Custom synthesis of diamond nanoparticles for photocatalytic hydrogen production
Diamond nanoparticles (nanodiamonds) are used in nanomedicine, quantum technologies, lubricants and advanced composites [1-2]. Our recent results show that nanodiamond can also act as a photocatalyst, enabling the production of hydrogen under solar illumination [3]. Despite its wide band gap, its band structure is adaptable according to its nature and surface chemistry [4]. 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 [5]. 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.
This PhD aims to develop a bottom-up approach to grow nanodiamond using a sacrificial template (silica beads) to which diamond seeds < 10 nm are attached by electrostatic interaction. The growth of diamond nanoparticles from these seeds will be achieved by microwave-enhanced chemical vapor deposition (MPCVD) using a homemade rotating reactor available at CEA NIMBE. After growth, the CVD-NDs will be collected after dissolution of the sacrificial pattern. Preliminary experiments have demonstrated the feasibility of this approach with the synthesis of faceted <100 nm nanodiamonds (so called CVD-ND), as shown in the scanning electron microscopy image.
During the PhD work, the nature of the diamond seeds (ultra-small NDs [size ˜ 5 nm] synthesized by detonation or HPHT, or molecular derivatives of adamantane) as well as CVD growth parameters will be studied to achieve better controlled CVD-NDs in terms of crystallinity and morphology. Nanodiamonds doped with boron or nitrogen will be also considered, playing on the gas phase composition. The crystalline structure, morphology and surface chemistry will be studied at CEA NIMBE using SEM, X-ray diffraction and Raman, infrared and photoelectron spectroscopies. A detailed analysis of the crystallographic structure and structural defects will be carried out by high-resolution transmission electron microscopy (collaboration). CVD FNDs will then be exposed to gas-phase treatments (air, hydrogen) to modulate their surface chemistry and stabilize them in water. The photocatalytic performance for hydrogen production under visible light of these different CVD-NDs will be evaluated and compared using the photocatalytic reactor recently installed at CEA NIMBE.
References
[1] Nunn et al., Current Opinion in Solid State and Materials Science, 21 (2017) 1.
[2] Wu et al., Angew. Chem. Int. Ed. 55 (2016) 6586.
[3] Marchal et al., Adv. Energy Sustainability Res., 2300260 (2023) 1-8.
[4] Miliaieva et al., Nanoscale Adv. 5 (2023) 4402.
[5] Buchner et al., Nanoscale 14 (2022) 17188.
Simplified Model for Rotary Tube Calcination
Since the vitrification lines at La Hague began operation in 1989, ORANO (formerly AREVA) has faced difficulties in controlling the calciner. Actions taken to significantly reduce these problems have considerably eased them, but without completely eliminating them. Most of the recommended actions are based on expert opinions, which themselves are based on inactive test results that don't cover all situations encountered by ORANO. To definitively resolve these control difficulties, it was decided to launch a more theoretical modeling study, while simultaneously investigating new calciner control instrumentation.
Electronic effects dans les cascades de collisions dans le GaN
In radiation environments like space and nuclear plants, microelectronic devices are subject to intense flux of particles degrading the devices by damaging the materials they are made of. Particles collide with atoms of the semi-conducting materials, ejecting them for their lattice site. Those displaced atoms also collide and set in motion a new generation of atoms, and so on, leading to a cascade of collisions which creates defects in the material. Moreover, primary or secondary particles (created following interaction with a neutron for example) also specifically interact with electrons of the target material, and lose kinetic energy in doing so by promoting electrons to higher energy bands. This aspect is called electronic stopping. Simulations of collision cascades must therefore describe both nuclei-nuclei collisions and electronic stopping effects.
The preferred method for collision cascades simulations at the atomic scale is Molecular Dynamics (MD). However, electronic effects are not included in this method as electrons are not taken into account explicitly. To circumvent this issue, additional modules have to be employed on top of MD to model electronic effects in a collision cascade. The state-of-the-art regarding electronic stopping simulation of a projectile in a target material is the real time - time dependent density functional theory (RT-TDDFT). The purpose of this thesis is to combine MD and RT-TDDFT to perform collision cascades simulations in GaN and study the influence of electronic effects. In addition to skills common to all thesis, the candidate will develop very specific skills in different atomic scale simulation methods, solid state physics, particle-matter interactions, linux environment and programming.
Development of Single-Ion Eutectogel Electrolytes through Polymerization of Deep Eutectic Solvents (DES)
The proposed PhD thesis focuses on the development of innovative polymer electrolytes for next-generation batteries, aimed at improving the safety and performance of energy storage systems.
