Magnetic ordering of dopants in diamond holds the prospect of exploiting diamond’s unique properties in the emerging field of spintronics. Several transition metal defects have been reported to order ferromagnetically in various semiconductors, however, low Curie temperatures and lack of other fundamental material properties have hindered practical implementation in room temperature spintronic applications. In this Thesis, we consider the energetic stability of 3d transition metal doped-diamond and its magnetic ordering properties at various lattice sites and charge states using ab initio Density Functional Theory methods. We find the majority of 3d transition metal impurities in diamond at any charge state to be energetically most stable at the divacancy site compared to substitutional or interstitial lattice sites, with the interstitial site being highly unstable (by ~8 - 10 eV compared to the divacancy site). At each lattice site and charge state, we find the formation energies of transition metals in the middle of the 3d series (Cr, Mn, Fe, Co, Ni) to be considerably lower compared to those early or late in the series. The energetic stability of transition metal impurities across the 3d series is shown to be strongly dependent on the position of the Fermi level in the diamond band gap, with the formation energies at any lattice site being lower in p-type or ntype diamond compared to intrinsic diamond. Further, we show that incorporation of isolated transition metal impurities into diamond introduces spin polarised impurity bands into the diamond band gap, while maintaining its semiconducting nature, with band gaps in both the spin-up and spin-down channels. These impurity bands are shown to originate mainly from s, p-d hybridization between carbon sp 3 orbitals with the 3d orbitals of the transition metal. In addition, the 4p orbitals contribute significantly to hybridization for transition metal atoms at the substitutional site, but not at the divacancy site. In both cases, the spin polarisation and magnetic stabilization energies are critically dependent on the lattice site and charge state of the transition metal impurity. By allowing magnetic interactions between transition metal atoms, we find that ferromagnetic ordering is likely to be achieved in divacancy Cr+2, Mn+2, Mn+1 and Co0 as well as in substitutional Fe+2 and Fe+1, indicating that transition metal-doped diamond is likely to form a diluted magnetic semiconductor which may successfully be considered for room temperature spintronic applications. In addition, these charge states correspond to p-type diamond, except for divacancy Co0, suggesting that co-doping with shallow acceptors such as B ( will result in an increase of charge concentration, which is likely to enhance mediation of ferromagnetic spin coupling. The highest magnetic stabilization energy occurs in substitutional Fe+1 (33.3 meV), which, also exhibits half metallic ferromagnetic ordering at the Fermi level, with an induced magnetic moment of 1.0 μB per ion, thus suggesting that 100 % spin polarisation may be achieved in Fe-doped diamond. / Physics / D. Litt. et Phil. (Physics)

Les mousses fragiles font aujourd'hui partie des nouveaux matériaux très performants dont le procédé de fabrication permet un contrôle précis de la microstructure finale. De nouveaux débouchés apparaissent dans des applications structurales (absorption de choc, allègement des structures) en raison de leur excellente tenue mécanique alliée à une grande légèreté. Dans les travaux réalisés dans le cadre de cette thèse, une mousse carbone à cellules ouvertes a été étudiée dans le but d'être utilisée pour assurer la protection des capots de protection d'emballages. Le comportement mécanique en compression a été caractérisé sous des sollicitations uniaxiales et multiaxiales. La surface de charge de la mousse ainsi que son évolution au cours du chargement ont été identifiés. Les principales propriétés mécaniques ont été évaluées et certaines d'entre elles ont été corrélées avec celles prédites par le modèle micro-mécanique de Gibson et Ashby développé pour les mousses fragiles. Grâce aux observations post-mortem sous microscope électronique à balayage et en micro-tomographie aux rayons X, les mécanismes de déformation et d'absorption d'énergie ont été également caractérisés. Pour modéliser le comportement multiaxial en compression de la mousse carbone, considérée comme un milieu continu homogène et isotrope, le modèle de Deshpande et Fleck (DF) a été adopté et adapté. Ce modèle a été implanté dans le code éléments finis LS-DYNA. Il a été identifié et validé sur l'ensemble des essais triaxiaux disponibles ainsi que sur des essais d'écrasement de mini-structure. Le comportement macroscopique global, obtenu à l'aide de simulations numériques, est prédit de manière satisfaisante. Il sera amélioré par la suite pour prendre en compte certains aspects non décrits actuellement. / Due to improvements in the manufacturing process that allow a better control of their microstructure, brittle foams are now part of the new efficient materials. New markets in the field of structural applications open up thanks to their excellent mechanical properties combined with light weight.In this study, a carbon foam with open cells has been studied in order to be used as shock absorber in packagings. Its compressive mechanical behavior has been characterized under various uniaxial and multiaxial loadings. The carbon foam yield surface and its evolution during loading have been identified. The main mechanical properties have been evaluated and some of them have been correlated with those predicted by the Gibson and Ashby micromechanical model. The mechanisms of deformation and the energy absorption have been studied using post-mortem observations by scanning electron microscopy (SEM) and X-Ray microtomography.The Deshpande and Fleck model (DF) has been adopted and slightly modified to model the compressive multiaxial behavior of the carbon foam. The latter is considered as an homogeneous continuum medium. The constitutive equations have been implemented in the finite element code LS-DYNA via a Umat routine. The model parameters have been identified and the model estimations validated on available triaxial tests as well as on crushing tests made on micro-structures. Numerical simulations are relevant on predicting the global macroscopic behavior. Nevertheless, the mechanical model needs to be improved to better account for some phenomena not currently described.

