Fluorescence photoswitching for excitonic gate
Förster Resonance Energy Transfer (FRET) enables the exciton diffusion between molecules through a characteristic distance of 1 to 10 nm. The association of multiple fluorophores represents a solution to facilitate exciton diffusion over a longer range, taking profit of homo-FRET and hetero-FRET phenomena. FRET is a fundamental aspect in the development of photo-switchable luminescent devices. At the molecular level, the design of photo-switchable systems relies on the association of two components: a luminescent material and a photochromic compound. The formation of nano-objects with similar molecules leads to intriguing responses in fluorescence and photochromic behavior due to multiple energy transfers. However, these systems are poorly used in molecular logic, and they switch between bright and dark states. Considering an emissive acceptor (a second bright state) would allow exciton diffusion over longer distances and enable its detection.
The FLUOGATE project objective is the preparation and characterization of photoswitchable luminescent molecular nanostructures that behaves as an excitonic gate. The initial step is the preparation and study of 2D photoswitchable monolayers with controlled organization. The combination of optical and local probe measurements will permit the characterization of fluorescence photoswitching following the structural change at the single molecule scale and determination of the quenching radius. Then, the preparation and study of 3D architectures will be undertaken. The strategy entails the successive deposition of various dyes. Layers of the donor fluorophore will be deposited just above the substrate, followed by layers of the photochromic compound and finally layers of the acceptor fluorophore. The ultimate goal will consist in exploring the replacement of the photochromic layer by a photochromic nanoparticle in a polymer matrix.
Understanding the fundamental properties of PrOx based oxygen electrodes through ab-initio and electrochemical modelling for solid oxide cells application
Solid Oxide Cells (SOCs) are reversible and efficient energy-conversion systems for the production of electricity and green hydrogen. Nowadays, they are considered as one of the key technological solutions for the transition to a renewable energy market. A SOC consists of a dense electrolyte sandwiched between two porous electrodes. To date, the large-scale commercialization of SOCs still requires the improvement of both their performances and lifetime. In this context, the main limitations in terms of efficiency and degradation of SOCs have been attributed to the conventional oxygen electrode in La0.6Sr0.4Co0.2Fe0.8O3. To overcome this issue, it has recently been proposed to replace this material with an alternative electrode based on PrOx. Indeed, this material has a high electro-catalytic activity for the oxygen reduction and good transport properties. The performance of cells incorporating this new electrode is promising and might enable to reach the targets required for large-scale industrialization (i.e. -1.5A/cm2 at 1.3V at 750°C and a degradation rate of 0.5%/kh). However, it has been shown that PrOx undergoes phase transitions depending on the cell operating conditions. The impact of these phase transitions on the electrode properties and on its performance and durability are still unknown. Thus, the purpose of the PhD is to gain an in-depth understanding of the physical properties for the different PrOx phases in order to investigate their role in the electrode reaction mechanisms. The study will contribute to validate whether PrOx based electrodes are good candidates for a new generation of SOCs and help to identify an optimized electrode using a methodology combining ab-initio calculation with electrochemical modelling.
Fracture dynamics in crystalline layer transfer technology
Smart Cut™ is a technology discovered at CEA and now industrially used for the manufacture of advanced substrates for electronics. However, the physical phenomena involved are still the focus of numerous studies at CEA. In Smart Cut™, a thin material layer is transferred from one wafer to another using a key fracture annealing step upon which a macroscopic fracture initiate & propagates at several km/s [i].
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Improving technology requires a solid understanding of the physical phenomena involved in the fracture step. The aim of this PhD project is thus to address the mechanisms involved in fracture initiation, propagation and post-fracture vibrations
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On the CEA-Grenoble site, with industrial interest, the student will use and further develop existing experimental setups to investigate the fracture behavior in brittle materials, including optical laser reflections [iv], time-resolved synchrotron diffracting imaging [iii], and ultra-fast direct imaging [ii].
In addition, python-based data analysis algorithms will be developed to extract quantitative information from the different datasets. This will enable the student to determine involved mechanisms and evaluate the influence of the wafer processing parameters on the fracture behavior, and thus propose improvement methods.
References :
[i] https://pubs.aip.org/aip/apl/article/107/9/092102/594044
[ii] https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.15.024068
[ii] https://journals.iucr.org/j/issues/2022/04/00/vb5040/index.html
[iv] https://pubs.aip.org/aip/jap/article/129/18/185103/158396
Chemical recycling of oxgenated and nitrogenated plastic waste by reductive catalytic routes
Since the 1950s, the use of petroleum-based plastics has created a modern consumerist world based on the use of disposable products. Global production of plastic waste is therefore considerable, and has almost doubled 20 years, now reaching 468 million tons/year. This non-biodegradable plastic waste causes a great deal of environmental pollution (disturbance of flora and fauna, water and soil pollution, etc.). Barely 9% of this waste is recycled, the rest being burnt or landfilled. The health, climate and social problems inherent in this linear economy mean that we need to create a circularity for these materials by developing effective and robust recycling routes. While current recycling methods rely mainly on mechanical processes and are limited to specific types of waste (e.g. plastic water bottles), the development of chemical recycling methods seems promising for treating waste for which there are no recycling channels. Such chemical processes make it possible to recover the carbonaceous matter in plastics in order to regenerate new plastics.
