Dissertations / Theses on the topic 'Alliages de Heusler – Propriétés électroniques'
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Neggache, Amina. "Propriétés électroniques des alliages d'Heusler Co1.5Fe1.5Ge et Co2MnSi." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0229/document.
Spin transfer is one way of switching the magnetization of a layer in a magnetic tunnel junction. The current needed at this task depends on the materials and in the current context, consume less became an important issue. Materials with a high spin polarization and a low magnetic damping are one solution of this problem. They are called half metal ferromagnets. Because of the existence of a pseudo-gap in the minority spin channel at the Fermi energy, these compounds show a 100% spin polarization and an extremely low magnetic damping. In theory, some Heusler, such as Co1.5Fe1.5Ge and Co2MnSi, possess theses properties if they crystallize in the good crystallographic phase. In practice, there is strong indication of this behavior by mean of indirect techniques. However, no direct evidence of this pseudo-gap has been observed. It is in this context that this thesis is. After having determined growth conditions of Co1.5Fe1.5Ge, by mean of several techniques and especially by anomalous diffraction, we determined the complete chemical order which is the one we were looking for. Magnetic properties measurements show results in agreement with the theory. But the use of this compound in magnetic tunnel junctions shows low tunnel magnetoresistance. Spin resolved photoemission spectroscopy measurements explain very well these results. In the same spirit, we started to study Co2MnSi which seems more promising as this pseudo-gap and low magnetic damping have been observed
Palin, Victor. "Heusler compounds for spin-orbitronics : exploration of topological effects and magnetic anisotropy engineering." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0031.
Over the last decades, the needs in storage capacity as shot up with computing development. The energy crisis that we are going through in the 21th century requires to develop new fundamental materials for data storage. It was with this purpose that physicist develop new ways to store information in order to reduce device’s scale, energy consumption and manufacturing cost while memories’ size and information’s speed has shot up. The research conducted in this thesis make use of two different ways to improve data storage:- The first one is by using emerging materials in science, called topological insulator, that host peculiar spin texture predicted to generate very high spin-to-charge interconversion. This non-trivial state of matter can be complex to stabilize and image. This is the goal of the first part of this thesis where topological insulators coming from the half-Heusler family are engineered by molecular beam epitaxy. Structural characterization are carried out by X-ray and electronic diffraction along with scanning tunneling microscopy and transmission electron microscopy that confirm an epitaxial growth in the desired structure predicted to host a non-trivial topology. Angle resolved photoemission spectroscopy is performed and reveals the presence of linear states around the Γ point of the Brillouin zone. Nonetheless, the complex Fermi surfaces imaged do not allow to draw clear conclusions on the non-trivial nature of both alloys. Transport measurements were performed to test the potential interconversion efficiency of our compounds and spin Seebeck experiments revealed a spin-to-charge conversion two to three times higher in our TIs compared to a Pt control sample.- The second way chosen to improve conventional magnetic memories is by playing with magnetic anisotropy. Here again, Heusler family offers a vast variety of compounds allowing to fulfill this goal. The Mn3Z family compounds has attracted a lot of attention owing to their tetragonalized unit cell that allows to stabilize perpendicular magnetic anisotropy (PMA) even in a thin film geometry. In this thesis, we investigate Mn(100-x)Ga(x) and Mn(100-x)Ge(x) alloys and manage to stabilize them in their D0(22) structure that offers PMA. A peculiar zoom is then done on Mn3Ge-based stacks composed of a second Heusler alloy with remarkable properties, the Co2MnZ’ family (Z' = Si, Ge). Co2MnZ’ compounds have a half-metallic behavior making them very suitable for spin transfer torque related applications due to their low magnetic damping and full spin polarization at the Fermi level. Here we develop Mn3Ge/Co2MnZ' heterostructures (bilayers and superlattices) and manage to grow both compounds in the desired structures. The overall system is perpendicularly magnetized (thanks to Mn3Ge), terminated with a half-metal magnet (thanks to Co2MnZ') and the thicknesses used for both layers allow to tune the magnetic properties and obtained 100% of remanence
Pradines, Barthélémy. "Structure électronique et propriétés magnétiques statiques et dynamiques d'alliages d'Heusler partiellement désordonnés et d'hétérostructures tout-Heusler." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30171/document.