Increasing energy demand draws attention to new materials for improving current energy storage technologies. Particular interest is directed at solid state batteries and glass Na3ClO electrolyte is a promising candidate. In this report we explore some of the properties of this new glass and its capabilities as a potential electrolyte for a solid-state battery. The two aims of the study were to model the amorphous structure of the glass using the stochastic quenching method based on density functional theory as well as assessing the electrochemical stability of it against a metallic sodium electrode. Using VASP, a computational code based on density functional theory, we performed calculations of two 150 atom supercells, where the atoms were moved around until the systems were relaxed to obtain two glass models and the resulting structures were analyzed and characterized. The characterization of the structures was made by means of partial radial distribution functions, angle distribution functions, coordination numbers and bond lengths, which showed that the two models are statistically equivalent and either one can be used for the stability assessment of the glass. The electrochemical stability was assessed by inserting an extra sodium atom in possible holes in the glass model and calculating the energetics of Na insertion in each of these holes. This was made for 30 different hole positions. The reduction potential indicates the stability of each hole and the results was plotted as an energy distribution. Two peaks in the energy distribution, located at positive and negative energies, indicating stable and unstable holes, respectively. This indicates that the amorphous structure of the glass allows Na ions to travel (unstable holes). The stable peak has a greater probability density, which indicates a stable electrolyte against sodium metal electrode, though a larger sampling of holes is required for better statistics. / Ökande krav på energiefterfrågan uppmärksammar nya material för att förbättra nuvarande energilagringsteknik, med fokus på solida batterier och glaset Na3ClO som en lovande kandidat för elektrolyt. I denna rapport undersöks några av egenskaperna för glaset samt möjligheten för denna att fungera som elektrolyt i ett solid-state batteri. Målen med projektet var att modellera den amorfa strukturen av glaset genom att använda stochastic quenching method som baseras på density functional theory samt undersöka den elektrokemiska stabiliteten mot en metallisk natrium elektrod. Genom användning av VASP, beräkningskoder baserade på density functional theroy, beräknades två superceller med 150 atomer vardera där atomerna flyttas runt tills dess att systemet var relaxerat och två modeller av glaset erhölls. Dessa var sedan visualiserades och karakteriserade. Karakterisering av strukturerna gjordes genom en partiella radiella fördelningsfunktioner, vinkel distrubitionsfunktioner, koordinationsnummer och bindningslängder. Detta visade på statistisk ekvivalens, vilket innebär att båda modellerna kan användas för vidare stabilitetsundersökning. Den elektrokemiska stabiliteten undersöktes genom att sätta in en extra natrium atom i möjliga hål i glas modellen samt beräkna dess energier av Na insättning i respektive hål. Detta gjordes för 30 olika positioner för hålen. Reduktionspotentialen indikerar stabiliteten för respektive hål, och resultatet plottades som en energidistribution. Två toppar i energidistributionen, lokaliserade vid positiva och negativa energier, indikerar stabila respeltive instabila hål. Detta indikerar på att den amorfa strukturen för glaset tillåter Na joner att färdas (instabila hål). Den stabila toppen har en större sannolikhetstäthet vilket indikerar på en stabil elektrolyt mot en metallisk natrium elektrod, men en större samling hål krävs för en bättre statistisk säkerhet.

