PhD subjects

One of the most promising architectures in large-scale quantum information processing is the one based on superconducting electrodynamic (bosonic) qubits. They rely on an elementary device: the Josephson tunnel junction, a tunnel barrier between two superconducting leads, which exhibit nonlinear and non-dissipative behavior. Josephson tunnel junctions are only an example of superconducting weak links, among which are also atomic contacts and semiconducting nanowire weak links. In these other examples, localized, fermionic states, known as Andreev levels, can be addressed. We recently performed their spectroscopy [1-4] and quantum manipulation [5,6].

Here we propose to design, fabricate and measure new hybrid qubits that combine bosonic and fermionic degrees of freedom in the quest to realize more robust quantum states.

We are looking for a strongly motivated student having a good understanding of quantum physics. She/he will be integrated in an active research group on quantum electronics and get acquainted with advanced concepts of quantum mechanics and superconductivity. He/she will also learn several experimental techniques: low temperatures, low-noise and microwave measurements, and nanofabrication.



[1] L. Bretheau, Ç. Ö. Girit , H. Pothier , D. Esteve , and C. Urbina, “Exciting Andreev pairs in a superconducting atomic contact” Nature 499, 312 (2013). arXiv:1305.4091
[2] L. Tosi, C. Metzger, M. F. Goffman, C. Urbina, H. Pothier, Sunghun Park, A. Levy Yeyati, J. Nygård, P. Krogstrup, “Spin-Orbit Splitting of Andreev States Revealed by Microwave Spectroscopy”, Phys. Rev. X 9, 011010 (2019).
[3] C. Metzger, Sunghun Park, L. Tosi, C. Janvier, A. A. Reynoso, M. F. Goffman, C. Urbina, A. Levy Yeyati, H. Pothier, “Circuit-QED with phase-biased Josephson weak links”, Phys. Rev. Research 3, 013036 (2021).
[4] F. J. Matute Cañadas, C. Metzger, Sunghun Park, L. Tosi, P. Krogstrup, J. Nygård, M. F. Goffman, C. Urbina, H. Pothier, A. Levy Yeyati, “Signatures of interactions in the Andreev spectrum of nanowire Josephson junctions”, arXiv:2112.05625
[5] C. Janvier et al., “Coherent manipulation of Andreev states in superconducting atomic contacts” Science 349, 1199 (2015), arXiv:1509.03961
[6] C. Meztger, “Spin charge effects in Andreev Bound States”, PhD thesis (2022)

Alkanes are essential molecules in the energy sector (fuels), as well as in specialty chemicals (cosmetics, adhesives, etc.) and fine chemicals. Today, they are mainly derived from non-renewable fossil resources, and their use contributes to climate change through the production of carbon dioxide. To achieve carbon neutrality, producing alkanes from renewable carbon sources such as biomass would appear to be an attractive alternative. In biomass, fatty esters of the RCO2R type have long alkyl chains, but the presence of oxygen atoms means they are not a direct substitute for petroleum-based alkanes.

The aim of this thesis is to develop homogeneous catalytic systems for the photocatalytic deoxygenation of esters into the corresponding alkanes, by simple extrusion of a CO2 molecule. The energy required for the reduction reaction will be provided by light. Throughout this thesis project, the focus will be on developing catalytic systems and understanding reaction mechanisms through experimental studies (kinetics, NMR studies, observation of reaction intermediates, etc.) combined with theoretical chemistry (DFT calculations).

The objective of this Phd is to develop an experimental device to perform in situ and real time elemental analysis of nanoparticles during their synthesis (by laser pyrolysis or flame spray pyrolysis). Laser-Induced Breakdown Spectroscopy (LIBS) will be used to identify the different elements present and to determine their stoichiometry.

Preliminary experiments conducted at LEDNA have shown the feasibility of such a project and in particular the acquisition of a LIBS spectrum of a single nanoparticle. Nevertheless, the experimental device must be developed and improved in order to obtain a better signal to noise ratio, to decrease the detection limit, to take into account the different effects on the spectrum (effect of nanoparticle size, complex composition or structure), to automatically identify and quantify the elements present.

In parallel, other information can be sought (via other optical techniques) such as the density of nanoparticles, the size or shape distribution.

Understanding the non-specific or specific interactions between biomolecules and nanomaterials is key to the development of safe nanomedicines and nanoparticles. Indeed, adsorption of biomolecules is the first process occurring after the introduction of biomaterials into the human body, which controls their biological response. In this thesis, we will simulate the interface between nanosystems and biomolecules on a scale of a hundred nanometers, using the new exascale computing resources available at the CEA from 2025 (Jules Verne machine installed at the CCRT).

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 their solubilty in water in order to study potential applications in biology. This project will be developed in collaboration with Physicists so the candidate will work in a multidisciplinary environment.

The recycling and chemical recovery of plastics are necessary and crucialsteps to accelerate the transition to a circular economy and reduce the pollution associated with these materials.

