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Personne :
Messaddeq, Younès

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Messaddeq

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Younès

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Université Laval. Département de physique, de génie physique et d'optique

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ncf11860592

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Voici les éléments 1 - 3 sur 3
  • PublicationAccès libre
    Atomic level structure of Ge-Sb-S glasses : chemical short range order and long Sb-S bonds
    (Elsevier Science, 2018-09-28) Pethes, Ildikó; Ari, Julien; Nazabal, Virginie; Messaddeq, Younès; Kaban, Ivan; Darpentigny, Jacques; Welter, Edmund; Gutowski, Olof; Bureau, Bruno; Jóvári, Pál
    The structure of Ge20Sb10S70, Ge23Sb12S65 and Ge26Sb13S61 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements at the Ge and Sb K-edges as well as Raman scattering. For each composition, large scale structural models were obtained by fitting simultaneously diffraction and EXAFS data sets in the framework of the reverse Monte Carlo (RMC) simulation technique. Ge and S atoms have 4 and 2 nearest neighbors, respectively. The structure of these glasses can be described by the chemically ordered network model: Ge-S and Sb-S bonds are always preferred. These two bond types adequately describe the structure of the stoichiometric glass while S-S bonds can also be found in the S-rich composition. Raman scattering data show the presence of Ge-Ge, Ge-Sb and Sb-Sb bonds in the S-deficient glass but only Ge-Sb bonds are needed to fit diffraction and EXAFS datasets. A significant part of the Sb-S pairs has 0.3–0.4 Å longer bond distance than the usually accepted covalent bond length (∼2.45 Å). From this observation it was inferred that a part of Sb atoms have more than 3 S neighbors.
  • PublicationAccès libre
    Silicon subwavelength grating waveguides with high-index chalcogenide glass cladding
    (Optical Society of America, 2021-06-17) Jean, Philippe; LaRochelle, Sophie; Shi, Wei; Messaddeq, Younès; Douaud, Alexandre
    Silicon subwavelength grating waveguides enable flexible design in integrated photonics through nano-scale refractive index engineering. Here, we explore the possibility of combining silicon subwavelength gratings waveguides with a high-index chalcogenide glass as a top cladding, thus modifying the waveguiding behavior and opening a new design axis for these structures. A detailed investigation of the heterogeneous SWG waveguide with high-index cladding is presented based on analytical and numerical simulations. We design, fabricate and characterize silicon subwavelength grating waveguide microring resonators with an As20S80 cladding. Thanks to As20S80 negative thermo-optic coefficient, we achieve near athermal behavior with a measured minimum thermally induced resonance shift of −1.54 pm/K, highlighting the potential of subwavelength grating waveguides for modal confinement engineering and to control light-matter interaction. We also show that the chalcogenide glass can be thermally reflowed to remove air gaps inside the cladding, resulting in a highly conformal structure. These types of waveguides can find application in reconfigurable photonics, nonlinear optics, metamaterials or slow light.
  • PublicationAccès libre
    Laser-induced dewetting of silver-doped chalcogenide glasses
    (Elsevier, 2018-03-19) Messaddeq, Sandra Helena; Messaddeq, Younès; Boily, Olivier; Douaud, Alexandre
    We report the observation of laser-induced dewetting responsible for the formation of periodic relief structures in silver-based chalcogenide thin-films. By varying the concentration of silver in the Agx(As20S80)100−x system (with x = 0, 4, 9 and 36), different surface relief structures are formed. The evolution of the surface changes as a function of laser parameters (power density, duration of exposure, and polarisation) as well as film thickness and silver concentration has been investigated. The scanning electron microscopy and atomic force microscopy images of irradiated spots show periodic ripples aligned perpendicularly to the electric field of incident light. Our results show that addition of silver into sulphur-rich chalcogenide thin-films improves the dewetting when compared to pure As20S80 thin-films. The changes in surface morphology were attributable to photo-induced chemical modifications and a laser-driven molecular rearrangement.