Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Engineering science >> Materials and applications
9 proposition(s).

High voltage PV power plant

Département des Technologies Solaires (LITEN)

01-01-2019

SL-DRT-19-0060

jeremy.martin@cea.fr

Recent developments in high-voltage semiconductors with Silicon Carbide open up prospects for major innovations for PV power plant technologies. INES wishes to position itself on the feasibility of a rise in voltage of high power plants operating at a voltage above 1500V. Future technological innovations should allow a reduction in the cost per kWh produced (? / kWh). The objective of this work will be to evaluate the performance of high voltage photovoltaic systems within the limit of the voltage ratings of commercially available semiconductor switches (15kV). A second step will be to select the most interesting architecture and build a prototype with reduced power of the technology.

Flexible nanosensors matrix for impact detection on sensitive surface

Département Systèmes

Laboratoire Autonomie et Intégration des Capteurs

01-09-2019

SL-DRT-19-0434

elise.saoutieff@cea.fr

The aim of the PhD thesis is to implement a matrix of flexible piezoelectric nanosensors, which enable the 3D reconstruction of a force or deformation field. The nanosensors based on GaN nanowires obtained by directed growth are fabricated and assembled at CEA. The candidate will tackle experimental aspects, which include the fabrication and the assembly of sensors and sensor networks (matrix) via controlled growth and deposition processes, first-level flexible electronic layers (interconnects), system integration on an object (mechatronics) and finally signal collection and processing through a dedicated reading electronics, to be designed based on the competences present in our laboratory. In parallel, the candidate will carry out studies at the fundamental level, such as investigating the mechanical transfer between the nanowire and its environment and its effect on the generated signal under deformation, or the study of the piezoelectric / pyroelectric coupling intrinsic to GaN nanowires. For this purpose, the candidate will have access to multi-physics simulation tools. Finally, investigations on the choice of materials and the characterisation thereof (structural, mechanical, thermal, optical, electrical) will be pertinent and may pursued. More generally, this PhD thesis will also provide the opportunity to develop applicable solutions in various fields such as deformation and impacts detectors for predictive maintenance, sensitive surfaces or electronic skin.

Study by transmission electron microscopy of the intergranular phases in NdFeB magnets for their magnetic property optimization

Département des Technologies des NanoMatériaux (LITEN)

Laboratoire de Nanocaractérisation et Nanosécurité

01-10-2019

SL-DRT-19-0571

laure.guetaz@cea.fr

The deployment of renewable energies and limitation of greenhouse gas emission involve a growing use of permanent magnets to build the cores of electrical machines. However, the most powerful magnets (NdFeB sintered) require a non-sustainable use of critical raw materials (Dy, Tb). Optimizing the magnet microstructure is widely recognized as the most promising route to mitigate the dependency to these problematic materials. In this context, knowledge of the chemical composition and structure of the phases along the grain boundaries has become crucial to better understand the magnetic properties of magnets and improve the process route. The main objective of the thesis is to study the microstructure of sintered magnets developed at CEA-Grenoble and, more particularly, to precisely characterize the intergranular phases. The PhD will used the different facilities available on the nano-characterization platform (PFNC). Specifically, she/he will use advanced electronic microscopy techniques such as nanodiffraction and STEM/HAADF (scanning transmission electron microscopy/high angle annular dark field) coupled with X-EDS (Xray energy dispersive spectroscopy) that allow analysis of the structure and the chemistry composition at the atomic scale. Secondly, from the identification of phases located at grain boundaries, she/he will use the data to set up micro-magnetic simulation. This work carried out in close collaboration with the team in charge of the magnet manufacturing will make it possible to propose an optimization of the magnet composition and process parameters.