The aim of this project is to develop catalytic systems for depolymerizing oxygenated and nitrogenous plastics into their monomers or derivatives (alcohols, amines, halides or even hydrocarbons). These methods, which enable the carbonaceous matter in polymers to be recovered under mild conditions in the form of chemical products useful to the chemical industry, are still underdeveloped and will, in the future, be virtuous processing routes for recycling certain plastics.

The aim of this doctoral project is to develop and use new metal molecular complexes (aluminium, zirconium, rare earths, etc.) and organic catalysts (boron-based), which

- are simple, inexpensive, recyclable and more selective than current catalysts (composed of iridium, ruthenium and boron), to depolymerize different types of plastics (polyesters, polycarbonates, polyurethanes and polyamides),
- allow, in the case of reductive catalysis, the use of hydrosilanes and hydroboranes, as well as the use of new reducing agents acting by transfer hydrogenation routes.

Finally, we will also consider the use of organic anhydrides to transform plastics into reactive organic compounds useful in organic chemistry.

Glycomics involves identifying oligosaccharides (OS) present in a biological fluid as a source of biomarkers for diagnosing various pathologies (cancers, Alzheimers disease, etc.). To study these OS, sample preparation involves 2 key phases, enzymatic cleavage (breaking the bond between OS and proteins) followed by purification and extraction (separation of OS and proteins). However, the materials currently used in the protocols impose numerous manual and time-consuming steps, incompatible with high-throughput analysis.

In this context, the LEDNA laboratory specialized in materials science has recently developed a sol-gel process for the manufacture of Hierarchical Porosity Monoliths (HPMs) in miniaturized devices. These materials have provided a proof of concept demonstrating their value for the second stage of glycomic analysis, i.e. the purification and extraction of oligosaccharides. The LEDNA is now looking to improve the first step, corresponding to enzymatic cleavage, which has become a limiting factor in the glycomics analysis process. Functionalization of porous materials, in particular HPMs, with enzyme would enable simple sample preparation in just a few hours with a single step.

The aim of this thesis is therefore to show that the use of porous materials with a dual function - catalytic and filtration - applied to the preparation of samples for glycomic analysis is a relevant means of simplifying and accelerating glycomic analysis, as well as employing them in hospital-related studies to identify new biomarkers of pathologies.

The research project will involve developing a device incorporating porous materials with catalytic and filtration functions. Several aspects will be addressed, ranging from the synthesis and shaping of these materials to characterization of their textural and physico-chemical properties. Particular emphasis will be placed on enzyme immobilization. The most promising prototype(s) will be evaluated in a glycomic analysis protocol, verifying the oligosaccharide profiles obtained from human biofluids (plasma, milk). Physico-chemical characterization will involve a variety of techniques (SEM, TEM, etc.), as well as characterization of porosity parameters (nitrogen adsorption, Hg porosimeter). Oligosaccharides will be analyzed by high-resolution mass spectrometry (mainly MALDI-TOF).

For this multidisciplinary thesis project, we are looking for a student chemist or physical chemist, interested in materials chemistry and motivated by the applications of fundamental research in the field of new technologies for health. The thesis will be carried out in two laboratories, LEDNA for the materials part and LI-MS for the use of materials in glycomics analysis. The research activity will be carried out at the Saclay research center (91).

In situ solid-state Nuclear Magnetic Resonance (ssNMR) is a valuable characterization tool to decipher the electrochemical phenomena during battery operation. However, the broad signal lineshapes acquired from the sample static condition often retrain from the full potential of ssNMR characterization. Ex situ ssNMR experiments, using Magic-Angle sample Spinning (MAS), are often necessary to interpret the in situ data. As in any ex situ characterizations, the analyses do not always represent the real electrochemistry because of unwanted artifacts from the ex situ sample preparation, i.e., cell dismantling and electrode separations. Consequently, in situ ssNMR applications have been limited. The PhD student will address this limitation by developing a spinning battery cell for acquiring high-resolution ssNMR data under MAS for in situ study, including a new method of spatially-resolved ssNMR spectroscopy. Combining in situ, MAS, and localized spectroscopy would lead to an unprecedented in situ ssNMR tool for deciphering fundamental insights into battery chemistry, which the student will emphasize by studying phenomena such as interfaces and dendrite formation in operating Li-ion batteries.

The major public health problem of sepsis requires breakthrough technologies for ultra-fast diagnosis. Dense, fluidized granular beds are ideal systems for liquid-solid or gas-solid exchange processes. They are widely used in industry thanks to their high surface-to-volume ratio. Over the past decade, microfluidics and lab-on-a-chip have enabled numerous advances, particularly in biological sample preparation. We propose to develop a versatile microfluidic platform that will enable the creation of such dense, fluidized beds. We will first work on the incorporation of membranes into microchannels, drawing on the patented know-how developed in the laboratory. We will then study and characterize the granular beds, and finally test them for the detection of bacteria in biological samples. This work will be carried out in collaboration with our physicists (LEDNA) and biologist (LERI) partners at CEA Saclay.

