Exploration of the energy deposition dynamic on short time scale with laser-driven electron accelerator in the context of the Flash effect in radiotherapy
The objective of the thesis project is to analyze the physicochemical processes resulting from the extreme dose rates that can now be obtained in water with the ultra-short (fs) pulses of relativistic electrons produced by laser-plasma acceleration. Indeed, first measurements show that these processes are probably not equivalent to those obtained with longer pulses (µs) in the FLASH effect used in radiotherapy. To achieve this, we propose to analyze the dynamics of formation/recombination of the hydrated electron, an emblematic species of water radiolysis, to qualify and quantify the dose rate effect over increasingly shorter times. This will be done in three stages in support of the necessary and now accessible technological progress, to have a dose per pulse sufficient to directly detect the hydrated electron. First, with the existing UHI100 facility, using the scavenging of the hydrated electron by producing a stable species; then producing a less stable but detectable species in real time and increasing the repetition rate of the electron source. Finally, by using an innovative concept named a “hybrid target”, based on a plasma mirror as an electron injector coupled to a laser-plasma accelerator, delivering larger doses with a narrower energy spectrum, we will be able to develop pump-probe detection allowing access to the shortest times, and to the formation in clusters of ionization, of the hydrated electron and measuring its initial yield.
Thermoelectric energy conversion control via coordination chemistry of transition metal redox ions in ionic liquids
Thermoelectricity, a materials’ capability to convert heat in to electric energy has been known to exist in liquids for many decades. Unlike in solids, this conversion process liquids take several forms including the thermogalvanic reactions between the redox ions and the electrodes, the thermodiffusion of charged species and the temperature dependent formation of electrical double layer at the electrodes. The observed values of Seebeck coefficient (Se = - DV/DT, the ratio between the induced voltage (DV) and the applied temperature difference (DT)) are generally above 1 mV/K, an order of magnitude higher than those found in the solid (semiconductor) counterpart. The first working example of a liquid-based thermoelectric (TE) generator was reported in 1986 using Ferro/ferricyanide redox salts in water.
However, due to the low electrical conductivity of liquids, its conversion efficiency was very low, preventing their use in low-temperature waste-heat recovery applications. The outlook of liquid TE generators brightened in the last decade with the development of ionic liquids (ILs). ILs are molten salts that are liquid below 100 °C. Compared to classical liquids, they exhibit many favorable features such as high boiling points, low vapour pressure, high ionic conductivity and low thermal conductivity accompanied by higher Se values. More recently, an experimental study by IJCLab and SPEC revealed that the complexation of transition metal redox couples in ionic liquids can lead to enhancing their Se coefficient by more than a three-fold from -1.6 to -5.7 mV/K, one of the highest values reported in IL-based thermoelectric cells. A clear understanding and the precise control of the speciation of metal ions therefore is a gateway to the rational design of future thermoelectrochemical technology.
Based on these recent findings, we proposes to further study the coordination chemistry of transition metal redox ions in ILs and mixtures. A long-term goal associated to the present project is to demonstrate the application potential of liquid thermoelectrochemical cells based on affordable, abundant and environmentally safe materials for thermal energy harvesting as an energy efficiency tool.
Hyperpolarized Xenon NMR to probe the functionality of biological barriers
Optical pumping of xenon, giving rise to an intense NMR signal, is a specialty of the LSDRM team. Xenon, which is soluble in biological media, has a wide range of chemical shifts, which we use here to study the properties of cell barriers. Numerous pathologies stem from an alteration of these barriers.
In this thesis, we aim to develop a specific methodology using hyperpolarized xenon to study the functionality (integrity, permeability, selectivity) of biological barriers, using in vitro and in vivo spectroscopy and imaging. The thesis will be divided into two parts: in vitro, the aim will be to develop a device and NMR protocols for studying model cell assemblies; in vivo, studies on rodents will enable us to assess xenon's ability to reach organs more or less close to the lungs while maintaining its polarization, and to measure kinetics across barriers. This topic will enable major instrumental and methodological advances, as well as a deepening of our knowledge of selective transport processes at different biological barriers.
All solid-state lithium batteries based on Pyrochlore solid electrolyte
Due to the increasing energy demand, developing efficient storage systems, both stationary and portable, is crucial. Among these, lithium-ion batteries stand out as the most advanced, capable of being manufactured using liquid or solid electrolytes. All-solid-state batteries have a bright future thanks to their non-flammable electrolytes and their ability to use metallic lithium to increase energy density. Although research on these batteries is dynamic, their commercialization is not yet a reality. Indeed, two significant obstacles to their development remain: the low intrinsic ionic conductivity of solids and the difficulty of obtaining good solid/solid interfaces within the composite electrodes and the complete system.
This thesis explores the potential of pyrochlore oxyfluoride as a new class of superionic material for all-solid-state batteries, which are more stable in air and have higher ionic conductivity than current solid oxide electrolytes. The electrochemical properties of all-solid-state batteries will be carefully examined using a combination of in situ and operando techniques, such as XRD, Raman, ion beam/synchrotron analysis, solid-state NMR, X-ray tomography, etc.
