Radiological large-scale accident dosimetry: use of EPR spectroscopy for population triage by measurements of smartphone screens
In the event of a large-scale radiological emergency involving sources of external irradiation, methods are needed to identify which members of the population have been exposed and require priority care. To date, there are no operational methods for such sorting. Smartphone touch screen lenses retain traces of ionizing radiation through the formation of so-called “radiation-induced” defects.Measuring and quantifying these punctual defects, in particular by electron paramagnetic resonance (EPR) spectroscopy, makes itpossible to estimate the dose deposited in the glass, and thus the exposure associated with irradiation. The thesis work proposed herefocuses in particular on the alkali-aluminosilicate glasses used in cell phone touch screens, which are currently the best candidates fordeveloping new measurement capabilities in the context of accidents involving large numbers of victims.
We will focus in particular on identifying point defects as a function of the glass model used in smartphones by simulating EPR spectra in order to optimize the proposed dosimetry method.
Wetting dynamics at the nanoscale
Wetting dynamics describes the processes involved when a liquid spreads on a solid surface. It's an ubiquitous phenomenon in nature, for example when dew beads up on a leaf, as well as in many processes of industrial interest, from the spreading of paint on a wall to the development of high-performance coating processes in nanotechnology. Today, wetting dynamics is relatively well understood in the case of perfectly smooth, homogeneous model solid surfaces, but not in the case of real surfaces featuring roughness and/or chemical heterogeneity, for which fine modeling of the mechanisms remains a major challenge. The main goal of this thesis is to understand how nanometric roughness influences wetting dynamics.
This project is based on an interdisciplinary approach combining physics and surface chemistry. The PhD student will conduct systematic model experiments, combined with multi-scale visualization and characterization tools (optical microscopy, AFM, X-ray and neutron reflectivity, etc.).
Thanks to the complementary nature of the experimental approaches, this thesis will provide a better understanding of the fundamental mechanisms of energy dissipation at the contact line, from the nanometric to the millimetric scale.
Understanding the signals emitted by moving liquids
Elasticity is one of the oldest physical properties of condensed matter. It is expressed by a constant of proportionality G between the applied stress (s) and the deformation (?): s = G.? (Hooke's law). The absence of resistance to shear deformation (G' = 0) indicates liquid-like behavior (Maxwell model). Long considered specific to solids, shear elasticity has recently been identified in liquids at the submillimeter scale [1].
The identification of liquid shear elasticity (non-zero G') is a promise of discoveries of new solid properties. Thus, we will explore the thermal response of liquids [2,3], exploit the capacity of conversion of mechanical energy into temperature variations and develop a new generation of micro-hydrodynamic tools.
At the nanoscopic scale, we will study the influence of a solid surface in contact with the liquid. It will be a question of studying by unique methods such as Inelastic Neutron Scattering and Synchrotron radiation, the dynamics of the solid-liquid interface using Very Large Research Facilities such as the ILL or the ESRF, as well as by microscopy (AFM). Finally, we will strengthen our collaborations with theoreticians, in particular with K. Trachenko of the Queen Mary Institute "Top 10 Physics World Breakthrough" and A. Zaccone of the University of Milan.
The PhD topic is related to wetting, macroscopic thermal effects, phonon dynamics and liquid transport.
Development and characterization of a reliable 13.5 nm EUV OAM carrying photon beamline
The Extreme UltraViolet (EUV) photon energy range (10-100 nm) is crucial for many applications spanning from fundamental physics (attophysics, femto-magnetism) to applied domains such as lithography and nanometer scale microscopy. However, there are no natural source of light in this energy domain on Earth because photons are strongly absorbed by matter, requiring thus vacuum environment. People instead have to rely on expensive large-scale sources such as synchrotrons, free electron lasers or plasmas from large lasers. High order laser harmonic generation (HHG), discovered 30 years ago and recognized by the Nobel Prize in Physics in 2023, is a promising alternative as a laboratory scale EUV source. Based on a strongly nonlinear interaction between an ultrashort intense laser and an atomic gas, it results in the emission of EUV pulses with femto to attosecond durations, very high coherence properties and relatively large fluxes. Despite intensive research that have provided a clear understanding of the phenomenon, it has up to know been mostly limited to laboratories. Breaching the gap towards applied industry requires increasing the reliability of the beamlines, subjects to large fluctuations due to the strong nonlinearity of the mechanism, and developing tools to measure and control their properties.