Within this objective of material circularity, this doctoral project aims to develop new chemical recycling routes for mixed oxygen/nitrogen plastic waste such as polyurethanes (insulation foam, mattresses, etc.) and polyamides (textile fibres, circuit breaker boxes, etc.), for which recycling routes are virtually non-existent. This project is based on a strategy of depolymerizing these plastics by the selective cleavage of the carbon-oxygen and/or carbon-nitrogen bonds to form the corresponding monomers or their derivatives. To do that, catalytic systems involving metal catalysts coupled with abundant and inexpensive reducing agents, such as alcohols and formic acid, will be developed. The use of dihydrogen, an industrial reducing agent, will also be considered. In order to optimize these catalytic systems, we will seek to understand how they proceed and the mechanisms involved.
Two-qubit gate made with Germanium heterostructures
We are working on germanium spin qubits, a promising and versatile base material to engineer spin quantum bits. In these "heterostructures", holes are hosted in a germanium layer sandwiched between two layers of silicon/germanium. These holes exhibit a very high mobility and unlike electron spins which are only sensitive to magnetic fields, hole spins can be manipulated by an electric field, ie by voltages on a gate. The all-electrical control comes with its own drawback: spins become sensitive to electrical, and therefore charge noise in the devices. The germanium heterostructures feature metallic top gates that mostly screen the charge noise from defects they covered; however, in regions not covered by top gates, unscreened charges are responsible for charge noise limiting the coherence time.
We are acquiring a world unique cleanroom equipment combining atomic layer deposition and atomic layer etching, which will allow for the development of original structures where the gates are penetrating deep within the heterostructure, in order to circumvent the effect of these lone charges on the surface in the case of top gates. With this novel scheme, the definition and manipulation of quantum dots will be extremely simplified, and we plan to obtain two-qubit gate devices well within the scope of this PhD.
Study of catalysis on stainless steels
The materials (mainly stainless steels) aging of the spent nuclear fuel reprocessing plant is the focus of an important R&D activity at CEA. The control of this aging will be achieved by a better understanding the corrosion mechanisms the stainless steels in nitric acid (the oxidizing agent used in the reprocessing steps).
The aim of the PhD is to develop a model of corrosion on a stainless steel in nitric acid as a function of temperature and the acid nitric concentration. This PhD represents a technological challenge because currently few studies exist on in situ electrochemical measurements in hot and concentrated nitric acid. The PhD student will carry out by coupling electrochemical measurements, chemical analyses (UV-visible-IR spectrometry...) and surfaces analyses (SEM, XPS,…). Based on these experimental results, a model will be developed, which will be incorporated in the future in a more global model of the industrial equipments aging of the plant.
The laboratory is specialized in the corrosion study in extreme conditions. It is composed of a very dynamic and motivated scientific team which has the habit to receive students.
Topological magnons in quantum materials
Topology has become an essential paradigm in condensed matter, making it possible to classify phases of matter according to properties that are invariant under continuous deformations. Early research has mainly focused on electronic band structures, leading to the discovery of “topological insulators” for example. However, there is growing interest in applying topological concepts to bosons, in particular magnons. Magnons, which are collective excitations in magnetic materials, illustrate how topology influences magnetic dynamics and affects heat and spin transport. Analogues of topological insulators and semi-metals appear in their band structures. Magnons thus offer a platform for studying the interplay between magnetic symmetries and topology, examining the effect of interactions on topological bands, and generating protected spin currents at interfaces. The search for materials containing topological magnons is therefore crucial, especially for applications in magnonics, which exploit spin waves for fast data storage and processing.
This thesis project is dedicated to exploring these topological aspects in candidate quantum materials using neutron and X-ray scattering techniques in large scale facilities (ILL, ESRF, SOLEIL) to probe the magnon band structure in search of topological features such as Dirac or Weyl points. Experimental results will be supported by numerical and theoretical calculations of magnonic bands incorporating topological concepts.
Strain field imaging in semiconductors: from materials to devices
This subject addresses the visualization and quantification of deformation fields in semiconductor materials, using synchrotron radiation techniques. The control of the deformation is fundamental to optimize the electronic transport, mechanical and thermal properties.