Devellopment of the coercivity in TRFe12 alloys for permanent magnets with low rare earth content

Département des Technologies des NanoMatériaux (LITEN)

Laboratoire Matériaux Avancés et mise en forme

01-10-2019

SL-DRT-19-0606

sorana.luca@cea.fr

In a context of significant development of engines and generators based on permanent magnets (hybrid vehicles, wind turbines) and limited raw material resources, it is necessary to reduce the amount of rare earths (TR) present in the NdFeB magnets. The research of new compounds, containing less TR, which could replace the NdFeB permanent magnets while keeping the high magnetic performances of these magnets, is essential. We are currently seeing a renewed interest in the TRFe12 phases known since 1990, which have interesting intrinsic magnetic properties for permanent magnets: saturation magnetization and anisotropy field equal to or even larger than for Nd2Fe14B. However, the work carried out in the scientific community does not make possible to obtain sufficient coercivity to be able to replace the magnets in Nd2Fe14B. The goal of this PhD thesis is: (1) the development of the TRFe12 alloys manufacturing process and sintering conditions; and (2) understanding and developing the coercivity in TRFe12 magnets. The student will use the experimental means of the Poudr'Innov platform of CEA-LITEN as well as those present at the CNRS - Institut Néel for the manufacture of magnets. Magnetic characterizations will be performed using conventional resources (hysteresis measurement, magnetometer at different temperatures) possibly large instruments (ILL). The expected results are: (1) the synthesis of the anisotropic TRFe12 phase, (2) the realization of sintered magnets of TR-Fe12 type by conventional and / or SPS methods, and (3) the understanding of the mechanisms of coercivity in magnets with low TR content.

Study and mitigation of ionomer degradation in PEMFC electrodes by combining electrochemistry and Operando Neutron/X-Ray characterizations

Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN)

Laboratoire Analyse électrochimique et Post mortem

01-10-2019

SL-DRT-19-0638

sylvie.escribano@cea.fr

Despite huge improvements in the past decade, advances in the performance and durability of PEMFC are still necessary for them to compete with existing technologies. The proton conducting ionomer, contained in the electrodes of PEMFC, is conjectured to be one of the major causes in performance losses. Few studies have been carried out on this ionomer within the electrodes because of the difficulty in characterizing its distribution and properties. Thus, the degradation mechanisms of the ionomer during operation, highly dependent on water content, are still largely hypothetical but believed to lead to modifications of its distribution, chemical and physical structure, transport properties and its contamination by cations. In this PhD, we wish to elucidate the mechanisms by coupling electrochemical and microstructural characterizations with in-situ and operando experiments using Neutrons (ILL) and X-Ray probes (ESRF, SOLEIL), furthermore including accelerated aging tests to simultaneously correlate performance degradation and local modifications of the materials. Specifically, the structure of the ionomer will be investigated by SANS and the water content in the electrodes using neutron radiography. As a result of these investigations we also aim at improving durability of PEMFC by tuning the composition of the electrodes or proposing more appropriate operating strategies as two kinds of mitigation pathways which will be validated towards selected ageing protocols. Achieving these goals is essential for the widespread adoption of PEMFC in clean transportation systems.

Atomic resolution imagery composition measure applied to superarrays

Département Technologies Silicium (LETI)

Autre laboratoire

01-10-2019

SL-DRT-19-0639

nicolas.bernier@cea.fr

For crystalline materials sensitive to electron beam radiation damage, it is necessary to quantify the chemical composition at the atomic scale while minimizing the electron dose. The usual analytical techniques in the transmission electron microscope (TEM) can not be used because of the high probe current and the relatively long acquisition time. On the other hand, atomic imaging, more precisely using the high-angle annular dark field (STEM-HAADF), is performed at a reduced dose and exhibits contrasts proportional to the atomic number of the elements. In addition, the TEMs Titan on the PFNC are equipped with an aberration corrector to acquire state-of-the-art HAADF images in terms of atomic resolution. However, for the contrast in these images to be quantitatively related to the chemical composition of the material, controlled TEM acquisition conditions and electronic scattering simulations must be developed. In parallel, another imaging technique in the TEM is attracting growing interest: ptychography, or "4D data STEM". This technique, consisting in acquiring a diffraction pattern for each position of the incident electron beam, provide the projected potential in the sample. The development of the quantitative aspect of these imaging techniques has many applications: the one targeted in this thesis is the understanding of the atomic order of GeTe / Sb2Te3 superlattices, materials considered as the most promising for phase change memories (PCRAM).

