Elaboration et étude des propriétés électro-optiques de matériaux hybrides à base de nanocristaux de carbure de silicium

Ce travail concerne l élaboration de matériaux hybrides à base de matrices polymères et de nanocristaux de carbure de silicium (SiC) et l étude de leurs propriétés électro-optiques (EO). Dans ce but, différents échantillons de SiC ont été synthétisés par pyrolyse laser et deux nanopoudres représentatives ont été exploitées. Les études ont révélé différents états de surface, conditionnant les interfaces au sein du composite final. A partir de suspensions SiC/polymère contrôlées, le dépôt de films minces de qualité optique a été effectué par spin-coating, suivi de traitements thermiques et électriques appropriés. Par une adaptation de la méthode de Sénarmont, les études systématiques ont révélé le rôle prépondérant des interfaces SiC/polymère sur la réponse EO des composites. Avec des coefficients EO effectifs de 5 à 7 pm/V, comparables à ceux des cristaux EO standards, une application potentielle du système SiC/polymère en tant que modulateur EO est démontrée.This work concerns the elaboration of hybrid materials based on host polymer matrices and silicon carbide nanocrystals (SiC) and the investigations of their electro-optical (EO) properties. In this aim, controlled SiC nanopowders were synthesized by laser pyrolysis and two representative samples have been exploited. The spectroscopic studies revealed different surface states, conditioning the interfaces within the final composite. From controlled SiC/polymer suspensions, thin films with good optical quality were deposited by spin-coating, then annealed and electrically poled. By using an adaptation of the Sénarmont method, the systematic investigations, taking into account various parameters, revealed the key role played by the SiC/polymer interfaces on the EO response of the composites. With effective linear EO coefficients in the range 5-7 pm/V, comparable with those of standard EO crystals, the potential application of the SiC/polymer systems as EO modulators is demonstrated.LE MANS-BU Lettres (721812108) / SudocLE MANS-BU Sciences (721812109) / SudocSudocFranceF

Contribution of hexagonal-like structure to the nonlinear optics in large sized SiC nanocrystallites

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Influence of silicon and carbon excesses on the aqueous dispersion of SiC nanocrystals for optical application

International audienceThe dispersion behaviour of laser-synthesized silicon carbide nanoparticles (npSiC) in water is investigated by photon correlation spectroscopy (PCS). With regard to previous studies and due to an application in the processing of optical materials, this paper concerns low npSiC contents (from 0.05 to 10 wt.%). The role played by the particle surface state is be pointed out through the consideration of stochiometric (C/Si = 1), carbon-rich (C/Si > 1) and silicon-rich (C/Si < 1) nanopowders. Suspensions made from stoichiometric and silicon-rich nanopowders are easily dispersed and stable with time. The PCS measurements reveal in this case more than 95% of isolated nanoparticles, pointing out the key role of the oxidized layer covering the grain of silicon-rich samples. At the opposite, the carbon-rich powders are hardly dispersed in pure water, correlated with the presence of a relatively inert graphitic carbon layer at the grain surface. However, by addition of a commercial polymeric dispersant, all nanopowders induce high quality suspensions. In particular, the carbon-rich samples are easily dispersed, and possible dispersion mechanisms of npSiC in presence of a polymeric surfactant are discussed. The influence of the npSiC loading and the time evolution of the suspension are also presented. By considering stoichiometric, as well as carbon- and silicon-rich samples, this paper demonstrates the possibility to achieve high quality dispersions of SiC nanoparticles, whatever the chemical composition of the powder, as an easy step for optical material processing

Composites polymère/nanocristaux pour la modulation électro-optique : Ou quand les nanocristaux commandent à la lumière...

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Some fundamental and applicative properties of [polymer/nano-SiC] hybrid nanocomposites

International audienceHybrid nanocomposites which combine polymer as host matrix and nanocrystals as active elements are promising functional materials for electronics, optics or photonics. In these systems, the physical response is governed by the nanocrystal features (size, surface and defect states), the polymer properties and the polymer-nanocrystal interface. This work reviews some selective nanostructured architectures based on active elements such as silicon carbide (SiC) nanocrystals and polymer host matrices. Beyond an overview of some key properties of the nanocrystals, a main part will be devoted to the electro-optical (EO) properties of SiC based hybrid systems where SiC nanocrystals are embedded in polymer matrices of different chemical nature such as poly-(methylmethacrylate) (PMMA), poly-vinylcarbazole (PVK) or polycarbonate. Using this approach, the organic-inorganic interface effects are emphasised with regard to the dielectric or hole transporting behaviour of PMMA and PVK respectively. These effects are illustrated through different EO responses associated with hybrid composites based on PMMA or PVK

Le SiC y met son grain : Nanocomposites polymères électro-optiques à base de nanocristaux de carbure de silicium

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Interface effects on the NLO properties of guest-host materials

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Hybrid nanocomposites based on silicon carbide : Electronic and electro-optical investigations

International audienceNanostructured materials based on the wide band gap semiconductor Silicon Carbide (SiC) nanoparticles as isolated objects, embedded in polymer matrixes or functionalized by thin layer (~2 nm) of conducting polymers were realized. The physical properties of several nanocomposites were investigated including electrical, dielectric, optical and electro-optical features. The Electro-optical properties are marked by enhanced Pockels parameters values due to polymer-nanoparticles interfaces effects. On the other hand, hybrid core-shell functionalization of the nanoparticle surfaces are marked by enhanced electrical conductivities of the network associated to good thermo-mechanical behaviour. The physical origin of the electrical conductivity in these nanomaterials is discussed based on the dynamics of polarons in the hybrid nanocomposites

Cluster approach to the electronic properties modeling of TiO2 nanocrystals sensitized by doping agents and dye molecules

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Electrooptic effect in hybrid polymer-SiC nanocrystals

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