On fundamental mechanisms in dye sensitized solar cells through the behaviour of different mesoporous titanium dioxide films

Understanding mechanisms in DSSCs is fundamental for their improvement; this includes the nanocrystalline semiconducting layer behaviour. Different mesoporous TiO2 layers are fabricated and analyzed for possible use in DSSC solar cells. The preparations included the addition of P123 triblock copolymer as structuring agent to the synthesized anatase sol. This preparation was also mixed with Degussa P25 nanoparticles in one case and polystyrene latex in another. Mesoporous mixed TiO2-SiO2 thin layers were also analyzed. The diverse morphology and features are studied by microscopic techniques and by means of spectral quantum efficiency of a photoelectrochemical cell (PEC) that uses as photoelectrode the unsensitized porous TiO\_2 layer. Contact angle measurements are also performed. We have found that a very high specific area due to very small nanocrystals and small pores can hinder electrolyte penetration in the pores formed by TiO\_2 nanograins, affecting photoelectrodes efficiency

GTL : Une interface User-Friendly pour l'analyse de données biologique pour le Centre Jean Perrin

International audienceGTL : Une interface User-Friendly pour l'analyse de données biologique pour le Centre Jean Perri

Expeditious calcination of inorganic membranes by an instant temperature increment

Rapid thermal treatments potentially allow for a significant reduction in production time of ceramic multilayered membranes, in turn aiding increased industrial application of these membranes and accelerating research on their development. Two methods are proposed for the rapid thermal treatment of thin supported inorganic membrane films. Both methods involve an instant increment in temperature imposed on the membrane. In the first method, the instant temperature step is enforced by placing the membrane in a preheated environment; in the second method, the membrane is placed directly onto a hot plate. The proposed methods can be used for a diverse range of materials. Mesoporous γ-alumina and microporous silica have been selected as model membrane materials. Both rapid heating methods require ∼20 min to yield mesoporous γ-alumina membranes that are comparable to membranes made via conventional calcination (∼1 day). Selective silica membranes have been obtained after 1 h exposure to an environment of 400 or 600 °C, and after 1 h contact with a hot plate of 550 °C (compared to up to 2 days for conventional calcination). The results indicate that, although prevention of contaminations needs continuous attention, both methods proposed for rapid heat treatment can reduce cost and time in ceramic membrane productio

Time-resolved plasma measurements in Ge-doped silica exposed to infrared femtosecond laser

Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO 2 and Ge-doped SiO 2. The fast trapping of electrons in the band gap is associated with the formation of self-trapped excitons (STE). The STE trapping is doping dependent in SiO 2. The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 ± 5 fs) when compared to pure silica (155 ± 5 fs). At our concentration level, this indicates that the plasma properties are determined by the presence of easily ionizable states such as the presence of Ge atoms in the glass network. Therefore, we suggest that in Ge-doped silica there exist an additional trapping pathway that leads to a significantly faster excitons trapping and a higher plasma density when compared to undoped silica. © 2011 American Physical Society

Ice-Templating of Alumina Suspensions: Effect of Supercooling and Crystal Growth During the Initial Freezing Regime

International audienceWe investigate the ice-templating behavior of alumina suspensions by in situ X-ray radiography and tomography. We focus herein on the formation and structure of the transitional zone, occurring during the initial instants of freezing. For many applications, this zone is undesirable as the resulting porosity is heterogeneous in size, morphology, and orientation. We investigate the influence of the composition of alumina suspensions on the formation of the transitional zone. Alumina particles are dispersed by three different dispersants, in various quantities, or by hydrochloric acid. We show that the dimensions and the morphology of the transitional zone are determined by the growth of large dendritic ice-crystals growing in a supercooled state much faster than the cellular freezing front. When the freezing temperature decreases, the degree of supercooling increases. This results in an initial faster freezing front velocity and increase in the dimensions of the transitional zone. It is therefore possible to adjust the dimensions of the transitional zone by changing the composition of alumina suspensions. The counter-ion Na+ has the most dramatic effect on the freezing temperature of suspensions, yielding a predominance of cellular ice crystals instead of the usual lamellar crystals

Preparation and characterization of non-supported microfiltration membranes from aluminosilicates

In the present work non-supported microfiltration ceramic membranes have been made from different aluminosilicate paste formulations. The cast green dopes were sintered at temperatures between 1100 and 1400°C. The membrane characterisation was made by scanning electron microscopy (SEM), mercury porosimetry, gas and water permeabilities and microorganisms rejection. The results indicate that an appropriate election of the size of the particles in the paste and of the final sintering temperature allows to obtain membranes with different mechanical and structural properties, with mean pore sizes within the range from 0.1 to 1 μm, that make them suitable for microfiltration.Fil: Almandoz, M.C.. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Marchese, Jose. Universidad de Valladolid; España. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Prádanos, P.. Universidad de Valladolid; EspañaFil: Palacio, L.. Universidad de Valladolid; EspañaFil: Hernández, A.. Universidad de Valladolid; Españ

Excitonic model of track registration of energetic heavy ions in insulators

The consequence of generation of dense electronic excitation along the paths of energetic heavy ions is discussed, emphasizing the fates of electron-hole pairs. It is pointed out that a substantial part of the energy imparted to electron-hole pairs in the materials in which excitons are self-trapped is converted directly to defect formation energy but do not contribute to heating. However, the thermal spike model can be an appropriate macroscopic model of the track registration of the materials in which excitons are self-trapped, because energy deposited to the material remains along the ion paths. The energy imparted to electron-hole pairs is diffused away from the ion paths in the materials in which excitons are not self-trapped. This explains the reason why the critical stopping power for track registration is higher in these materials. The difficulty for application of the thermal spike model to these materials is pointed out and it is suggested that nominal defects in densely excited region nucleate fragmental tracks. (C) 1998 Published by Elsevier Science B.V. All rights reserved