Fabrication and characterization of high thermal conductivity SiCf/SiC composites
SiCf/SiC ceramic matrix composites are foreseen candidates for structure materials and claddings in fast neutron reactor of 4th generation. However, their use may be limited because of their too low thermal conductivity in the operating conditions (< 10 W/mK).
SiCf/SiC ceramic matrix composites are now elaborated by chemical vapour infiltration (CVI). In order to improve their thermal conductivity (reduced porosity), it is planned to develop a hybrid elaboration process combining CVI and liquid routes.
The objective of this study is to determine the conditions of elaboration of a SiC matrix by liquid routes and then to characterize the thermo-mechanical behaviour of the hybrid composites, particularly in relation to CVI references.
Large-area processing and design of functional piezoelectric nanomaterials for flexible sensors and systems
CEA LETI develops innovative highly flexible strain sensors which exploit the piezoelectric properties of self-organized gallium nitride nanowires. The fabrication steps are basically: i) nanowire growth, ii) nanowire assembly, iii) encapsulation, iv) contacting. First demonstrators with small active area (1.5 cm²) have already been achieved using the Langmuir Blodgett (LB) technique for the assembly of nanowires. The present project is concerned with the scaling-up of the assembly process over large surface areas, as well as controlled patterning of nanowire assemblies in 1D and 2D by using an innovative CEA LITEN roll-to-roll technology called Boostream® which has the same functionalities as LB in its basic function.
The aim of the post doc is to develop a new building block for the Boostream® equipment enabling a controlled assembly of wires with a pre-defined design. The candidate will carry out studies to optimize the wire assembly, develop the process of film patterning and fabricate, integrate and characterize GaN nanowire piezoelectric transducers with dimensions of 15x15 cm².
More generally, this post doc will also provide the opportunity to develop a generic knowledge to manipulate micro or nano wires or fibers giving new solutions in various fields such as surface structuration, electronic skin, energy...
Etudes sur la physique des gaz et des interactions matière/laser pour la démonstration à l’échelle laboratoire de l’épuration isotopique du palladium (naturel).
Le palladium est un métal rare dont la demande mondiale est en forte augmentation. Or, il est présent en tant que produit de fission dans les combustibles nucléaires usés qui sont retraités en France. Il serait donc intéressant de recycler ce métal. Pour cela, il est nécessaire de procéder à une épuration isotopique, afin de supprimer un des isotopes du palladium, le 107, qui est un radionucléide artificiel à vie longue émetteur béta. Dans le cadre d'un nouveau projet sur 4 ans construit en réponse à l'appel d'offre du Plan d'Investissement et d'Avenir de l’État, le Service d’Etude des Procédés d’Enrichissement propose un contrat post-doctoral ayant pour objectif la compréhension des interactions gaz/laser dans le procédé de séparation isotopique du palladium par Lasers actuellement en cours de développement. L’objectif principal du projet est la démonstration finale de la faisabilité de séparation de palladium naturel (et non radioactif) pour la phase suivante de développement d’un premier pilote.
Le post-doctorant devra en particulier assurer l’étude du mode de production de la vapeur atomique près du point de fusion du métal pur, des mesures de spectroscopie par laser dans l’UV afin d’affiner les séquences sélectives de photoionisation des isotopes désirés. Pour ce faire, il participera à la définition, au montage et au développement de l'évaporateur, et au couplage des lasers du procédé avec l’enceinte à vide. Des échanges seront mis en place sur ce sujet spécifique avec des spécialistes reconnus au sein de la Direction de la Recherche Fondamentale du CEA. Les mesures de diagnostics des lasers mais aussi les mesures provenant des interactions gaz/laser sont à développer. La programmation (en Python et/ou sous Labview) de ces outils est un point essentiel du poste proposé. Une attention particulière sera portée sur les publications à réaliser essentiellement dans le cadre des interactions gaz/laser (photoionisation sélective des atomes d’intérêt et extraction).
This study aims at the chemical synthesis of infrared emitting nanocrystals for integration in LEDs.
These nanocrystals will be characterized by TEM, XRD, EDX, UV-vis, PL, NMR, FTIR. Formulation of colloidal solutions suitable for deposition via inkjet printing.
The candidate will work in the partner lab INAC/LEMOH
Proton conducting interpenetrating polymer networks as new PEMFC membranes
This subject takes place in the frame of the development of proton exchange membrane fuel cells (PEMFC) and the main objective is to increase their performance and durability for operation above 100°C at low relative humidity.
The current standard membranes for use in PEMFC applications remain perfluorosulfonated ionomers such as Nafion® due their good proton conductivity and chemical stability. Nevertheless, their proton conductivity decreases for relative humidity below 70% especially at high temperature because of a too low density of proton conducting groups. This characteristic is a limitation for their use in the working conditions of the requirements for the automotive application. With these polymers, an increase of the proton conducting group density leads to a decrease of mechanical and dimensional stability. Yet, this stability is already quite low and decreases the PEMFC durability. The goal of this subject is to develop new membrane structures based on interpenetrating polymer networks that do not present this antagonism between good mechanical stability and proton conductivity. This strategy which has recently been patented by CEA (patent application number 08 06890) is based on the association of two entangled polymer networks, one sulfonated for proton conductivity and one fluorinated for mechanical and chemical stability.
The applicant will make the membranes and then will characterize their mechanical properties, proton conductivity as well as gas permeability. He will also quantify their performance and durability in a running fuel cell.