The Backend Selector: from material development to device performance

Département Composants Silicium (LETI)

Laboratoire de Composants Mémoires

01-10-2019

SL-DRT-19-0659

gabriele.navarro@cea.fr

The maturity of non-volatile resistive memory technologies NVRM (such as phase-change memory PCM) for both Storage Class Memory (SCM) and embedded applications has demonstrated in recent years the need for the development of a reliable backend selector device to replace transistor selection. This technology allows the stacking of multiple levels of memory in 3D, in a so-called "Crossbar" architecture, increasing the storage density while taking advantage of the extraordinary performances of NVRM devices. LETI is today at the state of the art regarding the development of materials for integration into backend selector devices, especially for Ovonic Threshold Switching selectors (OTS). In the framework of this PhD new materials will be explored to meet the required specifications in terms of endurance, temperature stability, threshold voltage and scalability capability becoming more and more stringent. For this, the understanding of the physics and of the phenomena related to the functionality of these devices becomes fundamental. In addition, innovative memory+selector co-integration architectures will be investigated to finally achieve the integration of these solutions in an advanced Crossbar demonstrator. The candidate should preferably have a very good level of knowledge in semiconductor physics and materials science. The candidate will be in contact with experts from different fields because of the multidisciplinary nature of the work (materials, integration, electrical and physicochemical characterization, and modeling). In addition, good team spirit and a good English language proficiency is required.

Embedding of high temperature resistant Fiber Bragg Gratings into metal structures obtained by additive manufacturing processes

DM2I (LIST)

Laboratoire Capteurs et Architectures Electroniques

01-10-2019

SL-DRT-19-0675

guillaume.laffont@cea.fr

LCAE laboratory from the Technological Research Division at CEA List, in partnership with the LISL laboratory from the CEA DEN, specialized in metal additive layer manufacturing processes, proposes a PhD thesis aiming at developing methods to integrate optical fiber sensors (OFS) based on high temperature resistant Fiber Bragg Gratings (FBGs) in metallic components obtained thanks to metal additive layer manufacturing processes either for the aerospace or for the nuclear industry. Thanks to recent developments, ultra-stable FBGs have been realized using direct writing processes into silica optical fibers with femtosecond lasers. These temperature and strain transducers combined with special optical fibers designed for very high temperature environments will be considered for the instrumentation of components obtained by metal additive layer manufacturing. This project aims at contributing to the adoption of in situ monitoring of 3D-printed metallic components, paving the way for their Structural Health Monitoring (SHM) to anticipate failures in the fabrication process and to optimize operating costs thanks to the development of predictive and conditional maintenance-based procedures.

4D ultrasonic imaging with fast reconstruction algorithms in the Fourier domain and data compression

Département Imagerie Simulation pour le Contrôle (LIST)

Laboratoire Instrumentation et Capteurs

01-10-2019

SL-DRT-19-0677

sebastien.robert@cea.fr

Ultrasonic array imaging is now a widespread technique in the field of non-destructive testing, and most industrial systems are able to image structures in real-time with arrays typically consisting of 64 elements. For larger arrays with 128 or 256 elements, the imaging systems are slowed down considerably because of the large volume of signals to be transferred from the acquisition unit to the processing unit, and the number of computational operations to form a large image. A typical example is 3D imaging with 16x16 matrix arrays requiring the transfer of 256x256 signals and the computation of 10e6 to 10e8 voxels to form 3D images. In this context, the thesis aims to accelerate imaging systems by optimizing the data transfer with compressed sensing techniques and by exploiting fast reconstruction algorithms in the Fourier domain, these are able to reduce computations time of images by a factor of 300 compared to more conventional methods operating in the time domain. Finally, another point that will be addressed at the end of the thesis is the reduction of the number of signals with various techniques, such as random plane-wave emissions or sparse arrays in receive mode.

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