High Power Impulse Magnetron Sputtering deposition of Pt inside fuel cell electrodes

International audienceHigh Power Impulse Magnetron Sputtering process is used to incorporate catalytic nanoclusters of platinum into microporous carbon. Such a process leads to an enhancement of the Pt species penetration into the porous media as evidenced by Rutherford backscattering spectroscopy analysis. Each catalyzed porous carbon is tested as a cathode of a proton exchange membrane fuel cell. An increase of 80 % at 0.65 V of the PEMFC power density for a low catalyst loading of 0.02 mg.cm-2 highlights the use of the HiPIMS process versus the conventional DC magnetron sputtering proces

Optimization of DC reactive magnetron sputtering deposition process for efficient YSZ electrolyte thin film SOFC

International audienceYttria-stabilized zirconia (YSZ, ZrO2:Y2O3) thin films were deposited by reactive DC magnetron sputtering with a high deposition rate from a metallic target of Zr/Y in an argon/oxygen atmosphere. Plasma parameters and composition analysis of the gas phase reveal that the sputtering process in the "compound" mode is reached for a 2.5 sccm oxygen flow rate. Deposition onto silicon in "metal" mode at a flow rate close to the transition, allows obtaining at very high deposition rates (> 10 µm.h-1) a compact columnar stoichiometric crystallized YSZ film. When deposited on NiO YSZ commercial anode, the obtained coatings show the same properties. In spite of the complexity of the substrate (roughness and porosity), a compact and conformed layer was formed. Annealing treatments in air or hydrogen do not significantly alter the structure of the layers. Electrochemical test at 850°C with a screen-printed LSM (LaSrMnO3) cathode exhibits a satisfying gastightness (OCV=900 mV) and a maximum power density of 350 mW.cm-2

Energy transferred to the substrate surface during reactive magnetron sputtering of aluminum in Ar/O2 atmosphere

International audienceA study of the reactive sputtering of aluminum was carried out by coupling energy flux measurements at the substrate location with conventional diagnostics of the gas phase and analyses of the deposited films. The main purpose was to get some insight into the elementary mechanisms involved at the substrate surface during the film growth in the well known metal and oxide regimes and at the transitions from one to another. Measurements were carried out in front of a 10 cmAl target at a power of 400W (i.e. 5 W/cm2) and a total pressure of 0.6 Pa. The flow rate ratio (O2/O2+Ar) was varied in the range 0 to 50 %. Different kinetics and values of energy transfer, denoting different involved mechanisms, were evidenced at metal-oxide (increasing flow rate) and oxide-metal (decreasing flow rate) transitions. The metal-oxide transition was found to be a progressive process, in agreement with optical emission spectroscopy and deposit analysis, characterized by an increase of the energy flux that could be due to the oxidation of the growing metal film. On the contrary, oxide-metal transition is abrupt, and a high energy released at the beginning that could not be attributed to a chemical reaction. The possible effect of O-ions at this step was discussed

Influence of the HiPIMS voltage on the time resolved platinum ions energy distributions

International audienceHigh Power Impulse magnetron sputtering (HiPIMS) is a common way to create a high and dense ionized metallic vapor without the use of an alternative ionizing device, like radio frequency loops. HiPIMS has been used to perform the deposition of platinum thin films in order to control their morphology. This feature known to depend on the energy of the Pt species incoming onto the substrate during the deposition has to be carefully studied. Therefore, it's necessary to study the ions energy distribution during the sputtering pulse and to follow its evolution with the HiPIMS regime. Pictures of this evolution are presented

Dynamique, évolUtion et inSTabilités de Poudres catalytiques par Pulvérisation Plasma Pulsé pour pile à Electrolyte Membranaire (Dust4Pem)

