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La fermentation en milieu solide (FMS) est un procédé biotechnologique particulièrement bien adapté au traitement de la biomasse végétale. Cette technologie, extrapolable à l’échelle industrielle, peut répondre aux besoins actuels du marché de l’alimentation animale en développant des produits fermentés visant à améliorer les qualités des matières premières d’un point de vue nutritionnel et fonctionnel. Les travaux de recherche présentés dans cette thèse développent ces aspects à partir du tourteau de colza issu du procédé de trituration des graines.Un premier criblage a mis en évidence le potentiel de certaines souches fongiques en prenant en compte les performances de croissance et leur capacité à enrichir le tourteau en protéines totales et digestibles. Des teneurs comparables à celles du tourteau de soja, principale source de protéine en nutrition animale, ont d’ailleurs été atteintes. Une activité biologique d’intérêt a ensuite été démontrée in vitro sur cellules immunitaires. Cette voie, inexplorée jusqu’à présent à partir de culture en milieu solide, confère une valeur ajoutée au produit fermenté via un apport en composés immunomodulateurs naturels d’origine fongique comme les β-glucanes. Ces derniers suscitent un intérêt croissant car ils représentent une alternative à l’utilisation des antibiotiques comme facteur de croissance. L’étude consacrée à la phase d’optimisation du procédé FMS a permis d’accroître les performances de croissance de la souche A. sojae et de définir une stratégie visant à maintenir les conditions optimales de croissance en réacteur pré-pilote à couche profonde. Des complications liées à la granulométrie très fine du tourteau de colza et à la qualité microbiologique qui évolue en cours de fermentation dans des conditions non stériles ont pu être identifiées mais le procédé mis en place a alors permis de les maîtriser en partie. / Solid state fermentation (SSF) is a biotechnological process particularly well adapted to the treatment of vegetable biomass. This technology adjustable to industrial scale, is adapted to current challenges in animal nutrition by developing fermented products in order to improve the quality of raw materials from a nutritional and functional point of view. The work presented in this thesis considers these issues using rapeseed meal from the oil crushing industry.A first screening study highlighted several fungal strains based on their growth performance and protein enrichment (total and digestible) of the substrate. Levels similar to those of soybean meal, the main protein source in animal nutrition, have also been reached. An interesting biological activity was then reported in vitro on immune cells. To date, this way has never been investigated concerning solid state culture. The presence of fungal immunomodulatory compounds as β-glucan confers added value to the fermented product. Recently, there has been growing interest in natural immunomodulators as they represent an alternative to the use of antibiotics for growth promotion in food animal production. SSF process optimization improved the growth performance of the strain A. sojae and helped to determine the best strategy to maintain optimum growth conditions at larger scale in the deep-bed pre-pilot reactor. Complications related to the fine particle size of the rapeseed meal and the changes in microbiological quality during fermentation under non-sterile conditions were also identified and partially controlled by the process.

Rokshana Parvin Molecular epidemiology and biological properties of avian influenza viruses of subtype H5N1 and H9N2 Institute of Virology Submitted in November 2014 Pages 106, Figures 7, Table 1, References 339, Publications 4 Keywords: Avian Influenza Virus, H5N1, H9N2, Reassortment, Mutation, Replication and Growth kinetics Introduction Avian influenza viruses (AIVs) are the major cause of significant disease outbreaks with high morbidity and mortality worldwide in domestic birds resulting in great economic losses. Especially the subtypes of highly pathogenic avian influenza viruses (HPAIV) H5N1 and low pathogenic avian influenza viruses (LPAIV) H9N2 became the most prevalent AIVs in poultry causing regular disease outbreaks in many countries of Asia, the Middle East and Europe and are still ongoing events. Therefore, continues monitoring, surveillance and characterization of the circulating viruses are of high priority. Objectives The current study was designed for three main objectives; i) Molecular epidemiology of the HPAIV H5N1 in migratory birds in Bangladesh, ii) Molecular characterization of the AIV subtype H9N2 and iii) Biological properties of the AIV subtype H9N2. Materials and methods In first the part of the investigations, two HPAIV H5N1 strains were confirmed from 205 pools of fecal surveillance samples in Bangladesh. The two isolated H5N1 viruses were characterized by genome amplification and sequence analysis of the all eight genome segments. In the second part of the investigations, a confirmed AIV H9N2 from a retrospective