Denis Chaumont

Microchip Random Laser based on a disordered TiO 2 -nanomembranes arrangement

We developed a new scheme for obtaining coherent random lasing based on a chip consisting of a polymer film doped with Rhodamine 6G, having as scatterers butterfly-like TiO(2) nanomembranes (TiO(2)-NM) supported on a glass substrate. The feedback mechanism for laser action is due to the multiple scattering of light by TiO(2)-NM rather than provided by localized variations of the refractive index in the polymer film. The above-threshold multiple spikes signature indicative of random laser emission with coherent feedback is confirmed. As nanomembranes are foreseen as new MEMS/NEMS building blocks, a new generation of combined active/passive photonic devices can be envisaged.

Study of the Influence of Alkaline Ions (Li, Na and K) on the Structure of the Silicate Entities in Silico Alkaline Sol and on the Formation of the Silico-Calco-Alkaline Gel

The study of silico-calco-alkaline gel is essential to warn against the degradation of concrete due to the alkali-silica reaction. In the laboratory, those gels are simulated by the destabilization of a silico-alkaline sol by calcium ions. Their speed of formation depends on the alkali species. The influence of alkaline ions (Li, Na and K) on the structure of silicate entities in sol and on the gel formation has been studied. The state of polymerization of the silico-alkaline sol was determined by NMR and depends on the alkali species and the molar ratio (Rm = [SiO2]/[A2O] with A = Li, Na or K). It appears that lithium enhances the polymerization. By scattering techniques (SAXS and ELS), the evolution of size and number of scattering particles during gelation can be determined from scattering curves with Guinier approximation. The mechanism of gelation appears as a hierarchic structure composed of several discrete sizes.

Electric field induced monoclinic phase stability in Ca doped Na0.5Bi0.5TiO3: Case of 0.93Na0.5Bi0.5 TiO3 – 0.07CaTiO3 ferroelectric ceramics

The ferroelectric perovskite complex 0.93Na0.5Bi0.5TiO3 – 0.07CaTiO3 (NBT –0.07CT) ceramics were studied by a simple X-ray diffraction upon application of an increasing electric field. It is shown that the field induced rhombohedral (R3c) to monoclinic (Cc) phase transition at room temperature. This induced phase is stable after removal the electric field. Our results has been interpreted by intrinsic polarization rotation theory, in comparison with Pb-base system such as PMT-PT, PZN-PT, …near the morphotropic phase boundary (MPB) region. Apparently, the NBT – 0.07CT pretends to have a ferroelectric and structural instability around room temperature.

Electrochemical Investigation of Lithium Intercalation in MOCVD Derived Nanostructured Anatase/Rutile TiO

In this paper we report on the lithium reversible storage in titanium dioxide (TiO2) prepared by metal-organic chemical vapor deposition (MOCVD). Electrochemical properties in terms of lithium reversible insertion depend on the deposited microstructure. For thick films deposited on silicon wafer electrochemical activity of the anatase type of TiO2 is registered in the potential range 1.8-2.1 V vs. Li. For thinner films the intercalation reaction takes place in two potential ranges: 1.8-2.1 V vs. Li and below 1.4 V vs. Li. The second electroactivity range is attributed to lithium insertion into rutile. We found that the decrease of the lower potential limit (0.5 V instead of commonly used 1 V) leads to an increase of the recovered capacity. In consequence the investigated MOCVD TiO2 demonstrates high reversible capacity of about 300 mAhg-1.

The structural properties of soda-silicate sols and of the lime-soda-silicate gel formation

Abstract Alkaline silicate solutions were prepared with varying SiO 2 –Na 2 O ratios, Rm=[SiO 2 ]/[Na 2 O]=2 or 3, with a constant silica concentration equal to 1.5 M. The structure and the number fraction of different silicate molecular species present in the solutions were classically determined for molar ratio Rm=2 using 29 Si nuclear magnetic resonance ( 29 Si NMR). In the case of the sample with Rm=3, for which no NMR data was available, we used small-angle X-ray scattering (SAXS) experiments to get this information. The SAXS model was previously tested with Rm=2 silicate solution. When Ca ++ is added to alkaline silicate solutions, a gel is obtained under well-defined conditions. The gel formation was studied by SAXS, small-angle neutron scattering (SANS) and elastic light scattering (ELS). For gelling solutions, during aggregation of the initial particles in the sol and for the resulting gels, the scattering data were fitted using a fractal model for the structure including a correlation cut-off distance and a contribution of remaining individual sol particles. Experimental and calculated scattering curves are in agreement for all studied samples. The results obtained may help to understand the mechanism of formation of silico-calco-alkaline gels in concrete chemistry.

Random laser based on TiO 2 -nanomembranes

We demonstrated directional random laser emission from a dye-doped polymer film in the presence of a scattering medium consisting of TiO2 nanomembranes. Evidence for coexistence of extended and localized modes are presented.

