The public health and veterinary importance of Gulf Coast ticks, Amblyomma maculatum Koch (1844) have become more apparent during the last several decades. In addition, new records of this three-host ixodid tick presently show a geographic distribution throughout much of the southern United States. Rickettsia parkeri, a spotted fever group rickettsia (SFGR) that is commonly found infecting the Gulf Coast tick, was only recently recognized as a human pathogen. Over the last decade, more than 20 human cases of disease caused by R. parkeri have been recognized in the Americas, all of which were similar in presentation to mild Rocky Mountain spotted fever. In addition, a novel, poorly characterized SFGR, “Candidatus Rickettsia andeanae”, was recently identified in A. maculatum from Peru, United States, Chile and Argentina. As the recognition of R. parkeri as a pathogen and “Ca. R. andeanae” as an additional SFGR in A. maculatum only recently occurred, a general gap exists in our understanding of the biology of these SFGRs. The overall objective of this dissertation was to contribute to our knowledge of SFGR infecting A. maculatum. In Chapter 3, we present a prevalence study of R. parkeri, and “Ca. R. andeanae” in A. maculatum from Mississippi where we detected 15.2% R. parkeri-singly infected ticks and 3.1% total “Ca. R. andeanae” infected ticks of which 1.7% were co-infected with R. parkeri. In Chapter 4, we discuss finding four genetically different populations of A. maculatum from Mississippi infected with a homogenous population of R. parkeri, using Single Strand Conformation Polymorphism analysis. Those initial data relating to “Ca. R. andeanae” provided a foundation for studies described in Chapters 5 and 6. We report the first morphological study of “Ca. R. andeanae” using transmission electron microscopy in Chapter 5 and isolation of this SFGR in ,A. maculatum cell co-culture in Chapter 6. We anticipate that results presented in this dissertation will contribute to our understanding of the ecology of ,A. maculatum as a vector for the human pathogen, R. parkeri, and increase the current understanding of both R. parkeri and “Ca. R. andeanae” in A. maculatum.

In dieser Arbeit untersuchen wir ultradünne (In,Ga)N Quantentöpfe (QW) in Form von kurzperiodischen Übergittern auf (0001) GaN. Wir charakterisieren dieser Strukturen mit verschiedenen Methoden, d.h.: die hochauflösende Transmissionselektronenmikroskopie, die Rastertransmissionselektronenmikroskopie, Röntgenbeugung und die hochenergetischer Refeflexionselektronenbeugung an Oberflächen, sowie die Photolumineszenz (PL) und die Kathodolumineszenz. Wir fokussieren uns dabei auf die Quantifizierung des Indiumgehaltes solche ultradünnen Schichten und diskutieren über grundlegende optische Eigenschaften dieser Übergitter. Wir finden, dass: 1. Der Indiumeinbau in GaN unter Exposition von In und N-Fluss ist selbst-begrenzend auf eine Zusammensetzung von 25% und eine Schichtdicke von einer Monolage. Die Variation der Wachstumsbedingungen führen weder nicht zu einer Höhung des Indiumgehalts noch der Schichtdicke. Diese Selbstbegrenzung ist im Ergebnis auf die Unterschiede in der Bildungsenthalpie von InN und GaN und auf die hohe Gitterfehlanpassung des Systems. Die niedrigste Energiekonfiguration ist einer (2»3×2»3)R30° Oberflächenrekonstruktion. 2. In diesen polaren In0.25Ga0.75N Übergitter Polarisationsfelder, Dickenfluktuationen oder Kompositionsschwankungen keine wesentliche Rolle spielen. Unsere optischen Studien in Kombination mit DFT-Berechnungen zeigen, dass der Rekombinationsprozess durch den Einschluss der Lochwellenfunktion in den Monoschichten gesteuert wird, dass mit abnehmender Barrieredicke verändert werden können. Im Gegenteil, ist die Elektronenwellenfunktion immer delokalisiert. Unsere Übergitter Phänomene sind als in konventionellen QWs, z.B. den nichtexponentiellen Abfall der PL-Intensität, die spektrale Abhängigkeit der PL Lebensdauer und eine S-förmige Temperaturabhängigkeit des Emissionspeaks. Die letzte lassen sich durch das Zusammenspiel von Ladunsgträgerlokalisation und nicht-strahliger Rekombination erklären. / In this work we investigate ultra-thin (In,Ga)N quantum wells (QWs) grown on (0001) GaN in the form of short-period superlattices (SLs). We perform a comprehensive study of these structures via various methods, i.e.: high resolution transmission electron microscopy, scanning transmission electron microscopy, x-ray diffraction and reflection high-energy electron diffraction, as well as photoluminescence (PL) and cathodoluminescence. We focus on the quantification of In incorporation and study basic optical properties of these SLs. The main results of our investigations are: 1. The In incorporation into GaN under exposure of In and N flux is self-limited to a composition of 25% and a layer thickness of one monolayer. Varying growth conditions do not increase the In content or the layer thickness. This self-limitation is a result of the differences in formation enthalpy of InN and GaN and the high lattice mismatch of the system. The lowest energy configuration that sets maximum In concentration to a fundamental limit of 25%, stable under various growth regimes, is the one with (2»3×2»3)R30° surface reconstruction. 2. Our polar In0.25Ga0.75N SLs serve as model system for recombination process in (In,Ga)N since their recombination is not suffering from polarization fields, well-width or high compositional fluctuations. The optical studies combined with DFT calculations show that the recombination process is governed by the confinement of the hole wavefunction in the QWs, that can be substantially weakened by decreasing barrier thickness. This leads to an increase of non-radiative recombination in the barriers. In the opposite, the electron wave function is always delocalized. Our SLs show common phenomena observed in conventional QWs or bulk alloys like a non-exponential decay of the PL intensity, spectral dependence of the decay time and S-shape temperature dependence. The latter can be explained by the interplay of carrier localization and non-radiative recombination.

