Wir untersuchen die Phasenbildung von Festkörperlösungen von (InxGa1-x)2O3 experimentell mittels Transmissionselektronenmikroskopie und stützen uns bei der Modellierung auf die Clusterexpansion. Epitaktische (InxGa1-x)2O3 Schichten auf kristallinen Substrate sind durch ausgeprägte Ordnung auf den Kationenuntergittern gekennzeichnet, bei welchem In und Ga sich auf Gitterplätze einbauen auf denen sie die energetisch günstigste Koordination zum Sauerstoff einnehmen. Ausgehend von diesem Befund, modifizieren wir das Modells der idealen Mischung so dass wir die Konfigurationsentropie auf den kationischen Untergittern mit spezifischer Koordinations getrennt betrachten um diese realistisch zu berechnen. Das resultierende Phasendiagramm ist durch enge thermodynamisch Stabilitätsbereiche für die jeweiligen Phasen gekennzeichnet, weil sich gleichzeitig große metastabile Zusammensetzungsbereiche ergeben bei Temperaturen die typisch für epitaktisches Wachstum sind: so ist die monokline Phase im Zusammensetzungsbereich x<0.5 metastabil, die hexagonale Phase für 0.55<x<0.7 und die kubische Bixbyit-Phase für x>0.91. Wird amorphes (InxGa1-x)2O3 kristallisiert in-situ im TEM, bildet sich im Zusammensetzungbereich bis x<0.22 die Spinellphase, die als ungeordnete Variante der monoklinen Phase beschrieben wird. Oberhalb dieser Zusammensetzung ist die kubische Phase stabil. Ursache hierfür ist der Einfluss der maximale Menge an Konfiguartionsentropie auf die Bildungsenthalpie in Strukturen mit vielfältigem Koordinationsumgebungen der Kationen. Der letzte Teil der Arbeit befasst sich mit dem Einflusses der Gitterordnung auf den Materialkontrast bei der Abbildung mittels HAADF (High Angle Annular Dark Field) STEM. Hier wird gezeigt, dass die Anregung des 2s-Bloch-Wellen-Zustands zu langperiodsichen Kontrastoszillationen führt, die die quantitaive Bestimmung der Zusammensetzung mittels Z-Kontrast erschwert es aber erlaubt den Ordnungsparameter bei bekaannter Zusammensetzung zu messen. / We investigate the phase formation in (InxGa1-x)2O3 solid solutions experimentally by means of transmission electron microscopy (TEM) and with computational support using cluster expansion. In the case of epitaxial growth on crystalline substrates, we find strong ordering on the cation sublattices of (InxGa1-x)2O3, energetically driven by the tendency of In and Ga to each assume their preferred coordination environment. Based on this experimental finding, we modify the model of the ideal mixture by considering the configurational entropy on the respective cation sublattices with different coordination separately in order to calculate it realistically. The resulting phase diagram is characterized by narrow thermodynamically stable ranges for each phase, while wide composition ranges of metastable compounds are predicted, which can be achieved at temperatures typical for epitaxy: the monoclinic phase is metastable in the composition range x<0.5, the hexagonal phase for 0.55<x<0.7, and the cubic bixbyite phase for x>0.91. If amorphous (InxGa1-x)2O3 is crystallized in-situ in the TEM, the spinel phase, which is described as a disordered variant of the monoclinic phase, is formed in the composition range up to x<0.22, while above this composition, the bixbyite phase is stable. This shift in stability is explained by the maximum amount of configurational entropy present during crystallization, which strongly influences the formation enthalpy in structures with diverse coordination environments of the cations. The last part of the work deals with the influence of the lattice order on the material contrast when imaging by HAADF (High Angle Annular Dark Field) STEM. It is shown that the excitation of the 2s-Bloch wave state leads to long-period contrast oscillations, which complicate the quantitative determination of the composition by Z-contrast but allows to quantify the order parameter for a given composition.

