At the commencement of this study, some sensitive overseas markets were rejecting chilled vacuum-packed New Zealand lamb due to higher than expected total viable counts, and counts of Enterobacteriaceae, a family of bacteria used to indicate sanitary condition. Of the many factors that influence the bacterial composition of chilled lamb in the overseas marketplace, the meat producer can only exert significant control over: Hygiene, ensuring the bacterial viable count on the meat prior to packaging is as low as possible, and comprised of as few species as possible that are capable of anaerobic growth at chilled meat temperatures. Maintaining the pH of the meat within acceptable limits, by careful animal selection and minimal pre-slaughter stress. Refrigeration temperatures, through rigorous maintenance of the cold-chain. The type of preservative packaging used, which is often limited by regulation in the marketplace. Initial work established that the bacterial microbiota present on the meat contact surfaces in the butchering facilities at some premises, in particular conveyor belting, was excessive and comprised of species that contributed to the high counts on the meat reported above. As a means of improving the hygiene of this process, this study investigated the hypothesis that some species of bacteria were able to form biofilms on the conveyor belt contact surfaces, becoming reservoirs for cross-contamination. This hypothesis was not been proven by this work; the results showing that biofilms were not present and that adequate hygiene of these surfaces instead depends on the ability to remove all meat-based residues from them at the completion of each day's processing. For premises operating interlocking belts from one manufacturer (Intraloxreg), a clean-in-place system is now available that is able to achieve this. Premises operating conventional disinfectant and water sanitisation of either continuous or interlocking belts must ensure that meat residue is completely removed before disinfection. The majority of New Zealand meat industry premises can now demonstrate that their hygienic processes in this area are under control. The microbiota of conveyor belting in this study was found to consist of bacteria from five taxonomic groups; the Flavobacteriaceae, the Actinomycetales, the Bacillus/Clostridium group, and the alpha and gamma branches of the Proteobacteria. The genera present on belts from premises whose hygiene was found to be in control did not contain species known to cause food-borne disease or spoilage of vacuum packaged meats. The bacterial viable count remains the most effective method available at this time for monitoring conveyor belt hygiene. Attempts to develop a monitoring system based on microscopy of an in-situ sampling device were unsuccessful due to an inability to penetrate the meat residue matrix. Denaturing Gradient Gel Electrophoresis (DGGE) may offer an alternative for rapid investigation of diversity, but further work is required before this can be validated for routine use.

Group-III-nitride semiconductors (GaN, InGaN, and AlGaN) are important for the fabrication of a range of optoelectronic devices (such as blue-green light emitting diodes, laser diodes, and UV detectors) as well as devices for high-temperature/high-power electronics. In the fabrication of these devices, ion bombardment represents a very attractive technological tool. However, a successful application of ion implantation depends on an understanding of the effects of radiation damage. Hence, this thesis explores a number of fundamental aspects of radiation effects in wurtzite III-nitrides. Emphasis is given to an understanding of (i) the evolution of defect structures in III-nitrides during ion irradiation and (ii) the influence of ion bombardment on structural, mechanical, optical, and electrical properties of these materials. ¶ Structural characteristics of GaN bombarded with keV ions are studied by Rutherford backscattering/channeling (RBS/C) spectrometry and transmission electron microscopy (TEM). Results show that strong dynamic annealing leads to a complex dependence of the damage buildup on ion species with preferential surface disordering. Such preferential surface disordering is due to the formation of surface amorphous layers, attributed to the trapping of mobile point defects by the GaN surface. Planar defects are formed for a wide range of implant conditions during bombardment. For some irradiation regimes, bulk disorder saturates below the amorphization level, and, with increasing ion dose, amorphization proceeds layer-by-layer only from the GaN surface. In the case of light ions, chemical effects of implanted species can strongly affect