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D. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / A novel low-cost ternary Mn-Fe-Cu (MFC) metal oxide nanocomposite adsorbent was fabricated using facile co-precipitation method and successfully applied for the sequestration of Cr(VI) and As(III) from simulated aqueous efflent. The central composite design (CCD) of the response surface methodology (RSM) optimization technique determined the optimal working parameters for the preparation of the ternary MFC metal oxide nanocomposite. The spectroscopic microstructural analysis of the ternary MFC metal oxide nanocomposite was performed using fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) spectroscopy. The spectroscopic analyses revealed a rough surface with hydroxyl groups and the presence of mixed metal oxides in different valence states. The BET surface area, pore volume and pore size of the nanostructured MFC ternary metal oxide composite were found to be 77.2427 m2/g, 0.2409 cm3/g and 14.7560 nm, respectively. The pH drift method determined that the pHpzc of the adsorbent was 6.75. The batch technique was employed to investigate the adsorption dynamics (effects of ionic strength, co-existing anions, adsorbent regeneration and reuse) and optimum parameters (solution pH, adsorbent dosage concentration, desorption) of Cr(VI) and As(III) adsorption onto the MFC nanocomposite. The fitting of non-linear kinetic (pseudo-first-order, pseudo-second-order and Elovich), diffusion (intraparticle and Boyd) and isotherm (Langmuir, Freundlich and Dubinin-Radushkevich) models to the Cr(VI) and As(III) experimental adsorption data gave an insight into the adsorption mechanisms. The Langmuir adsorption capacities, qm (mg/g), were 168.71 at solution pH 3 and 35.07 at solution pH 9 for Cr(VI) and As(III) adsorption, respectively. The adsorption of Cr(VI) onto the ternary MFC metal oxide nanocomposite was physical and formed outer-sphere surface complexes through electrostatic interactions, while the removal of As(III) was specific due to inner-sphere surface complexation and ligand/ion exchange reactions. The results from XPS and FTIR analysis after the adsorption of Cr(VI) and As(III) showed that the surface hydroxyl groups on the MFC nanocomposite interacted with the Cr(VI) and As(III) species during the formation of the surface complexes. To facilitate ease of adsorbent removal from the treated simulated aqueous effluent, the ternary MFC metal oxide system was co-precipitated onto biochar support.