analysis derived from a poultry farm in Bangladesh was characterized. Furthermore, three AI-H9N2 viruses were isolated and characterized from a commercial broiler and broiler breeder flock with clinical respiratory manifestations in Egypt. Full length genome amplification, cloning, sequencing and comprehensive phylogenetic analyses were performed for all eight genome segments. In the final part of the study, four selected Eurasian lineage H9N2 viruses - three G1 sub-lineages H9N2 and one European wild bird H9N2 virus - were propagated in embryonated chicken eggs (ECE) and Madin-Darby canine kidney epithelial cell culture systems. The ECE-grown and cell culture-grown viruses were monitored for replication kinetics based on tissue culture infectious dose (TCID50), hemagglutination assay (HA) and quantitative real time RT-PCR (qRT-PCR). The cellular morphology after infections was analyzed by immunofluorescence assay and cellular ELISA was performed to screen the sensitivity of the viruses to amantadine. Results The two newly isolated HPAIV H5N1 strains from migratory birds belonged to clade 2.3.2.1 and clustered together with other recently isolated viruses in Bangladesh derived from ducks, chickens, quails and crow. The amino acid sequences were also genetically similar although, some unique amino acid substitutions were observed. These substitutions were not related to the known conserved region of the molecular determinants of the virus. The phylogenetic analyses of the isolated AIV H9N2 from Bangladesh and Egypt revealed their close relationship with their respective contemporary isolates and maintained ancestor relation with A/Quail/HK/G1/1997 confirming that all studied H9N2 belonged to G1 sub-lineage. All six internal gene segments of the Bangladeshi AIV H9N2 showed high sequence homology with the HPAIV subtype H7N3 from Pakistan. In addition, also the PB1 internal gene showed high nucleotide homologies with a recently circulating HPAI-H5N1 virus from Bangladesh. Thus, the Bangladeshi AIV H9N2 is genetically a unique strain which shares internal gene segments with different HPAI viruses and takes part in reassortment events. On the other hand, the internal gene segments of the Egyptian H9N2 viruses were similar to the other members of the G1 sub-lineage with no evidence of reassortment events. In this virus rather point mutations within their respective gene segments are observed. With regard to the biological characterization, the three G1-H9N2 viruses produced comparatively higher titer than the Eurasian wild type-AIV H9N2. Overall, the ECE-grown viruses yielded higher titers than cell culture-grown viruses. Following a single passage in cell culture, individual nucleotide substitutions were noticed in HA, NA and NS gene sequences but none of them are related to the conserved region that can alter virus pathogenesis or virulence. All of the studied H9N2 viruses were sensitive to amantadine. Conclusion The present study demonstrated for the first time the presence of HPAI H5N1 in the wild migratory bird population in Bangladesh and determine as one of the major cause to introduce the new clade of HPAIV H5N1 into the Bangladeshi poultry flocks. The Bangladeshi AIV H9N2 strain has exhibited two independent reassortment events with HPAIV of subtype H7N3 and H5N1.The Egyptian AIV H9N2 strains were limited to regular point mutations which is very common for AIVs. The G1-H9N2 viruses showed a higher replication profile when compared to European wild bird-AIV H9N2. Both the ECE and MDCK cell system allowed efficient replication but the ECE system is considered as the better cultivation system for H9N2 viruses in order to get maximum amounts of virus within a short time period. In this study new strains of AIV H9N2 and H5N1 with significant genetic constitutions were described. Thus, continuous monitoring of the field samples, rapid reporting soon after outbreaks, molecular characterization to confirm the emergence of new reassortant strains and the biological properties to know its impact on the virulence are recommended. / Rokshana Parvin Molekulare Epidemiologie und biologische Charakterisierung von aviären Influenzaviren der Subtypen H5N1 und H9N2 Institut für Virologie Eingereicht im November 2014 Seiten 106, Abbildungen 7, Tabelle 1, Literaturangaben 339 , Publikationen 4 Schlüsselwörter: Aviäres Influenza Virus, H5N1, H9N2, Reassortment, Mutation, Replikation und Wachstumskinetik Einleitung Weltweit kommt es in der Geflügelproduktion durch Infektionen mit aviären Influenzaviren (AIV) zu hohen Morbiditäts- und Mortalitätsraten und damit verbunden zu hohen wirtschaftlichen Verlusten. Zu den bedeutenden AIV in der Geflügelwirtschaft werden die hoch pathogenen aviären Influenzaviren (HPAIV) des Subtyps H5N1 sowie AIV des Subtyps H9N2 gezählt. Letztere besitzen die Charakteristika von niedrigpathogenen aviären Influenzaviren. Durch diese Subtypen kommt es regelmäßig in vielen Ländern in Asien, im Nahen Osten und Europa zu wiederholten Krankheitsgeschehen. Dies bedingt die dringende Notwendigkeit von andauerndem Monitoring, Überwachung