The Heusler alloy family contains several compounds considered to be prime candidates to be integrated as magnetic electrode into high-?performance spintronic devices. Some of these alloys indeed exhibit high Curie temperatures, have been predicted theoretically to be half-?metallic, and display a low Gilbert damping parameter. Nevertheless, the experimental results are generally less convincing than those reported numerically. The first part of this thesis is devoted to the ab initio study of hypotheses that are usually used to explain the differences between experimental and theoretical results. Calculations, based on the density functional theory, are then used to understand the impact of structural defects (partial chemical disorders, tetragonal deformation, vacancies) on the static and dynamic electronic and magnetic properties of Co-?based bulk full-Heusler alloys (Co2MnSi, Co2MnSn, Co2MnAl et Co2FeAl). In the second part of this thesis we propose to study, with the same numerical tools, the physical characteristics of "all-Heusler" heterostructures promising for spintronics and rare in the literature. We have focused on the variations of electronic properties in the vicinity of the "half-metal/insulator" (Fe2TiSi/Co2MnSi, CoTiAs/Co2MnSi) or "half-metal/non-magnetic metal" (Fe2VAl/Co2MnSi, RhNiSi/Co2MnSi) interfaces composing the studied multilayers. The obtained results highlight the interest of these structures for spintronic devices such as spin valves or magnetic tunnel junctions
Abdallah, Iman. "Spin dynamics and structural modifications of Co2MnSi Heusler alloys by helium ions irradiation." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30079/document.
Spintronic, which involve electron's in addition to its charge, has emerged from the discovery of Giant Magnetoresistance (GMR) by A. Fert and P. Grunberg in 1988, rewarded by a Nobel Prize in 2007. It has revolutionized the field of sensor devices. The basic mechanism of GMR and also of the Tunneling Magneto Resistance (TMR) relies on the spin polarization. Therefore there is today an intense research to find materials with both high spin polarization and low damping coefficient for the development of new generation of spintronic devices. In this field, one promising route concerns the Co2MnSi (CMS) Heusler alloy which is predicted to be half metals (i.e.100% spin polarization), with a weak Gilbert damping coefficient below 10-3, about one order of magnitude below the usual ferromagnetic material used in microelectronics. Its high Curie temperature up to 800° K also provides stability for devices working at room temperature. In this work, we study the correlations between the structural and magnetic properties of the Co2MnSi. To achieve our goal, we measure the evolution of the static and dynamic magnetic parameters of the Co2MnSi alloy in which atomic disorder is induced by He+ ion irradiation at 150 KeV. The samples are grown by magnetron sputtering on MgO substrates and then irradiated with light He+ ions. In order to correlate the structural and magnetic modifications of the alloy we combined several experimental techniques. CMS structure was investigated by X-ray diffraction and Transmission Electron Microscopy (TEM), in particular HAADF-STEM imaging mode. The evolution of the static and dynamic magnetic properties of the samples has been measured by means of Magneto Optic Kerr Effect (MOKE), Physical Properties Measurements System (PPMS) at the LPCNO laboratory in Toulouse and Ferromagnetic Resonance (FMR). The FMR set-up has been developed at the CEMES during this PhD. The main results of this work consists of correlation between the tetragonal deformations of the crystalline structure followed by the appearance of uniaxial anisotropy in the material upon irradiation. Furthermore, we demonstrate that the magnetic parameters of the B2 order are slightly affected by irradiation. But for the L21 phase, static and dynamic magnetic properties are drastically affected by irradiation, by the decrease in magnetization saturation, and exchange constant due to the Mn/Co disorder type and an increase of the cubic anisotropy and dynamic relaxation
Berger, Claire. "Propriétés électroniques des alliages quasicristallins AlMn." Grenoble 1, 1987. http://www.theses.fr/1987GRE10067.
Tuzcuoglu, Hanife. "Corrélation entre les propriétés structurales et magnétiques des couches minces et nanostructures de Co₂FeAl." Thesis, Paris 13, 2014. http://www.theses.fr/2014PA132035/document.