CEA/LIDYL and Imagine Optic have recently joined their expertise in a join laboratory to develop a stable EUV beamline dedicated to metrology and EUV sensors. The NanoLite laboratory, hosted at CEA/LIDYL, is based on a high repetition rate compact HHG beamline providing EUV photons around 40eV. Several EUV wavefront sensors have been successfully calibrated in the past few years. However, new needs have emerged recently, resulting in the need to upgrade the beamline.
The first objective of the PhD will be to install a new HHG geometry to the beamline to enhance its overall stability and efficiency and to increase the photon energy to 92eV, a golden target for lithography. He will then implement the generation of a EUV beam carrying orbital angular momentum and will upgrade Imagine Optic’s detector to characterize its OAM content. Finally, assisted by Imagine Optic engineers, he will develop a new functionality to their wavefront sensors in order to enable large beam characterization.
Advanced characterization of ferroelectric domains in hafnia-based thin films
Les mémoires ferroélectriques à accès aléatoire (FeRAM en anglais) à base d'oxyde d’hafnium et de zirconium (HZO) sont intrinsèquement ultra-faibles en consommation grâce au mécanisme de changement de tension, au potentiel de mise à l'échelle du HZO en dessous de 10 nm et à la compatibilité CMOS complète. De plus, elles présentent une faible latence nécessaire à une grande variété d'applications de logique et de mémoire. La compréhension des mécanismes sous-jacents et de la cinétique du ‘switching’ des domaines ferroélectriques est essentielle pour une conception intelligente des FeRAMs avec des performances optimales.
Cette thèse porte sur la caractérisation complète des domaines ferroélectriques (FE) dans des films HZO ultra-minces. L'étudiant utilisera plusieurs techniques d'imagerie de surface (microscopie à force piézoélectrique, PFM, microscopie électronique à basse énergie, LEEM, et microscopie électronique à photoémission de rayons X, PEEM) combinées à des méthodes avancées de caractérisation operando (détection résolue dans le temps couplée au rayonnement synchrotron). Ce projet marquera une avancée importante dans la recherche fondamentale des mécanismes de basculement de polarisation des couches FE ultra-minces à base d'hafnium, en élucidant les effets spécifiques de l'interface électrode métallique/couche FE dans le comportement électrostatique des condensateurs étudiés. Il permettra à terme une avancée significative dans le développement industriel des mémoires émergentes ferroélectriques, essentielles pour les applications d'intelligence artificielle (IA) à grande échelle.
Influence of ionization density in water on fluorescent solutes. Application to the detection of alpha radiation
The location and rapid identification, at a distance, of sources of alpha and beta particle emissions on surfaces or in wet cavities or solutions, in nuclear facilities undergoing decommissioning or to be cleaned up, is a real challenge.
The aim of the proposed PhD project is to develop a concept for the remote detection of fluorescence light from water radiolysis processes on molecules or nano-agents. Temporal characterization using fluorescence lifetime measurements will enable detection to be attributed to a type of radiation, depending on its linear energy transfer (LET). In the Bragg peak of alpha radiation, where the TEL is maximal, the ionization density due to this TEL influences the fluorescence lifetime. However, dose rate effects also need to be considered.
Molecules and nanoparticles that are candidates for forming fluorescent products and are sensitive to the ionization density and radicals produced in traces at very short times will be identified by guided bibliography work, then tested and compared by measurements. Spectral measurements (absorption and fluorescence) and fluorescence lifetimes of the corresponding fluorescent species will be carried out using the multi-channel (16-channel) TCSPC (Time Corelated Single Photon Counting) method. Ion beams or alpha particles from sealed sources will be used for proof-of-concept. Ion beams or alpha particles from sealed sources will be used for proof-of-concept in the CEA clean-up/dismantling program.