und Charakterisierung der zirkulierenden Viren. Ziele der Untersuchungen Die vorliegende Studie soll folgende drei Hauptfragestellungen beantworten: i) Molekulare Epidemiologie des HPAIV H5N1 bei Zugvögeln in Bangladesch, ii) Molekulare Charakterisierung von AIV des Subtyps H9N2 und iii) Biologische Eigenschaften von AIV des Subtyps H9N2. Materialien und Methoden Der erste Teil der Arbeit befasst sich mit zwei HPAIV Stämmen des Subtyps H5N1, welche im Monitoring Programm in Bangladesch von insgesamt 205 gepolten Kotproben, isoliert wurden. Die Charakterisierung der beiden Isolate erfolgte durch Vervielfältigung der acht Genomsegmente und nachfolgende phylogenetische Analysen. Der zweite Teil der Arbeit beschreibt die retrospektive Analyse eines AIV des Subtyps H9N2, welches von einer Geflügelproduktionsanlage in Bangladesch eingesandt wurde. Weiterhin wurden aus einer Geflügelmast- und Legehennenhaltung mit respiratorischer Symptomatik drei AIV des Subtyps H9N2 isoliert und charakterisiert. Auch hier wurde das gesamte Genom amplifiziert, kloniert und nachfolgend phylogenetisch analysiert. Im letzten Teil der Studie wurden vier europäische AIV H9N2 Isolate, von welchen 3 Isolate zur H9N2 Sublinie G1 gehören und ein Isolat von einem Wildvogel selektiert und in embryonierten Hühnereiern (EHE) und auf Madin-Darby canine kidney (MDCK) Zellen passagiert. Mittels 50% tissue culture infectious dose (TCID50), Hämagglutinationstest (HA) und RT-real-time-PCR (qRT-PCR) wurden von diesen so passagierten Viren die Vermehrungskinetik bestimmt. Die Morphologie der infizierten Zellen nach Infektion wurde mittels Immunfluoreszenztest analysiert. Eine Bestimmung der Amantadin Empfindlichkeit dieser Viren erfolgte mit einem ELISA. Ergebnisse Die beiden neuen HPAIV des Subtyps H5N1 von Zugvögeln können in die Clade 2.3.2.1 eingeordnet werden und clustern mit kürzlich aus Enten, Hühnern, Wachteln und Krähen isolierten AIV aus Bangladesch. Eine Verwandtschaft der Viren konnte auch auf Ebene der Aminosäure Sequenz gezeigt werden, obwohl einige einzigartige Aminosäure Austausche nachgewiesen wurden. Diese Austausche zeigen keine Verbindung mit bekannten konservierten Regionen der molekularen Determinanten der Viren. Die phylogenetische Analyse der AIV aus Bangladesch und Ägypten zeigt eine deutliche Verbindung mit den derzeit zirkulierenden AIV auf diesem geographischen Gebiet sowie die Verwandtschaft zu dem Isolat A/Quail/HK/G1/1997. Dies bestätigt, dass die in dieser Studie analysierten AIV zu der Subline G1 gehören. Alle sechs internen Gensegmente des AIV H9N2 aus Bangladesch zeigen eine hohe Sequenz Homologie mit einem HPAIV des Subtyps H7N3 aus Pakistan. Zusätzlich zeigt das interne Gene PB1 eine hohe Homologie auf Nukleinsäureebene zu einem derzeit in Bangladesch zirkulierenden HPAIV des Subtyps H5N1. Somit ist das AIV H9N2 aus Bangladesch als ein einzigartiges Isolat anzusehen, welches durch Reassortierung interne Gensegmente mit hochpathogenen AIV teilt. Im Gegensatz dazu, sind die internen Gene des AIV H9N2 aus Ägypten sehr ähnlich zu anderen Mitgliedern der Sublinie G1, welche keine Hinweise auf Reassorierung zeigen. Nur einzelne Punktmutationen konnten in den entsprechenden Gensegmenten nachgewiesen werden. In Hinblick auf die biologische Charakterisierung, konnte in den drei AIV H9N2 der Sublinie G1 vergleichsweise höhere Titer nachgewiesen werden als in einem europäischen AIV H9N2 Wildtypisolat. Insgesamt zeigten die in EHE passagierten Viren höhere Titer als die MDCK-Zell passagierten Viren. Schon nach einer Passage auf Zellkultur konnten einzelne Nukleotidaustausche in den HA, NA und NS kodierenden Gensegmenten nachgewiesen werden, wobei keine dieser Veränderungen einen Einfluss auf konservierte Regionen haben, die die Pathogenese oder Virulenz der Viren beeinflussen. Alle untersuchten H9N2 Viren sind sensitiv gegenüber Amantadin. Schlussfolgerungen Die vorliegende Studie zeigt erstmalig das Vorkommen von HPAIV H5N1 bei Zugvögeln in Bangladesch, welches als Haupteintragsquelle der neuen HPAIV H5N1 in der dortigen Geflügelhaltung angesehen wird. Das AIV H9N2 aus Bangladesch zeigt zwei unabhängige Reassortierungen mit HPAIV des Subtyps H7N3 und H5N1. Hingegen zeigt das ägyptische AIV H9N2 Punktmutationen, welche sehr typisch für diese Viren sind. Die hier untersuchten AIV H9N2 der Sublinie G1 zeigen im Vergleich zu einem europäischen AIV H9N2 eine höhere Replikationsrate. Eine Replikation der Viren konnte in EHE und MDCK-Zellen gezeigt werden, jedoch wird das EHE als das geeignetere System für die Kultivierung von H9N2 Viren betrachtet, da hier in einer kürzeren Zeitspanne mehr Virus produziert werden kann. Des Weiteren konnten in dieser Studie neue Isolate von AIV des Subtyps H9N2 und H5N1mit einem bedeutenden genetischen Aufbau beschrieben werden. Daher wird ein kontinuierliches Monitoring von Feldproben, unverzügliche Meldung von Ausbruchsgeschehen, die molekulare Charakterisierung zur Dokumentation eventuell auftretender neuer Reassortanten sowie Untersuchungen der biologischer Eigenschaften zur Virulenzbestimmung empfohlen.