ACorrelation between structural and magnetic properties of Co₂FeAl thin films and nanostructures Co₂FeAl (CFA) is a very attractive Heusler alloy for spintronic applications. Their structural and magnetic properties depend strongly on the crystalline orientations and the interfaces quality. Therefore, the aim of this thesis is the study effects of the film thickness (dCFA), the substrate (MgO, Si and SrTiO₃(STO)) as well as the annealing temperature (Ta) on these properties. The structural analysis revealed a good epitaxial growth for films deposited on MgO and STO, in contrast to the Si substrate. The chemical order varies from the partially ordered B2 phase to the disordered A2 phase as dCFA or Ta decreases, regardless of the substrate. The ferromagnetic resonance (FMR) measurements show the superposition of a uniaxial and fourfold anisotropies for films grown on MgO and STO and only a weak uniaxial anisotropy for the samples grown on Si. The fourfold anisotropy is directly correlated to the crystal structure of the samples. The FMR and Brillouin light scattering measurements reveal the presence of a large negative perpendicular uniaxial anisotropy induced by CFA/MgO interface, which increases with 1/dCFA and with Ta. The relaxation mechanisms have carefully been studied and Gilbert damping coefficients of 0.0011 have been measured making CFA as a potential candidate for spin transfer torque-based devices. Finally, the study of submicron arrays of stripe obtained by patterning of the continuous CFA films reveals a spin waves quantization due to the finite stripes width
Mezhoudi, Amina. "Etude des propriétés électroniques et optiques d'alliages amorphes silicium azote préparés par pulvérisation réactive." Lyon 1, 1986. http://www.theses.fr/1986LYO19045.
Chaïb, Cheikh. "Contribution à l'étude des propriétés électroniques d'alliages métalliques liquides, métal noble-polyvalent, métal de transition-polyvalent." Metz, 1987. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1987/Chaib.Cheikh.SMZ8708.pdf.
In the present work we determine experimentally the electronic properties (resistivity and absolute thermoelectric power of metallic liquid alloys Cu-Pb and Mn-Sn. The theorical interpretation is in the frame work of Faber-Ziman theory. A new resistivity and TEP simultaneous measure cell has been elaborated. It is based on the fact that since the works of Roberts (1985), the tungsten can be taken as reference electrode for the TEP. Our attention has been fixed on the Cu-Pb system which presents a miscibility gap. Our aim was to determine if the presence of gap has an influence on electronic properties above the miscibility curve. We have studied the influence Bhatia-Thornton partials interference functions SNN and Snc which has been measured by neutron diffraction with the isotonic substitution method. The theoretical interpretation of the TEP of metallic ally can be realized according to the Faber-Ziman theory. The TEP is expressed as a function of energy dependent phase shifts. Anormal concentration dependence of the temperature coefficient of the resistivity and of the thermopower indicate some premonition of the phase separation. If we take into account the Bhatia-Thornton experimental interference functions, we improve considerably by resistivity calculation. Computation of TEP by using the energy dependence contribution the calculated TEP very new to the experimental one
Zaoui, Ali. "Etude des propriétés structurales, électroniques et optiques des semi-conducteurs de type AN B8-N et de leurs alliages." Metz, 1999. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1999/Zaoui.Ali.SMZ9943.pdf.
Ortiz, Hernandez Guillermo. "Élaboration et étude des propriétés physiques de couches minces monocristallines d'alliage de Heusler à faible amortissement magnétique pour composants hyperfréquences." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2045/.
This thesis fits in the framework of magnetic materials for microwave applications. The magnetic materials most commonly used in microwave devices are ferrites, especially garnets, which have a very low magnetic damping (about 0. 0001). The needs of miniaturization in current technologies bring some problems related to the integration of ferrites in microwave components. Theses materials, containing iron oxides, generally require very high deposition temperatures that may damage other parts within a same circuit. One solution lies in the use of ferromagnetic materials, which can be deposited at moderate temperatures. However, this type of material usually has high damping factors making them incompatible with the characteristics desired in microwave components. In this context, the Heusler alloys are particularly attractive. Indeed, the latter have high magnetizations and Curie temperatures, and ab initio calculations predict extremely low damping factors. The first step of this work was to develop a Ferromagnetic Resonance setup capable of studying materials in the microwave domain. This step was followed by the preparation of epitaxial thin film of Co2MnSi, by sputtering deposition, on MgO (001) and MgO/Cr (001) substrates. A thorough structural study (RHEED, X-ray diffraction, transmission electron microscopy) allowed verifying the high crystalline quality of samples. Their magnetic properties were studied by static and dynamic techniques in order to provide a complete characterization of their magnetic parameters as a function of thickness: saturation magnetization, exchange constant, damping factor, gyromagnetic ratio, anisotropy constants. The samples studied show low magnetic damping factors ranging between 0. 002 and 0. 007. The magnetic parameters (magnetocrystalline anisotropy, gyromagnetic factor) are strongly modified with the implementation of a Cr buffer layer. This suggests that the magnetic properties of Heusler alloys thin films are closely related to strains at interfaces. This work shows that Co2MnSi could constitute a building bloc for the realization of microwave components. The buffer layer engineering is set to be a key to making these alloys compatible with the needs of current technologies. This work should make possible the study of more complex systems such as magnonic crystals based on Heusler alloys
Beaulieu, Nathan. "Propriétés électroniques et magnétiques sous excitation laser femtoseconde, du Gd monocristallin aux alliages ferrimagnétiques." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00953656.