Polymer electrolytes represent a promising solution to replace traditional liquid electrolytes. However, their development is limited by challenges related to ionic conductivity and low ion transport numbers. The addition of Deep Eutectic Solvents (DES) into the polymer matrix enhances ionic conductivity. Furthermore, the "single-ion" approach, based on grafting the counter-ion onto the polymer chain, leads to unipolar conduction.
CEA has recently developed "single-ion eutectogel" electrolytes, obtained by polymerizing a DES composed of a single-ion monomer and a hydrogen bond donor (HBD). These electrolytes exhibit very promising performance, achieving unipolar ionic conductivities greater than 0.1 mS/cm at room temperature. However, it is essential to further explore the relationships between formulation, structure, and properties, as well as the conduction mechanisms within these materials, in order to continue their development.
The thesis will be structured in three main phases:
Study of the reference system: Establish a research methodology to link polymerizable formulations, polymer structure, and their electrochemical properties. This will include the study of the starting DES and the electrolyte resulting from its polymerization. The study of conduction mechanisms within these electrolytes will be a central focus of this phase.
Optimization of properties: Based on the results from the previous phase, optimize the properties of the electrolytes through formulation work to select the most promising electrolyte for the next phase.
Integration into a complete system: Explore the integration of the electrolyte into a battery cell, using the in situ polymerization process to synthesize the electrolyte directly within the cell.
Physicochemical techniques (NMR, DSC, TGA, FTIR, RAMAN, SEC, SAXS, ...) and electrochemical techniques (EIS, CV, GCPL, ...) will be used throughout the project.
The PhD will be carried out in collaboration with CEA and LEPMI, providing access to state-of-the-art infrastructures and recognized expertise in formulation, polymer chemistry, and polymer electrolyte electrochemistry.
Simulation and characterization of integrated structures during and after the millisecond laser annealing step
Laser annealing processes are now used in a large range of applications in most advanced microelectronics technologies. Whether in the context of advanced planar CMOS components or 3D integration technologies, the specific characteristics of laser annealing enables to reach very high temperatures in very short times, at die scale, and to work in conditions out of thermodynamic equilibrium. This has many advantages in terms of physical effects (activation of high dopants with low diffusions, transformation of silicides, etc.), but also thermal budget (high temperatures which remain on the surface of the material). However, this kind of ultrashort optical annealing can generate pattern effect temperature variations on the chip surface between two zones with different radiative andor thermal properties. These temperature differences may alter the electrical performances of the devices and thus have to be evaluated and overcome. A part of this work will consist, by the help of bibliography study, in finding integrative solutions (design, absorbent layer,…), in order to encounter this issue. Besides, at LETI, a wide knowledge of Nanosecond Laser Annealing (NLA) is in place for many years, and process teams are in the acquisition phase of a millisecond laser equipment (DSA). This work will represent, thanks to the numerical simulation, one of the essential building blocks for the development of the millisecond laser annealing at LETI which is mandatory for advanced technologies roadmap.
This interdisciplinary research will encompass fields such as numerical simulations, materials science, microelectronic manufacturing processes. You will benefit from the support of laboratories specializing in integration processes, as well as TCAD simulation environments.
Multiscale modeling of the magnetic response of heterogeneous material
The spectral dependence of the permeability of magnetic materials, whether in composite or dense materials, remains a complex issue due to the different scales of the phenomena involved. Approximate analytical models are often used to describe the frequency response of magnetic materials, particularly to improve their performance in areas such as power electronics. Recent results have shown that micro-magnetism codes can now predict the response of a system of coupled nanoparticles or a particle representing the volume of the materials in question. This thesis aims to use these tools to improve existing analytical models. An inclusion immersed in an effective field will be the paradigm from which the domain structure and the spectral response of the particle will be calculated using a micro-magnetism code. The materials studied include spherical particles or those with a high aspect ratio (magnetic oxides, ferromagnetic petals) at varying concentrations, ranging from dilute media to dense materials. This work will identify pathways to optimize the microstructure of materials for better performance in applications such as power electronics and microwave components. To this end, CEA provides a scientific computing environment with access to HPC resources, as well as facilities for sample preparation and static and dynamic magnetic characterization. At the end of this work, the candidate will have gained a solid understanding of the microstructure-property relationships described by a numerical approach applied to magnetic materials. More generally, this approach is expanding in the field of materials to improve their properties in various fields, under the designation "materials by design".
Development and study of laminated composite material with carbon nanotubes functionalisation dedicated to launcher linerless cryogenic tank
The use of composite materials in the space field has led to great weight improvements. To continue to achieve significant weight gain, composite cryogenic tank is the next technological application to reach by replacing the current metal alloy cryogenic propellant tanks. Lighter reinforced organic matrix composite materials (that are at least as efficient from a mechanical, thermal, chemical and ignition resistance point of view) are a realistic target to be reached that has been explored in recent years. Many research approaches tend to answer to this technological lock, but the potentialities of Carbon NanoTubes (CNTs) in terms of mechanical and physical properties, need to be explored deeper.