High-entropy alloys (HEAs) have attracted significant interest in the materials science community over the last 15 years. At the first moment, what caught the attention was the fact that these alloys tend to form solid solutions at room temperature, despite being composed of multiple elements in equiatomic or near-equiatomic concentrations. It was initially concluded that the configurational entropy plays a key role in the stabilization of the solid solutions. Later studies revealed the importance of lattice strain enthalpies, enthalpies of mixing, structural mismatch of constituents, and kinetics in phase formation/stability. The study presented in this thesis was branched into three major parts, all related to understanding phase formation, stability, or metastability in this class of alloys. The first part deals with developing an empirical method to predict single-phase solid solution formation in multi-principal element alloys. The second, which makes the core of this thesis, are non-equilibrium solidification studies of CrFeNi and CoCrNi medium-entropy alloys, and CoCrFeNi, Al0.3CoCrFeNi, and NbTiVZr high-entropy alloys. The last part is devoted to understanding the thermophysical properties of CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys. An empirical approach, based on the theoretical elastic-strain energy, has been developed to predict the phase formation and its stability for complex concentrated alloys. The conclusiveness of this approach is compared with the traditional empirical rules based on the atomic-size mismatch, enthalpy of mixing, and valence-electron concentration for a database of 235 alloys. The proposed “elastic-strain energy vs. valence-electron concentration” criterion shows an improved ability to distinguish between single-phase solid solutions, mixtures of solid solutions, and intermetallic phases when compared to the available empirical rules used to date. The criterion is especially strong for alloys that precipitate the μ phase. The elastic-strain-energy parameter can be combined with other known parameters, such as those noted above, to establish new criteria which can help in designing novel complex concentrated alloys with the on-demand combination of mechanical properties. The solidification behavior of the CoCrFeNi high-entropy alloy and the ternary CrFeNi and CoCrNi medium-entropy suballoys has been studied in situ using high-speed video-camera and synchrotron X-ray diffraction (XRD) on electromagnetically levitated samples at Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden) and German Synchrotron DESY, Hamburg. In all alloys, the formation of a primary metastable body-centered cubic bcc phase was observed if the melt was sufficiently undercooled. The delay time for the onset of the nucleation of the stable face-centered cubic fcc phase, occurring within bcc crystals, is inversely proportional to the melt undercooling. The experimental findings agree with the stable and metastable phase equilibria for the (CoCrNi)-Fe section. Crystal-growth velocities for the CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys, extracted from the high-speed video sequences in the present study, are comparable to the literature data for Fe-rich Fe-Ni and Fe-Cr-Ni alloys, evidencing the same crystallization kinetics. The effect of melt undercooling on the microstructure of solidified samples is analyzed and discussed in the thesis. To understand the effect of Al addition on the non-equilibrium solidification behavior of the equiatomic CoCrFeNi alloy, the Al0.3CoCrFeNi HEA has been studied. While the quaternary alloy melt could be significantly undercooled, this was not possible in the five-component alloy. Therefore, the investigations on phase formation, crystal growth, and microstructural evolution were confined to the low undercooling regime. In situ XRD measurements revealed that the liquid crystallized into a fcc single-phase solid solution at this undercooling level. However, ex situ XRD revealed the precipitation of the ordered L12 phase for a sample solidified with ΔT = 30 K. Crystal growth velocities are shown to be smaller than in the CoCrFeNi, CrFeNi, and CoCrNi alloys; nonetheless, they are in the same order of magnitude. Spontaneous grain refinement, without the formation of crystal twins, is observed at low undercooling of ΔT = 70 K, which could be explained by the dendrite tip radius dependence on melt undercooling. In situ studies of the equiatomic NbTiVZr refractory high-entropy alloys revealed the effect of processing conditions on the high-temperature phase formation. When the melt was undercooled over 80 K, it crystallized as a bcc single-phase solid solution despite solute partitioning between the dendritic and interdendritic regions. When the sample was solidified from the semisolid state, it resulted in the formation of two additional bcc phases at the interdendritic regions. The crystal growth velocity, as estimated from the high-speed videos, showed pronounced sluggish kinetics: it is 1 to 2 orders of magnitude smaller compared to literature data of other medium and high-entropy alloys. The study of the linear expansion coefficient α and heat capacity at constant pressure 𝐶𝑝 of the equiatomic CoCrFeNi and the medium-entropy CrFeNi and CoCrNi alloys revealed an anomalous behavior with S-shaped curves in the temperature range of 700 – 950 K. The anomalous behavior is shown to be reversible as it occurred during the first and second heating. However, a minimum is only observed on the first heating, while in the second heating a sudden increase of both the α and 𝐶𝑝 occurs at the temperature of the onset of the minima in the first heating. Magnetic moment measurements as a function of temperature showed that the observed anomaly is not associated with the Curie temperature. Consideration of the structural and microstructural evaluation discards a first-order phase transformation or recrystallization as probable causes, at least for the CoCrFeNi and CoCrNi alloys. Based on literature evidence, the anomalies in the temperature dependences of the linear expansion coefficient and heat capacity are believed to be caused by a chemical short-range order transition known as the K-state effect. However, to reveal the exact nature of this phenomenon, further experimental and theoretical studies are required, which is outside the frame of the present work.:Abstract ....................................................................................................................... I Kurzfassung .............................................................................................................. IV Chapter 1: Motivation and Fundamentals .................................................................. 1 1.1 Introduction .......................................................................................................... 1 1.2 The high-entropy alloy (HEA) design concept ...................................................... 