Chetouane, Abdelkrim. "Contribution à l'étude des spectres optiques des semi-conducteurs en présence d'une impureté substitutionnelle isoélectronique." Metz, 1987. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1987/Chetouane.Abdelkrim.SMZ8715.pdf.
In this research paper, we have studied the modification of optical absorption spectrum due to the disorder created in the pure systeme by the introduction of the isoelectronic substitutionnal impurity of weak concentration. The interest of this is to have access on the one hand, to symetry points of the Brillouin zone and on the other hand to give a simple and complete interpretation of spectrum optical of diluted alloys. In fact the presence of impurity introduces new structures into the spectrum optical after the break of the lattice periodicity. At the begining we possess the formalism of the dielectric constant of Parlebas and Mills, available in the case of metals and insulator. We have extended this model to a study of binary semiconductors with multiples bands. This study has first been testeed in the case of a binary diatomic chair. In the tridimensional case, we have considered a semi-conductor of the metal type with two independant bands. The study of the differential and spectrum has enableed to show the impurity created from supplementary and lacking structures due either to direct transitions or to indirect transitions. We have shown the activation of these transition find its origine in the electronic structure of the alloys. More over, we have applied the calculation of the dielectric constant to the "4f" (by taking one of the two non dispersive bands of Terre-rare this study enables a qualitative interprétation of absorption spectrum in the Terre-rare system such as SMS during the metallic semi-conductor transition
Basrour, Skandar. "Contribution à l'étude des propriétés physico-chimiques et électroniques des alliages amorphes de SiGe:H déposés par PECVD." Grenoble 1, 1990. http://www.theses.fr/1990GRE10072.
Adouby, Kopoin. "Influence de l'élément chalcogène sur la formation de composés définis dans les systèmes SnX-Bi2X3 (X = Te, Se, S). Conséquences sur les propriétés électroniques." Montpellier 2, 1998. http://www.theses.fr/1998MON20056.
Plenet, Jean-Claude. "Formation de phases amorphes ou quasicristallines dans les systèmes AlMn et AlFe par mixage ionique : étude de leurs propriétés de transport." Lyon 1, 1991. http://www.theses.fr/1991LYO10189.
Rhazi, Assia. "Contribution à l'étude des propriétés de transport électronique d'alliages liquides à base d'indium et de métaux de transition." Metz, 1997. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1997/Rhazi.Assia.SMZ9733.pdf.
The purpose of this thesis was to study the electronic transport properties of In-Ni and In-Y binary alloys and In-Ni-Mn ternary alloys. From our knowledge, no resistivity and absolute thermoelectric power of these alloys are available in the literature. In-Ni and In-Y system analyses show the dependance of the resonance connected to the d states in the materials where the d orbitals are nearly full as for nickel and where the d orbitals contain only one electron as yttrium. We have been able to show that the phase shift n2 of nickel has a resonance which is not detected for yttrium. In the In-Ni-Mn system, a concave resistivity curve has been observed for the first time experimentally. Only negative value for the absolute thermoelectric power were found when analysing alloy containing a high concentration of manganese. We were able to qualitatively explain such phenomena with a good correlation by using theory presented for our work
Souifi, Abdelkader. "Etude par spectroscopies de photoluminescence et d'admittance des propriétés électroniques d'hétérostructures Si1-xGex : Si pour composants avances de la microélectronique silicium." Lyon, INSA, 1993. http://www.theses.fr/1993ISAL0093.
