Synthesis of high-nitrogen heterocyclic molecules
One of the CEA DAM's objectives is the design of new explosive compositions with optimized properties. As such, the search for new molecules of interest, likely to be integrated into innovative formulations, is a fundamental activity.
The objective of the post-doctorate is to synthesize, on a laboratory scale, energetic molecules with structures capable of meeting the specifications in terms of performance and insensitivity. These are mainly highly nitrogenous heterocyclic molecules (pyrazoles, triazoles, oxadiazoles, etc.). The work will include both the synthesis of intermediates, whether they are considered energetic or not, and that of the final products.
This approach is supported by modeling work carried out upstream, intended to set up tools to propose new structures and evaluate their properties by calculation. This subject will require, in interaction with the modeling team, using these tools and putting them to good use to guide the choice of targets that will be studied experimentally in the laboratory.
Optimizing chemical reactivity with interpretabe machine learning
In organic synthesis, many molecular and macroscopic parameters can influence the outcome of chemical reactions. It is therefore difficult to correlate the obtained yields with the reaction conditions. This project aims to develop interpretable machine learning models to predict and improve the efficiency of oxidation reactions of electron-deficient heterocycles, a real challenge in organic chemistry. The main challenge will be to best represent and leverage the variables associated with the complexity of a real reaction system (chemical nature of the substrate, temperature, reaction time, etc.) to feed machine learning algorithms and extract clear rules. The ultimate goal is to provide chemists with predictive tools to rationalize and develop these transformations.
Solvothermal synthesis of carbon dots for optoelectronic applications
Carbon dots (C-dots) are nano-sized particles of carbon that exhibit unique electronic, optical and chemical properties due to their exceptional physico-chemical properties. These small, high surface-to-volume ratio materials are semiconductors that glow under irradiation, making them ideal for detecting ionizing radiation. Conventional plastic scintillators rely on energy transfer from the ultraviolet to visible light via organic fluorophores. The ability of CDs to absorb photons in the ultraviolet range and emit them in the visible range means that they could potentially replace organic fluorophores in their role as a bridge between ultraviolet and visible light. With low production costs, they can be synthesized either by conventional stepwise organic synthesis or, more rapidly, by top-down or bottom-up single-step approaches using a variety of chemicals. In this context, we have recently developed an interesting synthesis route enabling the preparation of C-dots emitting at different wavelengths, thus covering the entire visible range.
Development and characterization of an oxide/oxide composite material
Fiber-reinforced ceramic matrix composites (CMCs) are a class of materials that combine good specific mechanical properties (properties relative to their density) with excellent high-temperature resistance (> 1000 °C), even in an oxidizing atmosphere. They generally consist of a carbon or ceramic fiber reinforcement and a ceramic matrix (carbide or oxide).
The proposed study focuses on the development of a fabrication process for oxide/oxide CMCs with long and/or short fibers that possess suitable dielectric, thermal, and mechanical properties.
Study of the Thermodiffusion of Small Polarons in UO2
The position is published on the CEA website at the following address:
https://www.emploi.cea.fr/job/emploi-post-doctorat-etude-en-ab-initio-de-la-thermodiffusion-des-petits-polarons-dans-UO2-h-f_36670.aspx
New semiconductor materials for neutron detection
The candidate will work at CEA LITEN on the development of organic-inorganic perovskite single crystals. The solution-growth protocols will be inspired by preliminary work from several internships and PhD. The student will vary the material's structure, chemical composition, or doping in order to optimize scintillation and direct detection performances for fast neutron detection. The best compositions selected based on their structural, optical properties, and responses under X-rays will then be integrated into detectors and characterized under various neutron fluxes and energies. Their performances and durability under irradiation will be studied and benchmarked to existing materials.
Holder of a PhD in materials science or chemistry, with the ability to work with multidisciplinary teams (collaboration with the teams at CEA LETI in Grenoble, IRESNE in Cadarache, and LIST in Saclay), good autonomy, and strong organizational skills will be major assets to successfully carry out this mission.
Excited electronic states in the GW Approximation coupled to the Projector Augmented-Wave Approach
This project aims to address a major gap in ab initio calculations by enabling reliable simulations of excited electronic states (GW method) using the Projector Augmented-Wave (PAW) approach. These advances will be integrated into the open-source software ABINIT, a recognized international collaborative project. The GW approximation is considered the gold standard for determining electronic energy levels in condensed matter, correcting the underestimated band gap in DFT. The PAW method, on the other hand, offers precision and flexibility and is widely used for ground state and material response calculations.
However, the combined GW+PAW approach encounters difficulties in some well-identified cases (e.g., zinc oxide), with underlying reasons understood but not yet fully resolved. Low-energy excited states are well described, but high-energy states remain problematic. The current debate focuses on the need to perform complete (but computationally expensive) calculations, to neglect certain terms (with complex error control), or to modify the PAW method (at the cost of reduced efficiency).
The project aims to adapt the PAW formalism to the GW approach, to develop a fast and accurate numerical scheme, and to clarify the current, somewhat confusing situation. The CEA team is a leading developer of ABINIT for PAW and GW and will ensure access to large computing resources. The postdoctoral objectives include theoretical development, implementation in ABINIT, and improving electronic properties for realistic solid systems (surfaces, semiconductor junctions, etc.).
Impact of Microstructure in Uranium Dioxide on Ballistic and Electronic Damage
During reactor irradiation, nuclear fuel pellets undergo microstructural changes. Beyond 40 GWd/tU, a High Burnup Structure (HBS) appears at the pellet periphery, where initial grains (~10 µm) fragment into sub-grains (~0.2 µm). In the pellet center, under high temperatures, weakly misoriented sub-grains also form. These changes result from energy loss by fission products, leading to defects such as dislocations and cavities. To study grain size effects on irradiation damage, nanostructured UO2 samples will be synthesized at JRC-K, using flash sintering for high-density pellets. Ion irradiation experiments will follow at JANNuS-Saclay and GSI, with structural characterizations via Raman spectroscopy, TEM, SEM-EBSD, and XRD. The postdoc project will take place at JRC-K, CEA Saclay, and CEA Cadarache under expert supervision.
Thermochemical and thermodynamic study of chloride molten salts
In today’s climate emergency, access to clean and cheap energy is more important than ever. Several ways have been envisaged for several years now, but a number of technological issues still need to be overcome before they can be put into practice, as they represent breakthroughts. Whether for energy storage than for fourth generation nuclear reactors, molten salt environment used as coolant and/or as fuel is highly corrosive requiring a complexe choice of structural materials.
The aim of this subject proposed in the Corrosion and Materials Behavior Section is to study in depth the chemical properties of different chloride molten salts : the basic ternary salt (NaCl-MgCl2-CeCl3) but also the corrosion/fission/activation products that can be produced (MxCly with M=Cr, Fe, Te, Nd, Ni, Mo,…). The activity coefficients and solubility limits of these metallic elements will be determined using various techniques such as electrochemistry and Knudsen cell mass spectrometry. If required, this study can be completed by the phase transition temperature and heat capacity measurements using differential scanning calorimetry.
Preparation and characterization of an oxide/oxide composite
Fiber-reinforced ceramic matrix composites (CMCs) are a class of materials that combine good specific mechanical properties (properties relative to their density) with resistance to high temperatures (> 1000 °C), even in oxidizing atmospheres. They are typically composed of a carbon or ceramic fiber reinforcement and a ceramic matrix (carbide or oxide.
The proposed study focuses on the development of a low-matrix oxide/oxide CMC with suitable dielectric, thermal, and mechanical properties.
This study will be conducted in collaboration with several laboratories at CEA Le Ripault.