4 1.3 Empirical rules of phase formation for HEAs ....................................................... 6 1.4 Calculation of phase diagrams of HEAs ............................................................. 18 1.5 The core effects of HEAs ................................................................................... 20 1.5.1 Lattice distortion .............................................................................................. 20 1.5.2 Sluggish diffusion ............................................................................................ 22 1.5.3 Cocktail effect................................................................................................... 23 1.6 Mechanical properties ........................................................................................ 24 1.6.1 Lightweight high-entropy alloys ....................................................................... 24 1.6.2 Overcoming the strength-ductility tradeoff ...................................................... 26 1.6.3 Cryogenic high-entropy alloys ......................................................................... 28 1.6.4 Refractory high-entropy alloys ........................................................................ 30 1.7 Functional properties .......................................................................................... 33 1.7.1 Soft magnetic properties ................................................................................. 33 1.7.2 Magnetocaloric properties ............................................................................... 35 1.7.3 Hydrogen storage ............................................................................................ 36 Chapter 2: Experimental .......................................................................................... 38 2.1 Sample preparation ............................................................................................ 38 2.2 Electromagnetic levitation .................................................................................. 40 2.3 In situ X-ray diffraction ........................................................................................ 43 2.4 Microstructural and structural analysis ............................................................... 44 2.5 Thermal analysis ................................................................................................ 45 2.6 Dilatometry ......................................................................................................... 45 2.7 Magnetic moment ............................................................................................... 46 2.8 Heat treatment ................................................................................................... 46 Chapter 3: In situ study of non-equilibrium solidification of CoCrFeNi high-entropy alloy and CrFeNi and CoCrNi ternary suballoys ...................................................... 47 3.1 Introduction ........................................................................................................ 47 3.2 Results ............................................................................................................... 48 3.2.1 In situ synchrotron X-ray diffraction ................................................................. 48 3.2.2 High-speed video imaging ............................................................................... 52 3.2.3 Microstructure of the solidified samples .......................................................... 62 3.3 Discussion .......................................................................................................... 64 3.3.1 bcc-fcc nucleation and growth competition ..................................................... 64 3.3.2. Crystal growth kinetics ................................................................................... 68 3.3.3. Microstructural evolution ................................................................................ 70 Chapter 4: The effect of Al addition to the CoCrFeNi alloy on the non-equilibrium solidification behaviour.............................................................................................. 72 4.1 Introduction ........................................................................................................ 72 4.2 Results and Discussion ...................................................................................... 73 Chapter 5: Non-equilibrium solidification of the NbTiVZr refractory high-entropy alloy ................................................................................................................................. 84 5.1 Introduction ........................................................................................................ 84 5.2 Results ............................................................................................................... 85 5.2.1 In situ synchrotron X-ray diffraction ................................................................. 85 5.2.2 Room temperature synchrotron X-ray diffraction ............................................ 88 5.2.3 High-speed video imaging ............................................................................... 89 5.2.4 Microstructure and structure analysis ............................................................. 91 5.3 Discussion .......................................................................................................... 94 5.3.1 Phase formation upon solidification ................................................................ 94 5.3.2 Crystal growth kinetics .................................................................................... 98 5.3.3 Structural and microstructural features............................................................ 99 Chapter 6: Solid-state thermophysical properties of CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys ........................................................................... 101 6.1 Introduction ...................................................................................................... 101 6.2 Results ............................................................................................................. 102 6.3 Discussion ........................................................................................................ 106 6.3.1 Thermophysical properties ............................................................................ 106 6.3.2 Short-range order in medium- and high-entropy alloys ................................. 109 Chapter 7: Summary ............................................................................................... 111 7.1 Empirical rule of phase formation of complex concentrated alloys ................... 111 7.2 Non-equilibrium solidification of medium- and high-entropy alloys ................... 