Next-Gen Surface Analysis for Ultrathin Functional Materials
Advanced nanoelectronics and quantum devices rely on ultrathin oxides and engineered interfaces whose chemical composition, stoichiometry and thickness must be controlled with sub-nanometer precision. LETI is installing the first 300-mm multi-energy XPS–HAXPES tool with angle-resolved capability, enabling quasi in situ chemical metrology from deposition to characterization.
This PhD will develop quantitative, multi-energy and angle-resolved XPS/HAXPES methodologies for ultrathin oxides and oxynitrides, validate measurement accuracy, and establish robust protocols for quasi in situ transfer of sensitive layers. Applications include advanced CMOS stacks and quantum Josephson junctions, where sub-2 nm AlOx barriers critically determine device performance.
The project directly supports the development of next-generation quantum technologies, advanced photonics and energy-efficient microelectronics by improving the reliability and stability of nanoscale materials. The work will be carried out within a strong multi-partner framework.
Bottom-up synthesis of nanographene and study of their optical and electronic properties
This project is part of an ANR project, which aims to synthesize perfectly soluble and individualized graphene nanoparticles in solution and incorporate them into spin electronics devices. To do this, we will draw on the laboratory's experience in synthesizing and studying the optical properties of graphene nanoparticles to propose original structures to several groups of physicists who will be responsible for studying the optical and electronic properties and manufacturing spin valve-type devices.
Characterization of radiolytic mechanisms in tritiated water–zeolite systems under storage conditions
The operation of the tritium facilities at Valduc generates low-activity tritiated liquid effluents, which are stored in an adsorbed form on 4A zeolite for operational reasons. Understanding the mechanisms of self-radiolysis of this confined water is essential for optimizing storage conditions.
Several PhD projects have already investigated these mechanisms by combining experiments and modelling. Early work showed that below 13% hydration, the radiolytic gases H2 and O2 can recombine within the zeolite. Subsequent studies, based on DFT calculations and molecular dynamics, identified the adsorption sites and the mobility of the gases. They revealed a hydration threshold (13–15%) above which gas diffusion becomes very low, consistent with the experimentally observed cessation of recombination. However, these simulations rely on idealized models.
The new proposed PhD aims to shift the project back toward experimental work in order to better reflect real storage conditions. It will begin with a detailed characterization of the zeolite used industrially. Water–zeolite reservoirs will then be irradiated to simulate the effect of tritium, and analyzed by NMR and possibly by Electron Spin Resonance (ESR) to detect reactive species. The experimental results may feed into a macroscopic model (Kinetic Monte Carlo, KMC), also developed previously, to predict the evolution of the system and identify possible optimizations for storage. The work will be carried out mainly at the NIMBE laboratory (CEA-CNRS), with simulation collaboration in Besançon and regular exchanges with CEA Valduc.
Development of 4D-STEM with variable tilts
The development of 4D-STEM (Scanning Transmission Electron Microscopy) has profoundly transformed transmission electron microscopy (TEM) by enabling the simultaneous recording of spatial (2D) and diffraction (2D) information at each probe position. These so-called “4D” datasets make it possible to extract a wide variety of virtual contrasts (bright-field imaging, annular dark-field imaging, ptychography, strain and orientation mapping) with nanometer-scale spatial resolution.
In this context, 4D-STEM with variable beam tilts (4D-STEMiv) is an emerging approach that involves sequentially acquiring electron diffraction patterns for different incident beam tilts. Conceptually similar to precession electron diffraction (PED), this method offers greater flexibility and opens new possibilities: improved signal-to-noise ratio, faster two-dimensional imaging at higher spatial resolution, access to three-dimensional information (orientation, strain, phase), and optimized coupling with spectroscopic analyses (EELS, EDX).
The development of 4D-STEMiv thus represents a major methodological challenge for the structural and chemical characterization of advanced materials, particularly in the fields of nanostructures, two-dimensional materials, and ferroelectric systems.
Mechanical degradation of Solid Oxide Cells: impact of operating and failure modes on the performances
Solid oxide cells (SOCs) are electrochemical devices operating at high temperature that can directly convert fuel into electricity (fuel cell mode – SOFC) or electricity into fuel (electrolysis mode – SOEC). In recent years, the interest on SOCs has grown significantly thanks to their wide range of technological applications that could offer innovative solutions for the transition toward a renewable energy market. However, despite of all their advantages, the large-scale industrialization of this technology is still hindered by the durability of SOCs. Indeed, the SOCs remain limited by various degradation phenomena including mechanical damage in the electrodes. For instance, the formation of micro-cracks in the so-called ‘hydrogen’ electrode is a major source of degradation. However, the precise mechanism and the full impact of the micro-cracks on the electrode performances are still unknown. By a multi-physic modelling approach, it is proposed in this thesis (i) to simulate the damage in the microstructure of the electrode and (ii) to calculate its impact on the loss of performances. Once the model validated on dedicated experiments, a sensitivity analysis will be conducted to provide relevant guidelines for the manufacturing of improved robust and performant electrodes.