Even-denominator states of the fractional quantum Hall effect (e.g. ??=5/2) are expected to host excitations that have non-abelian anyonic statistics, making them promising candidates for the realization of topological quantum computing [1]. While the demonstration of these non-abelian statistics has long been an extremely challenging endeavor, recent experiments in GaAs semiconductor heterostructures have shown that the edge thermal conductance of the ??=??/?? state is quantized in half-integer values of the thermal conductance quantum [2,3]. This half-integer quantization is known to be an universal signature of non-abelian statistics, including of Majorana fermions [4]. However, many of the suspected candidates for the ground state of ??=5/2 have complex edge structures exhibiting counterpropagating neutral modes, which can modify the edge thermal conductance and give them non-integer values similar to that of a non-abelian edge. A very recent experiment [3] has circumvented the issue by finding a way to separate the contributions of the different channels at the edge, confirming the existence of a non-abelian channel with half-integer quantized electrical and thermal conductance. The next obvious interrogation is whether this result is truly universal: does it hold for different material, and different even-denominator states?

In this project, we propose to address these questions by performing heat transport measurements in fractional quantum Hall states in bilayer graphene. Bernal-stacked bilayer graphene (BLG) has recently shown to host a large variety of robust even-denominator fractional quantum Hall states [5-8], both hole- and electron-type. This provides an excellent test-bed on which to probe the thermal conductance, as these fractions are expected to be described by different (possibly non-abelian) ground states; furthermore, the ability to apply electric displacement fields allows a further degree of control over the even-denominator states, which can be investigated in terms of heat transport.

This experimental project relies on ultra-low temperature, high magnetic field thermal transport [9] based on high sensitivity-sensitivity electrical measurements. We are looking for highly motivated candidates whoe are interested in all aspects of the project, both experimental (sample fabrication, low noise measurements, cryogenics) and theoretical.

[1] Nayak, et al., RMP 80, 1083 (2008) [2] Banerjee, et al., Nature 559, 205 (2018)
[3] Dutta, et al., Science 377, 1198 (2022) [4] Kasahara, et al., Nature 559, 227 (2018)
[5] Ki, et al., Nano Letters 14, 2135 (2014) [6] Li, et al., Science 358, 648 (2017)
[7] Zibrov, et al., Nature 549, 360 (2017) [8] Huang, et al., PRX 12, 031019 (2022)
[9] Le Breton, …, Parmentier, PRL 129, 116803 (2022)

Our ability to manufacture metal oxide nanoparticles (NPs) with well-defined composition, morphology and properties is a key to accessing new materials that can have a revolutionary technological impact, for example for photocatalysis or storage of energy. Among the different nanopowders production technologies, Flame Spray Pyrolysis (FSP) constitutes a promising option for the industrial synthesis of NPs. This synthesis route is based on the rapid evaporation of a solution - solvent plus precursors - atomized in the form of droplets in a pilot flame to obtain nanoparticles. Unfortunately, mastery of the FSP process is currently limited due to too much variability in operating conditions to explore for the multitude of target nanoparticles. In this context, the objective of this thesis is to develop the experimental and numerical framework required by the future deployment of artificial intelligence for the control of FSP systems. To do this, the different phenomena taking place in the synthesis flames during the formation of the nanoparticles will be simulated, in particular by means of fluid dynamics calculations. Ultimately, the creation of a digital twin of the process is expected, which will provide a predictive approach for the choice of the synthesis parameters to be used to arrive at the desired material. This will drastically reduce the number of experiments to be carried out and in consequence the time to develop new grades of materials

To meet the increasing energy demand and diversify energy resources, fuel cells emerge as a promising solution. This Ph.D work aims to contribute to the development of Proton Exchange Membrane Fuel Cells (PEMFCs), with a specific focus on bipolar plates (BPs) which ensure gas distribution and current collection. The first objectives are to design and manufacture stainless steel BPs using 3D printing (SLM - Selective Laser Melting) and to develop organic and inorganic anticorrosion coatings. Multiple channel architectures will be designed and characterized, including in-situ assessments with membrane-electrode assemblies (MEAs). Coatings will also be characterized, particularly in terms of their corrosion resistance through polarization methods. In the second phase, the aim is to integrate the optimized BPs with MEAs and thoroughly study the performance of PEMFCs using electrochemical techniques to gain fundamental insights into the mechanisms that limit PEMFCs performance.

Among nanoscale semiconductors, nanodiamonds (ND) have not been really considered yet for photoelectrocatalytic reactions in the energy-related field. This originates from the confusion with ideal monocrystalline diamond featuring a wide bandgap (5.5 eV) that requires a deep UV illumination to initiate photoreactivity. At the nanoscale, ND enclose native defects (sp2 carbon, chemical impurities such as nitrogen) that can create energetic states in the diamond’s bandgap decreasing the light energy needed to initiate the charge separation. In addition, the diamond electronic structure can be strongly modified (over several eV) playing on its surface terminations (oxidized, hydrogenated, aminated) which can open the door to optimized band alignments with the species to be reduced or oxidized. Combining these assets, ND becomes competitive with other semiconductors toward photoreactions. The aim of this PhD is to investigate the ability of nanodiamonds in reducing CO2 through photoelectrocatalysis. To achieve this goal, electrodes will be made from nanodiamonds with different surface chemistries (oxidized, hydrogenated and aminated), either using a conventional ink-type approach or a more innovative one that results in a porous material including nanodiamonds and a PVD-deposited matrix. Then, the (photo)electrocatalytic performances under visible illumination of these nanodiamond-based electrodes toward CO2 reduction will be investigated in terms of production rate and selectivity, in presence or not of a transition metal macrocyclic molecular co-catalyst.

