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

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

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

Ora

Dust Particle Growth in a Sputtering Discharge with Krypton

PosterInternational audienceDust particles can be grown in a plasma, either by injecting reactive gases or by sputtering materials. In the last case, molecular precursors are injected into the gas phase and we will have similar processes than with reactive gases. The sputtering efficiency and the gas phase reactions can be affected by the gas type and particularly by the ion mass. Once the dust particles have been grown, the behaviour and structure of the cloud are also dependent of this parameter. In this work, we present experimental results concerning dust particle growth by sputtering a polymer layer exposed to a Krypton plasma. These experiments are performed in a capacitively-coupled rf discharge at low power (~ 3 W) and a Kr pressure of about 1 mbar. Growth kinetics, instabilities induced by the dust particle presence and structure of the dust cloud are investigated and compared to the Argon case

Phénomènes non linéaires dans les plasmas poussiéreux : Apparition d'oscillations multimodales

PosterNational audienceLes oscillations multimodales (Mixed-Mode Oscillations ou MMOs) sont une variété de signaux qui se rencontrent dans de nombreux domaines. Cette alternance d'oscillations de petite et grande amplitude est caractéristique de certaines réactions chimiques oscillantes et de l'activité neuronale. Dans ce travail, nous mettons en évidence que ces oscillations existent également dans un tout autre domaine scientifique : les plasmas poussiéreux. Ce mélange de plasma et de poussières est le siège de nombreuses instabilités et de phénomènes dynamiques complexes dont certains correspondent à des MMOs. Des résultats expérimentaux ainsi qu'une analyse préliminaire de ces comportements sont présentés dans ce papier