Development of new processes for the fabrication of advanced interconnect structures of solar cells
The fabrication of solar cells with high performances at a reduced cost is a key challenge addressed by many research institutions and industrials worldwide. Many technological solutions are being investigated. Among them, a promising approach consists in forming narrower metal lines to limit shadowing of active areas of the cells. This work aims at replacing serigraphy by new fabrication processes able to reduce line width. For this purpose, the conducting substrate is coated by an insulating mask in which the lines are defined. The metal is then directly plated selectively onto the weakly conducting portions of the substrate, i.e. the lines, using electrolytic or electroless reactions. The process conditions will be adapted with regard to the nature of the initial conducting surfaces.
Multiscale approach of f elements aqueous solutions modeling
A post-doctoral position is available for one year at CEA-Marcoule
The study will be the modeling of concentrated aqueous phases of heavy metal salts using both microscopic and mesoscopic modeling.
Separation processes for heavy metals recycling usually use liquid-liquid extraction with the transfer of ionic species from a concentrated aqueous phase to an organized organic phase.
This post-doctoral research subject relates to the chemical properties of these processes, and especially to the characterization of the aqueous phase using as accurate as possible models. The goal is to understand the various effects (solvation, electrostatic and van der waals forces, entropy…) influencing the structural and energetic properties of these solutions. A multi-scale approach will be used to study some systems of interest for both fundamental and industrial point of view, the aim being the characterization of these solutions from their molecular structure to their thermodynamic properties. The tools and the approach used here have to be be valid for separative chemistry overall.
Modelling of interstitial cluster evolution in body-centered cubic metals after helium implantation
Under irradiation, structural materials inside nuclear reactors undergo changes in mechanical properties, which result from the formation of point defect clusters, such as cavities (clusters of vacancies) and interstitial dislocation loops (clusters of self-interstitial atoms). Understanding the formation processes of such clusters is thus of prime importance. Recently, three-dimensional interstitial clusters, known as C15 clusters, have been shown theoretically to be highly stable in iron. In order to detect such clusters experimentally, an idea is to make them grow, as shown for dislocation loops after helium implantation. This approach will be carried out experimentally in various bcc metals in the framework of the ANR project EPigRAPH, in collaboration with Chimie ParisTech, GEMaC and LPS.
In this project, the following modelling tasks will be performed by the postdoc:
- Electronic structure calculations will be done to obtain the energetic properties of point defects and point defect clusters in the bcc metals envisaged in the project.
- These data will then be used to parameterize a kinetic model based on cluster dynamics. This formalism is particularly well adapted to simulate the evolution of point defect clusters over long physical times.
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.