Dans une machine à induction, le diagnostic de défauts par analyse du signal du courant électrique nécessite la connaissance du comportement dynamique de la machine. En plus des sources externes d'excitation, le comportement du moteur est gouverné par un ensemble de phénomènes périodiques liés sa géométrie angulairement périodique et couplés par leur caractère multiphysique. En présence d’un défaut de roulement, les grandeurs mesurables présenteront des composantes à sa fréquence caractéristique combinée aux fréquences caractéristiques du moteur. La compréhension des interactions, en particulier de modulation, passe par la mise en place de modèles numériques qui représentent les manifestations des phénomènes couplés. Ce travail de thèse propose donc un modèle électro-magnéto-mécanique d'une machine à induction à cage d'écureuil couplé à un modèle de palier à roulement à billes dans un cadre original d'écriture appelé "Approches Angulaires". En conservant dans la modélisation la relation "Angle-Temps" il est possible d'étendre aisèment la modélisation aux conditions de fonctionnement non-stationnaires et d'introduire un couplage fort entre les modèles mécanique et électromagnétique. Ainsi, on montre que la vitesse angulaire instantanée est la grandeur qui assure la transmission du défaut mécanique localisé aux grandeurs électriques. Le modèle proposé offre ainsi un décryptage des phénomènes de modulation présents sur la voie de transfert et décrits par les couplages de comportements dynamiques cycliques (réseau de perméances, chargement des éléments roulants,...) et/ou périodiques (résonances de structure, résonance électriques, ...). Ces travaux ouvrent la voie à une meilleure compréhension du comportement couplé multiphysique d'une machine électrique pour mieux spécifier les outils de surveillance à mettre en œuvre. Les futurs développements peuvent maintenant s'orienter ver une complexification des modèles ou l'exploitation de comportements dynamiques fins en régime non-stationnaire. / In an induction machine, the diagnosis of defects by analysis of the electrical current signal requires knowledge of the dynamic behavior of the machine. In addition to external excitation sources, the behavior of the motor is governed by a set of periodic phenomena related to its angularly periodic geometry and coupled by their multiphysical character. In the presence of a bearing defect, measurable quantities will have components at its characteristic frequency combined with the characteristic frequencies of the engine. The understanding of interactions, in particular modulation, requires the implementation of numerical models that represent the manifestations of coupled phenomena. This thesis work proposes an electro-magneto-mechanical model of a squirrel-cage induction machine coupled to a rolling bearing model in an original writing frame called "Angular Approaches". By keeping the "Angle-Time" relation in modeling, it is possible to easily extend the modeling to non-stationary operating conditions and to introduce a strong coupling between the mechanical and electromagnetic models. Thus, it is shown that the instantaneous angular speed is the quantity which ensures the transmission of the localized mechanical defect to the electrical quantities. The proposed model thus offers a decryption of the modulation phenomena present on the transfer path and described by the couplings of cyclic dynamic behaviors (permeance network, loading of the rolling elements, etc.) and / or periodic (structural resonances, electrical resonance, etc.). This work opens the way for a better understanding of the multiphysical coupled behaviors of an electrical machine to better specify the monitoring tools to be used. Further developments can now be directed to a complexity of models or to the exploitation of fine dynamic behaviors in a non-steady operating conditions.

Orogenic belts are fundamental features of plate tectonics. The crustal structure of orogens around the world shows a wide range of deformation styles from narrow, asymmetric wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros or the Himalaya. The primary controlling factor on the size and structure of an orogen is the amount of convergence between the colliding plates. However, there are important additional factors providing major controls on the structural development of orogens. Among the potential parameters that can affect the style of deformation are the crustal strength, inherited weaknesses, and the surface processes. These parameters have been studied extensively in the past but their relative importance remains unclear. The aim of this thesis is to improve our understanding of: (1) How surface processes affect mountain building, with a special focus on the relationship between thin-skinned foreland and thick-skinned internal deformation of orogens. (2) How inherited extensional structures affect mountain building. The study was carried out using the Pyrenees as a special reference case. To answer our research questions we have used a wide range of state-of-the-art numerical modelling tools. In paper 1 we present a new method where we couple a structural-kinematic model and a thermo-kinematic model to evaluate the consistency of existing balanced section reconstructions with independent thermochronology data. In papers 2 and 3 we use 2D lithospheric scale thermo-mechanical models with surface process algorithms. Using the above toolset, we demonstrate that syntectonic sedimentation results in longer basement thrust sheets as well as longer thin-skinned thrust sheets and a generally wider orogen. Conversely erosion tends to narrow the wedge and reduce the orogenic loading of the colliding plates, limiting the space available for deposition in the flexural foreland deeps. We also demonstrate that inherited extensional structures play a crucial role in mountain building as they