The exceptional properties of nanocrystals (NCs) are strongly influenced by many different characteristics, such as their size and shape, but also by characteristics on the atomic scale, such as their crystal structure, their surface structure, as well as by potential microstructure defects. While the size and shape of NCs are frequently determined in a statistical manner, atomic-scale characteristics are usually quantified only for a small number of individual NCs and thus with limited statistical relevance. Within this work, a characterization workflow was established that is capable of determining relevant NC characteristics simultaneously in a sufficiently detailed and statistically relevant manner. The workflow is based on transmission electron microscopy, networked by a correlative multiscale approach that combines atomic-scale information on NCs obtained from high-resolution imaging with statistical information on NCs obtained from low-resolution imaging, assisted by a semi-automatic segmentation routine. The approach is complemented by other characterization techniques, such as X-ray diffraction, UV-vis spectroscopy, dynamic light scattering, or alternating gradient magnetometry. The general applicability of the developed workflow is illustrated on several examples, i.e., on the classification of Au NCs with different structures, on the statistical determination of the facet configurations of Au nanorods, on the study of the hierarchical structure of multi-core iron oxide nanoflowers and its influence on their magnetic properties, and on the evaluation of the interplay between size, morphology, microstructure defects, and optoelectronic properties of CdSe NCs.:List of abbreviations and symbols 1 Introduction 1.1 Types of nanocrystals 1.2 Characterization of nanocrystals 1.3 Motivation and outline of this thesis 2 Materials and methods 2.1 Nanocrystal synthesis 2.1.1 Au nanocrystals 2.1.2 Au nanorods 2.1.3 Multi-core iron oxide nanoparticles 2.1.4 CdSe nanocrystals 2.2 Nanocrystal characterization 2.2.1 Transmission electron microscopy 2.2.2 X-ray diffraction 2.2.3 UV-vis spectroscopy 2.2.3.1 Au nanocrystals 2.2.3.2 Au nanorods 2.2.3.3 CdSe nanocrystals 2.2.4 Dynamic light scattering 2.2.5 Alternating gradient magnetometry 2.3 Methodical development 2.3.1 Correlative multiscale approach – Statistical information beyond size and shape 2.3.2 Semi-automatic segmentation routine 3 Classification of Au nanocrystals with comparable size but different morphology and defect structure 3.1 Introduction 3.1.1 Morphologies and structures of Au nanocrystals 3.1.2 Localized surface plasmon resonance of Au nanocrystals 3.1.3 Motivation and outline 3.2 Results 3.2.1 Microstructural characteristics of the Au nanocrystals 3.2.2 Insufficiency of two-dimensional size and shape for an unambiguous classification of the Au nanocrystals 3.2.3 Statistical classification of the Au nanocrystals 3.2.4 Advantage of a multidimensional characterization of the Au nanocrystals 3.2.5 Estimation of the density of planar defects in the Au nanoplates 3.3 Discussion 3.4 Conclusions 4 Statistical determination of the facet configurations of Au nanorods 4.1 Introduction 4.1.1 Growth mechanism and facet formation of Au nanorods 4.1.2 Localized surface plasmon resonance of Au nanorods 4.1.3 Catalytic activity of Au nanorods 4.1.4 Motivation and outline 4.2 Results 4.2.1 Statistical determination of the size and shape of the Au nanorods 4.2.2 Microstructural characteristics and facet configurations of the Au nanorods 4.2.3 Statistical determination of the facet configurations of the Au nanorods 4.3 Discussion 4.4 Conclusions 5 Influence of the hierarchical architecture of multi-core iron oxide nanoflowers on their magnetic properties 5.1 Introduction 5.1.1 Phase composition and phase distribution in iron oxide nanoparticles 5.1.2 Magnetic properties of iron oxide nanoparticles 5.1.3 Mono-core vs. multi-core iron oxide nanoparticles 5.1.4 Motivation and outline 5.2 Results 5.2.1 Phase composition, vacancy ordering, and antiphase boundaries 5.2.2 Arrangement and coherence of individual cores within the iron oxide nanoflowers 5.2.3 Statistical determination of particle, core, and shell size 5.2.4 Influence of the coherence of the cores on the magnetic properties 5.3 Discussion 5.4 Conclusions 6 Interplay between size, morphology, microstructure defects, and optoelectronic properties of CdSe nanocrystals 6.1 Introduction 6.1.1 Polymorphism in CdSe nanocrystals 6.1.2 Optoelectronic properties of CdSe nanocrystals 6.1.3 Nucleation, growth, and coarsening of CdSe nanocrystals 6.1.4 Motivation and outline 6.2 Results 6.2.1 Influence of the synthesis temperature on the optoelectronic properties of the CdSe nanocrystals 6.2.2 Microstructural characteristics of the CdSe nanocrystals 6.2.3 Statistical determination of size, shape, and amount of oriented attachment of the CdSe nanocrystals 6.3 Discussion 6.4 Conclusions 7 Summary and outlook References Publications

