Interactions optiques entre nanoparticules métalliques et systèmes moléculaires à indice de réfraction variable

Ce travail de thèse porte sur l étude de l interaction optique entre nanoparticules mé-talliques (NPM) et des systèmes moléculaires à indice de réfraction variable. L une des proprié-tés remarquables de ce type de particules est liée à l excitation d ondes de surface, appelées plasmon de surface (PS) dont la position spec-trale dépend de plusieurs paramètres (l indice de réfraction du milieu environnant ). Ces PS sont associés à de forts confinements du champ proche optique exalté. Une NPM irradiée sous certaines conditions se comporte comme une nanosource de lumière très confinée qui, en présence d un photopoly-mère à seuil bien déterminé, induit une photo-polymérisation locale grâce à l effet inhibiteur de l oxygène. Ainsi, une nanophotopolymérisa-tion anisotropique en champ proche a lieu, générant une particule hybride mé-tal/polymère. Ceci induit également une distri-bution anisotropique de l indice de réfraction autour de la NPM. La résonance plasmon de surface (RPS) dépend alors de la polarisation du champ incident et une levée de dégénérescence spectrale est observée. Enfin, on étudie le contrôle de la position de la RPS par une orientation électrique de cristaux liquides à biréfringence positive, en particulier, l effet d une élévation de l indice de réfraction à proximité d une paire de NPM, par analyse spectrale. On montre l influence de l indice de réfraction local qui se matérialise par un déca-lage de la position de la RPS qui traduit l affaiblissement du couplage type champ pro-che entre NPM avec la diminution du gapThis thesis is related to the study of optical interaction between metal nanoparticles MNP and molecular systems of variable refraction index. One of these properties is related to the excitation of surface waves, called surface plasmons (SP), whose spectral position depends on several parameters of which the refraction index of the surrounding medium. These SP are associated to a strong confinement effect and optical near field enhancement. A MNP illuminated under certain conditions, behave like a confined nanosource of light. Associated to a photosensitive polymer with well determined threshold energy of polymeri-zation, it induces a reduced photopolymeriza-tion thanks to the inhibiting effect of oxygen. Thus, an anisotropic nanpolymerization takes place, and one creates a hybrid metal/polymer particle. This polymerization also induces an anisotropic distribution of the refraction index around the MN. The surface plasmon reso-nance (SPR) gets dependent on the incident field polarization. The result of such an anisot-ropic distribution is a spectral degeneracy breaking of the SP mode. Finally, we can control the SPR position by an electrical orientation of liquid crystal with posi-tive birefringence. We study the effect of a rise of the local refraction index near a pair of MNP by spectra analysis. One shows the influence of the local refraction index which is materialized by a shift of SPR position. It represents a de-crease of the near field coupling yield between MNP with the reduction of the gap interparti-clesTROYES-SCD-UTT (103872102) / SudocSudocFranceF

Towards the manufacture of nano hybrid metallic/polymer nanoparticles using local-field enhancement around metallic structures embedded in a photopolymerizable solution

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Polydopamine as a promising candidate for the design of high performance and corrosion-tolerant polymer electrolyte fuel cell electrodes

Carbon materials such as carbon black or nanotubes suffer from degradation when subjected to harsh conditions occurring in a Polymer Electrolyte Membrane Fuel Cells (PEMFCs) electrode. Hence, nowadays it is more and more important to search for alternative support materials. The present work shows the results for the incorporation of alternative materials into PEMFCs electrode architectures. Commercially available Multi-Walled NanoTubes (MWNTs) are used as a support for Pt nanoparticles in combination with Polydopamine (PDA). The role of MWNTs is to confer a high electronic conductivity and help to form a porous network. On the other side the role of polydopamine is both to promote the proton conductivity similarly to ionomers such as Nafion and to protect the MWNTs against corrosion. The fuel cell polarization test shows a maximum power density of 780 mW cm− 2 and a Pt utilization of 6051 mW mg(Pt)− 1. The Pt utilization reached in this work is almost three times higher than for Pt/MWNTs electrodes containing the same Pt loading. Beside this, it is also shown for the first time that PDA serves as protective layer against carbon corrosion

Spectral degeneracy breaking in plasmon resonance of single metal nanoparticles by nanoscale near-field photopolymerization

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Spectral degeneracy breaking of the plasmon resonance of single metal nanoparticles by nanoscale near-field photopolymerization

We report on controlled nanoscale photopolymerization triggered by enhanced near fields of silver nanoparticles excited close to their dipolar plasmon resonance. By anisotropic polymerization, symmetry of the refractive index of the surrounding medium was broken: C∞v symmetry turned to C2v symmetry. This allowed for spectral degeneracy breaking in particles plasmon resonance whose apparent peak became continuously tunable with the incident polarization. From the spectral peak, we deduced the refractive-index ellipsoid fabricated around the particles. In addition to this control of optical properties of metal nanoparticles, this method opens new routes for nanoscale photochemistry and provides a new way of quantification of the magnitude of near fields of localized surface plasmons