111 7.3 Thermophysical properties of the medium- and high-entropy alloys ................ 113 Chapter 8: Outlook ................................................................................................. 115 Appendix 1 .............................................................................................................. 117 Appendix 2 ............................................................................................................. 123 Appendix 3 ............................................................................................................. 133 Appendix 4 ............................................................................................................. 134 References.............................................................................................................. 140 Acknowledgments .................................................................................................. 164 List of publications .................................................................................................. 166 Erklärung ......................................................................................................................... 167

Die vorliegende Arbeit präsentiert eine erste umfassende Wachstumsstudie, und erste quantitative Wachstumsmodelle, von Gruppe-III und IV Oxiden synthetisiert mit sauerstoffplasmaunterstützter Molekularstrahlepitaxie (MBE). Diese entwickelten Modelle beinhalten kinetische und thermodynamische Effekte. Die erworbenen Erkenntnisse sind auf fundamentale Wachstumsprozesse in anderen Syntheseverfahren übertragbar, wie zum Beispiel der Laserdeposition oder metallorganische Gasphasenepitaxie. Die Wachstumsraten und Desorptionsraten werden in-situ mit Laser-Reflektometrie bzw. Quadrupol-Massenspektrometrie (QMS) bestimmt. Es werden die transparenten halbleitenden Oxide Ga2O3, In2O3 und SnO2 untersucht. Es ist bekannt, dass sich das Wachstum von Gruppe-III und IV Oxiden, aufgrund der Existenz von Suboxiden, fundamental von anderen halbleitenden Materialien unterscheidet. Es stellt sich heraus, dass die Wachstumsrate der untersuchten binären Oxide durch die Formierung und Desorption von Suboxiden flussstöchiometrisch und thermisch limitiert ist. Es werden die Suboxide Ga2O für Ga2O3, In2O für In2O3 und SnO für SnO2 identifiziert. Ein Suboxid ist ein untergeordneter Oxidationszustand, und es wird gezeigt, dass die untersuchten Oxide über einen Zwei-Stufen-Prozess gebildet werden: vom Metall zum Suboxid, und weiterer Oxidation vom Suboxid zum thermodynamisch stabilen festen Metalloxid. Dieser Zwei-Stufen-Prozess ist die Basis für die Entwicklung eines ersten quantitativen, semiempirschen MBE-Wachstumsmodells für binare Oxide die Suboxide besitzen. Dieses Model beschreibt und erklärt die gemessenen Wachstumsraten und Desorptionsraten. Es wird die Kinetik und Thermodynamik des ternären Oxidsystems (InxGa1−x)2O3 untersucht. Die gemittelten Einbauraten von In und Ga in ein makroskopisches Volumen von (InxGa1−x)2O3 Dünnschichten werden ex-situ mit energiedispersiver Röntgenspektroskopie gemessen. Diese Einbauraten werden systematisch analysiert und im Rahmen kinetischer und thermodynamischer Grenzen beschrieben. Es wird gezeigt, dass Ga den In-Einbau in (InxGa1−x)2O3 aufgrund seiner stabileren Ga–O Bindungen thermodynamisch verhindert. In diesen Zusammenhang wird ein neuer katalytisch-tensidischer Effekt des In auf den Einbau von Ga gefunden. Eine Folge dieses katalytisch-tensidischen Effektes ist die Formierung der thermodynamisch, metastabilen hexagonalen Ga2O3 phase mit sehr hoher Kristallqualität. Ein thermodynamisch induziertes, kinetisches Wachstumsmodel für (InxGa1−x)2O3 wird entwickelt, mit dem sich alle makroskopischen Metall-Einbauraten und Desorptionsraten vorhersagen lassen. Mögliche (InxGa1−x)2O3 Strukturen gewachsen mit MBE werden mittels Röntgenkristallographie bestimmt. Mit Hilfe der Röntgenstrukturanalyse wird ein erster makroskopischer Ansatz zur Bestimmung der mikroskopischen In Konzentration X in möglichen (InXGa1−X)2O3 Phasen hergeleitet. Es werden Löslichkeitsgrenzen von In bzw. Ga in monoklinem und kubischem (InXGa1−X)2O3 bestimmt. / The present thesis presents a first comprehensive growth investigation and first quantitative growth models of group-III and IV oxides synthesized by oxygen plasma-assisted molecular beam epitaxy (MBE). The developed models include kinetic and thermodynamic effects. The obtained findings are generally valid for fundamental growth processes in other growth techniques, such as pulsed laser deposition and metal-organic vapor phase-epitaxy. The growth rates and desorption rates are measured in-situ by laser reflectometry and quadrupole mass spectrometry (QMS), respectively. The binary transparent semiconducting oxides Ga2O3, In2O3, and SnO2 are investigated. It is known that the growth of group-III and IV oxides is fundamentally different as compared to other semiconductor compounds and due to the existence of suboxides. It is found that the growth rate of the binary oxides investigated is flux-stoichiometrically and thermally limited by the formation and desorption of their respective suboxide. These suboxides are identified as Ga2O for Ga2O3, In2O for In2O3, and SnO for SnO2. A suboxide is a lower oxidation state, and it is shown, that the investigated oxides grow via a two-step oxidation process. That means, all metal oxidizes to the suboxide, and the suboxide can be further oxidized to the thermodynamic stable solid metal-oxide. This two-step oxidation process is the basis for the development of a first quantitative semi-empirical MBE growth model which predicts and explains the measured growth rates and desorption rates, for binary oxides possessing suboxides. The kinetics and thermodynamics of the ternary oxide system (InxGa1−x)2O3, grown by MBE, is investigated. The average In and Ga incorporation rates into a macroscopic volume of (InxGa1−x)2O3 are measured ex-situ by energy dispersive X-ray spectroscopy. These incorporation rates are systematically analyzed and explained in the framework of kinetic and thermodynamic limitations. It is shown that Ga thermodynamically inhibits the incorporation of In into (InxGa1−x)2O3 due to its stronger Ga–O bonds. In this context, a new catalytic-surfactant effect of In on the formation of Ga2O3 is found. As a consequence of this catalytic-surfactant effect the metastable hexagonal Ga2O3 with very high crystal quality is formed. A thermodynamically induced kinetic growth model for (InxGa1−x)2O3 MBE is developed. It predicts all macroscopic metal incorporation rates and desorption rates. Possible (InxGa1−x)2O3 phases grown by MBE are investigated by X-ray crystallography. By means of X-ray diffraction analysis, a first macroscopic approach to determine the microscopic In concentration X in possible (InXGa1−X)2O3 phases is derived. The solubility limits of In and Ga in monoclinic and cubic (InXGa1−X)2O3 phases, respectively, are identified.

