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Periodic multi-scale structuring of surfaces by self-assembly of colloidal masks : shape-size coupling effects

Abstract : The Langmuir-Blodgett (LB) process, recently acquired at IRCER, associated with a laser ablation deposition technique allows the synthesis of composites - thin films of controlled architectures. On a monocrystalline silicon or sapphire substrate, a monolayer of polystyrene spheres of strictly identical size (about 2-5 μm in diameter), self-organized, is deposited in a compact structure by the LB process and is used as a colloidal mask allowing photolithography. This mask, coupled with metallic thin films by pulsed laser ablation, makes it possible to generate 2D structures (self-organized quasi-triangles) whose sub-micron dimensions are a function of the sizes of the initial spheres. The metal covering area of approximately 9% is independent of the size of the spheres used, the characteristic geometry is of fractal dimension. In this document, two different and complementary types of metals are used to generate these architectures, iridium and gold. At these scales, gold exhibits significant dewetting effects around 500 ° C unlike iridium. A rigorous study on the modifications of gold metallic structures induced by the temperature between 20 ° C and 1000 ° C is presented (dewetting in the solid state). The metallic architectures, of fixed geometries or modified by annealing, are then embedded in a matrix of VO2, synthesized at 500 ° C. Vanadium dioxide is a so-called "intelligent" oxide, known for its phase transition at 68 ° C accompanied by a drastic change in its physicochemical properties (insulating-metal transition). The Ir / VO2 and Au / VO2 composites developed in this thesis exhibit fascinating optical absorption properties, in the visible and especially in the near infrared range. Local surface plasmon resonances (LSPR) linked to the metallic architectures and to the nature of the metals used are observed and simulated by the FDTD (Finite Difference Time Domain) approach. These LSPRs are adjustable in amplitude and tunable, up to more than 600 nm, depending on the temperature of the VO2 matrix and the nature of the elements making up the metallic architecture. The appearance of singular metal core-shell structures in a dielectric matrix, demonstrated by RAMAN spectroscopy and confirmed by infrared spectroscopy, justifies the shift in absorption wavelengths observed in the infrared range. In addition, the metallic inclusions embedded in the VO2 allow this characteristic oxide to be probed and provide valuable information on the evolutions of the phases and lattice parameters during its transition.
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Submitted on : Wednesday, September 14, 2022 - 1:01:57 AM
Last modification on : Friday, October 21, 2022 - 3:45:28 AM

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Adrian-Ionut Bercea. Periodic multi-scale structuring of surfaces by self-assembly of colloidal masks : shape-size coupling effects. Materials. Université de Limoges, 2021. English. ⟨NNT : 2021LIMO0103⟩. ⟨tel-03776657⟩

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