Nano-silicon based negative composite electrode for lithium-ion batteries
With the aim of improving the battery type lithium-ion batteries, many works are devoted to research of new materials for the manufacturing of high-capacity electrodes. Silicon is an attractive material as an element of negative electrode instead of graphitic carbon with its high capacity that can theoretically reach almost 3579 mAh/g (Li15Si4, ten times more than the graphite (372 mAh / g, LiC6) . However, one major problem that has prevented the development of such electrodes is the high coefficient of volumetric expansion of silicon which leads to rapid degradation of the material (cracked, spraying the electrode ,....) and its performance. In this context, the work of post-doc will be to explore the electrochemical performance of negative electrodes prepared from silicon nanoparticles synthesized by laser pyrolysis CEA. The work will be to incorporate nanoparticles in a negative composite electrode and test its performance. The understanding work will be focused on the dual influence of nanostructuration of silicon particles and of the composition / implementation of the composite electrode on the performance. Thus, this work will be located at the junction of two CEA laboratory specialists from both key points of the study (Synthesis in Saclay, development and characterization of batteries in Grenoble).
Couplings between the distributions of water and current density in operating Proton Exchange Membrane Fuel Cell (PEMFC)
The post-doc work will be focused on the measurement of the current density and of the water distributions in an operating fuel cell with a real design, in order to give a better understanding of PEMFC operation as a function of the operating parameters (Temperature, Gas hydration, Pressure, Gas composition). The measurement of the distribution of the current density will be performed using a reliable commercial setup on a full size cell. CEA developed a technique based on Small Angle Neutron Scattering (SANS) as a non-intrusive tool in order to quantify the water distribution during fuel cell operation within and without the membrane. CEA benefits for international recognition on this topic. These measurements will be conducted in high flux neutron reactors, such Institut Laue Langevin (ILL). Some specific high and low resolution neutron imaging experiments could be also be conducting additionally in order to have a complete 3D view of water repartition.
Minimizing modifications at III-V pattern sidewalls after plasma etching for heterointegrated optoelectronics and nonlinear photonics
This project will focus on understanding plasma-induced damage at the sidewalls of micro-nano-patterned III-V semiconductors to find relevant technological solutions capable to minimize this damage. There is a clear need of knowledge on by which mechanisms and to what extent the plasma etching process modifies the III-V pattern sidewalls and the consequences it has on the device optical performances. The selected III-V semiconductor will be aluminium gallium arsenide which exhibits excellent optoelectronic properties and strong nonlinear parametric gain.
The student will be mainly focused on understanding how the key plasma process parameters influence the structural and chemical changes at the III-V sidewalls, as well as changes of optical properties. This will require the development of a methodology for a 3D quantitative characterization of the sidewalls at the nanoscale, based on Auger microscopy and cathololuminescence. The main objective will be to correlate plasma-induced structural defects and modifications of the optoelectronics properties. The second step will consist in developing optimized plasma etching processes for III-V semiconductors, exploring alternative plasma technologies. You will also be involved in the development of processes for restoring and passivating the AlGaAs sidewalls.
Detection of traces of narcotics in saliva by electrochemiluminescence on diamond electrodes
The consumption of narcotics is becoming a problem for road safety because 23% of road deaths in France occur in an accident involving at least one driver who tested positive. Thus, one objective of road safety in consultation with the concerned ministries (Ministry of Transport, Ministry of Interior, Ministry of Health and Ministry of Economy) is to improve the fight against road insecurity linked to narcotics consumption. In particular, this involves increasing and facilitating roadside checks using a portable device dedicated to controlling the use of narcotics on the roadside, similar to what is already done for breathalyzer tests. Such a device is not commercially available today. The main prerequisites of this device will be to provide reliable, immediate confirmation results with evidentiary value for the courts as well as a purchase cost compatible with large-scale deployment on French road networks. In this context, the subject of study proposed aims to study the possible detection of traces of narcotics in saliva using electroluminescence on a boron-doped diamond electrode. This method is considered promising for such an application because it potentially allows extremely low detection thresholds to be reached and, in accordance with legislative requirements, offers multiple possibilities aimed at achieving high selectivity towards chemical targets, with a high detection capacity. miniaturization of equipment and a relatively low cost of apparatus compared to analytical tools such as mass spectrometer, IMS, etc.
Plastic recycling enabled by toxic additives extraction using green solvents
It is important to develop the scientific knowledge and stimulate innovations to recycling Plastics. The extremely large variety of plastic based objects that we use in our daily life are made of a wide range of plastic materials covering many different polymers, many different formulations. Plastics objects are also used for many purposes and there is therefore the need of various ways to collect, sort and treat them.
Methods of recycling of plastics are generally divided into four categories: primary, secondary, tertiary, and qua-ternary (see Figure 9). Primary recycling or closed loop recycling method is considered when the materials after recycling present equal or improved properties compared to the initial or virgin materials. When the recyclates present a decrease in the properties level, one may spook about secondary or down-cycling method. In tertiary (also known as chemical or feedstock) recycling method, the waste stream is converted into monomers or chemicals that could be advantageously used in the chemical industries. Finally, quaternary (also known as thermal recycling, energy recovery, and energy from waste) recycling method corresponds to the recovery of plastics as energy and is not considered as recycling for Circular Economy.
Various processes can be considered for chemical recycling which present different level of maturity. Hence this project that will study the decontamination of various PVC formulations using green solvents, and more particularly supercritical CO2
This work located in Saclay, France, in the heart of the University Paris-Saclay and will benefit from a very multidisciplinary and international environment.
This work will benefit from the prestigious framework of the France 2030 funding, and more precisely the PEPR Recycling (https://www.cnrs.fr/fr/pepr/pepr-recyclabilite-recyclage-et-reincorporation-des-materiaux-recycles ). It will be supervised by Dr. Jean-Christophe P. Gabriel: linkedin.com/in/jcpgabriel).