness of a deposed dielectric were controlled. Whenever we change the geometric parameters of the metallic nanostructure, we see changes in nanoparticle's plasmonic response. Adjusting the theoretical curve to experimental LSPR curve allowed the geometry of the plasmonic interface to be fixed and evaluation of the change in the wavelength at resonance (lambda(R)) as a function of the SiOx overlayers thickness. The theoretical data were compared with experimental results obtained on glass/Au nanowires/SiOx and glass/Au Nanowires/Si3N4 interfaces

Introduction à une théorie des systèmes composites : exemples simples de matériaux lamellaires

Cet article de revue est essentiellement une introduction à la théorie de la réponse linéaire dans les systèmes composites. Les matériaux composites sont définis ici comme étant formés de parties homogènes différentes reliées par des interfaces. Ce type de matériaux peut être construit à partir de "briques" homogènes découpées dans des matériaux infinis. Ces opérations de découpage sont effectuées par l'intermédiaire d'opérateurs de clivage. Les "briques" sont ensuite assemblées grâce à un opérateur de couplage. Cette façon de construire un système composite permet d'obtenir une équation générale reliant la fonction réponse (appelée aussi fonction de Green) du système composite aux éléments des fonctions réponses des matériaux infinis et aux opérateurs de clivage et de couplage. Une formulation générale unifiée valable aussi bien en algèbre des matrices pour les systèmes discrets qu'en algèbre différentielle pour les systèmes continus en résulte. Toute théorie générale est abstraite ; sa compréhension est grandement facilitée par la pratique d'exemples simples. Le but principal de cet article de revue est d'introduire une théorie générale des systèmes composites grâce à des exemples simples et analytiques empruntés au domaine des phonons, des magnons et des électrons dans les matériaux composites lamellaires (multicouches). Afin d'atteindre ce but, les développements mathématiques des exemples sont donnés le plus explicitement possible. Une revue bibliographique de ce qui a été déjà réalisé en théorie de la réponse dans les matériaux composites est donnée également. Une étude prospective et non exhaustive des très nombreux domaines où cette théorie peut être utile prolonge la revue bibliographique

Magnons dans les super-réseaux ferromagnétiques à 3 - couches

A brief study of bulk and surface magnons in 3-layer Heisenberg ferromagnetic superlattices is presented. Each layer is modelled by a simple-cubic lattice of spins coupled via nearestneighbor exchange interactions. The superlattice has a larger periodicity in the direction perpendicular to the slabs and therefore many magnon branches in the folded Brillouin zone. In the gaps existing between these magnon branches appear the surface-localized magnons. We give closed-form expressions for bulk and surface magnons in 3-layer superlattices, together with the corresponding dispersion curves for one spectific case. An application is also done for a Fe/Co superlattice.Une brève étude des magnons de volume et de surface dans les super-réseaux à 3-couches est présentée. Chaque couche est modélisée par un réseau cubique simple de spins couplés par des interactions d'échange entre premiers voisins. Le super-réseau possède une grande périodicité dans la direction perpendiculaire aux couches et en conséquence, il existe plusieurs branches de magnons dans la zone de Brillouin réduite. Dans les gaps existants entre ces branches de magnons apparaissent des magnons localisés à la surface. Nous donnerons sous forme analytique les relations de dispersion des magnons de volume et de surface d'un super-réseau a 3 couches que nous illustrons par un exemple. Une application est aussi donnée pour un super-réseau Fe/Co

Evolution of localized surface plasmon resonance made of gold nanowire chain embedded in WS2multilayers

International audienceRecently, the transition metal dichalcogenides (TMDs) have emerged as a new class of building blocks for engineering enhanced plasmonic sensors. This class of materials can be made with a low production cost and can be easily hybridized with metallic nanoparticles whereby desired molecules are thoroughly detected. In this work, we evidence coupling between metallic gold nanowires and a WS2multi-layer. The novelty lies in the resilient stability of the effect of the thickness layer variation on both, the sensitivity performances and the electric field distribution in the visible and near-infrared spectra. Such configuration can consequently be regarded as an unwavering avenue towards conception of promising and reliable new generation of sensors. © 2021 Elsevier Ltd. All rights reserved

Effect of pinning fields on the spin wave band gaps in comblike structures

We consider, in the frame of the long-wavelength Heisenberg model, the effect of a pinning field on the spin wave band gaps and transmission spectra of one-dimensional comb-like structures. Using a Green's function method, we obtained closed-form expressions for the band structure and the transmission coefficients for an arbitrary value of the number N of sites (N'of resonators) in the comb-like structure. We report the opening-up of stop bands inside the pass-bands due to the effect of the pinning field at the ends of the resonators of the comb. These structures, composed of one-dimensional ferromagnetic materials, may exhibit large gaps where the propagation of spin waves is forbidden. The width and frequency position of these gaps depends on the strength of the pinning field

The influence of capping layers on surface phonon polaritons in superlattices

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