Discovery of new chromogenic probes for toxic using Chemistry-Trained Machine Learning

Today national and international situation justify new researches on the colorimetric detection of toxic and polluting gases (referred to as analytes in the following). For the already known and studied compounds, improvement of the detection capabilities involves increasing contrast and selectivity. For potential new analytes, it is also important to prepare for rapid identification of specific chromogenic probes. The objectives of the thesis will be to discover new chromogenic probes by using computational chemistry.
First stage of the thesis: Training of the model (ML/AI) on available database. This part of the thesis will focus on establishing a precise and robust model to classify the large experimental database available from our laboratory's previous work. This involves correlating the colorimetric results with the structures and chemical properties of the molecules described by state-of-the-art methods (e.g., https://pubs.acs.org/doi/10.1021/acs.chemrev.1c00107). At the end of this learning process, we will have a predictor (SVM, LCA, PCA…) validated on our data.
Second stage: Use of the predictor model to screen in silico several hundred thousand candidate probe molecules from commercial chemical libraries (and others), correlated with their chemical structure and property descriptions as in the first stage. After this initial screening, DFT prediction of the chromogenic response will be used to refine the selection of the best candidate molecules.
Third stage: Definition and implementation of an experimental chemical testing campaign. A fast organic synthesis platform HTE (high throughput experimentation) based on the miniaturization and parallelization of chemical reactions to optimize the implementation of synthesis reactions and tests, will save considerable time, while significantly increasing the number of possible combinations. HTE also enables the synthesis of libraries of analogous compounds. Following these massive tests, a second version of the predictor will be trained and will lead to the discovery of a new generation of chromogenic molecules.

Ultrasensitive static/dynamic flexible force transducer

In this thesis, the principles and challenges in the development by printing and characterisation of conformable organic piezoelectric matrices for medical use under stress will be examined. A stretchable/conformable piezoelectric sensor, produced on a stretchable substrate, will be developed with materials (PVDF-TrFE type polymer or composite). These developments will make it possible to study the feasibility of using such piezoelectric components in various fields.
The aim of the study carried out to date has been to produce a flexible piezoelectric device based on the principle of a double-sided sensor so as to eliminate the contribution of bending. This sensor must also be stiff enough to be deployed through a 3mm diameter catheter. In this context, the work carried out in this thesis will focus on the development of a flexible piezoelectric sensor capable of converting the mechanical energy of low stresses, coupled with a piezoresistive sensor capable of measuring static stresses. The use of polymers offers greater flexibility, and they are implemented in the form of thin films, making them lightweight and space-saving. In order to achieve these objectives, a dedicated sensor structure guaranteeing redundant measurement (piezoelectric and piezoresistive sensor) will be studied, produced and characterised. The sensor manufacturing process will have to be optimised to increase their efficiency. Optimisation of the architecture of the electrodes and the geometry of the active layers will be tested on a test bench in order to assess their ability to measure static and dynamic stresses simultaneously over the widest possible range of forces. At the same time, fundamental characterisations of the material will be carried out in order to establish correlations between the structure and electrical properties of the sensors.

Develoment of lithium mediated ammonia electrolyzer

Recent developments in electrochemical ammonia (NH3) synthesis using lithium (Li) metal deposition in THF-based electrolytes in the presence of protic species, reinvigorated the research interest in direct NH3 electrolyzes technology thanks to its surprisingly high performance in terms of synthesis rate and faradaic efficiency. However, the main drawback is poor energy efficiency due to minimum voltage requirements associated to Li metal deposition and H2 oxidation reactions on the opposite electrodes. In this project, we propose to study the nitridation reaction of Li-alloy forming metals that can enable the decrease in electolyzer voltage. This study will be performed using a 3-electrode electrochemical pressure cell and differential scanning calorimetry – thermogravimetric analysis under N2, H2 pressures. The goal here is to couple existing knowledge in chemical looping synthesis of ammonia with electrochemical synthesis. Porous (carbon or steel tissue) electrodes will be developed with nanoparticles of Li-alloy forming metals and their performance will be studied in an electrolyzer. The assumed 3-step reaction mechanism to form NH3 is as follows: Li deposition > nitridation > protonation. This mechanism is already a subject of discussion for pure Li metal which will be further complicated with the use of alloy forming metals. Therefore, we propose an in-depth study using x-ray photoemission spectroscopy. The ultimate objective of the project is to accelerate the direct NH3 electrolysis technology and address the Power-to-X needs of renewable electricity sources.