Catalysis is today at the core of chemical industrial applications. For example, the conversion of nitrile to amide, which is relevant in pharmaceuticals, agrochemicals, synthetic chemistry and polymer chemistry, by hydration requires an efficient catalyst due to its slow kinetics. For environmental reasons, it is crucial to discover catalysts without transition metals, neither toxic nor corrosive, and cheap. One example of such catalyst is hydroxide choline.

During this thesis, the student will learn how to perform ab initio molecular dynamics simulations coupled with a method which can reconstruct the free-energy landscape of the hydration reaction for different aromatic nitriles in different in silico experimental conditions. He or she will also have to perform quantum chemistry calculations at a level that can describe all the required intra and intermolecular interactions. This theoretical approach has already been successfully used within our team to describe other chemical reactions in aqueous solution and will be applied to the innovative field of green chemistry.

Ultra-short, high-energy (up to few GeVs) electron beams can be accelerated over just a few centimeters by making an ultra-intense laser interact with a gas-jet, with a technique called “Laser Wakefield Acceleration” (LWFA). Thanks to their small size and the ultra-short duration of the accelerated electron beams, these devices are potentially interesting for a variety of scientific and technological applications. However, LWFA accelerators do not usually provide enough charge for most of the envisaged applications, in particular if a high beam quality and a high electron energy are also required.

The first goal of this thesis is to understand the basic physics of a novel LWFA injector concept recently conceived in our group. This injector consists of a solid target coupled with a gas-jet, and should be able to accelerate a substantially higher amount of charge with respect to conventional strategies, while preserving at the same time the quality of the beam. Large scale numerical simulation campaigns and machine learning techniques will be used to optimize the properties of the accelerated electrons. The interaction of these electron beams with various samples will be simulated with Monte Carlo code to assess their potential for applications such as Muon Tomography and radiobiology/radiotherapy. The proposed activity is essentially numerical, but with the possibility to be involved in the experimental activities of the team.

The PhD student will have the opportunity to be part of a dynamic team with strong national and international collaborations. They will also acquire the necessary skills to participate in laser-plasma interaction experiments in international facilities. Finally, they will acquire the required skills to contribute to the development of a complex software written in modern C++ and designed to run efficiently on the most powerful supercomputers in the world: the state-of-the-art Particle-In-Cell code WarpX (prix Gordon Bell en 2022). The development activity will be carried out in collaboration with the team led by Dr. J.-L. Vay at LBNL (US), where the candidate could have the opportunity to spend a few months during the thesis.

Ultra-short, high-energy (up to few GeVs) electron beams can be accelerated over just a few centimeters by making an ultra-intense laser interact with a gas-jet, with a technique called “Laser Wakefield Acceleration” (LWFA). Thanks to their small size and the ultra-short duration of the accelerated electron beams, these devices are potentially interesting for a variety of scientific and technological applications. However, LWFA accelerators do not usually provide enough charge for most of the envisaged applications, in particular if a high beam quality and a high electron energy are also required. The goal of this thesis is to implement a novel LWFA injector concept in several state-of-the-art laser facilities, in France and abroad. This injector concept, recently conceived in our group, consists in a solid target coupled with a gas-jet, and should be able to accelerate a substantially higher amount of charge with respect to conventional strategies, while preserving at the same time the quality of the beam. The proposed activity is mainly experimental, but with the possibility to be involved in the large-scale numerical simulation activities that are needed to design an experiment and to interpret its results. The PhD student will have the opportunity to be part of a dynamic team with strong national and international collaborations. They will also acquire the necessary skills to participate in laser-plasma interaction experiments in international facilities. Finally, they’ll have the possibility to be involved in the numerical activities of the group, carried out on the most powerful supercomputers in the world with a state-of-the-art Particle-In-Cell code (WarpX, Gordon Bell prize in 2022).

The central topic of the thesis is a recently proposed form of matter called altermagnetism. In common with simple antiferromagnets these are magnetic materials supporting long-range magnetic order with no net moment. In simple antiferromagnets the up and down spin electronic bands are degenerate. But in altermagnets they are not. One way of thinking about these materials is that they are nonmagnetic in real space but magnetic in momentum space thus combining features of ferromagnets and antiferromagnets. These materials have generated a great deal of interest in the spintronics community. Roughly speaking this community has, for a long time, been interested in antiferromagnets that support spin currents because antiferromagnets are insensitive to stray fields and can support faster device switching than in typical ferromagnets. Altermagnets have the potential to realize the dreams of antiferromagnetic spintronics. At the same time, altermagnets are of fundamental interest in condensed matter physics. It turns out that altermagnetism is grounded in a peculiar type of symmetry breaking described by the theory of spin groups.