facilitate the migration of deformation into the undeformed basement of the overriding plate. Moreover, a significant amount of lower-crustal/mantle-lithospheric material is preserved at shallow depths only in the presence of extensional inheritance, but significant erosion is needed in order to bring this material to the surface. Our models also show that thin-skinned thrust sheets are generally rooted in the footwall of basement thrusts as they form outward-propagating sequences. As soon as a new basement thrust forms, the thin-skinned sequence situated on top of the new basement thrust-sheet is abandoned in favour of starting a new sequence in the footwall of the new thrust. Regarding our case study, it was possible to reproduce the section restoration using a structural-kinematic model with high accuracy up to the 36-Ma time slice and with limited accuracy up to the 50-Ma time slice. The thermochronometric ages predicted by the thermo-kinematic modelling are generally in good agreement with both the high- and low-temperature thermochronology data available in the Central Pyrenees; hence we conclude that the restoration is to a first order consistent with these datasets. The predicted thermochronological ages approximate the available low-temperature thermochronology data better by taking into account the late-stage burial and re-excavation scenario affecting the southern flank of the Pyrenean wedge presented by Coney et al. (1996), and quantified by Fillon and van der Beek (2012). In conclusion, our model experiments suggest, that extensional inheritance played a prime role in the structural evolution of the Pyrenees, with the major characteristics of the North Pyrenean Unit, including the presence of steep, inverted normal faults, the relative tectonic quiescence of the area after the early inversion and the presence of a lower-crustal body at shallow depth below the unit, best recaptured by our accordion models. / Orogenic belts are fundamental features of plate tectonics. The crustal structure of orogens around the world shows a wide range of deformation styles from narrow, asymmetric wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros or the Himalaya. The primary controlling factor on the size and structure of an orogen is the amount of convergence between the colliding plates. However, there are important additional factors providing major controls on the structural development of orogens. Among the potential parameters that can affect the style of deformation are the crustal strength, inherited weaknesses, and the surface processes. These parameters have been studied extensively in the past but their relative importance remains unclear. The aim of this thesis is to improve our understanding of: (1) How surface processes affect mountain building, with a special focus on the relationship between thin-skinned foreland and thick-skinned internal deformation of orogens. (2) How inherited extensional structures affect mountain building. The study was carried out using the Pyrenees as a special reference case. To answer our research questions we have used a wide range of state-of-the-art numerical modelling tools. In paper 1 we present a new method where we couple a structural-kinematic model and a thermo-kinematic model to evaluate the consistency of existing balanced section reconstructions with independent thermochronology data. In papers 2 and 3 we use 2D lithospheric scale thermo-mechanical models with surface process algorithms. Using the above toolset, we demonstrate that syntectonic sedimentation results in longer basement thrust sheets as well as longer thin-skinned thrust sheets and a generally wider orogen. Conversely erosion tends to narrow the wedge and reduce the orogenic loading of the colliding plates, limiting the space available for deposition in the flexural foreland deeps. We also demonstrate that inherited extensional structures play a crucial role in mountain building as they facilitate the migration of deformation into the undeformed basement of the overriding plate. Moreover, a significant amount of lower-crustal/mantle-lithospheric material is preserved at shallow depths only in the presence of extensional inheritance, but significant erosion is needed in order to bring this material to the surface. Our models also show that thin-skinned thrust sheets are generally rooted in the footwall of basement thrusts as they form outward-propagating sequences. As soon as a new basement thrust forms, the thin-skinned sequence situated on top of the new basement thrust-sheet is abandoned in favour of starting a new sequence in the footwall of the new thrust. Regarding our case study, it was possible to reproduce the section restoration using a structural-kinematic model with high accuracy up to the 36-Ma time slice and with limited accuracy up to the 50-Ma time slice. The thermochronometric ages predicted by the thermo-kinematic modelling are generally in good agreement with both the high- and low-temperature thermochronology data available in the Central Pyrenees; hence we conclude that the restoration is to a first order consistent with these datasets. The predicted thermochronological ages approximate the available low-temperature thermochronology data better by taking into account the late-stage burial and re-excavation scenario affecting the southern flank of the Pyrenean wedge presented by Coney et al. (1996), and quantified by Fillon and van der Beek (2012). In conclusion, our model experiments suggest, that extensional inheritance played a prime role in the structural evolution of the Pyrenees, with the major characteristics of the North Pyrenean Unit, including the presence of steep, inverted normal faults, the relative tectonic quiescence of the area after the early inversion and the presence of a lower-crustal body at shallow depth below the unit, best recaptured by our accordion models.

