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Metallic thin films consisting of separated nanostructures are fabricated by evaporative glancing angle deposition at room temperature. The columnar microstructure of the Ti and Cr columns is investigated by high resolution transmission electron microscopy and selective area electron diffraction. The morphology of the sculptured metallic films is studied by scanning electron microscopy. It is found that tilted Ti and Cr columns grow with a single crystalline morphology, while upright Cr columns are polycrystalline. Further, the influence of continuous substrate rotation on the shaping of Al, Ti, Cr and Mo nanostructures is studied with view to surface diffusion and the shadowing effect. It is observed that sculptured metallic thin films deposited without substrate rotation grow faster compared to those grown with continuous substrate rotation. A theoretical model is provided to describe this effect

Study of the metastable phases obtained by non-equilibrium processing techniques has come a long way during the past five decades. New metastable phases have often given new perspectives to the research on synthesis of novel materials systems. Metastable materials produced by two non-equilibrium processing methods were studied for this dissertation- 304-type austenitic stainless steel (SS304 or Fe-18Cr-8Ni)+aluminum coatings produced by plasma enhanced magnetron sputter-deposition (PEMS) and nanocrystalline Ti, Zr and Hf powders processed by mechanical milling (MM). The objective of the study was to understand the crystallographic and microstructural aspects of these materials. Four SS304+Al coatings with a nominal Al percentages of 0, 4, 7 and 10 wt.% in the coatings were deposited on an SS304 substrate by PEMS using SS304 and Al targets. The as-deposited coatings were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and three-dimensional atom probe microscopy (3DAP). Surface morphology and chemical analysis were studied by SEM. Phase identification was carried out by XRD and TEM. The microstructural features of all the coatings, as observed in the TEM, consisted of columnar grains with the columnar grain width (a measure of grain size) increasing with an increase in the Al content. The coatings had grains with average grain sizes of about 100, 290, 320 and 980 nm, respectively for 0, 4, 7 and 10 wt.% Al. The observed grain structures and increase in grain size were related to substrate temperature during deposition. XRD results indicated that the Al-free coating consisted of the non-equilibrium ferrite and sigma phases. In the 4Al, 7Al and 10Al coatings, equilibrium ferrite and B2 phases were observed but no sigma phase was found. In 10Al coating, we were able to demonstrate experimentally using 3DAP studies that NiAl phase formation is preferred over the FeAl phase at nano scale. During mechanical milling of the hexagonal close packed (HCP) metals Hf, Ti and Zr powders, unknown nanocrystalline phases with face centered cubic (FCC) structure were found. The FCC phases could be either allotropes of the respective metals or impurity stabilized phases. However, upon MM under high purity conditions, it was revealed that the FCC phases were impurity stabilized. The decrease in crystallite size down to nanometer levels, an increase in atomic volume, lattice strain, and possible contamination were the factors responsible for the transformation.

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No description available.

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No description available.

Bed bugs (Hemiptera:Cimicidae) are a common, hematophagous ectoparasite of humans and other animals, and are experiencing an international resurgence. Cimicids have been implicated in the transmission many disease agents, including various Bartonella species, however disease transmission has not yet been confirmed. Bartonella spp. are transmitted by a variety of arthropods, including fleas, lice and sand flies, and it is speculated that bed bugs may also serve as a potential vector. In this study, we used an artificial membrane to feed two groups of adult Cimex lectularius rabbit blood, either infected or uninfected with Bartonella henselae. After two weeks, the presence of Bartonella henselae was assessed via PCR, and salivary glands from infected and uninfected bed bugs were dissected and processed for transmission electron microscopy. We were unable to visually identify Bartonella henselae in the images, and therefore unable to confirm the role of bed bugs in B. henselae transmission.