This work reports on the characterization of Si1-xGex/Si heterostructures grown on Si by rapid thermal chemical vapour deposition (RT-CVD). The goal of this study, was to contribute to a better understanding of the electronical properties of this strained system, and to analyse the quality of this material for its application to heterojunction bi polar transistors (HBTs). A detailed study, of the photoluminescence (PL) properties of Sit-xGex strained layers is presented. The excitonic transitions, observed for the first time in thick Si Ge strained layers, have been used to give the band gap variations as a function of germanium content, at low temperatures. The effects of band gap narrowing (BGN) du to heavy boron doping have been also studied by PL rneasurements on Sio,s2Geo,18 strained films. The relaxation process bas been studied by rneans of PL rneasurements, and electrical characterizations (I(V), C(V), deep level transient spectroscopy (DLTS)), in order to know accurately the limits of stability of the strained layers. Deep levels correlated to the relaxation defects have been detected by spacialy resolved DLTS measurements. This procedure allows us to observe separately, the levels associated to the interfacial misfit dislocations, and the dislocations within the SiGe layers. Finally, this study leads us to conclude on the excellent quality of the RT-CVD heteroepitaxial Iayers, and hence, on the ability to use this strained system for the realisation of advanced Si-based devices
Vergnat, Michel. "Hydrogénation d'alliages semi-conducteurs amorphes : Structure et propriétés électroniques des alliages amorphes hydrogènes SI::(1-X)SN::(X):H." Nancy 1, 1988. http://www.theses.fr/1988NAN10322.
Gargouri, Koubaa Nabila. "Pseudopotentiel de Bachelet, Hamann et Schlüter : calcul du facteur de forme et des propriétés de métaux et alliages liquides." Metz, 1990. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1990/Gargouri_koubaa.Nabila.SMZ906Pri.pdf.
Lecouturier, Florence. "Contribution au développement des champs magnétiques pulsés très intenses : R & D des conducteurs renforcés." Toulouse, INSA, 1995. http://www.theses.fr/1995ISAT0027.
Carrère, Hélène. "Conception, élaboration et caractérisation de structures à puits quantiques GaInAsN/GaAs pour composants optoélectroniques émettant à 1,3 [micromètre]." Toulouse, INSA, 2002. http://www.theses.fr/2002ISAT0030.
This work deals with the plasma assisted molecular beam epitaxy growth and optical and structural characterisation of (Ga,In)(As,N) bulk and quantum well structures in the view to realise lasers for optical telecommunications. The first section of this report relates the very recent history of (Ga,In)(As,N) and its potentiality for fabricating laser devices. The second chapter is focused on the study or the RF plasma cell used as the nitrogen source. We investigate the influence of the RF cell utilisation parameters on the nitrogen incorporation in the material and on the nature of species (atomic or molecular) which incorporate. We also present the experimental conditions we used for determining quantitatively the nitrogen contents by SIMS. The third chapter deals with the (Ga,In)(As,N) growth optimisation. We study the influence of growth temperature, growth rate and V/III atom flux ratio on the incorporation of nitrogen and on the optical quality of GaInAsN/GaAs quantum wells. We also investigate the influence of the RF plasma cell parameters on the incorporation of impurities and the ion-induced damage of the samples. Finally, the fourth chapter is dedicated to the physical properties of the material. Firstly, we present the modelling of quantum well laser structures based on the band anticrossing model. Secondly, we present the results obtained from photoluminescence and resonant Raman spectroscopy measurements performed on GaInAsN quantum wells and bulk GaAsN
Tomic, Sylvia. "Propriétés électroniques des composés (TMTSF)₂X et de leurs alliages : rôle des anions sur l'état fondamental et le comportement de basse température." Paris 11, 1986. http://www.theses.fr/1986PA112017.
We have studied the modifications in the behaviour of the electron gas at low temperatures and the ground state of single-chain quasi-1d conductors (TMTSF)2X associated with the presence of non-centrosymmetric anions (X). The ground states can be either insulating (due to the formation of a spin density wave phase or ta the anion ordering), or superconducting, or even metallic. Our study confirms the important role of pressure in establishing the SC ground state and shows the dominant effect of non-magnetic impurities on the mutual stability of SC and AF phases. Applied pressure provides the conditions necessary for SC coupling and transforms staggered anion ordering into an uniform one compatible with the metallic behaviour and the SC ground state. However in those compounds with dipolar anions or in the alloys, the SC ground state is easily suppressed due to the strong random potential along the conducting chains which is created by the anions. Moreover, the degree of order on the anion chains plays a decisive role in the competition between the AF and SC phases: the disorder favours the former, while a uniform order is compatible with the latter. We discuss the extreme sensitivity of the superconductivity ta the presence of non-magnetic defects in the framework of two theoretical models depending on whether the SC ground state is singlet or triplet. However, the proximity of the AF and SC ground states in the phase diagram, as well as the fact that the magnetic susceptibility is almost temperature independent are somewhat more compatible with triplet pairing. Nevertheless, independently of the nature of the SC ground state we conclude that a one-particle approach is too restrictive and that an analysis taking into account cooperative precursor effects is necessary to understand the unusual properties of the SC ground state in the (TMTSF)2X compounds and their alloys
Siari, Ahmed. "Propriétés magnétiques et électroniques d'alliages amorphes à base de terres rares ou d'uranium." Nancy 1, 1987. http://www.theses.fr/1987NAN10055.