damage buildup. For heavier ions, an increase in the density of collision cascades strongly increases the level of stable implantation-produced lattice disorder. Physical mechanisms of surface and bulk amorphization and various defect interaction processes in GaN are discussed. ¶ Structural studies by RBS/C, TEM, and atomic force microscopy (AFM) reveal anomalous swelling of implanted regions as a result of the formation of a porous structure of amorphous GaN. Results suggest that such a porous structure consists of N$_{2}$ gas bubbles embedded into a highly N-deficient amorphous GaN matrix. The evolution of the porous structure appears to be a result of stoichiometric imbalance, where N- and Ga-rich regions are produced by ion bombardment. Prior to amorphization, ion bombardment does not produce a porous structure due to efficient dynamic annealing in the crystalline phase. ¶ The influence of In and Al content on the accumulation of structural damage in InGaN and AlGaN under heavy-ion bombardment is studied by RBS/C and TEM. Results show that an increase in In concentration strongly suppresses dynamic annealing processes, while an increase in Al content dramatically enhances dynamic annealing. Lattice amorphization in AlN is not observed even for very large doses of keV heavy ions at -196 C. In contrast to the case of GaN, no preferential surface disordering is observed in InGaN, AlGaN, and AlN. Similar implantation-produced defect structures are revealed by TEM in GaN, InGaN, AlGaN, and AlN. ¶ The deformation behavior of GaN modified by ion bombardment is studied by spherical nanoindentation. Results show that implantation disorder significantly changes the mechanical properties of GaN. In particular, amorphous GaN exhibits plastic deformation even for very low loads with dramatically reduced values of hardness and Young's modulus compared to the values of as-grown GaN. Moreover, implantation-produced defects in crystalline GaN suppress the plastic component of deformation. ¶ The influence of ion-beam-produced lattice defects as well as a range of implanted species on the luminescence properties of GaN is studied by cathodoluminescence (CL). Results indicate that intrinsic lattice defects mainly act as nonradiative recombination centers and do not give rise to yellow luminescence (YL). Even relatively low dose keV light-ion bombardment results in a dramatic quenching of visible CL emission. Postimplantation annealing at temperatures up to 1050 C generally causes a partial recovery of measured CL intensities. However, CL depth profiles indicate that, in most cases, such a recovery results from CL emission from virgin GaN, beyond the implanted layer, due to a reduction in the extent of light absorption within the implanted layer. Experimental data also shows that H, C, and O are involved in the formation of YL. The chemical origin of YL is discussed based on experimental data. ¶ Finally, the evolution of sheet resistance of GaN epilayers irradiated with MeV light ions is studied {\it in-situ}. Results show that the threshold dose of electrical isolation linearly depends on the original free electron concentration and is inversely proportional to the number of atomic displacements produced by the ion beam. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 C. Results also show that both implantation temperature and ion beam flux can affect the process of electrical isolation. This behavior is consistent with significant dynamic annealing, which suggests a scenario where the centers responsible for electrical isolation are defect clusters and/or antisite-related defects. A qualitative model is proposed to explain temperature and flux effects. ¶ The work presented in this thesis has resulted in the identification and understanding of a number of both fundamental and technologically important ion-beam processes in III-nitrides. Most of the phenomena investigated are related to the nature and effects of implantation damage, such as lattice amorphization, formation of planar defects, preferential surface disordering, porosity, decomposition, and quenching of CL. These effects are often technologically undesirable, and the work of this thesis has indicated, in some cases, how such effects can be minimized or controlled. However, the thesis has also investigated one example where irradiation-produced defects can be successfully applied for a technological benefit, namely for electrical isolation of GaN-based devices. Finally, results of this thesis will clearly stimulate further research both to probe some of the mechanisms for unusual ion-induced effects and also to develop processes to avoid or repair unwanted lattice damage produced by ion bombardment.