In a dual technique approach we will combine the determination of the local deviatoric strain tensor by scanning the sample under a polychromatic nano beam (µLaue) and a monochromatic full field imaging with a larger beam (dark field x ray microscopy, DFXM).
New developments of the analysis will be focused on 1/ the improvement of the accuracy and speed of the quantitative strain field determination, 2/ the analysis of strain gradient distributions in the materials, and 3/ the determination of the dynamic strain field in piezoelectric materials through stroboscopic measurements. To illustrate these points, three scientific cases corresponding to relevant microelectronic materials of increasing complexity will be studied:
1- Static strain fields surrounding metallic contacts, such as high-density through silicon vias (TSV) in CMOS technology.
2- Strain gradients in Ge/GeSn complex heteroepitaxial structures with compositional variations along the growth direction.
3- Dynamical strain in LiNbO3 surface acoustic wave resonators with resonance frequency in the MHz range bulk
Establishing this approach will mean moving a step forward towards more efficient microelectronics and strain engineering.
Self Forming Barrier Materials for Advanced BEOL Interconnects
Context : As semiconductor technology scales down to 10 nm and below, Back End of Line (BEOL) scaling presents challenges, particularly in maintaining the integrity of copper interconnects, where line/via resistance and copper fill are key issues. Copper (Cu) interconnections must resist diffusion and delamination while maintaining optimal conductivity. In the traditional Cu damascene process, metal barriers and a Cu seed layer are deposited by PVD to enable electrochemical copper deposition. As dimensions shrink, it becomes increasingly difficult to incorporate tantalum-based diffusion barriers, even with techniques like atomic layer deposition (ALD), as the barrier thickness must be reduced to just a few nanometers. To address this challenge, a self-forming barrier (SFB) process has been proposed. This process uses copper alloys containing elements such as Mn, Ti, Al, and Mg, which segregate at the Cu-dielectric interface, forming an ultra-thin barrier while also serving as a seed layer for electroplating.
Thesis Project: The PhD candidate will join a leading research team to explore and optimize materials for SFBs using Cu alloys. Focus areas include:
- Material Selection & Characterization: develop and analyze Cu alloy thin films by electrochemical and PVD methods to study their microstructure and morphology.
- Barrier Formation: Control alloy migration at the Cu/dielectric interface during thermal annealing and assess barrier effectiveness.
- Electrical & Mechanical Properties: Evaluate SFB impact on electrical resistance, electromigration, and delamination, especially in accelerated tests.
Required skills : Master's degree in electrochemistry or materials science with a strong interest in applied research. A pronounced interest in experimental work, skills in thin film deposition, electrochemistry and materials characterization (AFM, SEM, XPS, XRD, SIMS). You should be able to conduct bibliographic research and organize your work efficiently.
Work Environment: The candidate will work in a renowned laboratory with state-of-the-art 200/300 mm facilities and will participate in the CEA’s NextGen Project on advanced interconnects for high reliability applications.
Atomistic investigation of the diffusion of small xenon clusters in the metallic nuclear fuel UMo
This project is centered on the application of atomistic methods in order to investigate the stability and diffusion of intra-granular xenon clusters within the metallic nuclear fuel UMo.
Uranium – molybdenum alloys UMo present excellent thermal properties and a good uranium density. For those reasons, they are considered as nuclear fuel candidates for research reactors. It is therefore crucial to deploy new computational methodologies in order to investigate the evolution of their thermophysical properties under irradiation conditions.
During this PhD project, you will be in charge of validating (and, if necessary, recalibrating) the atomistic computational models for UMo that have been published in the literature. You will then apply those to the simulation of the stability and diffusion of small xenon clusters (typically up to 5 xenon atoms) within UMo crystals. Those computations will be performed leveraging accelerated molecular dynamics methods, and systematically compared to the results obtained for the reference nuclear fuel UO2. The results will also be analyzed by comparison to experimental measurements performed within the department, as well as used as reference data for larger-scale nuclear fuel performance codes. The results of your research will be published in scientific journals, and you are expected to attend international conferences to present your findings.
Those different investigations will allow you to acquire a set of competences applicable to many areas of materials science: ab initio calculations, machine-learning adjustment of interatomic potentials, classical and accelerated molecular dynamics, as well as many elements of statistical physics and condensed matter physics, which are among the areas of expertise of the PhD advisors.
The PhD will be based in the Fuel Behavior Modeling Laboratory (IRESNE Institute, CEA Cadarache), a dynamic research environment within which you will have the opportunity to interact with other PhD students. You will also benefit from a rich collaborative network (experimental researchers from the department, ISAS Institute at CEA Saclay, CINAM Laboratory in Marseille), that will allow you to become a member of the nuclear materials research community.