Investigations of binder infiltration in a powder bed during the Binder Jetting process

Binder jetting (BJ) is an additive manufacturing process (also called 3D printing), that consists in jetting a binder on a powder bed made of metallic or ceramic particles, so that to build a part from a 3D model. Once the binder has cured, the part is extracted from the powder bed and sintered. A major challenge of this process is to predict the state of the part after printing (density, homogeneity, defects). Printing strategy, powder size/shape and binder type all have an impact on the part before densification. The aim of this thesis is to study the interaction between the binder and the powder during the printing process. Ultimately, this should help to optimize the process. The thesis will focus on developing a model for droplet infiltration in a powder bed. To achieve this objective, the proposal is to use innovative numerical methods to model the fluid-structure interaction operating in the powder bed, taking into account capillary forces and dynamic effects (droplet fragmentation, particle displacement). Experimental investigations are also planned, firstly to calibrate the numerical parameters associated with the model, and secondly to validate the model. In fact, a dedicated experimental bench was previously developed, and will be used to characterize the surface state of the powder bed before and after infiltration.

Polycrystallines perovskite layers for medical X-ray imaging: impact of doping

The CEA is a major player in research into X-ray imagers for medical applications. For several years now, our laboratory at LITEN has been working in collaboration with LETI on a new generation of direct detectors based on halogenoplumbates perovskite photoconductors for applications in radiography, mammography and cardiac imaging. The laboratory has developed several processes for manufacturing thick films (>100µm) of perovskite semiconductors with state-of-the-art performances. However, they still need to be stabilized and improved to meet the stringent specifications of medical imaging. By analogy with other semiconductors (Si, Ge, CdTe, CZT, a-Se), it seems reasonable to assume that improving the performances of perovskite detectors will require advanced control of the bulk and surface properties of the semiconductor layer.
The candidate will be inspired by the developments of the perovskite community around high-purity single crystals for gamma detectors, and will transfer this know-how to the case of polycrystalline perovskite layers for X-rays. Initially, he will study the effects of unintentional extrinsic doping linked to the environment on the performance of X-ray detectors. Secondly, it will work to reduce the unintentional intrinsic doping by developing techniques for purifying precursor materials. At the same time, particular attention will be paid to the grain boundaries of polycrystalline layers and the feasibility of passivating surface defects using chemical treatments. The layers will then be tested in X-ray or gamma-ray detector devices. A thesis launched in parallel at LETI will characterize the density and nature of intrinsic carriers as a function of material and process conditions. Depending on the progress of the thesis, the possibility of intentionally doping the perovskite material could be explored. We hope that the results obtained as part of the thesis will enable us to improve the performance of X-ray detectors in order to meet medical imaging specifications, and to develop expertise in perovskite-based gamma detection. The work will be carried out in a highly collaborative environment involving laboratories from the CEA (LITEN, LETI, IRESNE), the CNRS (Institut Néel) and foreign laboratories. The PhD student will interact with several PhD students on a common topic.