Une solution pour réduire la consommation de Si de haute pureté dans les cellules solaires à base de Si cristallin est de faire croître une couche active mince de haute qualité sur un substrat à faible coût. L'Epitaxie en Phase Liquide (EPL) est l'une des techniques les plus appropriées, car la croissance est réalisée dans des conditions proches de l'équilibre. On s'intéresse plus particulièrement au développement et l'optimisation d'une technique de croissance stationnaire et isotherme basée sur l'évaporation du solvant : l'Epitaxie en Phase Liquide par Evaporation d'un Solvant métallique (EPLES). Les principaux critères concernant le choix du solvant, de l'atmosphère de croissance et du creuset sont d'abord présentés et permettent de concevoir une première configuration d'étude. Un modèle analytique est ensuite développé pour comprendre les mécanismes mis en œuvre et étudier la cinétique d'évaporation du solvant et de croissance. Les différentes étapes du procédé de croissance dans le cas de l'EPLES de Si sont examinées et mettent en évidence un certain nombre de difficultés technologiques liées à cette technique : contrôle de la convection dans le bain, réactivité du bain Si-M avec le creuset, transport par différence de température et dépôt pendant la phase de refroidissement. Des solutions techniques sont proposées et mise en place pour contourner les difficultés rencontrées. Des couches épitaxiées de Si uniformes comprises entre 20 et 40 µm sont alors obtenues par EPLES avec des bains Sn-Si et In-Si sur substrat Si monocristallin entre 900 et 1200°C sous vide secondaire. Les vitesses de croissance expérimentales atteintes sont comprises entre 10 et 20 µm/h et sont conformes aux prédictions du modèle cinétique. La qualité structurale obtenue est comparable à celle des couches obtenues par EPL. Des couches de type P, avec un bain dopé In et In(Ga) sont obtenues avec une concentration en dopants proches de 1017 at.cm3 compatible avec une application PV. Enfin le potentiel de l'application de cette technique est évalué en basant la discussion sur la réalisation d'une couche de Si obtenue par EPLES sur substrat multicristallin avec un bain In-Si. / Crystalline Si thin films on low-cost substrates are expected to be alternatives to bulk Si materials for PV applications. Liquid Phase Epitaxy (LPE) is one of the most suitable techniques for the growth of high quality Si layers since LPE is performed under almost equilibrium conditions. We investigated a growth technology which allows growing Si epitaxial thin films in steady temperature conditions through the control of solvent evaporation from a metallic melt saturated with silicon: Liquid Phase Epitaxy by Solvent Evaporation (LPESE). We studied the main requirements regarding selection of solvent, crucible and growth ambient, and a first experimental set up is designed. An analytical model is described and discussed, aiming to predict solvent evaporation and Si crystallization rate. Growth experiments are implemented with a vertical dipping system. Growth procedure is presented and the influence, on Si growth, of melt convection, temperature gradient in the melt and Si-M reactivity with the material crucible are discussed. Solutions are proposed to improve and optimise the growth conditions. Experimentally, Si thin films were grown from Sn-Si and In-Si solution at temperatures between 900 and 1200°C under high vacuum. We are able to achieve epitaxial layers of several micrometers thickness (20-40µm). The predicted solvent evaporation rate and Si growth rate are in agreement with the experimental measurements. Regarding the structural quality, it is comparable to the crystal quality of layers grown by LPE. With In and In(Ga) melts, we can obtain P-type epitaxial layers with doping level in the range 1017 at.cm3, which is of great interest for the fabrication of solar cells. Finally, the growth of Si thin films on multicrystalline Si substrates by LPESE is discussed to assess the potential application of this technique.

The content of this thesis is about preparation and processing of lead-free piezoceramic materials with perovskite structure. Potassium sodium niobate (KNN) powder was prepared by solid state reaction (SSR) and liquid phase reaction (sol-gel reaction). The powders were formed by uniaxial and isostatic pressing and further sintered. The density, grain size and morphology were determined on the sintered samples. The powder, synthesised by SSR and sintered in a conventional furnace, was chosen as a standard. The maximum density achieved on samples after optimization of sintering cycle was 93 %TD. The sintering optimization involved a homogenization step at 950 °C, which promotes the correct development of the phase composition and microstructure, followed by sintering at 1120 °C. The same approach and sintering cycle were used for sintering the samples, prepared by sol-gel synthesis. The maximum density of the samples prepared by sol-gel reaction and sintered in a conventional way, was 92 %TD. For further comparison, both of the synthesised powders were sintered using SPS (spark plasma sintering), which increased their final density up to 97 %TD. The approximate value of the piezoelectric coefficient d33 (pC/N) has been measured on selected SSR samples with pure phase composition ((K0,5Na0,5)NbO3). The best measured value of d33 was around 100 pC/N.

Les whiskers, filaments métalliques qui poussent sur des surfaces métalliques, sont unproblème très important pour la fiabilité des composants électroniques. Depuis ces dernièresannées, il y a eu un regain d’intérêts industriels dans le domaine de la croissance des whiskers,principalement en raison de la miniaturisation des dispositifs électroniques et des réglementationsenvironnementales interdisant l'utilisation du plomb.Alors que la plupart des recherches concernent les whiskers d'étain, il y a encore peu detravaux sur les whiskers de zinc. Les revêtements d’électrodéposés de zinc sont utilisés commeprotection anticorrosion pour les aciers faiblement alliés dans diverses industries, commel'automobile, l'aéronautique ou l'énergie, ainsi que dans les structures de soutien ou les planchersfaux plafonds dans les centres de données informatiques. Afin d'atténuer, de prévenir et deprédire les défaillances causées par les whiskers de zinc, les mécanismes de sa croissance doiventêtre compris.Grâce à des tests de stockage accéléré et à des observations par microscopie électronique àbalayage (MEB), la cinétique de croissance des whiskers de zinc a été étudiée sur des tôles d'acierau carbone faiblement allié, galvanisé et chromé. Afin de comprendre les mécanismes de lacroissance des whiskers de zinc, la caractérisation quantitative ainsi que les excroissances (densité,volume et vitesse de croissance) ont été reliées aux paramètres suivants: la