National audienceLe projet Dust4Pem vise à synthétiser des catalyseurs bimétalliques PtX performants pour pile à combustible à membrane (architectureCCM, catalyst coated membrane) par une technologie plasma, différente de la pulvérisation magnétron conventionnelle. Bien que cettedernière permette de diminuer considérablement les quantités de métaux nobles dans les piles, cette technique trouve ses limites lorsqu’ils’agit de contrôler la géométrie, la taille, la qualité cristalline et la ségrégation des catalyseurs multi-métalliques. Un meilleurcontrôle de la phase d’agrégation des nanoparticules est donc nécessaire. Dans le projet Dust4Pem, les nanoparticules catalytiques ontété synthétisées dans le milieu plasma (technique de condensation en phase gazeuse) et sont ensuite injectées dans l’enceinte dedépôt afin de recouvrir une membrane échangeuse d’ions type Nafion. Par cette méthode prometteuse, en rupture avec l’état de l’artactuel, nous visons, à terme, une amélioration des densités de puissance des CCM, tout en conservant des charges catalytiquesfaibles

Occurrence of Mixed-Mode Oscillations in a Dusty Plasma

OralInternational audienceNonlinear instabilities can appear in laboratory plasmas containing dust particles. They are easily observed during experiments and their analysis reveals mixed-mode oscillations (MMOs). In this presentation, experimental results and preliminary analyses are presented. Dusty (or complex in analogy with complex fluids) plasmas are partly ionized gases containing dust particles. These solid bodies acquire an electric charge that strongly perturbs the surrounding plasma. Dusty plasmas are thus multi-component systems with similarities with colloidal suspensions or granular media. They are encountered in many environments such as astrophysics, industrial processes and thermonuclear fusion. A dust-free region (void) is often observed in the plasma center, resulting from the balance of two forces of opposite directions. Self-excited oscillations of the void size can appear due to a break in this equilibrium. This "heartbeat" instability (due to its apparent similarity with a beating heart) can stop by its own through the occurrence of more and more failed contractions similar to MMOs. MMOs consist of an alternation of small and large (spikes) amplitude oscillations often considered as subthreshold oscillations and relaxation mechanisms. They exist in many fields such as chemistry (Belousov-Zhabotinskii reaction) and natural sciences (Hodgkin-Huxley model of neuronal activity). MMOs are intensively studied with dynamical system theories (canards, subcritical Hopf-homoclinic bifurcation ...)

Formation d’analogues aux aérosols : Les plasmas poudreux

National audienceLes plasmas sont des gaz ionisés qui se rencontrent dans l’industrie mais qui sont également très présents dans la nature. En effet, constituants principaux des étoiles, ils se rencontrent également dans les comètes et certaines atmosphères planétaires. Sur Terre, on les trouve notamment dans les éclairs ou les aurores boréales. Ces plasmas contiennent souvent des particules solides en suspension et on parle alors de plasmas poudreux (ou poussiéreux, en anglais dusty plasmas ou complex plasmas). Au laboratoire GREMI, ces plasmas sont étudiés depuis de nombreuses années, notamment grâce à des diagnostics électriques et optiques. Des poudres micrométriques sont injectées artificiellement dans le plasma ou elles sont formées au sein de celui-ci par l’intermédiaire de précurseurs gazeux. Dans ce dernier cas, des gaz réactifs à base de silicium (silane) ou de carbone (méthane, acétylène) sont généralement utilisés. Des liquides (alcools légers) sont également vaporisés pour certaines applications liées à la formation de suies issues de biocarburants. Généralement, les poudres se forment et croissent via une succession complexe de réactions chimiques et physiques par des processus de nucléation, coagulation, agglomération et adsorption.Du fait des interactions entre les particules chargées du plasma (ions, électrons) et les poudres, ces dernières se chargent électriquement. Elles acquièrent généralement une charge négative, due à la plus grande mobilité des électrons, qui va déterminer leurs mouvements, leur transport au sein du plasma et leurs interactions. Lorsque la densité de poudres est élevée, les caractéristiques du plasma environnant se trouvent fortement affectées avec une réduction des électrons libres et parfois l’apparition d’instabilités à basse fréquence

Formation et comportement de poussières dans un plasma

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