Thin film coatings are used to improve the properties of components and products in such diverse areas as tool coatings, wear resistant biological coatings, miniature integrated electronics, micro-mechanical systems and coatings for optical devices. This thesis focuses on understanding the development of intrinsic stress and microstructure in coatings of the technologically important materials of aluminium nitride (AlN) and titanium vanadium nitride (TiVN) deposited by filtered cathodic arc deposition. Thin films of AlN are fabricated under a variety of substrate bias regimes and at different deposition rates. Constant substrate bias was found to have a significant effect on the stress and microstructure of AlN thin films. At low bias voltages, films form with low stress and no preferred orientation. At a bias voltage of -200 V, the films exhibited the highest compressive stress and contained crystals preferentially oriented with their c axis in the plane of the film. At the highest bias of -350 V, the film forms with low stress yet continue to contain crystallites with their c axis constrained to lie in the plane of the film. These microstructure changes with bias are explained in terms of an energy minimisation model. The application of a pulsed high voltage bias to a substrate was found to have a strong effect on the reduction of intrinsic stress within AlN thin films. A model has been formulated that predicts the stress in terms of the applied voltage and pulsing rate, in terms of treated volumes known as thermal spikes. The greater the bias voltage and the higher the pulse rate, the greater the reduction in intrinsic stress. At high pulsing and bias rates, a strong preference for the c axis to align perpendicular to the substrate is seen. This observation is explained by dynamical effects of the incident ions on the growing film, encouraging channelling and preferential sputtering. For the first time, the effect of the rate of growth on AlN films deposited with high voltage pulsed bias was investigated and found to significantly change the stress and microstructure. The formation of films with highly tensile stress, highly compressive stress and nano-composites of AlN films containing Al clusters were seen. These observations are explained in terms of four distinct growth regions. At low rates, surface diffusion and shadowing causes highly porous structures with tensile stress; increased rates produced Al rich films of low stress; increasing the growth rate further led to a dense AlN film under compressive stress and the highest rates produce dense, low stress, AlN due to increased levels of thermal annealing. Finally this thesis analyses the feasibility of forming ternary alloys of high quality TiVN thin films using a dual cathode filtered cathodic arc. The synthesised films show exceptional hardness (greater than either titanium nitride or vanadium nitride), excellent mixing of the three elements and interesting optical properties. An optimum concentration of 23% V content was found to give the highest stress and hardness.

à venir

Bien que mon activité de recherche a été principalement axée sur la caractérisation structurale des phases d'Aurivillius en relation avec leurs propriétés ferroélectriques, je me suis aussi intéréssé à divers aspects liés à la synthèse de ces phases que ce soit sous forme de monocristaux, de poudres ou encore de films (voie chimique). Une première section consacrée à la synthèse ouvrira donc cette deuxième partie. Dès mon arrivée au SPCTS, une part importante de mon activité a été consacrée à l'étude des intercroissances à longues périodes qui ont pu être observées dans divers systèmes mais dont les caractéristiques structurales restaient inconnues. Sur la base de nos observations expérimentales, un modèle cristallographique généralisé utilisant le formalisme des groupes de super-espace a été développé pour les stuctures de type Aurivillius. Ce travail est issu d'une collaboration étroite avec l'équipe du Prof. J.M. Perez-Mato de l'Université de Bilbao. Cette nouvelle approche cristallographique et son utilisation constitueront la deuxième section. L'étude des relations structure/propriétés dans ces composés a constitué une autre part importante de mes recherches au SPCTS avec, notamment, le co-encadrement de la thèse de Jenny Tellier. Les divers aspects de la transition ferroélectrique-paraélectrique (FE-PE) rencontrés dans les composés de type Aurivillius ont été abordés que ce soit dans le cas des termes simples, des composés d'intercroissances que dans le cas, moins classique, des composés présentant un comportement ressemblant à celui de "relaxeurs" tel que Pb(Mg1/3Nb2/3)O3. Ce travail visant à décrire les mécanismes structuraux associés à la transition FE-PE fera l'objet de la troisième et dernière section.