Les études épidémiologiques sur les effets de la fraction ultrafine de la pollution particulaire et les études sur la toxicité in vitro et in vivo des nanoparticules manufacturées témoignent d’un danger potentiel pour l’homme en raison de nouvelles propriétés physico-chimiques de la matière à l’échelle nanométrique. L’évaluation du risque lié à des expositions professionnelles ou environnementales ou le diagnostic d’un lien causal entre ces expositions et d’éventuelles pathologies peuvent être limités par l’absence de méthode de référence pour caractériser et quantifier les particules nanométriques dans les tissus et fluides biologiques. Ce travail a permis de mettre au point une méthode remplissant ces objectifs, basée sur la préparation des échantillons par digestion alcaline et microfiltration et sur l’analyse en microscopie électronique analytique. L’application de cette méthode dans deux études a permis de confirmer qu’une translocation des particules nanométriques était possible d’une part au niveau pleural avec concentration dans les black spots et d’autre part à travers le placenta avec une possible exposition du foetus. Ce travail a également permis de caractériser des sources d’expositions professionnelles ou environnementales aux particules nanométriques. Sous réserve d’optimiser le coût et le temps nécessaire pour ce type d’analyse, cette méthode pourrait permettre de définir des valeurs de référence sur des échantillons plus larges et représentatifs de la population générale ou être utilisée dans le cadre de la surveillance de travailleurs exposés. / Epidemiologic studies on the health effects of ultrafine particles from atmospheric pollution and in vitro or in vivo studies on manufactured nanoparticles toxicity suggest that potential hazards may result from new physico-chemical properties of materials at nanometric scale. To assess human health risk after occupational or environmental exposure or to demonstrate a causal relationship between such exposures and diseases may be hindered by the lack of reference method to characterize and quantify nanometric particles in biological tissues and fluids. This work allowed us to develop such a method based on samples preparation by alkaline digestion and microfiltration followed by analytical electron microscopy analysis. This method applied in two studies allowed us to confirm that pleural translocation of nanometric particles and accumulation in black spots were possible in human and that they also may pass through the placental barrier with potential fetal exposure. This work also allowed us to characterize some sources of occupational and environmental exposures. After time-cost optimization of this method, it could be used to define reference values on larger population-representative samples or used for the medical follow-up of exposed workers.

<p>  </p> <p>Stress corrosion cracking (SCC) is a longstanding critical materials challenge in austenitic stainless steels (AuSS). Recently, there has been mounting concern regarding the potential for Chloride-induced stress corrosion cracking (CISCC) along arc weld seams on austenitic stainless-steel canisters used as spent nuclear fuel (SNF) dry storage containers, due to the residual stress from the welding process and exposure to chloride-rich coastal air at storage sites. To ensure the safety of the SNF storage, fundamental understanding and mitigation methods of CISCC are critical in both engineering design and maintenance of the storage canisters before and after their deployment. With the recent development of high-resolution characterization and analysis techniques, a more robust and comprehensive understanding of the fundamental TGCISCC mechanism starts to be more accessible. In this thesis, comprehensive state-of-the-art techniques, including SEM, EBSD, HREBSD, FIB, ATEM, TKD, potential dynamic measurement, XRD, and nanoindentation will be used to further understand the mechanistic mechanism of TGCISCC in AuSS from macroscopic scale down to atomistic scale. </p>

<p>  </p> <p>Aluminum (Al) possesses a plenitude of remarkable properties, such as strong corrosion resistance, high thermal and electrical conductivity, and high specific strength. However, Al and its alloys are still remarkably weaker than most high strength steels and susceptible to drastic softening at high temperatures, preventing many applications where its low density would be beneficial. Severe plastic deformation can yield ultra-fine grained Al alloys with similar strengths as steels, although they are highly unstable even at room temperature. Nanotwinned (NT) metals have demonstrated concomitant strength and ductility, enabled by twin boundaries which simultaneously act to inhibit dislocation motion and generate partial dislocations that aid in plasticity. In spite of having a high stacking fault energy, nanotwins have been introduced into Al alloys using transition metal solutes during magnetron sputtering. This thesis aims to explore the impact Zr has on the microstructure, deformation, and thermal stability of nanotwins in NT Al.</p> <p>Our studies identify how Zirconium (Zr) aids in the formation of a significant volume fraction of 9R phase and an abundance of finely spaced incoherent twin boundaries, leading to a maximum hardness of 4.2GPa. They further uncover through <em>in-situ</em> micropillar compression that NT Al-Zr alloys are highly deformable and reach a flow stress of ~1.1GPa. Constant strain rate nanoindentation tests demonstrate the enhanced strain rate sensitivity in NT Al-Zr alloys. Zr is also identified to be a remarkable thermal stabilizer when incorporated into NT Al-Co alloys, with no apparent softening up to 450 °C (0.78 T­m). The influence of substrate texture on nanotwinned Al-Zr alloys microstructure was also thoroughly explored.</p>

No description available.