In general, electric propulsion offers very high efficiency but relatively low thrust. To remedy this, several ion engines can be assembled in a clustered configuration and operated in parallel. This requires the careful design of a frame to accommodate the individual propulsion systems. This frame must be modular to be used in different cluster sizes, and verify thermal and mechanical requirements to ensure the nominal operation of the thrusters. The present report aims to show the design process of such a frame, from preliminary modelling to the experimental study of a prototype. This document features an overview of the iterative design process driven by thermal simulations rendered on COMSOL Multiphysics. This process led to the conception of a 2-thruster and 4-thruster cluster frame. A lumped-parameter model of the electric propulsion system was also created to model its complex thermal behaviour. In addition, the 2-thruster frame was studied mechanically with analytical calculations and simulations of simple load cases on SolidWorks. Lastly, a prototype based on the 2-thruster frame model was assembled. The prototype was used to conduct temperature measurements while hosting two operating thrusters inside a vacuum chamber. The temperature distribution in the cluster was measured, and compared to simulation results. Thermal simulations of the 2-thruster and 4-thruster frame showed promising results, while mechanical simulations of the 2-thruster version met all requirements. Moreover, experimental results largely agreed with thermal simulations of the prototype. Finally, the lumped-element model proved instrumental in calibrating the models, with its high flexibility and quick computation time. / Generellt erbjuder elektrisk framdrivning hög verkningsgrad men relativt låg dragkraft. För att avhjälpa detta kan flera jonmotorer sättas samman i en klusterkonfiguration och drivs parallellt. Detta kräver en noggrann utformning av en ram för att rymma de enskilda framdrivningssystemen. Denna ram måste vara modulär för att kunna användas i olika klusterstorlekar och verifiera termiska och mekaniska krav för att säkerställa den nominella driften av motorerna. Föreliggande rapport syftar till att visa designprocessen för en sådan ram, från preliminär modellering till experimentell studie av en prototyp. Detta dokument innehåller en översikt över den iterativa designprocessen, driven av termiska simuleringar gjorda med COMSOL Multiphysics, som ledde till uppfattningen av en 2 motorer och 4 motorer ram. En klumpelementmodell av jonmotorn skapades också för att modellera dess komplexa termiska beteende. Dessutom var den 2 motorer ram studeras mekaniskt med analytiska beräkningar och simuleringar av enkla laddafall med SolidWorks. Slutligen monterades en prototyp baserad på den 2 motorer rammodellen. Prototypen användes för att göra temperaturmätningar medan den är värd för 2 jonmotorer i en vakuumkammare. Temperaturfördelningen i klustret mättes och jämfördes med simuleringsresultat. Termiska simuleringar av den 2 motorer och 4 motorer ramen visade lovande resultat, medan mekaniska simuleringar av den 2 motorer versionen klarade alla krav. Dessutom överensstämde experimentella resultat till stor del med termiska simuleringar av prototypen. Slutligen var klumpelementmodellen mycket användbar för att kalibrera de andra modellerna med sin höga flexibilitet och snabba beräkningstid.

L’électronique de puissance a un rôle de plus en plus grandissant dans les systèmes de transports : voitures électriques et hybrides, trains et avions. Pour ces applications, la sécurité est un point critique et par conséquent la fiabilité du système de puissance doit être optimisée. La connaissance du temps de fonctionnement avant défaillance est une donnée recherchée par les concepteurs de ces systèmes. Dans cette optique, un indicateur de défaillance précoce permettrait de prédire la défaillance des systèmes avant que celle-ci soit effective. Dans cette thèse, nous nous sommes intéressés à la caractérisation électromécanique des puces de puissance IGBT et MOSFET. L’exploitation de cette caractérisation devrait permettre, à plus long terme, de mettre en évidence un indicateur de l’état mécanique des assemblages de puissance à des fins de fiabilité prédictive. / Power electronics has a role increasingly growing up in transport:electric and hybrid vehicles, trains and aircraft. For these applications, security is a critical point, thus the reliability of the power assembly must be optimized. The knowledge of time to failure is very important information for the designers of these systems. Inthis context, an early failure indicator would predict system failuresbefore it becomes effective. In this thesis, we focused on the electromechanical characterization of power transistors: MOSFET and IGBT. Based on these results this electromechanical characterization should help us in the longer term, to highlight an early failure indicator of the power assembly.