<p>The technique of Nanoindentation <em>in situ</em> Transmission Electron Microscope has been implemented on a Philips CM20. Indentations have been performed on Si and Sapphire (<em>α-Al</em><em>2</em><em>O</em><em>3</em>) cut from wafers; Cr/Sc multilayers and <em>Ti</em><em>3</em><em>SiC</em><em>2</em> thin films. Different sample geometries and preparation methods have been evaluated. Both conventional ion and Focused Ion Beam milling were used, with different ways of protecting the sample during milling. Observations were made of bending and fracture of samples, dislocation nucleation and dislocation movement. Basal slip was observed upon unloading in Sapphire. Dislocation movement constricted along the basal planes were observed in <em>Ti</em><em>3</em><em>SiC</em><em>2</em>. Post indentation electron microscopy revealed kink formation in <em>Ti</em><em>3</em><em>SiC</em><em>2</em> and layer rotation and slip across layers in Cr/Sc multilayer stacks. Limitations of the technique are presented and discussed.</p>

One taphonomic problem plaguing archaeologists and physical anthropologists, whether their research is in North American cultures or hominid sites in Africa, is the difficulty in distinguishing bone altered by burning and heating from bone altered by soil processes. Archaeologists working to understand the recent prehistory of the Southern Oregon Coast face the same challenge. Two relatively new tools were investigated to determine their usefulness to resolving this problem. These are scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM has been well-tested in African sites and experimental studies to identify hominid-created cut marks on bone and to reconstruct heating temperatures of burnt bone. However, SEM and its ability to sample chemistry, as well as XRD's ability to detect diagentic alteration in bone minerals, have not been tested on material from coastal Oregon. The purpose of this research was: (1) to test these methods to see whether they could distinguish between burning and soil alteration, using cervid bone from site 35CS43 near Bandon, Ore., as a test sample, and (2) to see whether the result, paired with archaeological, ethnographic, taphonomic and faunal evidence, could be used to understand how the Coquille were procuring, processing and cooking cervids as insights into their adaptation. The outcome suggests that SEM and XRD, without use of other evidence, are unable to distinguish between burning and soil alteration because the similarities between the two lie not only in changes to the bone's macrostructure (discoloration) but also in bone chemistry, where it was hoped differences could be found. However, these techniques, when paired with the other lines of evidence, did provide insights in understanding the taphonomy and the Coquille's use of cervids - the interaction of bone and soil; the extent of mimicry between burning and soil alteration; and ultimately that discoloration of cervid bone at 35CS43 was likely due to soil alteration, that burning as the result of fire roasting was most likely not occurring at the site, and that the Coquille employed other methods of cooking. / Graduation date: 2003

The cyclic-compression behavior of a Cu45Zr45Al5Ag5 bulk metallic glass (BMG) was investigated in order to elucidate the damage initiation and growth mechanisms. The present Cu45Zr45Al5Ag5 BMG was found to have the highest fatigue-endurance limit for BMGs reported to date. Fracture under cyclic compression occurred in a pure shear mode. In addition to many shear bands and cracks, areas of “chipping” were commonly found on the outside surfaces of the fatigue specimens. Crack growth rates were found decrease with cycles. The effects of the as-cast specimen size, cooling rate, and the free volume content on the monotonic and cyclic compression behavior of a Zr-based BMG was investigated. The smaller samples experienced a faster cooling rate, resulting in a higher free volume content. The smaller samples displayed superior monotonic compression and cyclic compression properties. This trend was attributed to a higher free volume content. The effect of the sample aspect ratio (height/diameter) on the cyclic compression behavior of a Zr-based BMG was explored. For smaller aspect ratios (0.5), the yield strength and compressive plastic strain significantly increased when compared to that for an aspect ratio of 2. In general, when the aspect ratio was 0.5, the fatigue lives were longer than when the aspect ratio was 2. The dramatic effect of the sample aspect ratio was attributed to the development of a hydrostatic stress state from the interaction of the uniaxial applied load and the friction stress developed at the interface of the top and bottom specimen surfaces and the platens. The stress-life fatigue behavior and fracture morphology of a (Cu60Zr30Ti10)99Sn1 BMG alloy was investigated under both 3-point and 4-point bending conditions. For all stress levels tested, the fatigue lifetimes tended to be higher for the 3-point loading condition. All fracture surfaces were found to be comprised of four main regions: a crack-initiation site, a stable crack-growth region, an unstable fast-fracture region, and a melting region. Finely spaced parallel marks oriented somewhat perpendicular to the direction of crack propagation were observed in the stable crack-growth region. Analyses of these marks found that their spacing increased with increasing stress intensity- factor range.

