Nano-architecture of gustatory chemosensory bristles and trachea in Drosophila wings

International audienceIn the Drosophila wing anterior margin, the dendrites of gustatory neurons occupy the interior of thin and long bristles that present tiny pores at their extremities. Many attempts to measure ligand-evoked currents in insect wing gustatory neurons have been unsuccessful for technical reasons. The functions of this gustatory activity therefore remain elusive and controversial. To advance our knowledge on this understudied tissue, we investigated the architecture of the wing chemosensory bristles and wing trachea using Raman spectroscopy and fluorescence microscopy. We hypothesized that the wing gustatory hair, an open-ended capillary tube, and the wing trachea constitute biological systems similar to nano-porous materials. We present evidence that argues in favour of the existence of a layer or a bubble of air beneath the pore inside the gustatory hair. We demonstrate that these hollow hairs and wing tracheal tubes fulfil conditions for which the physics of fluids applied to open-ended capillaries and porous materials are relevant. We also document that the wing gustatory hair and tracheal architectures are capable of trapping volatile molecules from the environment, which might increase the efficiency of their spatial detection by way of wing vibrations or during flight

Etude du mécanisme de nanostructuration oxydante de ZrAu (application à la synthèse de nanocomposites or-zircone pour microcapteurs de gaz)

L'étude de l'alliage ZrAu a permis de déterminer ses structures cristallines, d'étudier sa cinétique d'oxydation unique sous air et à 25C et d'envisager des perspectives d'applications de type microcapteurs catalytiques. ZrAu est triphasé en température : Pour TC>569C sa structure est une structure de CsCI. Pour 400569C, ZrAu is a CsCI superstructure. For 400<TC<569 and TC<400, it is respectively monoclinic and triclinic evolutions of the first structure. The oxidation phenomenon is an atmospheric type one and its kinetic is linear in time (2 m per day). Resulting gold and monoclinic zirconia nanoparticles are meanly 3-5 nm sized. The nucleation-growth process of gold nanoparticles has been studied. The formation of monoclinic zirconia phase for such weak sizes has been explained by a modification of the Gibbs law. From this unique degradation phenomenon, we consider in the last part its application for the synthesis of nanostructured thin films for catalysis applications.TOULON-BU Centrale (830622101) / SudocSudocFranceF

Auto-assemblage de nanocristaux d'oxalate de cuivre

La nanostructuration de la matière par auto-assemblage est actuellement un des domaines de recherche fondamentale les plus dynamiques et ouvre de vastes perspectives technologiques. Cette thèse se propose d étudier l'auto-assemblage de nanocristaux d'oxalate de cuivre. Ce composé peut être considéré comme système modèle dont les propriétés permettent une transposition à l'élaboration de nanostructures complexes. Une étude bibliographique portant d'une part sur le phénomène d'auto-assemblage à l'échelle mésoscopique, d'autre part sur le cas particulier des oxalates de métaux divalents constitue la première partie de ce travail. Puis, la caractérisation structurale des nanocristaux d'oxalate de cuivre et l'influence des conditions de synthèse sur leur auto-assemblage permettent d'aboutir à un modèle de mésocristaux issus d'une orientation des nanocristaux par reconnaissance de faces cristallines. Enfin, les modifications morphologiques des mésocristaux en présence d'additifs et l'étude spectroscopique de ces nanostructures confirment le modèle proposé par la mise en évidence d'une adsorption sélective des additifs sur certaines faces des nanocristaux.The nanostrucuration of matter by self-assembly is nowadays one of the most dynamic areas in fundamental research and opens many technological perspectives. In this PhD thesis is studied the self-assembly of copper oxalate nanocrystals. This compound can be considered as a model system whose properties can be transposed to the elaboration of complex nanostructures. A bibliographical study, covering on one hand the self-assembly phenomenon at the mesoscopic scale, and on the other hand the particular case of divalent metal oxalates constitutes the first part of this work. Then, the structural characterization of copper oxalate nanocrystals and the influence of the synthesis conditions on their self-assembly lead to a model of mesocrystals built from an orientation of nanocrystals by crystal faces recognition. Finally, the morphological modifications of mesocrystals in presence of additives and the spectroscopic study of these nanostructures confirm the prpoposed model by highlighting a selective adsorption of additives on some of the nanocrystals faces.TOULON-BU Centrale (830622101) / SudocSudocFranceF

Nanocrystalline vanadium dioxide: synthesis and mid-infrared properties

Abstract This work describes the ®rst successful synthesis of nanocrystalline thermochromic VO 2 powder using the low temperature irreversible structural transformation of the metastable VO 2 (B). At this step, the transformation is associated with a total rearrangement of VO 6 octahedra, and a strong increasing of density. The reversible metal±insulator phase transition (MIPT) of vanadium dioxide (T t 68°C) is associated with strong changes in electrical, magnetic and optical properties. The contrast of the optical transition in mid-infrared (MIR) region and the optical transparency are remarkably increased for these nanosized particles. Modi®cations in coloration are also observed.