The goal of this thesis project is to extend our understanding of spin groups in condensed matter especially in the direction of altermagnetism and topological materials.

Summary :
The student will develop attosecond spectroscopy techniques making use of the new high reprate Ytterbium laser sources. The ultrafast photoemission dynamics will be studied to reveal in real time the processes of electron scattering/rearrangement as well as electron-ion quantum entanglement, using the charged-particle coincidence techniques.

Detailed summary :
In recent years, there has been spectacular progress in the generation of attosecond (1 as=10-18 s) pulses, rewarded by the 2023 Nobel Prize [1]. These ultrashort pulses are generated from the strong nonlinear interaction of short intense laser pulses with gas jets [2]. A new laser technology based on Ytterbium is emerging, with stability 5 times higher and reprate 10 times higher than the current Titanium:Sapphire technology. These new capabilities represent a revolution for the field.
This opens new prospects for the exploration of matter at the electron intrinsic timescale. Attosecond spectroscopy thus allows studying in real time the quantum process of photoemission, shooting the 3D movie of electronic wavepacket ejection [3,4], and studying quantum decoherence resulting from, e.g., electron-ion entanglement [5].
The first objective of the thesis work is to develop on the ATTOLab laser platform the attosecond spectroscopies using the new Ytterbium laser sources. The second objective is to take advantage of charged particle coincidence techniques, enabled by the high reprate, to study the dynamics of photoemission and quantum entanglement with unprecedented precision.
The student will be trained in ultrafast optics, atomic and molecular physics, quantum optics, and will acquire a broad mastery of XUV and charged-particle spectroscopy techniques.

References :
[1] https://www.nobelprize.org/prizes/physics/2023/summary/
[2] Y. Mairesse, et al., Science 302, 1540 (2003)
[3] V. Gruson, et al., Science 354, 734 (2016)
[4] A. Autuori, et al., Science Advances 8, eabl7594 (2022)
[5] C. Bourassin-Bouchet, et al., Phys. Rev. X 10, 031048 (2020)

Attosecond science focuses on the study of dynamics in matter at ultimate timescales, using light pulses of attosecond (10-18 s) duration. Our laboratory has pioneered the development and use of these pulses to investigate the ultrafast response of matter. In particular, we operate several platforms dedicated to attosecond spectroscopy of solids.

During this PhD project, we will develop original attosecond experiments aimed at elucidating the dynamics of one of the most important and intriguing degree of freedom of solids: the spins of its electrons. This quantity is responsible for the magnetic properties of materials, with applications ranging from data storage devices to spintronic components. Typically, existing devices use electric currents to convey and manipulate information.
Here, we aim to answer one apparently simple question: can we use a laser field, instead of a current, to control the electronic spins of a solid? While this would have the concrete potential of orders-of-magnitude faster operation, answering this question first requires fascinating fundamental investigations. Indeed, the response of magnetic materials at optical frequencies – below 10 fs – is almost completely unknown to this day. We propose to address this problem by performing experiments that combine spin sensitivity and attosecond resolution for the first time. By carefully shaping attosecond pulses and using state-of-the art detection schemes, we aim to establish a technique called attosecond magnetic dichroism, which will reveal the spin response of materials on the timescale of the electric field of light. We will first focus on simple tridimensional ferromagnetic and antiferromagnetic systems, before evolving towards their bi-dimensional counterparts. Indeed, so-called 2D materials are expected to provide enhanced, or even fundamentally novel light-spin interactions. By understanding how light interacts with electronic spins in 2D, we will provide key elements towards the integration of future low-dimensionality spintronic components.

The student will acquire practical knowledge about experimental ultrafast optics and of time resolved spectroscopy of condensed matter, especially magnetic materials. He/she will become an expert in attosecond physics and technology, as well as acquire valuable skills in complex data acquisition and analysis.

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.

The last few decades of condensed matter research have seen the emergence of a rich new physics, based on the notion of spin liquids. Interest in these new states of matter stems from the fact that they exhibit large-scale quantum entanglement, a property that is fundamental to quantum computation. By directly exploiting this notion of entanglement, a quantum computer would enable revolutionary approaches to certain classes of problems, compared with conventional computers.

The study of spin liquids is therefore a key technological issue, and the aim of this thesis project is to contribute to this fundamental research effort.

In view of the challenges posed by global warming, some fundamental research is focusing on optimizing the properties of materials for gas capture (e.g. CO2), filtration, desalination or the conversion of water to H2 by photocatalysis. Two-dimensional materials (graphene, MoS2, hBN, etc.) nanostructured by ion irradiation have recently shown unique and original properties to improve the efficiency of these processes. The introduction of surface modifications to these materials can be used to tailor their properties to specific requirements. Irradiation by fast heavy ions, such as those produced on the GANIL facility, or by low-energy ions produced on CIMAPs PELIICAEN device, induces surface modifications on the nanometric scale.