température, le bainpour l’électrodéposition du zinc, la chromatation, l’épaisseur du substrat d’acier, l’épaisseur durevêtement de zinc ainsi que la contrainte résiduelle.En outre, la microstructure et la cristallographie du revêtement de zinc, des racines deswhiskers ainsi que des whiskers elles-mêmes ont été étudiées par diffraction des électronsrétrodiffusés (EBSD), microscopie électronique à transmission (MET), microanalyse par rayon X(EDX) et le dispositif ASTAR pour l'orientation locale des grains; la préparation des échantillonsa été réalisée à l’aide d’un faisceau d'ions focalisés (FIB). La recristallisation ainsi que lesdislocations dans les whiskers et les excroissances ont été observés; aucun composéintermétallique n’a été observé que ce soit dans les échantillons issus de différents bainsélectrolytes ou encore dans les films / whiskers.Il a été montré que la relaxation de contrainte de compression résiduelle et la croissance deswhiskers sont deux phénomènes différents mais fortement reliés et thermiquement activés.Chacun d'entre eux suit un mécanisme différent; les énergies d'activation apparentes des deuxphénomènes ont été établies, et la diffusion aux joints de grains est proposée comme le principalmécanisme de diffusion pour la croissance des whiskers.Des cinétiques de la croissance des whiskers, à la fois analytique et phénoménologique sontproposées. Une bonne estimation de la croissance des whiskers et de leur vitesse de croissance àdes températures proches des conditions de fonctionnement est obtenue par comparaison avecles données expérimentales. / Whiskers, conductive metallic filaments that grow from metallic surfaces, are a very importantissue for reliability of electronic components. Through recent years, there has been a renewedindustrial interest on whisker growth, mainly due to the miniaturization of electronic devices andthe environmental regulations forbidding the use of lead.While most of the research has been focused on tin whiskers, there is still little reference tozinc whiskers. Electroplated zinc coatings are actually used as anticorrosive protection for lowalloy steels in diverse industries such as automotive, aerospace or energy, as well as for supportstructures or raised-floor tiles in computer data centers. In order to mitigate, prevent and predictthe failures caused by the zinc whiskers, the mechanisms of growth must be understood.By accelerated storage tests and Scanning Electron Microscopy (SEM) observation, kinetics ofgrowth of zinc whiskers was studied on low alloy chromed electroplated carbon steel.Quantitative characterization of both whisker and hillocks (density, volume and growth rate) wasrelated with the parameters temperature, electroplating electrolyte, presence of chrome, steelsubstrate thickness, zinc coating thickness and residual stress, in order to understand themechanisms of growth.Additionally, both microstructure and crystallography of zinc coating, whisker roots and actualwhiskers were studied by Electron Backscatter Diffraction (EBSD), Transmission ElectronMicroscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and local grain orientationwith ASTAR setup, using Focused Ion Beam (FIB) for samples preparation. Recrystallization aswell as dislocations were observed in both whiskers and hillocks; no intermetallic compoundswere seen in neither electroplated nor whiskers.It is found that compressive residual stress relaxation and whiskers growth are two differentbut strongly interconnected phenomena both thermally activated, an each of them follows adifferent mechanism; apparent activation energies of the two phenomena are calculated, andgrain boundary diffusion is established as the main diffusion mechanism for whiskers growth.Whiskers growth kinetics, both analytical and phenomenological is proposed. Goodestimation of whiskers growth and whiskers growth rate at temperatures close to operationconditions is obtained when compared with experimental data. / Whiskers, filamentos metálicos que crecen en superficies metálicas, son un problema muyimportante para la fiabilidad de componentes electrónicos. Durante los últimos años, ha habidoun renovado interés industrial en el crecimiento de whiskers, debido principalmente a laminiaturización de dispositivos electrónicos y a las regulaciones ambientales que prohíben lautilización de plomo.La mayoría de las investigaciones se concentran en los whiskers de estaño y hay todavía pocostrabajos sobre los whiskers de zinc. Los recubrimientos de zinc electrodepositado son utilizadoscomo protección anticorrosión para los aceros de baja aleación en diversas industrias, comoautomotriz, aeronáutica o energética, así como en la estructuras de soporte o tejas de techosfalsos en los centros de datos informáticos. Para atenuar, prevenir y predecir las fallas causadaspor los whiskers de zinc, los mecanismos de crecimiento deben ser comprendidos.Gracias a experimentos de almacenamiento de muestras y a observaciones por microscopíaelectrónica de barrido (SEM), la cinética de crecimiento de whiskers de zinc ha sido estudiada enaceros de baja aleación recubiertos de zinc y cromados. Para comprender los mecanismos decrecimiento de whiskers de zinc, la caracterización cuantitativa de whiskers y de protuberancias(densidad, volumen y velocidad de crecimiento) fue relacionada con los parámetros siguientes:temperatura, electrolito usado en la electrodeposición de zinc, cromado, espesor del substrato deacero, espesor del recubrimiento de zinc al igual que el estrés residual.Adicionalmente, microestructura y cristalografía del recubrimiento de zinc, de raíces dewhiskers así como de los propios whiskers fueron estudiadas por medio de la difracción deelectrones por retrodispersión (EBSD), microscopía electrónica de transmisión (TEM),microanálisis por rayos X (EDX) y el dispositivo ASTAR para la orientación local de granos; lapreparación de muestras fue realizada con la ayuda de un haz de iones localizados (FIB). Larecristalización así como las dislocaciones en whiskers y protuberancias fueron observadas;ningún compuesto intermetálico ha sido observado en los recubrimientos ni en los whiskers.Se determinó que la relajación del estrés residual de compresión y el crecimiento de whiskersson dos fenómenos diferentes pero fuertemente interconectados y térmicamente activados. Cadauno de ellos sigue un mecanismo diferente; las energías de activación aparentes de los dosfenómenos han sido establecidas, y la difusión por bordes de grano es propuesta como elprincipal mecanismo de difusión para el crecimiento de whiskers.Cinéticas de crecimiento de whiskers, a la vez analíticas y fenomenológicas son propuestas.Una buena estimación del crecimiento de whiskers y su velocidad de crecimiento a temperaturascercanas a las condiciones de operación es obtenida por comparación con los datosexperimentales.