Natural products have been a significant source of new drugs, especially in treating cancer, infectious diseases, hypertension, and neurological disorders. Although many natural metabolites have been screened and yielded pharmaceutically important drugs, many potential sources of natural product drug therapies still need to be investigated, including lichens. Lichens are symbiotic systems consisting of a filamentous fungus and a photosynthetic partner (an eukaryotic alga and/or cyanobacterium). Lichens produce an impressive variety of unique secondary compounds and have been used as ingredients in folk medicines for centuries. Demonstrated biological roles based on lichen chemistry include: antibiotics, anti-proliferative, antioxidants, anti-HIV, anti-cancer, immunomodulation, and anti-protozoans. Although North America is home to an impressive variety of lichen species, there is limited research to examine the biological potentials of these lichens. The core goal of this dissertation research has been to investigate some of the biological roles including, antibiotic, antioxidant, and anticancer potentials using lichen crude extracts and their metabolites collected from various locations in the United States. Antibiotic screening of crude extracts of 36 lichen species demonstrated inhibitory effects against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Methicillin-resistant S. aureus (MRSA). Generally, acetone extractions were found to be more effective than methanol extractions. It has also been shown that L. vulpina extract was bacteriocidal against MRSA with a relatively slow kill rate that disrupts cell membrane integrity and cell division as possible modes of action. Antioxidant screening of extracts from 11 lichen species, using the Oxygen Radical Absorbance Capacity (ORAC) assay, showed that lichen extracts inhibited the oxidative degradation of the fluorescent molecule (fluorescein-sodium salt) by the oxygen free radical initiator AAPH (2,2'-azobis(2-aminidopropane) dihydrochloride Acetone extracts as well as pure compounds from lichen species showed cytotoxic effects against Burkitt's lymphoma (Raji) cells and a colon cancer cell line (HT29 and SW620). They decreased proliferation, arrested cell cycle at various stages and force the cell to undergo apoptosis. The tested extracts or pure compounds were not toxic to normal cells. In colon cancer apoptosis took place independent of casapase-3. The results of this dissertation showed that lichen compounds merits for further investigation.

<p>Ni-base superalloys are among the highest temperature capable alloys and are used pervasively throughout the transportation, energy, and nuclear industries. However, their microstructures have been largely limited to containing the γ´ (cubic) and γ´´ (tetragonal) phases to enable high strength at elevated temperatures, and this fixation has restricted alloy development opportunities. In the past three decades, a new set of alloys, strengthened by the γ´´´ (orthorhombic) phase, was developed by Haynes International. The alloys exhibit comparable strength to existing Ni-based superalloys and show a 25% decrease in the thermal expansion coefficient, designed for tighter clearances (thus improving engine efficiency) and help to reduce thermally induced fatigue from engine cycling. </p> <p>The newest iteration of such alloys, HAYNES^® 244^®, has a nominal composition of Ni-22.5Mo-8Cr-6W (wt.%), and each alloying element is used to help precipitate the γ´´´-Ni₂(Cr, Mo, W) phase. The deformation mechanisms of this material are currently unknown. Previous studies investigating the predecessor alloy, HAYNES^® 242^® alloy, showed deformation twinning to be the dominant deformation mechanism during mechanical testing, but the physical phenomena responsible for this mode of deformation were not clearly elucidated. As a result, the primary motivation of this project is to understand the deformation behavior of the 244 alloy from the atomistic level and upwards. </p> <p>This work details efforts to elucidate these deformation mechanisms using an integrated computational and experimental approach. First-principles calculations were performed to determine the entire generalized stacking fault energy (GSFE) surface and slip pathways of the γ´´´ phase for dislocation slip. The various planar defects that could form from dislocation slip were predicted to provide significant barriers for dislocation motion due to their very high planar defect energies (~1000 mJ/m²), likely precluding shearing of the precipitates. We incorporated these results into phase field dislocation dynamics (PFDD) to simulate dislocation-precipitate interactions of finite size. These results showed that the planar defect energies of the γ´´´ phase largely govern the deformation behavior and critical resolved shear stress for precipitate shearing, regardless of precipitate shape, size, or orientation. Extensive mechanical testing conducted from room temperature up to 760 ºC over strain rates ranging from 10^-9 s^-1 to 10^-4 s^-1 combined with transmission electron microscopy validated the predicted deformation structures of creep and tensile samples. Shearing of individual precipitates by intrinsic and extrinsic stacking faults, as well as extensive deforming twinning, was observed. The integrated GSFE and PFDD simulations showed that the precipitates would resist dislocation shearing and favor twinning as the preferred deformation mechanism at all temperatures and strain rates investigated. These results provide pathways for microstructural and composition modification to further increase the strength of γ´´´ strengthened alloys in the future.</p> <p><br></p>

Convolutional neural networks are equivariant to translations; equivariance to other symmetries, however, is not defined and the class output may vary depending on the input's orientation. To mitigate this, the training data can be augmented at the cost of increased redundancy in the model. Another solution is to build an equivariant neural network and thereby increasing the equivariance to a larger symmetry group. In this study, two convolutional neural networks and their respective equivariant counterparts are constructed and applied to the symmetry groups D4 and C8 to explore the impact on performance when removing and adding batch normalisation and data augmentation. The results suggest that data augmentation is irrelevant to an equivariant model and equivariance to more symmetries can slightly improve accuracy. The convolutional neural networks rely heavily on batch normalisation, whereas the equivariant models achieve high accuracy, although lower than with batch normalisation present.