Keywords :
Solid electrolyte, All-solid battery, Nuclear magnetic resonance, Electrochemistry, Pyrochlore Oxyfluoride, in situ/operando, Spectroscopy, Synchrotron
Synthesis and optical properties of quantum dots
Graphene as a constituent of graphite was close to us for almost 500 years. However, it is only in 2005 that A. Geim and K. Novoselov (Nobel Prize in 2010) reported for the first time the obtaining of a nanostructure composed by a single layer of carbon atom. The exceptional electronic properties of graphene make it a very promising material for applications in electronic and renewable energies.
For many applications, one should be able to modify and control precisely the electronic properties of graphene. In this context, we propose to synthesize chemically graphene nanoparticles and study their absorption and photoluminescence properties. We will focus on families of elongated nanoparticles, with the aim of studying how size can enable us to observe and control multiexcitonic processes in these materials. This project will be developed in collaboration with Physicists so the candidate will work in a multidisciplinary environment.
Plasma Mirrors: towards extreme intensity light sources and high-quality compact electron
Research objectives:
expand the capabilities of the WarpX Partice-In-Cell code for lower cost-to-convergence using mesh refinement.
Devise a high-charge high quality injector for laser-plasma accelerators.
Determine feasibility of the proposed scheme on a 100-TW-class laser system.
The researcher will benefit from a large variety of training available at CEA on HPC and computer programming as well as training at our industrial partners (ARM, Eviden) and Université Paris Saclay. The activities will be carried out in the framework of the Marie Sklodowska Curie Action Doctoral Network EPACE (European compact accelerators, their applications, and entrepreneurship)
Electrocatalyzed Reductive Couplings of Olefins and Carbonyls for the synthesis of sustainable molecules.
The LCMCE aims to develop a sustainable method for the reductive functionalization of carbonyl derivatives with olefins via electrochemistry. Traditional redox processes in organic synthesis often rely on thermochemical methods using stoichiometric oxidants or reductants and produce waste products. The electrification of these processes will improve their atom- and energy economy. The novelty of this project lies in the generation of "metal-hydride" catalytic species by cathodic reduction of organometallic complexes in the presence of protons rather than by adding chemical reductants, as described in the literature. Inserting an alkene function into the metal-hydride bond will lead to the formation of reactive intermediates for coupling with electrophilic carbonyls. The substrates for this project have been selected to provide rapid proof of concept and allow the study of more ambitious reactivities, including carboxylation reactions in which CO2 is the electrophile. Particular attention will be paid to the design of homogeneous catalysts and their synergy with electrochemical conditions to lead to active and selective species. The project will also focus on deciphering the mechanisms involved in these reactions.
Theoretical design of quasi-atomic systems in the band gap of semiconductors/insulators for quantum application
The rise of room-temperature applications like single photon emission of the negatively charged nitrogen-vacancy NV center in diamond has renewed the interest in the search for materials having a quasi-atomic system QAS analogous to that of NV, mainly characterized by the presence of well localized in-gap defect levels generate occupied by electrons and leading to high spin states. In this Ph.D. work, theoretical methods will be used to design new QASs analogous to the NV center as well as, in selected QAS, to predict charge states and explore the effect of the proximity of the surface on the thermodynamic stability and on the spin state structure. The objectives are to design new QASs; To predict charge states of selected QASs in the bulk of the host material; To study changes in the charge state brought by the proximity of the surface; To extend the Hubbard model used to compute the excited states and to account for the electron-lattice interaction in the calculation of the excited states; To study the effect of the presence of deep level states in the band gap on the transport of electrons and phonons. The methodology developed at LSI to design new QASs with high spin states will be exploited and new systems analogous to the NV center will be looked for. Density functional theory (DFT) and a Hubbard model developed at LSI will be the main tools of this PhD.
Porphyrin-based nanostructures
The aim of this project is the synthesis of new molecular structures based on porphyrins for the formation of 0D, 1D and 2D nanostructures. Porphyrins are an important class of molecules that are essential to life through oxygen transport or photosynthesis. Beyond, their importance in Nature, porphyrin derivatives exhibit outstanding optical, electronic, chemical and electrochemical properties that make them promising candidates for applications in catalysis, electrocatalysis, optoelectronics and medicine.
In this project, the porphyrins will be studied in collaboration with several groups of Physicists in order to fabricate 1D or 2D covalent networks on surface via the "bottom-up" approach and to study their electronic and optical properties.
Interfaces in super-concentrated aqueous electrolytes: machine learned simulations at the exascale era
Improving the performance of liquid electrolytes is one of today's major challenges in the field of batteries, with the aim of improving efficiency, safety and economy. Recent advances include superconcentrated media such as WIS (“Water-In-Salts”) solutions. Their properties depend crucially on the chemistry and physics of the interfaces between water and ions (Li+ for lithium-ion batteries, but also Na+, K+, Zn2+), both at a distance and close to the electrodes.
Atomic-scale modeling of these superconcentrated liquid electrolytes requires the study of nanoscopic structures and phenomena taking place over long timescales. One relevant solution is to build potentials by machine learning, based on ab initio molecular dynamics (AIMD) trajectories. This method combines an accurate description of the interactions between ions and water molecules, including the breaking and forming of chemical bonds, with fast calculation speed. In particular, the DeePMD kit has recently been successfully ported to GPU architectures, paving the way for calculations on exascale supercomputers (whose power exceeds 10^18 floating-point operations per second).
This theoretical study will be supported by an experimental counterpart, thanks to direct collaboration with a team in the unit specializing in electrochemistry.