Covalent 2D organic nanostructures by optically controlled cross-linking of molecular self-assemblies
The self-assembly of molecules on crystalline substrates leads to non-covalent 2D structures with interesting properties for various fields such as optoelectronics and sensors. The stabilization of these 2D networks into covalent networks, while preserving these properties, is a major challenge and a topical issue. Various demonstrations show that crosslinking can be triggered by thermal processes. Photocrosslinking, on the other hand, is poorly described and the few examples that have been found involve ultra-high vacuum conditions.
Building on our previously developed know-how and the additional expertise of chemist collaborators, we therefore propose to carry out photocrosslinking of 2D networks at atmospheric pressure. We will use a model oligophenyl system that will be functionalized to allow photocrosslinking towards the production of a covalent 2D network. The resulting networks will be characterized through the correlation of optical spectroscopy and local probe microscopy to monitor and highlight photo-induced cross-linking processes at wavelength scale.
Design and implementation of cryogenic electronics for signal acquisition at cryogenic temperatures
The aim of our proposed thesis is to demonstrate that it is possible to integrate at cryogenic temperatures the entire instrumentation chain for reading and controlling quantum components at cryogenic temperatures
qubits. In other words, we are seeking to place in-situ, in the cryostat and as close as possible to the quantum components
(qubits), all the systems that are currently located outside. In addition, to achieve a major breakthrough
we are aiming for a fully programmable microwave chain (> 2 GHz). This is the subject of an ongoing thesis
financed by the Agence Innovation Défense (AID) and the Commissariat à l'Énergie Atomique (CEA) and a RAPID-type project application.
RAPID type project.
As part of this thesis, we will start at a few hundred MHz. Several main problems
are identified and need to be solved, including
- design and integration of chiplets in System-in-Packages (SiPs) compatible with cryogenic temperatures ;
- interfacing and integrating the Analog to Digital Converter (ADC), Digital to Analog
Converter (DAC) and processing components;
- manage high data rates (several tens of Gbit/s per qubit);
- maximum roundtrip latency of 200 ns;
- energy management (a few tens of mW budget per qubit);
- choice of cryogenic stages adapted to the different processing stages;
- choice of independent technologies
Innovative syntheses of perovzalates and rationalization of the formation mechanism by synchrotron methods
“Perovzalates” are a new family of hybrid perovskites based on oxalate, with around ten examples listed since 2019 (AILi3MII(C2O4)3, with A = K+, Rb+, Cs+, NH4+; M = Fe2+, Co2+, Ni2+). Just like conventional perovskites, they are potentially interesting for countless applications (catalysis, optics, solar etc.), presenting additional advantages linked to the oxalate anion, which allows the incorporation of larger cations than in other hybrid pervovskites, while preserving a crystal structure similar to oxide perovskites.
However, this class of new materials is still barely explored, and the syntheses far from being mastered: the few reports to date systematically produce mixtures of phases, and relate to single crystals taken from heterogeneous solutions. In this context, the major problem is to synthesize an extended class of pure perovzalates.
This thesis addresses this challenge by exploiting a property discovered in the laboratory: the crystallization of metal oxalates by co-precipitation in water passes through transient “mineral emulsions”, that is to say nano-droplets rich in reagents which separate from water. The originality of this thesis is to exploit the nanostructuring provided by these mineral emulsions, and to test in particular using nanotomographic techniques accessible in synchrotron if they make it possible to confine the cations until crystallization.
Optimization of the catalytic layer for CO2 electroreduction integrated into a PEM electrolyzer
This thesis focuses on optimizing the catalytic layer for CO2 electroreduction in an acidic medium, integrated into a proton-exchange membrane (PEM) electrolyzer. The aim is to upgrade CO2 by converting it into valuable chemicals, such as carbon monoxide. The acidic environment inherent to PEM electrolyzers helps limit carbonate formation, improving CO2 conversion efficiency. However, CO2 reduction in acidic media competes with the hydrogen evolution reaction, which reduces the selectivity of electroreduction products. This work seeks to develop noble-metal-free catalysts inspired by those used for oxygen reduction in fuel cells, improve the properties of carbon supports, and optimize the design of the catalytic layer, in particular thickness, porosity and hydrophobicity, to maximize CO2 conversion into target molecules. Finally, the active layer will be integrated into a 16 cm² PEM electrolyzer to assess overall performance and gain insights into the mechanisms involved through electrochemical characterization.