Цель работы – установление влияния нейтронного облучения на стабильность структуры и фазового состояния ферритно-мартенситной стали ЭП823. Данная работа посвящена анализу влияния нейтронного облучения на фазовые и структурные составляющие стали. Исследования проводились на образцах оболочек твэлов, облученных в составе материаловедческой сборки в реакторе БН-600 при температурах 570, 600, 660 ˚С до повреждающих доз 51,3, 75,1 и 81,1 сна. Определялись методами металлографии и стереометрического анализа характеристики структурных составляющих, вторичных фаз, образовавшихся в процессе облучения, оценивались характеристики радиационной пористости, плотность дислокаций. Исследования были выполнены на сканирующем электронном микроскопе MIRA3 FEG-SEM, оснащенном детекторами вторичных и отраженных электронов и приставкой энергодисперсионного анализа характеристического рентгеновского излучения x-Act 6 фирмы Oxford Instruments. Так же проводились исследования на просвечивающем электронном микроскопе фирмы JEM-2000EX при ускоряющем напряжении 100 кВ в просвечивающем режиме. Количественная обработка изображений для получения размерных характеристик выделений проводилась с использованием программного обеспечения «Цифровая фотолаборатория SIAMS Photolab», а также при помощи программного обеспечения сканирующего электронного микроскопа MIRE3 FEG-SEM. Проведенное исследование стали Х12НМВБФСР в исходном состоянии показало, что ее структура состоит из мартенсита, остаточного феррита, крупных карбидов на основе Nb и по границам ферритных зерен и мартенситных реек, образуются карбиды типа М23С6. После нейтронного облучения содержание карбидов типа М23С6 увеличивается, в зернах феррита образуется χ-фаза, у которой с повышением температуры облучения понижается концентрация и увеличивается в размерах, по границам обнаружена мелкодисперсная α-фаза, обогащенная хромом, которая при повышенных температурах исчезает, так же по границам зерен мартенсита наблюдается небольшое количество радиационных пор. Прошедшие изменения микроструктуры под воздействием нейтронного облучения не привели к существенным изменениям механических свойств. / The aim of the work is to establish the effect of neutron irradiation on the stability of the structure and phase state of the EP823 ferrite-martensitic steel. This work is devoted to the analysis of the effect of neutron irradiation on the phase and structural components of steel. The studies were carried out on samples of fuel rod shells irradiated as part of a materials science assembly in the BN-600 reactor at temperatures of 570, 600, 660 ℃ to damaging doses of 51.3, 75.1, and 81.1 dpa. The characteristics of structural components and secondary phases formed during irradiation were determined by metallography and stereometric analysis, and the characteristics of radiation porosity and dislocation density were evaluated. The studies were performed using a MIRA3 FEG-SEM scanning electron microscope equipped with secondary and reflected electron detectors and an x-Act 6 energy dispersive analysis of characteristic X-ray radiation from Oxford Instruments. Studies were also carried out on a transmission electron microscope of the JEM-2000EX company at an accelerating voltage of 100 kV in the transmission mode. Quantitative image processing to obtain the dimensional characteristics of the secretions was carried out using the software "Digital Photo Laboratory SIAMS Photolab", as well as using the software of the scanning electron microscope MIRE3 FEG-SEM. The study of steel X12NMVBFSR in the initial state showed that its structure consists of martensite, residual ferrite, large carbides based on Nb and along the boundaries of ferritic grains and martensitic rails, carbides of the M23C6 type are formed. After neutron irradiation, the content of carbides of the M23C6 type increases, a χ-phase is formed in the ferrite grains, in which the concentration decreases and increases in size with an increase in the irradiation temperature, a fine alpha-phase enriched in chromium is found along the boundaries, which disappears at elevated temperatures, as well as a small number of radiation pores are observed along the boundaries of martensite grains. The past changes in the microstructure under the influence of neutron irradiation did not lead to significant changes in the mechanical properties.

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During recent decades metallic nanoparticles have been found very interesting due to their unique characteristics which make them suitable for different applications. In this research, for the very first time, we tried to perform selective surface photo activation chemistry on the targeted facets of nanoparticles while they are in suspension. This technique enabled us to form desired assemblies of nanoparticles. We focused on elongated shaped gold nanorod due to its unique surface plasmon resonance and probable biomedical applications. In this research we formed a dumbbell shape assembly of nanoparticles in suspension. A probable application for these assemblies can be in vivo imaging. Initially, we reproduced gold nanorods using existing techniques in prior papers and optimized them according to our research needs. A low rpm centrifugal separation technique was developed to efficiently separate synthesized gold nanorods from other shapes. Several characterization techniques were utilized to characterize nanoparticles at each step including UV-absorbance, zeta potential, and dynamic light scattering. Different generations of oligomers were synthesized to be used as gold nanorods coating, and each coating was tested and characterized using appropriate techniques. Our two-step coating replacement method using one of these photocleavable oligomers enabled us to achieve, for the very first time, selective UV photo activation of gold nanorod tips. The photo activated tips were then exposed to oppositely charged gold nanospheres to form dumbbell shape assemblies of gold nanorods and nanospheres. Furthermore, dumbbell shape assembly of nanoparticles was investigated and characterized. / Master of Science