Caractérisation de nano-colloïdes bimétalliques Pd-Sn par techniques de rayons X et sondes électroniques

New technologies for the metallization of non-conducting polymers involve the deposition of nanometric size palladium-tin colloids. Understanding the phenomenon taking place during the different phases of the process requires the study of the chemical and structural state of the palladium-tin clusters in the solution, and the analysis of the evolution of the adsorbed particles. Combination of different probes appears very fructuous: electron energy loss spectroscopy (EELS) and all the usual electron microscopy techniques allow the characterization of the deposited particles at the different steps, wide angle X-ray scattering (WAXS) applied to the colloids in solution, but mainly deposited on different substrates structurally close to an ABS surface, is well suited for the identification of metallic structures and their accurate characterization, EXAFS provides its efficiency as a local structural probe. The synthesis of preliminary results allows us to propose a core-shell model for the particles, deposited and in solution. This palladium-rich, well-crystallized metallic core is surrounded by a tin-rich shell, rapidly evolving towards amorphous tin oxide when exposed to air. Complementary studies are still necessary in order to accurately define the nature of the core alloy, and also the oxidation kinetics of the surface.Les nouvelles technologies pour la métallisation des plastiques non-conducteurs font appel au dépôt de colloïdes palladium-étain de taille nanométrique. La compréhension des phénomènes mis en jeu au cours des différentes phases du traitement passe par une étude de l'état chimique et structural des "clusters" palladium - étain dans la solution, et une analyse de l'évolution des particules adsorbées. L'association de différentes sondes se révèle extrêmement fructueuse: la spectrométrie de pertes d'énergie d'électrons (EELS) ainsi que toutes les techniques classiques de microscopie électronique permet une caractérisation de l'état des particules déposées aux différentes étapes, la diffusion des rayons X aux grands angles (WAXS) sur les colloïdes en solution, et surtout déposés sur différents substrats représentatifs d'une surface d'ABS, est bien adaptée pour l'identification des structures métalliques et leur caractérisation précise, l'EXAFS apporte ses capacités de sonde structurale locale. La synthèse encore préliminaire des résultats permet de proposer pour les particules déposées comme en solution un modèle coeur-coquille comportant un coeur métallique bien cristallisé à forte teneur en palladium. Une coquille riche en étain évolue rapidement vers un oxyde d'étain amorphe. Des études complémentaires sont nécessaires pour préciser la nature de l'alliage au coeur, ainsi que la cinétique d'oxydation de la surface

Towards improved understanding of the applicability of uncertainty forecasts in the electric power industry

Around the world wind energy is starting to become a major energy provider in electricity markets, as well as participating in ancillary services markets to help maintain grid stability. The reliability of system operations and smooth integration of wind energy into electricity markets has been strongly supported by years of improvement in weather and wind power forecasting systems. Deterministic forecasts are still predominant in utility practice although truly optimal decisions and risk hedging are only possible with the adoption of uncertainty forecasts. One of the main barriers for the industrial adoption of uncertainty forecasts is the lack of understanding of its information content (e.g., its physical and statistical modeling) and standardization of uncertainty forecast products, which frequently leads to mistrust towards uncertainty forecasts and their applicability in practice. This paper aims at improving this understanding by establishing a common terminology and reviewing the methods to determine, estimate, and communicate the uncertainty in weather and wind power forecasts. This conceptual analysis of the state of the art highlights that: (i) end-users should start to look at the forecast's properties in order to map different uncertainty representations to specific wind energy-related user requirements; (ii) a multidisciplinary team is required to foster the integration of stochastic methods in the industry sector. A set of recommendations for standardization and improved training of operators are provided along with examples of best practices

Electrothermally Induced Highly Responsive and Highly Selective Vanadium Oxide Hydrogen Sensor Based on Metal-Insulator Transition

We report highly effective hydrogen gas detection based on the metal insulator transition (MIT) by the electrothermally induced Pd-nanoparticles-decorated vanadium oxide (VO2) nanowire prepared by the efficient and size-controllable growth method originating from V2O5 thin film driven by supercooled liquid nanodroplets. By irradiating a well-defined electron beam into the nanowires, we could significantly increase the conductivity up to four times with only a modest change in the semiconductor-to-metal transition temperature (<2 degrees C). When exposed to trace amounts of hydrogen gas in a single nanowire configuration, the enhanced conductivity gave rise to about a two times as fast transition to metallic phase even near room temperature (similar to 35 degrees C), by reaching much faster (similar to 3x) a critical current density at which the self-heating initiates. Consequently, we achieved the greatly shorter response time as well as lower operating temperature and voltage for the detection of hydrogen gas in a single VO2 nanowire device, which can be attributed to the self-heating effect accelerated by the increase in the conductivity. The single nanowire sensor also shows the capability of detecting selectively hydrogen of different three gases (O-2, CO, and ethylene).close81

Tin-Oxide-Nanowire-Based Electronic Nose Using Heterogeneous Catalysis as a Functionalization Strategy

An electronic nose (e-nose) strategy is described based on SnO(2) nanowire arrays whose sensing properties are modified by changing their operating temperatures and by decorating some of the nanowires with metallic nanoparticles. Since the catalytic processes occurring on the metal nanoparticles depend on the identity of the metal, decorating the semiconducting nanowires with various metal nanoparticles is akin to functionalizing them with chemically specific moieties. Other than the synthesis of the nanowires, all other steps in the fabrication of the e-nose sensors were carried out using top-down microfabrication processes, paving the way to a useful strategy for making low cost, nanowire-based e-nose chips. The sensors were tested for their ability to distinguish three reducing gases (H(2), CO, and ethylene), which they were able to do unequivocally when the data was classified using linear discriminant analysis. The discriminating ability of this e-nose design was not impacted by the lengths or diameters of the nanowires used.close2