Die Untersuchung von III-V-Heterostruktur-Grenzflächen spielt aufgrund des starken Einflusses der Grenzflächen auf die Eigenschaften von Halbleiterbauelementen eine elementare Rolle. Die Transmissionselektronenmikroskopie (TEM) hat sich als eines der geeignetsten Methoden für die Analyse von Grenzflächen erwiesen. Jedoch stellt die Interpretation von zweidimensionalen Projektionen, insbesondere bei dreidimensionalen (3D) Strukturen, eine Herausforderung dar, da die Information über die Tiefe in der Projektion verloren geht. In dieser Arbeit wird diskutiert, dass Grenzflächen als 3D Objekte gesehen werden können, insbesondere bei großen Rauheiten oder chemischen Durchmischungen. Zur Charakterisierung von vergrabenen III-V-Halbleitergrenzflächen wurde eine neue analytische Methode auf Basis der Elektronentomographie entwickelt. Diese Methode wird anhand eines (Al,Ga)As/GaAs-Mehrschichtsystems als Fallstudie vorgestellt. Es wird gezeigt, dass die tomographische Rekonstruktion von Grenzflächen ausgenutzt werden kann, um sogenannte Iso-Konzentrationsflächen zu erhalten, welche die Lage einer festgelegten Konzentration an der Grenzfläche beschreiben. Sie erlauben die Erstellung topographischer Höhenkarten, die die Rauheit von Grenzflächen visualisieren und ermöglichen die Bestimmung wesentlicher Grenzflächenparameter wie die quadratische Rauheit oder die lateralen und vertikalen Korrelationslängen. Zusätzlich wurden Isoflächen an unterschiedlichen Konzentrationsniveaus verwendet, um topographische Karten der Grenzflächenbreite zu erzeugen. Die Stärke der Methodik liegt in der Möglichkeit, alle chemisch-strukturellen Parameter von vergrabenen Grenzflächen mit einer einzelnen Tomographiemessung zu bestimmen. Die Applikation dieser neuen Grenzflächentomographie-Technik wird an unterschiedlichen Halbleitermaterialien für optische Anwendungen demonstriert: An einer (Al,Ga)As/GaAs-Mikrokavität, einem (Al,Ga)N/GaN-Bragg-Reflektor und einem 3D (In,Ga)N/GaN-Nanodraht. / The investigation of III-V heterostructure interfaces plays a key role in developing novel semiconductor devices due to the strong influence of interfaces on device characteristics. Transmission electron microscopy (TEM) has proven to be one of the most suitable tools for an interface analysis. The interpretation of two-dimensional projections can be challenging, especially for three-dimensional (3D) structures, since the depth information is lost in the projection. It is discussed in this thesis that interfaces can be seen as 3D objects, particularly when interfaces are subject to large roughnesses or chemical intermixing. A new analytical method for the comprehensive characterization of buried III-V semiconductor interfaces based on electron tomography was developed. This method is applied to an (Al,Ga)As/GaAs multilayer system as a case study. It is shown that the tomographic reconstruction of a tomography needle of this material can be exploited to obtain so-called iso-concentration surfaces. These surfaces describe the positions of a chosen concentration value at the interfaces. They enable the creation of topographic height maps revealing the roughness of several interfaces. The height maps allow the determination of essential interface parameters as the quadratic mean roughness or the lateral and vertical correlation lengths using the height-height correlation function. In addition, height-difference maps based on isosurfaces corresponding to different concentration levels were used to generate topographic maps of the interface width. The methodology’s main strength is the ability to determine all chemical-structural parameters of buried interfaces with a single measurement. This thesis presents the application of this new interfacial tomography technique on semiconducting materials used for optical application purposes: An (Al,Ga)As/GaAs microcavity, an (Al,Ga)N/GaN Bragg reflector and a complex, 3D (In,Ga)N/GaN multi-shell nanowire.

The main automotive catalytic media, precious metal-doped ceria-zirconia oxides, fundamental system character is unknown. Understanding the catalytic system properties should allow for the production of an optimal model catalyst. This goal of this study is to gain understanding of ceria-zirconia-palladium systems and to determine a reproducible method for preparing catalysts with minimal surface-carbon. This study investigates ceria-zirconia-palladium catalyst preparation via aqueous chemistry methods and a sputter deposition technique for doping ceria-zirconia oxide mixtures. Prepared catalysts are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XPS allows the surface species, after catalyst doping and annealing, to be evaluated. Prepared catalyst EM analysis allows for surface morphology and particle characteristic evaluation. Prepared catalysts are exposed to UHV conditions, palladium sputtered-coated, and annealed at various temperatures. Temperature dependency is observed in both percentage of carbon, metal, and oxygen species present. This study led to a reproducible, low-carbon content, doping method for use in future pollutant reaction studies.