In this thesis, we propose to gain a better understanding of the processes involved in ion-beam structuration and the modification of 2D material properties as a function of the influence of different irradiation parameters on the local radiation-induced modifications.

The combined demands of increasing energy production and the need to reduce fossil fuels to limit global warming have paved the way for an urgent need for clean energy harvesting technologies. One interesting solution is to use solar energy to produce fuels. Thus, low-cost materials such as semiconductors have been intensively studied for photocatalytic reactions. Among them, 1D nanostructures hold promise due to their interesting properties (high specific and accessible surfaces, confined environments, better charge separation). Imogolite, a natural hollow nanotube clay belongs to this category. Although it is not directly photoactive in the visible light range (high band gap), it exhibits a permanent wall polarization due to its intrinsic curvature. This property makes it a potentially useful co-photocatalyst for charge separation. Moreover, this nanotube belongs to a family sharing the same local structure with different curved morphologies (nanosphere and nanotile). In addition, several modifications of these materials are possible (wall doping with metals, coupling with metal nanoparticles, functionalization of the internal cavity) allowing tuning band gap. The proof of concept (i.e., photocatalytic nanoreactor) was only obtained for the nanotube form.

This phD project aims to study the whole family (nanotube, nanosphere, and nanotile, with various functionalizations) as nanoreactors for reduction reactions of protons and CO2 triggered under irradiation.

Recent studies with electron and proton beams have shown that irradiation at dose rates above 40 Gy/s can be as effective in inhibiting tumor growth as irradiation at the conventional dose currently used (typically 1 Gy/min) but much less toxic to healthy tissues. This phenomenon is known as the “FLASH effect”. This effect is considered one of the most important discoveries in the recent history of radiobiology due to its potential to improve the therapeutic window between tumor control and normal tissue toxicity. Recent studies show that the biological mechanisms of the FLASH effect are linked to differential tissue oxygenation. However, the exact mechanisms of the cellular biological effects of FLASH irradiations are not completely clear and some are even contradictory.

The objective of this project is a molecular characterization of the FLASH effect on a model system perfectly controlled in vitro. FLASH irradiations of cancer cells and healthy cells will be compared to conventional dose rate irradiations using electrons and carbon ions in the two associated laboratories. The differential effect will be related to the oxygenation condition of the cells, REDOX/mitochondrial metabolism and general changes in cellular metabolism.

Thermoelectric (TE) materials that are capable of converting heat into electricity have been considered as one possible solution to recover the low-grade waste-heat (from industrial waste-stream, motor engines, household electronic appliances or body-heat).

At SPHYNX, we explore thermoelectric effects in an entirely different class of materials, namely, complex fluids containing electrically charged nanoparticles that serve as both heat and electricity carriers. Unlike in solid materials, there are several inter-dependent TE effects taking place in liquids, resulting in Se values that are generally an order of magnitude larger that the semiconductor counterparts. Furthermore, these fluids are composed of Earth-abundant raw materials, making them attractive for future TE-materials that are low-cost and environmentally friendly. While the precise origins of high Seebeck coefficients in these fluids are still debated, our recent results indicate the decisive role played by the physico-chemical nature of particle-liquid interface.

The goal of the PhD project is two-fold :
- First, we will investigate the underlying laws of thermodynamic mechanisms behind the thermoelectric potential and power generation and other associated phenomena in nanofluids. More specifically, we are interested in how the particles Eastman entropy of transfer is produced under the influence of thermal, electrical and concentration gradients. The results will be compared to their thermos-diffusive and optical abosrption properties to be obtained through research collaborations.
- Second, the project aims to test the promising nanofluids in the proof-of-concept hybrid solar-collector devices currently developed within the group to demonstrate the co-generation capability of heat and electricity. The hybrid device optimization is also within the projects scope

The proposed research project is primarily experimental, involving thermos-electrical, thermal and electrochemical measurements; implementation of automated data acquisition system and analysis of the resulting data obtained. The notions of thermodynamics, fluid physics and engineering (device) physics, as well as hands-on knowledge of experimental device manipulation are needed. Basic knowledge of optics and electrochemistry is a plus. For motivated students, numerical simulations using commercial CFD software, as well as the optical absorption measurements at the partner lab (LNO/CNR, Florence, Italy) can also be envisaged.

The aim of this thesis is to carry out the first experimental measurement of the energy dissipated in the boundary layers during turbulent convection in the Rayleigh-Bénard configuration. Indeed, some theories assert that this quantity controls the heat flux transported from the hot wall to the cold wall, while the efficiency of turbulent transport in convection is the subject of debate. Yet the properties of turbulent transport are essential to understanding the dynamics of climate and many astrophysical objects.

To estimate the energy dissipated, we need to be able to measure the norm of the velocity gradient. This quantity is difficult to access with conventional anemometry techniques, which measure velocity fields with limited resolution. These gradients are also expensive to obtain numerically over long time scales. But we have developed a technique for directly measuring the norm of velocity gradients using Multiple Scattering Spectroscopy. This will enable us to measure dissipative structures and the rate of energy dissipation in boundary layers.