Study of impurity transport in negative and positive triangularity plasmas
Nuclear fusion in a tokamak is a promising source of energy. However, a question arises: which plasma configuration is most likely to produce net energy? In order to contribute to answering this, during this PhD, we will study the impact of magnetic geometry (comparison between positive and negative triangularity) on the collisional and turbulent transport of tungsten (W). The performance of a tokamak strongly depends on the energy confinement it can achieve. The latter degrades significantly due to turbulent transport and radiation (primarily from W). On ITER, the tolerated amount of W in the core of the plasma is about 0.3 micrograms. Experiments have shown that the plasma geometry with negative triangularity (NT) is beneficial for confinement as it significantly reduces turbulent transport. With this geometry, it is possible to reach confinement levels similar to those of the ITER configuration (H-mode in positive triangularity), without the need for a minimum power threshold and without the associated plasma edge relaxations. However, questions remain: what level of W transport is found in NT compared to a positive geometry? What level of radiation can be predicted in future NT reactors? To contribute to answering these questions, during this PhD, we will evaluate the role of triangularity on impurity transport in different scenarios in WEST. The first phase of the work is experimental. Subsequently, the modeling of impurity transport will be carried out using collisional and turbulent models. Collaboration is planned with international plasma experts in NT configurations, with UCSD (United States) and EPFL (Switzerland).
Development of a new method for analyzing the manufacturing range of cladding tubes for fourth-generation nuclear reactors
Austenitic steel AIM1 is considered as benchmark alloy for fuel cladding in fourth-generation lead (RNR-pb) or sodium (RNR-Na) reactors. This alloy is currently undergoing qualification testing. The solution treatment of titanium carbides is a key point to obtaining a microstructure that is resistant to irradiation and, in particular, to the phenomenon of irradiation swelling (condensation of vacancies that form cavities in the material). It depends mainly on the quality of the thermomechanical treatments carried out during industrial manufacturing. New approaches to fine characterization (combining electron microscopy, atom probe tomography (APT), and thermoelectric power (TEP)) make it possible to specify microstructural changes during the manufacturing process.
In this thesis, we propose to study a new criterion for assessing the manufacturing quality of AIM1. The primary objective is to determine to which extent the variations in the material's thermoelectric power (TEP) can contribute to the implementation of an acceptance test that can be applied industrially. We will seek to acquire the knowledge that will enable us to perform a simple measurement to validate the metallurgical state of the tubes by having a precise understanding of the microstructures that produce the TEP signal intensity.
This study, which will combine experimental work and modeling, will enable to acquire skills in transmission electron microscopy, atom probe tomography, behavior under ion irradiation, and cluster dynamics modeling.
Spatiotemporal shaping of high-order harmonic emission in nanostructured crystals
We propose to study the spatiotemporal manipulation of radiation emitted by high harmonic generation, leveraging advances in nanofabrication technologies. The approach involves transposing methods developed for meta-optics to the strong-field regime specific to harmonic generation. The candidate will explore various design strategies to control the spatiotemporal properties of this radiation, which is intrinsically linked to the broad spectral bandwidth of attosecond pulses. These concepts will then be implemented and experimentally validated. This project aims to enhance the integration of high harmonic generation into optoelectronic devices, paving the way for new applications in ultrafast photonics.
New concepts for cold neutron reflectors
The CEA and the CNRS have launched an initiative to design a new neutron source using low-energy proton accelerators, the ICONE project [1]. The goal is to build a facility that will provide an instrumental suite of about ten spectrometers available to the French and European scientific community. Alongside ICONE, the LLB is also participating in HiCANS R&D work on the construction of a platform in Bilbao to facilitate European collaborations.Neutron scattering experiments require thermal and cold neutrons. The design of the moderator is therefore a crucial component of the project to maximize the source's performance.
One avenue for improving the moderator performances is to enhance the efficiency of the reflector, and more specifically, the cold neutron reflector. In this study, we propose to investigate the specific scattering properties of cold neutrons on nanostructured materials. Indeed, cold neutrons have long wavelengths (> 0.4 nm) and can therefore be coherently scattered by nanostructured materials. Scattering efficiency is not only amplified by coherent scattering effects, but it is potentially possible to direct this scattering if the reflecting material is anisotropic. This control over the scattering direction can further increase the moderator's brightness.
The first part of the work will consist of identifying the most promising nanostructured materials and modeling their cold neutron reflectivity performance. In a second step, these materials will be shaped and their properties characterized using neutron scattering devices at neutron scattering facilities such as the ILL in Grenoble or the PSI in Switzerland.
CONTEXT: strain - texture neutron instrumentation for ICONE
The CEA and the CNRS have launched an initiative to design a new neutron source using low-energy proton accelerators, the ICONE project. The objective is to build a facility that will offer an instrumental suite of about ten spectrometers available to the French and European scientific community. The project is currently in the Preliminary Design phase, with the aim of refining as much as possible all technical aspects.
We are proposing a PhD thesis on the modeling and development of a new neutron scattering spectrometer for measuring textures and stresses in materials. This technique makes it possible to probe residual stresses in materials after machining, heat treatment, and/or use, and to measure the crystallographic anisotropy of alloys to exploit the induced mechanical properties.
Part of the work will take advantage of the start-up of the DREAM and MAGIC spectrometers at ESS in Sweden, in which the LLB participated in the construction, so that the candidate can become familiar with time-of-flight neutron scattering techniques (measurements and data analysis).
In the second part of this work, we propose to implement statistical modulation techniques for the construction of an instrument, CONTEXT, on ICONE, which will allow to best exploit the potential of ICONE's long pulses. The objective will be to create a digital twin of the future instrument using various Monte Carlo simulation tools.