Dridi, Zoulikha. "Les propriétés structurales et électroniques des alliages AlxGa1-xN, InxGa1-xN, et InxAl1-xN : étude par la méthode ab initio des ondes planes augmentées avec linéarisation et potentiel total." Caen, 2003. http://www.theses.fr/2003CAEN2076.
Baghdadli, Tewfik. "Etude des propriétés structurales et électroniques de nouveaux matériaux à base d'alliages III-N pour l'optoélectronique." Thesis, Metz, 2009. http://www.theses.fr/2009METZ019S/document.
This thesis work concerns the electrical and optical characterization of new III-N nitride alloys for optoelectronics and the optimization of ohmic and Schottky contacts on these materials. The first part of this thesis was related to the realization of metallic contacts, particularly difficult for these high bandgap materials, by the optimization of the surface treatment, multi-layer metallization and thermal annealing. We developed annealing processes at relatively low temperature (between 200°C and 500°C) and studied the effect of the chemical treatment and annealing in order to find the optimal conditions for ohmic contacts. We obtained for instance Ti/Al contacts with an excellent ohmicity and used Pt to process Schottky functional diodes. The second part of this thesis was related to the study of the electronic and structural properties of the new BGaN alloy grown by MOVPE in our laboratory. The electric characterization showed for the first time a dramatic increase in the resistivity associated to the decrease of the free carriers’ concentration when the composition of boron in BGaN increases. The variation of the resistivity in BGaN with respect to the temperature was analyzed by using a theoretical model which takes into account the free carriers’ interaction with impurities and phonons and the variation of resistivity with boron in BGaN was discussed in this framework and linked to a compensation phenomenon of the residual dopants. On the other hand a very interesting correlation was carried out between Raman and electrical results through the phonon-plasmon coupling
Masquelier, Nicolas. "Caractérisation et modélisation de transformations microstructurales pour la mise au point d'une nouvelle génération d'alliages d'aluminium pour conducteurs électriques." Rouen, 2012. http://www.theses.fr/2012ROUES011.
New aluminium alloy had been developed for electrical cable application. This alloy has good mechanical properties at high temperature, and also good electrical properties. Its microstructure had been characterized at atomic scale with the goal to link microstructure and physical properties. Thanks to this correlation, microstructure was adjusted to optimize the physical properties of this alloy. Microstructure of the alloy was also modelized to predict the evolution of physical properties with time. Finally, linking characterization and modelling, thermodynamical datas had been determined. These datas was unknown for this particular alloy and could be useful for the future
Jouiad, Mustapha. "Caractéristiques mécaniques et état d'ordre de la phase gamma de superalliages base nickel." Toulouse 3, 1996. http://www.theses.fr/1996TOU30193.
Lavielle, Denis. "Influence du dopage sur les propriétés de transport de semiconducteurs III-V (AlxGa1-xAs, InP) et de microstructures associées." Toulouse, INSA, 1990. http://www.theses.fr/1990ISAT0021.
Grenouilloux, Thomas. "Etude des mécanismes de diffusion dans les alliages HgCdTe pour la détection infrarouge." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAD020.
This thesis work focuses on the modeling of the different diffusion phenomena that occur during the processing steps of the p/n HgCdTe technology. Hg/Cd interdiffusion is essential for the passivation of the HgCdTe and so was addressed. In a monocrystalline material, the interdiffusion coefficient is calculated with the Darken law. It includes the thermodynamic factor which temperature dependence was determined. Indium exodiffusion and diffusion in HgCdTe were also studied. Arsenic is used as a p dopant and so is activated in Hg-rich conditions. Its diffusion was studied firstly in classic conditions, and then after its incorporation in HgCdTe with the influence of out of equilibrium point defects
Libot, Jean-Baptiste. "Méthodologie d'évaluation de la durée de vie des assemblages électroniques sans plomb en environnements thermique et vibratoire." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/18560/1/Libot_1.pdf.