Study and development of thermoelectric devices by additive manufacturing

With decarbonisation, global increase of inflation, rising energy cost, etc., need for energy with low environmental impact have considerably shot up. Among all available technologies, thermoelectric generators (TEG) are solid-state devices converting heat into electricity thanks to Seebeck effect. TEGs present several advantages such as having no moving part, completely silent (unlike internal combustion or stirling engines), low-maintenance, renewable energy source that are simple to install, safe to store, and cost-effective.
For more than 20 years, the laboratory L3M has acquiered a big experience in thermoelectricity (TE), mainly in thin films and bulk technologies. Moreover, for 10 years, L3M has also acquiered a strong experience in additive manufacturing (AM), mainly for metallic materials. The use of AM for TE offers new perspectives, and enables to create new and original geometries (leading to an optimization of yield and/or a better integration), with less materials losses, a significant decrease of the integration and interface challenges, a faster manufacturing time, a lower cost and the possibility to manufacture TE devices very quickly compared to other technologies. The main barrier consists in obtaining materials with as good quality (in terms of density and microstructure) as with other technologies, which will be possible thanks to a deep development and understanding of the process.
L3M has started this new technology for 3 years. Researches are focused on TE materials based on silicon-germanium alloys, which are very good materials for high temperatures applications (500K to 700K) as for spatial, metalworking industry, etc.
The objective of this PhD study will be, from one side, to continue current studies about optimization of SiGe manufacturing process by AM (and more specifically by Laser Powder Bed Fusion (L-PBF) technology), and from the other side, to manufacture the first TEG demonstrators. For the first part, the study will have to lead to the understanding of the specifities of AM mechanisms on SiGe structural properties. This structural study will include measurement of mechanical properties, as well as microscopic analysis. This study will be also correlated to experimental measurements of manufactured materials TE properties (Seebeck coefficient, electrical and thermal properties).
For the second part, TE generator manufacturing needs to associate two TE materials (n- and p-type SiGe) and assemble together, by optimizing electrical contacts between these two materials. CEA-Liten has deposited a patent about the original manufacturing of such device by AM. The realisation and electrical characterization of a TE generator will be also developed in the framework of this study, leading to highlight advantages of this manufacturing technique.
It should be noted that this work will be performed in the framework of a European project launch.

Development of innovative medical devices from new bacterial polyhydroxyalkanoates (PHA) derivatives.

To address the future challenges of wearable or implanted medical devices (MDs), which are less invasive and increasingly personalized and effective, it is necessary to have a broad range of biocompatible materials with diverse mechanical properties. Preferably, these biomaterials should be of biological origin and employed under mild conditions (preferably in water) to reduce the risk of releasing toxic by-products. Material biodegradability is another key characteristic to master for the development of prostheses and devices with a lifespan adapted to their use. In this context, the ANR PHAMOUS aims to demonstrate the high potential of bacterial polyhydroxyalkanoates (PHA) for designing innovative MDs.
In this framework, the doctoral candidate will initially be responsible for the chemical modification of various PHAs to enhance their water solubility (e.g., pendant PEG groups), introduce photo-crosslinkable groups (e.g., methacrylates), and incorporate specific functions (peptides) to enhance cellular adhesion and antimicrobial properties. The doctoral candidate will then use the different functionalized PHAs to develop two demonstrators implemented through two different processes. Photo-crosslinkable and solvent-soluble PHAs will be formulated to manufacture a prototype of a bronchial stent using "vat polymerization" 3D printing processes. Simultaneously, electrospinning of PHAs will be used to develop micro-structured and porous membranes.

Design of 4D printable and biocompatible polysaccharide hydrogels for biomedical applications.

The 3D printing of stimuli-responsive materials is called “4D printing” and is of great interest for the development of innovative medical devices (dynamic synthetic tissues, soft robotic actuators, controlled drug release systems etc.). Reported examples of these printable smart materials are programmed to autonomously change their shape in response to specific stimuli (e.g. temperature, light, magnetic field, pH, etc.) but are almost exclusively based on synthetic polymers.
To transpose this concept to biomedical application, this PhD project aims at designing 3D printable, biocompatible and stimuli-responsive polysaccharide hydrogels. In particular, the targeted hydrogels will be able to deform under two different stimuli: (i) a temperature variation or (ii) the application of a near-infrared (NIR) beam for the material activation without deterioration of biological tissues. These will be achieved by combining (i) polysaccharide chains functionalized with thermoresponsive groups and (ii) photothermal nanoparticles capable of converting NIR light into heat.
This interdisciplinary project is at the interface between Chemistry (polymer chemistry, nanoparticle synthesis), Physical Chemistry (formulation and characterization of hydrogels), Materials Science (3D printing studies, mechanical tests) and Biology (cytocompatibility studies). An additional originality is that the experimental data collected by the PhD candidate will be fed into artificial intelligence tools which, in turn, should provide guidelines to accelerate the discovery of the targeted materials.