Materials in the glassy state are of great practical interest and can be found in many applications: silica glass as a construction or transport material, plastics which are generally at least partially glassy, or glassy metal alloys for advanced applications. However, the physical properties of these materials (e.g. the strength of a telephone screen) depend on the heat treatment they receive during their formation, and more specifically on the rate of cooling from the liquid state. While industrial glass manufacturing processes are obviously well mastered, the non-equilibrium thermodynamic nature of these systems makes it particularly difficult to investigate the physical mechanisms at work theoretically and numerically. This calls for an experimental approach aimed at probing these fundamental mechanisms.

The aim of this PhD thesis is to study experimentally the very non-equilibrium response of polar liquids, using a device recently developed in the laboratory which enables us to apply a very rapid temperature change to a liquid and follow its re-equilibration dynamics. Measurements of linear response should reveal more about the physical mechanisms governing equilibration, while non-linear measurements will provide information about the cooperative nature of structural rearrangements.

Scientific and technological development of the Terahertz (THz) frequency range, a domain of the electromagnetic spectrum that is located in between microwaves and infrared photonics, is timely and subjected to an intense research activity recently. We have recently developed TeraHertz cavities using a plasmonic mechanism based on the surface plasmons of a doped semiconductor. We have demonstrated the remarkable property of these resonators of being able to confine TeraHertz photons in record volumes of the order of 10-7 times smaller than the diffraction limit. This plasmonic mechanism also allows the functionalization and tunability of the cavities thanks to external parameters such as the electric or magnetic field or the temperature, among others. The aim of this thesis will be to develop THz plasmonic cavities and in particular to study their nonlinear behaviour when subjected to intense THz pulses. The aim will be to TeraHertz frequency conversion based on this nonlinearity.

N-doped oxides and/or oxinitrides constitute a booming class of compounds with a broad spectrum of useable properties and in particular for novel technologies of carbon-free energy production and multifunctional sensors. In this research field the search for new materials is particularly desirable because of unsatisfactory properties of current materials. The insertion of nitrogen in the crystal lattice of an oxide semiconductor allows in principle to modulate its electronic structure and transport properties enabling new functionalities. The production of corresponding single crystalline thin films is highly challenging. In this thesis work, single crystalline oxynitride heterostructures will be grown by atomic plasma-assisted molecular beam epitaxy. The heterostructure will combine two N doped layers: a N doped BaTiO3 will provide ferroelectricity and a heavily doped ferrimagnetic ferrite whose magnetic properties can be modulated using N doping to obtain new artificial multiferroic materials better suited to applications. The resulting structures will be investigated with respect to their ferroelectric and magnetic characteristics as well as their magnetoelectric coupling, as a function of the N doping. These observations will be correlated with a detailed understanding of crystalline and electronic structures.

The student will acquire skills in ultra-high vacuum techniques, molecular beam epitaxy, ferroelectric and magnetic characterizations as well as in state-of-the-art synchrotron radiation techniques.

Raw earth materials, which have found multiple uses for millennia, now offer considerable potential for helping to adapt to the changing climate, thanks to their natural ability to regulate heat and water, as well as their low-CO2 production and shaping. However, scientific advances are still needed to get a more precise understanding of these materials, up to the nanometric scale.

This thesis focuses on the link between the mechanical properties of raw earth soil materials and their nanostructure, emphasizing the roles of confined water, ions and organic substances. Two approaches, based on the expertise on nanoporous media developed at CEA, Saclay and Marcoule, will be followed: the analysis of old materials using spectroscopic and radiation scattering methods, and the development of a screening protocol to identify physicochemical parameters important for durability. This research, which ultimately aims to optimize the formulation of raw earth materials, will be carried out in collaboration with architects specialists in the field.

Our recent results show that nanodiamond can also act as a photocatalyst, enabling the production of hydrogen under solar illumination [1]. Despite its wide band gap, its band structure is adaptable according to its nature and surface chemistry [2]. Moreover, the controlled incorporation of dopants or sp2 carbon leads to the generation of additional bandgap states that enhance the absorption of visible light, as shown in a recent study involving our group [3]. The photocatalytic performance of nanodiamonds is therefore highly dependent on their size, shape and concentration of chemical impurities. It is therefore essential to develop a tailor-made nanodiamond synthesis method, in which these different parameters can be finely controlled, in order to provide a supply of controlled nanodiamonds, which is currently lacking.

The aim of this PhD is to develop a bottom-up approach to nanodiamond synthesis using a sacrificial template (silica beads or fibers) to which diamond seeds 10 nm are attached by electrostatic interaction. The growth of diamond nanoparticles from these seeds will be achieved by exposing these objects to a microwave-enhanced chemical vapor deposition (MPCVD) growth plasma, allowing very fine control of (i) the incorporation of impurities into the material (ii) its crystalline quality (sp2/sp3 ratio) (iii) its size. This growth facility, which exists at the CEA NIMBE, is used for the synthesis of boron-doped diamond core-shells [4]. In the second part of the thesis, an innovative process (patent pending) is implemented to achieve MPCVD growth of diamond nanoparticles by circulating the sacrificial templates in a gas stream. During this work, different types of nanodiamonds will be synthesized: intrinsic nanoparticles (without intentional doping) and nanoparticles doped with boron or nitrogen.