Mit der vorliegenden Arbeit sollten mit Hilfe elektronenmikroskopischer Methoden verschiedene Liposomen-DNA-Komplexe zum Gentransfer charakterisiert sowie die Aufnahme und Verteilung in der Zellkultur untersucht werden. Dabei waren vor allem solche Präparationen von besonderem Interesse, die in unserer Arbeitsgruppe 'Drug Targeting' getestet oder entwickelt und verwendet wurden, wie Sendai-Virus Liposomen (HVJ-Liposomen), Virosomen sowie DAC-Chol und DOCSPER-Liposomen als Vertreter der kationischen Lipide.<br /> <br /> Im ersten Teil der Arbeit wurden fusogene Liposomen und Virosomen charakterisiert. Bei diesen Untersuchungen wurden folgende Ergebnisse erzielt:<br /> ·Sendai-Viren fusionieren mit Liposomen unterschiedlicher Lipidzusammensetzung. <br /> ·Die daraus resultierenden HVJ-Liposomen sind mit elektronenmikroskopischen Methoden identifizierbar.<br /> ·Die Spikes auf den HVJ-Liposomen besitzen fusogene Eigenschaften. <br /> ·HVJ-Liposomen eignen sich auf Grund der geringen Ausbeute sowie der geringen Transfektionseffizienz nicht zum in vitro Gentransfer.<br /> ·Virosomen stellen einen weiteren Typ fusogener Gentransfervesikel dar.<br /> ·Ihre Größe und fusogenen Eigenschaften sind abhängig von der externen Zugabe einer optimierten Lipidmischung.<br /> ·Im Innenraum der Virosomen kann mit Poly-L-Lysin vorkomplexierte DNA verkapselt werden.<br /> ·Die fusogenen Eigenschaften der Virosomen wurden mit Hilfe immunelektronenmikroskopischer Techniken und monoklonaler Antikörper gegen Hämagglutinin/Neuraminidase und das Fusionsprotein sowie mit polyklonalen Antiseren gezeigt.<br /> ·An Hand goldmarkierter DNA sind Virosomen nach der Transfektion in der Zelle nachweisbar.<br /> <br /> Da in unserer Arbeitsgruppe bevorzugt kationische Liposomen zum Gentransfer verwendet werden, wurde auch die Struktur der Liposomen untersucht und folgende Ergebnisse dokumentiert:<br /> ·Die Struktur und die Größe kationischer Liposomen werden hauptsächlich durch die Lipidzusammensetzung bestimmt. <br /> ·Die Bildung von Liposomen-DNA-Komplexen ist mit einer Größenzunahme der Komplexe gekoppelt.<br /> ·Die Anzahl gebundener Plasmide steigt mit der Größe der Lipoplexe. <br /> ·Gentransferaktive Lipopolyplexe (mit Protaminsulfat komplexierte DNA und DAC-Chol- Liposomen) sind kleiner als Lipoplexe. Ihre Struktur wird von der Zusammensetzung bestimmt. <br /> <br /> Eine weitere wichtige Frage betrifft den Weg der Gencarrier in der Zelle. Kenntnisse über diese Vorgänge sind vorteilhaft, um die einzelnen Schritte zu verstehen und möglichst gezielt zu verbessern.<br /> Bei der Untersuchung der Partikel im Hinblick auf zelluläre Barrieren beim Gentransfer konnten folgende Ergebnisse erzielt werden: <br /> ·Die Bindung der Partikel an die Zellmembran und Aufnahme sind abhängig von den eingesetzten Zellen und Komplexen sowie derInkubationszeit.<br /> ·Die Aufnahme erfolgt über endozytotische Mechanismen, wobei Lipopolyplexe schneller als Lipoplexe in die Zellen gelangen. Nicht alle gebundenen Komplexe werden aufgenommen.<br /> ·Die aufgenommenen Partikel befinden sich in Endosomen und werden ins Innere der Zelle transportiert. <br /> ·Freisetzung der DNA und Eintritt in den Zellkern über Kernporen konnte nicht beobachtet werden.