Thomas Lecas

PdPt catalyst synthesized using a gas aggregation source and magnetron sputtering for fuel cell electrodes

, +33 (0)2 3849 4352 KEYWORDS. gas aggregation source, magnetron sputtering, platinum, nanoclusters, catalyst. Abstract. PdPt catalysts with different morphologies and atomic ratios have been synthesized on native SiO2/Si and on proton exchange membrane. The combination of the gas-aggregation source and of the magnetron sputtering techniques allows the formation of quasi core-shell Pd0.97Pt0.03@Pt nanoclusters. Transmission electron microscopy and grazing incidence wide angle X-ray scattering measurements on Pd-rich core reveal a mean diameter of 4 nm and a fcc structure. The Pt shell around the half of the Pd-rich core is formed by magnetron sputtering which leads to the increase of nanocluster diameter (up to 10 nm) and of the overall Pt content (up to 85%). The membranes coated by PdPt core catalyst and PdPt@Pt catalyst (resulting in the formation of catalyst coated membrane) are incorporated into fuel cells and their electrical characteristics are measured. The association of the two deposition techniques resulting in the formation of quasi core-shell PdPt@Pt nanoclusters improves the startup step of the fuel cell.

Deposition of Pt inside fuel cell electrodes using high power impulse magnetron sputtering

The high power impulse magnetron sputtering (HiPIMS) 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 medium, as evidenced by Rutherford backscattering spectroscopy analysis. Each sample of catalyzed porous carbon is tested as a cathode of a proton exchange membrane fuel cell (PEMFC). 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 process.

Optical diagnostics of dusty plasmas during nanoparticle growth

Carbon-based thin films deposited on surfaces exposed to a typical capacitively-coupled RF plasma are sources of molecular precursors at the origin of nanoparticle growth. This growth leads to drastic changes of the plasma characteristics. Thus, a precise understanding of the dusty plasma structure and dynamics is required to control the plasma evolution and the nanoparticle growth. Optical diagnostics can reveal some particular features occurring in these kinds of plasmas. High-speed imaging of the plasma glow shows that instabilities induced by nanoparticle growth can be constituted of small brighter plasma regions (plasmoids) that rotate around the electrodes. A single bigger region of enhanced emission is also of particular interest: the void, a main central dust-free region, has very distinct plasma properties than the surrounding dusty region. This particularity is emphasized using optical emission spectroscopy with spatiotemporal resolution. Emission profiles are obtained for the buffer gas and the carbonaceous molecules giving insights on the changes of the electron energy distribution function during dust particle growth. Dense clouds of nanoparticles are shown to be easily formed from two different thin films, one constituted of polymer and the other one created by the plasma decomposition of ethanol.

Energy Transferred From a Hot Nickel Target During Magnetron Sputtering

The energy influx emanating from a sputtered Nickel target in a magnetron apparatus is studied using an energy flux diagnostic. An image of the Ni target before, during, and after the sputtering process is presented and correlated to the energy flux results. For an input power above 50 W (i.e., ≈10 W/cm2), an abrupt increase of the energy flux is observed. This phenomenon is associated to the emission of visible and IR lights by the target, and to an increase of the sputtering rate.

Zoom Into Dusty Plasma Instabilities

In a krypton plasma, the growth of dust particles can strongly affect the plasma characteristics by inducing many types of instabilities. These unstable phenomena are studied by analyzing their frequency evolution as a function of time and by emphasizing the appearance of plasma spheroids. Different phases are evidenced due to a detailed analysis of the form and the frequency of the discharge current. Concerning the plasma spheroids, interesting motions in the plasma bulk are evidenced.

Characterization of low frequency instabilities in a Krypton dusty plasma

The occurrence of low frequency instabilities in a plasma can be due to the presence of a high density of grown dust particles. These instabilities are characterized by analyzing the discharge current, evidencing the existence of successive phases marked by distinct frequency evolutions. The main characteristics of these phases are determined as a function of the gas pressure. Particular attention is paid to the changes of the instability appearance time, duration and frequencies. These parameters seem to be related to global amount of grown dust particles. The instability appearance time is the first parameter that can be easily measured during an experiment and all the other parameters can be estimated from this simple measurement.

Unstable Plasmoids in Dusty Plasma Experiments

Low-frequency instabilities are easily obtained in dusty plasmas formed using reactive gases or material sputtering. These unstable phenomena can be characterized by complex and impressive features affecting the plasma glow luminosity. In this paper, we report on a particular phase of an instability, where moving bright plasma spots are observed in between the electrodes of a capacitively coupled radio-frequency discharge in krypton. These plasmoids show complex behaviors, such as mutual interactions, consisting in their merging or splitting.

Nanoparticle formation in a low pressure argon/aniline RF plasma

The formation of nanoparticles in low temperature plasmas is of high importance for different fields: from astrophysics to microelectronics. The plasma based synthesis of nanoparticles is a complex multi-scale process that involves a great variety of different species and comprises timescales ranging from milliseconds to several minutes. This contribution focuses on the synthesis of nanoparticles in a low temperature, low pressure capacitively coupled plasma containing mixtures of argon and aniline. Aniline is commonly used for the production of polyaniline, a material that belongs to the family of conductive polymers, which has attracted increasing interest in the last few years due to the large number of potential applications. The nanoparticles which are formed in the plasma volume and levitate there due to the collection of negative charges are investigated in this contribution by means of in-situ FTIR spectroscopy. In addition, the plasma is analyzed by means of plasma (ion) mass spectroscopy. The experiments reveal the possibility to synthesize nanoparticles both in continuous wave and in pulsed discharges. The formation of particles in the plasma volume can be suppressed by pulsing the plasma in a specific frequency range. The in-situ FTIR analysis also reveals the influence of the argon plasma on the characteristics of the nanoparticles.The formation of nanoparticles in low temperature plasmas is of high importance for different fields: from astrophysics to microelectronics. The plasma based synthesis of nanoparticles is a complex multi-scale process that involves a great variety of different species and comprises timescales ranging from milliseconds to several minutes. This contribution focuses on the synthesis of nanoparticles in a low temperature, low pressure capacitively coupled plasma containing mixtures of argon and aniline. Aniline is commonly used for the production of polyaniline, a material that belongs to the family of conductive polymers, which has attracted increasing interest in the last few years due to the large number of potential applications. The nanoparticles which are formed in the plasma volume and levitate there due to the collection of negative charges are investigated in this contribution by means of in-situ FTIR spectroscopy. In addition, the plasma is analyzed by means of plasma (ion) mass spectroscopy. The ex...

An efficient way to evidence and to measure the metal ions fraction in high power impulse magnetron sputtering (HiPIMS) post- discharge with Pt, Au, Pd and mixed targets

The proportion of metal ions in a High Power Impulse Magnetron Sputtering discharge is a key information for the potential development of new materials and new layer architectures deposited by this technique. This paper aims to measure this proportion by using a homemade system consisting of a quartz crystal microbalance and a grid energy analyzer assembly. Such a system yields relevant results on the composition of the post-discharge depending on the nature of the gas (Ar, Kr, Xe) and the target materials (Pt, Pd, Au, Pt50Au50 and Pt5Pd95). In our conditions, the highest proportions of metal ions in the post-discharge are obtained by using Ar gas and reaches 10 %, 12 %, 50 %, 19 % and 88 % for respective Pt, Au, Pd, Pt50Au50 and Pt5Pd95 target, respectively.

Influence of the High-Power Impulse Magnetron Sputtering Voltage on the Time-Resolved Platinum Ions Energy Distributions

High-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 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 is 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.