Diese Arbeit liefert einen Beitrag zur mathematischen Untersuchung der Darwin-Howie-Whelan (DHW) Gleichungen. Sie werden üblicherweise zur Beschreibung und Simulation der Diffraktion schneller Elektronen in der Transmissionselektronenmikroskopie (TEM) verwendet. Sie bilden ein System aus Gleichungen für unendlich viele Enveloppenfunktionen, das aus der Schrödinger-Gleichung abgeleitet werden kann. Allerdings wird für Simulation von TEM Bildern nur ein endlicher Satz von Enveloppenfunktionen verwendet, was zu einem System von gewöhnlichen Differentialgleichungen in Richtung der Dicke der Probe führt. Bis jetzt gibt es keine systematische Analyse zur Genauigkeit dieser Näherungen in Abhängigkeit von der Auswahl der verwendeten endlichen Sätze von Enveloppenfunktionen. Diese Frage wird hier untersucht, indem die mathematische Struktur des Systems analysiert wird und Fehlerabschätzungen zur Bewertung der Genauigkeit spezieller Näherungen hergeleitet werden, wie der Zweistrahl-Approximation oder der sogennanten systematischen Reihe. Anschließend wird ein mathematisches Modell und eine Toolchain für die numerische Simulation von TEM-Bildern von Halbleiter-Quantenpunkten entwickelt. Es wird eine Simulationsstudie an Indium-Gallium-Arsenid-Quantenpunkten mit unterschiedlicher Geometrie durchgeführt und die resultierenden TEM Bilder werden mit experimentellen Bildern verglichen. Schließlich werden die in TEM Bildern beobachteten Symmetrien im Hinblick auf die DHW Gleichungen untersucht. Dazu werden mathematische Resultate formuliert und bewiesen, die zeigen dass die Intensitäten der Lösungen der DHW Gleichungen unter bestimmten Transformationen invariant sind. Durch die Kombination dieser Invarianten mit spezifischen Eigenschaften des Deformationsfeldes können dann die in TEM Bildern beobachteten Symmetrien erklärt werden. Die Ergebnisse werden anhand ausgewählter Beispiele aus dem Bereich der Halbleiter-Nanostrukturen wie Quantensichten und Quantenpunkte demonstriert. / In this thesis a mathematical study on the Darwin--Howie--Whelan (DHW) equations is provided. The equations are commonly used to describe and simulate the scattering of fast electrons in transmission electron microscopy (TEM). They are a system for infinitely many envelope functions, derived from the Schrödinger equation. However, for the simulation of images only a finite set of envelope functions is used, leading to a finite system of ordinary differential equations in the thickness direction of the specimen. Until now, there has been no systematic discussion about the accuracy of approximations depending on the choice of the finite sets used. This question is approached here by studying the mathematical structure of the system and providing error estimates to evaluate the accuracy of special approximations, like the two-beam and the systematic-row approximation. Then a mathematical model and a toolchain for the numerical simulation of TEM images of semiconductor quantum dots (QDs) is developed. A simulation study is performed on indium gallium arsenide QDs with different shapes and the resulting TEM images are compared to experimental ones. Finally, symmetries observed in TEM images are investigated with respect to the DHW equations. Then, mathematical proofs are given showing that the intensities of the solutions of the DHW equations are invariant under specific transformations. A combination of these invariances with specific properties of the strain profile can then explain symmetries observed in TEM images. The results are demonstrated by using selected examples in the field of semiconductor nanostructures, such as quantum wells and quantum dots.

Novel semiconductor nanostructures possess a range of notable properties that have the potential to be harnessed in the next generation of optical devices. Electron microscopy is uniquely suited to characterising the complex microstructure, the results of which may be related to the growth conditions and optical properties. This thesis investigates three such novel materials: (1) GaN/InGaN core/shell nanowires, (2) n-GaN/InGaN/p-GaN core/multi-shell microrods and (3) Zn₃N₂ nanoparticles, all of which were grown at Sharp Laboratories of Europe. GaN nanowires were grown by a Ni-catalysed VLS process and were characterised by various techniques before and after InGaN shells were deposited by MOCVD. The majority of the core wires were found to have the expected wurtzite structure and completely defect free – reflected in the strong strain-free photoluminescence peak –with a- and m- axis orientations identified with shadow imaging. A small component, <5%, were found to have the cubic zinc-blende phase and a high density of planar faults running the length of the wires. The deposited shells were highly polycrystalline, partially attributed to a layer of silicon at the core shell interface identified through FIB lift-out of cross section samples, and accordingly the PL was very broad likely due to recombination at defects and grain boundaries. A high throughput method of identifying the core size indirectly via the catalyst particle EDX signal is described which may be used to link the shell microstructure to core size in further studies. An n-GaN/InGaN/p-GaN shell structure was deposited by MOCVD on the side walls of microrods etched from c-axis GaN film on sapphire, which offers the possibility of achieving non-polar junctions without the issues due to non-uniformity found in nanowires. Threading dislocations within the core related to the initial growth on sapphire were shown to be confined to this region, therefore avoiding any harmful effect on the junction microstructure. The shell defect density showed a surprising relationship to core size with the smaller diameter rods having a high density of unusual 'flag' defects in the junction region whereas the larger diameter sample shells appeared largely defect free, suggesting the geometry of the etched core has an impact on the strain in the shell layers. The structure of unusual 'flag' defects in the m-plane junctions was characterised via diffraction contrast TEM, weak beam and atomic resolution ADF STEM and were shown to consist of a basal plane stacking faults meeting a perfect or partial dislocation loop on a pyramidal plane, the latter likely gliding in to resolve residual strain due to the fault formed during growth. Zn₃N₂ has the required bandgap energy to be utilised as a phosphor with the additional advantage over conventional materials of its constituent elements not being toxic or scarce. The first successful synthesis of Zn₃N₂ nanoparticles appropriate to this application was confirmed via SAD, EDX and HRTEM, with software developed to fit experimental polycrystalline diffraction patterns to simulated components suggesting a maximum Zn₃N₂ composition of ~30%. There was an apparent decrease in crystallinity with decreasing particle size evidenced in radial distribution function studies with the smallest particles appearing completely amorphous in 80kV HRTEM images. A rapid change in the particles under the electron beam was observed, characterised by growth of large grains of Zn₃N₂ and ZnO which increased with increasing acceleration voltage suggesting knock-on effects driving the change. PL data was consistent with the bandgap of Zn₃N₂ blue shifted from 1.1eV to around 1.8eV, confirming the potential of the material for application as a phosphor.