Sharper Structural Insight in Nanoelectronics with Dark-Field X-Ray Microscopy
Dark-field X-ray microscopy (DFXM) is an emerging, non-destructive synchrotron technique capable of imaging strain and crystalline defects with 30–100 nm resolution over large fields of view. Recent upgrades at the ESRF and the ID03 beamline have increased X-ray intensity by two orders of magnitude, enabling investigation of the most challenging nanoscale structures produced in cleanroom environments. This PhD aims to exploit DFXM for the analysis of advanced microelectronic architectures subjected to critical thermo-mechanical stress. DFXM will provide 3D mapping of strain, orientation and buried defects in complex devices without sample destruction. A comparative study will be performed against complementary local X-ray techniques also available at synchrotron facilities such as Laue microdiffraction and scanning X-ray diffraction microscopy. Multi-scale correlations will be established with TEM and Raman spectroscopy. Finite-element simulations will support interpretation by modelling the mechanical behavior under thermal or operational loads. The objective is to define a robust methodology for multiscale strain analysis in microelectronics devices.
This PhD will take place at the CEA–Leti on the Nanocharacterization platform and is embedded in a strong ESRF@ID03 collaboration and supports advances in quantum technologies, photonics and energy-efficient microelectronics. This work will contribute to improved reliability and design optimization of next-generation devices.
Self-healing of radiation-induced defects in silicon solar cells for space
Over the last decades, the development of alternative space photovoltaic (PV) solutions to the III-V premium standard has shifted the focus to silicon solar cells. Indeed, leveraging on existing maturity of terrestrial PV silicon devices and processes offers significant potential for innovation and cost reduction. Many satellites nowadays evolve in Low Earth Orbit, a proton and electron rich environment. Such irradiations induce electrically active defects in the material which affect the PV performances. Interestingly, some of the irradiation-induced defects can be healed upon external factors such as temperature and/or photons flux.
The main goals of this PhD thesis will be to i) understand the bulk & interface electron/proton irradiation-induced degradation mechanisms driving the evolution of the optoelectronic properties of silicon passivated contacts solar cells ii) develop a comprehensive understanding of the self-healing effects in irradiated modern silicon solar cells through experimental studies and modeling iii) identify design / fabrication process routes to control & boost the self-healing capability.
To reach these goals, this PhD work will go through defined steps: bibliography review, solar cells fabrication, material/device ageing under proton & electron irradiations, advanced characterizations and modeling. This PhD work will be conducted at CEA/Liten, on the INES campus (Le Bourget du Lac, FR) with frequent interactions with CNES (Toulouse, FR) facilities.
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.
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.
https://iramis.cea.fr/lidyl/pisp/150720-2/
Recent advances in ultrafast optics and the control of highly nonlinear light–matter interactions now make it possible to generate attosecond light pulses (1 as = 10?¹8 s) through High-Order Harmonic Generation (HHG). This process converts a femtosecond laser pulse into coherent, ultrashort radiation in the extreme ultraviolet (XUV) range (10–150 eV). These unique light sources enable access to electronic dynamics on sub-femtosecond timescales and allow the probing of element-specific transitions that were previously only achievable at large-scale facilities such as synchrotrons. The Attophysics Group at LIDYL, a pioneer in the generation, characterization, and application of attosecond pulses, has recently developed sources driven by beams carrying spin (SAM) or orbital (OAM) angular momentum, opening new avenues for studying chiral and magnetic dynamics. Building on these advances, this PhD project aims to synthesize light fields with time- and space-dependent chirality, exploiting in particular the often-neglected longitudinal component of the electric field. Three regimes will be explored: a linear regime (XUV/IR pump–probe), a strongly nonlinear regime (structured visible–IR fields in chiral samples), and a weakly nonlinear regime (IR pump/XUV probe). This work will open a new class of attosecond physics experiments, bridging fundamental exploration and emerging applications.
The student will acquire practical knowledge about lasers, in particular femtosecond lasers, and hands on spectrometric techniques of charged particles. They will also study strong field physical processes which form the basis for high harmonic generation. They will become an expert in attosecond physics. The acquisition of analysis skills, computer controlled experiments skills will be encouraged although not required.
Details at https://iramis.cea.fr/lidyl/pisp/150720-2/
Effect of water radiolysis on the hydrogen absorption flux by austenitic stainless steels in the core of a nuclear pressurized water reactor
In pressurized water nuclear reactors, the core components are exposed to both corrosion in the primary medium, pressurized water at around 150 bar and 300°C, and to neutron flux. The stainless steels in the core are damaged by a combination of neutron bombardment and corrosion. In addition, radiolysis of the water can have an impact on the mechanisms and kinetics of corrosion, the reactivity of the medium and, a priori, the mechanisms and kinetics of hydrogen absorption by these materials. This last point, which remains unexplored, may prove problematic, as hydrogen in solid solution in steel can lead to changes in (and degradation of) the mechanical properties of the steel or induce premature cracking of the part. The pioneering work developed in this highly experimental thesis will focus on the impact of radiolysis phenomena on the mechanisms and kinetics of corrosion and, above all, hydrogen pick-up in 316L stainless steel exposed to the primary environment under irradiation. Hydrogen will be traced by deuterium, and neutron irradiation simulated by electron irradiation on particle accelerators. An existing permeation cell will be modified into a unique setup to allow in operando measurement by mass spectrometry of the deuterium permeation flux through a sample exposed to the simulated primary water under radiolysis conditions. The distribution of hydrogen in the material, as well as the nature of the oxide layers formed, will be analysed in detail using state-of-the-art techniques available at the CEA and in partner laboratories. The doctoral student will ultimately be required to (i) identify the mechanisms involved (corrosion and hydrogen entry), (ii) estimate their kinetics and (iii) model the evolution of hydrogen flux in the steel in connection with radiolysis activity.