A first phase to assess the interest of CNTs for space applications (collaboration CNES/CEA/I2M/CMP Composite) was carried out to associate CNTs with a cyanate ester matrix in layered composite materials through three processes: (i) transfer of aligned CNTs mats by hot pressing (ii) dispersion of entangled CNTs mixed with resin, or (iii) growth of nanotubes aligned directly on the dry ply. Knowing mechanical and thermal loads, the aim is to demonstrate the efficiency of CNTs and influence of their characteristics with regard to damage tolerance of the material and consist in delaying the cracking process of the composite nearby the CNT layer and thus blocking the percolation of the cracking network which leads to the loss of tightness. For the preferred development process identified, the aim of this doctoral work is now to consolidate the material functionalisation with CNTs (shape, density, etc.) and the understanding of the mechanical behaviour (at room temperature and at low temperature) for the development of the layered material integrating CNTs.
Knowing the potential final application as cryogenic tank or for the improvement of structural materials sustainability in dual application, relevant tests will be performed to demonstrate the impact in terms of damage development and tightness in comparison with the same material without CNTs.
Study of the thermomechanical properties of solid hydrogen flows
IRIG's Department of Low Temperature Systems (DSBT) is developing several research themes around cryogenic solid hydrogen and its isotopes. The applications of this research range from the production of renewable micrometre-sized solid hydrogen targets for the generation of high-energy protons for laser-plasma acceleration, to the formation and injection of millimetre- or centimetre-sized hydrogen ice cubes for the supply and control of plasma in fusion reactors using magnetic or inertial confinement. A cross-cutting issue in these applications is the need for a detailed understanding of the mechanical properties of solid hydrogen, in order to gain a better understanding of the physics of extrusion and target production, as well as the formation and acceleration of icicles for injection into fusion plasmas.
The subject of this thesis focuses on the study of solid hydrogen extrusion under pressure. Using this technology, the DSBT has been developing several cryostats for over 10 years, enabling the production of ribbons of solid hydrogen, ranging in size from a few millimetres to a few tens of micrometres, extruded at speeds of a few millimetres per second.
The main objective of the research is to gain a better understanding of extrusion mechanisms to enable the development of numerical predictive tools for extrusion system design. This experimental thesis will be based on cryogenic rheometry using a capillary rheometer and/or a duvet experiment developed during a previous thesis. This study will be carried out in collaboration with the Laboratoire de Rhéologie et Procédés at Grenoble Alpes University.
Towards eco innovative, sustainable and reliable piezoelectric technology
Are you looking for a Phd position at the intersection of eco-innovation and high-tech? This subject is for you!
You will participate in efforts aimed at reducing the environmental footprint of piezoelectric (PZE) technology applied to micro actuators and sensors, while maintaining optimal levels of electrical performance and reliability. Currently PZE technology primarily relies on PZT material (Pb(Zr,Ti)O3) which contains lead, as well as electrodes made from materials such as Pt, Ru, and Au, along with doping elements like La, Mn and Nb to enhance piezoelectric properties and electrical performance. These materials not only come with a significant ecological cost but are also facing proven or imminent shortages. In the context of the necessary frugality associated with the energy transition, this PhD position aims to explore more environmentally friendly and sustainable microsystem technologies. The research will create a comparative analysis assessing the ecological footprint, electromechanical performance, and reliability of existing technologies (with lead) versus those under development (lead free). To achieve these objectives, you will employ Life Cycle Analyses (LCA), electromechanical measurements, and reliability tests (accelerated aging tests).
This interdisciplinary research will encompass fields such as eco design materials science, and microelectronic manufacturing processes You will benefit from the support of laboratories specializing in microsystems manufacturing and integration processes, as well as electrical characterization and reliability Collaboration with the “eco innovation” unit at CEA Leti will also enhance the resources available for this project.
Etude du comportement d'un composite CMC en température par essais in situ en tomographie X
The proposed topic concerns the study of the mechanical behavior of an oxide/oxide ceramic matrix composite material at temperature (up to 1000°C). The originality of the subject lies in the use of in situ X-ray tomography to access, on the one hand, the macroscopic deformation of the tested specimens and, on the other hand, the microscopic damage mechanisms that characterize this type of so-called "damageable" material.
This technique was developed at room temperature during a previous thesis: the aim here is to apply it at higher temperature and to more complex stresses (e.g., traction-torsion). The aim will also be to propose developments to the existing volumetric image correlation analysis protocol.