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Self-organization of silver nanoparticles with femtosecond laser in TiO2 matrix: Applications to plasmonic colours, multiple hidden images and Colour Image-Multiplexing

Abstract : Self-organization of metallic nanoparticles in a medium is an efficient and a low-cost way to produce plasmonic systems that can be used for applications to active colour display, image encoding, and security. Such nanocomposite systems must be synthesized in form of stable films which could be coated on any kind of surface for laser processing. This doctoral thesis focuses on laser‐induced self‐organization of nanocomposite thin films of silver and mesoporous titania. In this work, we first investigate synthesizing mesoporous TiO2 thin films using hydrolytic process, which is easy to implement, to provide crystallized films starting at 100°C. First activation energies in mesoporous TiO2 films using Raman spectroscopy in combination with the phonon quantum confinement model are reported in this work. Further, growth mechanisms of nanocrystals in mesoporous TiO2 films are investigated in form of ellipsometric measurements highlighting its effect on film porosity and crystallinity with annealing temperature. The second study demonstrates fabrication of different nanocomposite structures using femtosecond laser scanning technique, triggering growth and self-organization of silver nanoparticles inside porous amorphous titania matrix giving rise to plasmonic dichroic colours. Further investigation on the parametric study of such nanocomposites gives rise to different nanostructures at two different scan speed regimes, which are formed at the surface and are embedded below due to excitation of surface and the guided modes. The flexibility of this laser-based marking technology also allows to fabricate hybrid nanostructures composed of different adjacent nanostructure types, interlaced to cover large areas. An extension of this study is concluded on plastic/flexible substrates to encode diffractive printed images. Here surface nanostructures (LIPSS) are formed by using the control of laser polarization and thus grating orientation, which is used to encode grey-level images that can be observed in diffraction modes. Further, this study is concluded by producing three image multiplexing which can be observed in three selected modes of observation under white light in reflection with non-polarized light and transmission between polarizers for two different polarization angles. This is due to the fact that the film birefringence and dichroism can be controlled to produce unprecedented colour gamuts for multiplexing. Such smart laser processing on nanocomposite thin films gives rise to artistic and security applications by encoding different images up to three under same area.
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Submitted on : Thursday, January 21, 2021 - 12:59:19 PM
Last modification on : Tuesday, May 4, 2021 - 3:24:02 AM
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  • HAL Id : tel-03117138, version 1

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Nipun Sharma. Self-organization of silver nanoparticles with femtosecond laser in TiO2 matrix: Applications to plasmonic colours, multiple hidden images and Colour Image-Multiplexing. Optics / Photonic. Université de Lyon, 2020. English. ⟨NNT : 2020LYSES032⟩. ⟨tel-03117138v1⟩

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