Aqueous chemical grafting of modified-PEG onto maghemite nanoparticles: Influence of grafting conditions

Abstract The synthesis of maghemite nanoparticles coated with triethoxysilanemonomethylether- PEG (Si-mPEG), is presented in aqueous conditions, by the “grafting to” process. This procedure is performed in one step, starting from anchored polymer and native nanoparticles. The maghemite nanoparticles obtained were first identified by XRD and the average diameter is about 10 nm according to the Nitrogen adsorption, XRD and TEM techniques. The nature of the catalysts (acetic acid, triethylamine, NH4OH and dibutyl-tin-dilaurate) used for the establishment of the covalent bond between the γ-Fe2O3 particles and the SimPEG, as well as the influence of the temperature and the reaction time, were evaluated on the grafting rate of the particles in water by TGA and FTIR techniques. Using the size exclusion chromatography, SEC technique, we showed that the monomethoxy-PEG was resistant to mild acidic up to strong basic conditions. The best ratio “time/amount of polymer” for the highest grafting rate was the use of tinbased organometallic compound (DBTL) at 80 °C during 48 h. In these conditions, a grafting rate of 54 % is achieved.

Relaxor behaviour and phase transition of perovskite ferroelectrics-type complex oxides (1− x )Na 0.5 Bi 0.5 TiO 3 − x CaTiO 3 system

Polycrystalline powders of (1–x)Na0.5Bi0.5TiO3–xCaTiO3 ((1–x)NBT–xCT, 0 ≤ x ≤ 0.55) have been synthesized by solid state route. The effects of simultaneous substitution of Na+/Bi3+ at A-site in NBT on structural and dielectric properties were investigated. X-ray diffraction analysis revealed the phase transition from rhombohedral structure (x = 0) to orthorhombic structure (x ≥ 0.15). A distinct behaviour in dielectric properties was obtained, where for x = 0, a normal ferroelectric behaviour was observed, whereas for x ≥ 0.15, a broad dielectric anomaly was revealed such that the maximum temperature (Tm) strongly depended on the frequency and shifted towards low temperature with CT. The dielectric dispersion indicated a relaxor behaviour revealed by the degree of diffuseness and modelled via Vogel–Fulcher relation. The study highlighted the relaxor behaviour as a function of frequency and proved the transformation from a relaxor high-frequency dependence to a paraelectric phase at temperature Ts. The distinct variation of the Raman spectra at room temperature was correlated with X-ray diffraction results and proved the already mentioned transition. On heating (-193–500 °C), the Raman spectra confirmed the structural stability (Pnma) of the materials. The phonon behaviour for x = 0.15 was discussed in terms of the appearance of polar nanoregions (PNRs) into a non-polar orthorhombic matrix responsible of the relaxor behaviour. For x = 0.20, unchanged phonon behaviour confirmed the variation in dielectric behaviour where the solids transformed from a relaxor to a paraelectric state without structural phase transition.

Influence of iron doping on morphological, structural and optical properties of zinc oxide thin films prepared by dip-coating method

Undoped zinc oxide and iron-doped zinc oxide thin films have been deposited by the sol-geldipcoating method. The Fe/Zn nominal volume ratio was 5% in the solution. The effects of Fe incorporation on morphological, structural, and optical properties of ZnO films were investigated. The scanning electron microscopy measurements showed that the surface morphology of the prepared thin films was affected by Fe doping. The X-ray diffraction patterns of the thin films showed that doped incorporation leads to substantial changes in the structural characteristics of ZnO thin films. The optical absorption measurements indicated a band gap in the range of 3.31 to 3.19 eV. The X-ray photoelectron spectroscopy demonstrated that Fe is incorporated in the ZnO matrix with 6.5 atomic percent (at %). The energy dispersive spectroscopy studies indicated the formation of ZnO with high efficiency.

Microwave synthesis of core-shell structured biocompatible magnetic nanohybrids in aqueous medium

In the past decade, biocompatible magnetic nanohybrids, i.e. materials consisting of an inorganic core encapsulated by a biocompatible polymeric corona, went throw various developments in biomedical applications especially in the fields of diagnosis and therapy. Numerous descriptions of their syntheses can be found in the literature (Zhang et al., 2002; Flesch et al., 2004; Fan et al., 2007; etc). These two-steps protocols often describe the use of organic or aqueous solvents, classical thermal heating, long time reaction as well as fastidious exchange and drying steps. In recent years, microwave heating has been proven to be a very original technology for nanoparticles synthesis due to its almost instantaneous “in core” heating of materials in a homogeneous and selective way. As a consequence, this technology allows an interesting control over crystallization rate and size of the nanomaterials (Bellon et al., 2001; Michel et al., 2001; etc). The formation of magnetic nanoparticles is usually realized in aqueous medium. However, the functionalization of magnetic nanoparticles is mainly conducted in organic solvent. For further biomedical applications, it seems favorable to realize these different grafting steps maintaining initial aqueous medium, thus avoiding the solvent exchanges and the particles drying. In this context, we can summarize the objective of this chapter as the study of new methods to obtain core-shell structured nanohybrids in aqueous medium from iron oxide nanoparticles and water-soluble biocompatible polymers. Is it possible to obtain iron oxide colloidal suspension and well-defined nanohybrids with simplified protocols and relatively short microwave heating time? This chapter is divided is three part, consisting for the first one, of a general presentation of biocompatible magnetic nanohybrids (properties, applications and synthesis). The second part deals with the principles of microwave heating and the description of microwave-assisted synthesis of inorganic nanoparticles. Finally, the last part is dedicated to the use of microwave heating towards magnetic nanohybrid synthesis compared to classical thermal heating process with a focus on nanoparticles characterization (morphology, size and grafted amount of polymer).