Nanocrystalline Soft Magnetic Composites: Powder morphology and design for controlling their magnetic properties for high frequency applications

Context: Achieving carbon neutrality by 2050 will require massive electrification of the power production systems. Power electronics (PE) is a key-enabler that will this transformation possible (renewables, integration of energy micro-grids, development of electric mobility)
Problem: Current developments in PE converters aim at increasing the switching frequencies of large bandgap switches (SiC or GaN). At low frequencies, magnetic components remain bulky, occupying up to 40% of the total footprint. At high frequencies (HF > 100 kHz), very significant gains are expected, but only if the losses generated by these components remain under control. Today, the main class of magnetic materials applied to HF is MnZn or NiZn ferrites, due to their low cost and convenient electrical resistivity (?elec > 1 O.m). The main drawbacks of these materials are their low saturation induction (Bsat < 0.4 T), which limits their size reduction, and their mechanical fragility. Nanocrystallines materials have better Bsat (1.3 T), but their ?elec is about 1.5 µO.m (6 times less resistive than ferrites), which generates significant induced current losses at HF.
Thesis objective: To develop magnetic composites by grinding nanocrystalline ribbons, electrically insulating the powders (coating fabricated by sol-gel), compacting of the powder at high pressure (1000-2000 MPa) for the core shaping and finally by applying an annealing treatment to relax the thermal constraints.

Study of NMC electrode materials for lithium-ion batteries by experimental and theoretical soft and hard X-ray photoemission spectroscopy

The photoemission spectroscopy (X-ray, XPS, or ultraviolet, UPS) is one of the direct probes of the electronic structure of materials change during redox processes involved in lithium ions-batteries at the atomic scale. However, it is limited by the extreme surface sensitivity, with a typical photoelectron path length of a few nanometers to the energies usually available in the laboratory , . Moreover, the spectra interpretation requires the ability to accurately model the electronic structure, which is particularly delicate in the case of transition metal based electrode materials. Upon lithium insertion and de-insertion, the charge transfer toward cations and anions induces local electronic structure changes requiring an adapted model that takes in account the electronic correlations between atoms.
In this thesis, we propose to use these limitations to our advantage to explore the electronic surface structure including the solid electrolyte interphase (SEI), and the bulk of the active cathode particle.
Thanks to the lab-based hard X-ray photoemission spectrometer (HAXPES), the electronic structure of the bulk of the electrodes (LiCoO2 and LiNiO2) materials have been studied up to about 30 nanometers , . To widen our picture on the role of cation and anion from surface to bulk in the lamellar metal oxide electrode for lithium-ion battery, this thesis will focus on mixed lamellar metal oxide Li(Ni1-x-yMnxCoy)O2 (NMC).
The comparison between the Soft-XPS and HAXPES spectra, during battery operation (operando) and post-mortem, will allow decoupling of the surface and core spectra for different NMC compositions and at different stages of the battery life cycle. The interpretation of the photoemission spectra will be done by direct comparison with ab-initio calculations combining density functional theory (DFT) with dynamical mean field theory (DMFT) , . This coupled approach will allow to go beyond the usual techniques based on cluster models, which do not take into account long-range screening, and to validate the quality of theoretical predictions on the effects of electronic correlations (effective mass, potential transfer of spectral weight to Hubbard bands) .
The thesis will include an instrumental (in particular, calibration of Scofield factor on model systems) and theoretical (prediction of core photoemission spectra based on DFT+DMFT calculations) development. The performance of electrochemical systems based on different cathode materials (NMC with different compositions) in combination with liquid and solid electrolytes and a Li metal anode will be studied in the frame of combined experimental and theoretical soft and hard X-ray photoemission spectroscopy.
The candidate will be hosted at the PFNC in the Laboratory of Characterization for the Energy of CEA Grenoble under the direction of Dr. Anass BENAYAD (department of Material) and LMP (Department of Electricity and Hydrogen for Transport) under the supervision of Dr. Ambroise Van Roekeghem.
Contact : anass.benayad@cea.fr et ambroise.vanroekeghem@cea.fr

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