Beyens, Christophe. "Développement et caractérisation de matériaux de surface innovants écologiques pour la sécurité et le confort automobile." Thesis, Lille 1, 2013. http://www.theses.fr/2013LIL10175.
Thermoplastic olefins (TPO) are polymeric materials produce by blending polypropylene, polyethylene and their copolymers. They are used especially in automotive industry to produce bumpers or as skin layer for interior parts such as dashboard. For this application, the shape of the part is given by thermoforming a grained TPO foil. During the process, the thickness of the foil decrease and the grain can be deformed. Thus the user-perceived quality of the final product doesn’t match with customer’s expectation. The treatment of TPO by electron beam (EB) was chosen in this work to modify some physic-chemical properties and potentially improve the thermoforming of TPO’s foil. A preliminary study concerns the irradiation of a commercial TPO mixture. Changes of mechanical and thermal properties are highlighted after treatment. The thermoformability of foil is improved too. However, the effect of EB on the commercial material is restricted by the degradation of polypropylene and some new formulation need to be developed. For this purpose, two different ways are investigated. In the first formulation, TPO is blended with some concentration of triblock copolymer. In the second, reactive monomers are added in the material. These formulations are irradiated by EB and the effect of the treatment is characterized by different methods (differential scanning calorimetry, thermogravimetric analysis, tensile test…). Changes of thermoformability are also evaluated for the developed materials
Fan, Yinan. "Rational synthesis of plasmonic/catalytic bimetallic nanocrystals for catalysis." Thesis, Sorbonne université, 2022. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2022SORUS189.pdf.
Among several nanocatalysts, those based on noble metal NPs deserve particular attention because of their electronic, chemical and even optical properties (in the case of plasmonic-enhanced transformations). Platinum or palladium are well known for their remarkable catalytic properties, but they are expensive and their resources are limited. In addition, single component nanocatalysts can only lead to a limited range of chemical reactions. Thus, our strategy was to develop bimetallic nanocatalysts composed of two metal elements that can exhibit synergistic effects between their physicochemical properties and enhanced catalytic activity. We have thus designed bimetallic nanocatalysts of the core-shell type composed of a silver core and a platinum shell. The interest is to combine the high and efficient catalytic activities of the platinum shell surface with the highly energetic silver core capable of enhancing the activities of the shell through its plasmonic properties. In addition, these bimetallic NPs often exhibit superior catalytic activity due to the modification of the Pt-Pt atomic bonding distance (i.e. the strain effect). In this thesis work, Ag@Pt NPs have been synthesized via a two-step process using chemically synthesized spherical Ag NPs as seeds on the one hand and platinum complexes with oleylamine on the other hand which are then reduced on the surface of the seeds at a controlled temperature. Different Ag seed sizes from 8 to 14 nm with a very low size distribution (<10%) have been obtained by adjusting the reaction time, temperature ramp, Ag precursor concentration and final temperature during the synthesis. The control of the shell thicknesses (from 1 to 6 atomic layers) has been possible by adjusting the ratio of platinum precursor to silver seed concentrations. The catalytic activity of the core-shell Ag@Pt NPs was tested by a model reaction of reduction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous phase. We have observed that the thickness of the Pt shell and the size of the Ag core influence the catalytic properties and led increased catalytic activity compared to pure silver or platinum. This was attributed to synergistic effects. Furthermore, we have observed an enhancement of the catalytic activity of Ag and Ag@Pt NPs under light irradiation. This is correlated to the generation of hot electrons in the Ag core. Finally, in order to develop a supported nanocatalysis platform, 3D self-assemblies also called supercrystals composed of Ag@Pt nanoparticles have been spontaneously obtained after deposition on a solid substrate due to their narrow size distribution and homogeneous shape. The catalytic activity of these supercrystals for the hydrogen evolution reaction (HER) has been studied by following in situ by optical microscopy the production of H2 gas nanobubbles. Three distinct behaviors in photo-catalytic activity (activity, intermittent activity and non-activity) have been observed on the supercrystals in the same region of interest. In addition, 50% of the assemblies were determined to be active for HER which was shown to be accompanied by oxidative corrosion of silver