After growth, the nanoparticles will be collected after dissolution of the template. Their crystal structure, morphology and surface chemistry will be studied at CEA NIMBE by scanning electron microscopy, X-ray diffraction and Raman, infrared and photoelectron spectroscopy. A detailed analysis of the crystallographic structure and structural defects will be carried out by high-resolution transmission electron microscopy.

Nanodiamonds will then be surface-modified to give them colloidal stability in water. Their photocatalytic performance for hydrogen production will be evaluated in collaboration with ICPEES (Strasbourg University).


References
[1] Patent, Procédé de production de dihydrogène utilisant des nanodiamants comme photocatalyseurs, CEA/CNRS, N° FR/40698, juillet 2022.
[2] Miliaieva et al., Nanoscale Adv. 2023.
[3] Buchner et al., Nanoscale (2022)
[4] Henni et al., Diam. Relat. mater. (under review)

Reducing the density of materials is one of the best ways to diminish our energy footprint. One solution is to replace massive materials by microlattices. Among these, random architecture structures inspired by bird bone structure offer the best advantages, with isotropic mechanical behavior and increased mechanical resistance, while meeting the challenges of the circular economy. These material-saving metamaterials are manufactured by 3D printing and can be compacted at the end of their life cycle. Among manufacturing technologies, UV polymerization of liquid organic resin or composite is the most promising. It produces mechanically resistant materials without generating manufacturing waste. It is also possible to include large quantities of bio-sourced fillers, reducing even further their environmental impact.

The PhD-thesis proposed here focuses on the development of polymeric nanocomposite microlattice structures from resin formulation to mechanical properties study (viscoelasticity, yield stress, fracture resistance) through printing and post-processing stages. From a more fundamental point of view, the aim is to study the link between the composition, shape and surface properties of the fillers on one hand, and the imprimability of the composite resine and the mechanical properties of the resulting metamaterial on the other hand. The thesis will focus on the study of cellulose-type fillers in nanoparticle, microparticle or fiber form. This multidisciplinary study bridges technology to science while producing data for a digital twin.

In the context of the search for processes that are less polluting and more energy-efficient than current processes, it is interesting to produce high-stake molecules such as C2H4 by developing alternative synthesis routes to steam cracking, which is used in the majority of cases, but is energy-intensive and based on fossil resources. Processes such as photocatalysis, which relies on the use of light energy, seem an attractive way of generating these molecules of interest. In this context, we have already shown that the use of TiO2-based photocatalysts decorated with copper particles enables the production of ethylene from an aqueous solution of propionic acid, with a selectivity (C2H4/other carbonaceous products) of up to 85%.

However, photocatalysis kinetics can be slow, and it can take a long time to identify the best catalysts or catalyst/reagent pairs for a given reaction. So, in order to determine whether radiolysis, which relies on the use of radiation to ionize matter, can be an effective method of screening catalysts, initial experiments have already been carried out on catalyst (TiO2 or Cu TiO2)/reagent (propionic acid more or less concentrated) pairs, previously studied in photocatalysis. Initial results obtained by radiolysis are encouraging. In these experiments, only dihydrogen production was measured. A significant difference was observed in this production depending on the system: it was high during radiolysis of propionic acid with TiO2 nanoparticles, and significantly lower in the presence of Cu TiO2 nanoparticles, suggesting a different reaction path in the latter case, in line with observations made during photocatalysis experiments.

The aim of this thesis work will be to extend these initial results by synthesizing nanoparticles (catalysts), preparing reagent/catalyst mixtures, then irradiating them and measuring the various gases produced by gas-phase micro-chromatography, with special attention on ethylene. Particular attention will be paid to determining the species formed, especially transient ones, in order to ultimately propose reaction mechanisms accounting for the differences observed for the different reagent/catalyst pairs. Comparisons will also be made with results obtained by photocatalysis.

As part of the energy transition, the production of hydrogen from solar energy appears to be an extremely promising means of storing and then producing energy. To develop on a large scale, water photoelectrolysis requires materials with high catalytic efficiency. Among the candidates considered, materials derived from barium titanates appear promising because their ferro- and piezoelectric properties could increase their photocatalytic effect. Therefore, we propose to synthesize BaTiO3 nanoparticles by flame spray pyrolysis and to make substitutions on Ba and O in order to study the effect of these modifications on the ferroelectric properties of the material. The addition of noble metal inclusions to the surface of the particles, likely to improve catalysis, will also be addressed. Finally, photocatalysis and piezocatalysis tests will make it possible to establish the links between ferroelectric and catalytic phenomena in this family of materials. This subject will be carried out in collaboration between the LEEL of the CEA and the SPMS of Centrale – Supelec.