<br /> ·DNA-haltige Vesikel in Kernnähe deuten auf einen weiteren Mechanismus hin (Vesikeltransfer zum Zellkern). / The aim of this work is the characterisation of several liposome DNA complexes for in vitro gene transfer and uptake as well as their distribution in cultured cell lines using electron microscopy. The particles used were fusogenic liposomes made from Sendai virus, virosomes and cationic liposomes. <br /> At first fusogenic liposomes and virosomes were characterised. The results obtained are summarised below:<br /> ·Sendai virus can fuse with liposomes made from different lipid composition.<br /> ·HVJ-liposomes are detectable using electron microscopy techniques. <br /> ·The spikes from HVJ-liposomes have fusogenic properties.<br /> ·HVJ-liposomes are not suitable for in vitro gene transfer due to the low amount of fusogenic liposomes leading to low transfection efficiency.<br /> ·Virosomes, reconstituted virus envelopes, are another type of fusogenic vesicles.<br /> ·Size and morphology of virosomes depends on the addition of an optimised lipid mixture. <br /> ·PLL treated DNA is entrapped into virosomes.<br /> ·Monoclonal and polyclonal antibodies and protein A gold technique can be used for the detection of viral glycoproteins on virosomes. ·Gold labelled DNA was used to show the distribution in cultured cells.<br /> <br /> In order to characterise the structure of cationic liposomes following results were obtained:<br /> ·Size and structure depends on the lipid composition.<br /> ·The formation of liposomes leads to an increase of the size.<br /> ·Larger lipoplexes contain more DNA.<br /> ·Lipopolyplexes composed of DNA complexed with protamine sulphate and DAC- Chol liposomes are smaller than lipoplexes. Their structure depends on the composition.<br /> <br /> To improve transfection ability examination of the cellular barriers is useful.<br /> With regard to the fate of lipoplexes following results were obtained.<br /> ·Binding depends on the cell line, kind of particles and incubation time.<br /> ·Uptake occurs through endocytosis. Lipopolyplexes enter the cells faster than larger lipoplexes.<br /> ·Lipoplexes are enclosed in endosomes and were carried into the centre of the cell.<br /> ·Escape of DNA from endosomes and entry into nucleus were not visible.<br /> ·Vesicles with DNA were observed near the nucleus. There is an opportunity for another pathway to the nucleus.

This dissertation has been focused on the synthesis and characterization of novel functionalized silica mesoporous crystals by using cationic surfactant and co–structure directing agents (CSDA), the central concept of the synthesis method is to build proper organic/inorganic interactions by introducing CSDA into the synthesis system. By using cationic surfactant as template and anionic CSDA, carboxylic group functionalized mesoporous silicas were successfully synthesized. Well ordered 2D p6mm, cubic Fm-3m, mixture of CCP (Fm-3m) and HCP (P63/mmc), and cubic Fd-3m with uniform carboxylic group distribution have been obtained. Besides, we have investigated the Fm-3m/Fd-3m type intergrowth and new type defects observed in the Fd-3m structure using transmission electron microscopy (TEM) and proposed a “polyhedron packing” model. New amphoteric, inorganic amino acid with highly ordered mesopores were synthesized. Uniform distribution of acid and base organic groups on the mesopore surfaces were formed by interactions between the counter charged surfactant head groups and ionic parts of CSDAs. It has been demonstrated that organic (–NH2 and –COOH) pairs incorporated in the mesopore walls behave as natural amino acids, collectively exhibiting an isoelectric point of ~6.0. Moreover, we have demonstrated that the inorganic amino acid is an efficient catalyst for the reaction between aldehydes and carbon nucleophiles.