Nanocrystalline vanadium dioxide: synthesis and mid-infrared properties

Abstract This work describes the ®rst successful synthesis of nanocrystalline thermochromic VO 2 powder using the low temperature irreversible structural transformation of the metastable VO 2 (B). At this step, the transformation is associated with a total rearrangement of VO 6 octahedra, and a strong increasing of density. The reversible metal±insulator phase transition (MIPT) of vanadium dioxide (T t 68°C) is associated with strong changes in electrical, magnetic and optical properties. The contrast of the optical transition in mid-infrared (MIR) region and the optical transparency are remarkably increased for these nanosized particles. Modi®cations in coloration are also observed.

Surface Interactions between Molecules and Nanocrystals in Copper Oxalate Nanostructures

International audienc

Self-Organized Assembly of Copper Oxalate Nanocrystals

International audienc

Effect of morphology and temperature treatment control on the photocatalytic and photoluminescence properties of SrWO 4 crystals

International audienceThis work reports the combined effect of the morphology and crystallization degree of the strontium tungstate (SrWO4) scheelite structure on its photocatalytic and photoluminescence properties. The difference in the precursor ratio leads to two morphologies, spindle and sphere, which remain unchanged with heat treatment up to 500 °C. However, the crystallite sizes of the as-obtained samples and samples treated at 300 and 500 °C are about 50–74 nm for spindles and 44–110 nm for spheres. Both morphologies and thermal treatments lead to the variation in the photoluminescence and photodegradation of rhodamine (RhB) and methylene blue (MB) dyes under UV irradiation. A stronger hotodegradation efficiency was found for RhB (90%) than for MB (72%). The photoinduced mechanism is more significant for RhB and becomes more efficient for samples treated at high temperature, while the photocatalysis of MB is weak due to the adsorption process. A broad visible photoluminescence band was observed at room temperature and chromaticity coordinates were identified, which confirmed the emission wavelength. The most intense photoluminescence was obtained for samples treated at 300 °C, corresponding to the optimal disordered structures and accompanied by a redshift wavelength for both spheres and spindles. In this case, the spindles showed the most intense photoluminescence, almost ten times higher than that in sphere

Optical properties of single diatom frustules revealed by confocal microspectroscopy

Optical properties of single diatom frustule valves from two different Coscinodiscus species (C. wailesii and C. centralis) are studied by transmission confocal hyperspectral imaging and numerical calculations. Light convergence, concentration, and trapping effects are observed and depend on both the wavelength and the valve orientation. These effects seem to occur independently of the incident light angle. From our results, a wavelength-dependent multifocal lens behavior can be explained by light diffraction related to the radial symmetry of the multiscaled 3D nanostructure

Surface Capping-Assisted Hydrothermal Growth of Gadolinium-Doped CeO₂ Nanocrystals Dispersible in Aqueous Solutions

Nanocrystals of 20 mol % Gd³⁺-doped CeO₂ dispersible in basic aqueous solutions were grown via hydrothermal treatment of anionic Ce­(IV) and Gd­(III) carbonate complexes at 125–150 °C for 6–24 h with N­(CH₃)₄⁺ as a capping agent. The nanocrystals were characterized in detail using dynamic light scattering (DLS), ζ-potential measurements, X-ray diffraction (XRD), specific surface area measurements based on the Brunauer–Emmett–Teller theory (SSA_BET), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, and Raman spectroscopy. DLS analysis revealed that the highly transparent product solution consisted of nanocrystals approximately 10–20 nm of hydrodynamic diameter with a very narrow size distribution, while the ζ-potential analysis results strongly suggested that the N­(CH₃)₄⁺ capped negatively charged sites on the nanocrystals’ surface and provided sufficient repulsive steric effect to prevent agglomeration. Moreover, the crystallite size (<i>d</i>_XRD) estimated from the XRD patterns and the equivalent particle size (<i>d</i>_BET) estimated from the SSA_BET data were in the range between 5–6 and 4–4.5 nm, respectively, and nearly constant independent of reaction time, indicating suppressed Ostwald ripening due to capping. Good agreement between the values obtained from the <i>d</i>_XRD and <i>d</i>_BET analyses with the size of the primary nanocrystals observed in the TEM image also confirmed that the primary nanocrystals were single crystals and nearly free from aggregation. Furthermore, the gadolinium content in the as-prepared nanocrystals was determined to be very close to 20 mol % and remained unchanged after HCl treatment, indicating successful doping of stoichiometric amount of Gd³⁺ into CeO₂ lattices. Finally, the Raman analysis suggested that only a slightly Gd³⁺-rich phase was present in the nanocrystals grown for shorter reaction times. By increasing the reaction time, even at 125 °C, the Gd³⁺ was homogeneously distributed into the CeO₂ lattices via solid state diffusion