Mixed metal oxides are ionic compounds containing at least two metal ions within an oxide structure. The literature contains a plethora of examples of mixed metal oxides on the bulk scale, which have been well characterised, however, mixed metal oxides on the nanoscale are far less well understood. The work presented here investigates the Bi2O3-CeO2-Nb2O5 mixed oxide system and characterises the resulting nanoparticles and crystal structures. Although the parent oxides are well known and much work has previously been done in analysing their crystal structures, combinations of these oxides have not been well characterised, especially on the nanoscale. Using high resolution electron microscopy (HRTEM), powder X-ray diffraction (PXRD), electron dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) as analytical tools, the structures of the nanoparticles in this system have been explored. As each of the parent oxides possess useful properties, which have been utilised in industrial applications such as electrolyte components in solid oxide fuel cells and as catalysts in a range of chemical reactions, it was hypothesised that if all three metal ions could be contained in one particle they could show novel and interesting characteristics. It was proposed that due to the more relaxed crystal structure in nanoparticles, the solid solubility of the metal ions should be increased, and a solid solution of ions would form. This work presents results showing the synthesis of binary and ternary oxides in the nano-form within the Bi2O3-CeO2-Nb2O5 system, including quantitative analysis of these particles. Secondly, and most importantly, it presents the first successful synthesis of quaternary oxide nanoparticles containing bismuth, cerium and niobium using the low temperature resin-gel method. Finally, the work attempts to explain how and why the ions are ordered in a given arrangement, with bismuth showing a preference for surface site occupation, as shown by XPS data, and describes some preliminary computational results which corroborate the experimental data.

abstract: The research of this dissertation has primarily involved using transmission electron microscopy (TEM) techniques to study several semiconductor materials considered promising for future photovoltaic device applications. Layers of gallium phosphide (GaP) grown on silicon (Si) substrates were characterized by TEM and aberration-corrected scanning transmission electron microscopy (AC-STEM). High defect densities were observed for samples with GaP layer thicknesses 250nm and above. Anti-phase boundaries (APBs) within the GaP layers were observed at interfaces with the Si surfaces which were neither atomically flat nor abrupt, contradicting conventional understanding of APB formation. Microcrystalline-Si (μc-Si) layers grown on crystalline-Si (c-Si) substrates were investigated. Without nanoparticle seeding, an undesired amorphous-Si (a-Si) layer grew below the μc-Si layer. With seeding, the undesired a-Si layer grew above the μc-Si layer, but μc-Si growth proceeded immediately at the c-Si surface. Ellipsometry measurements of percent crystallinity did not match TEM images, but qualitative agreement was found between TEM results and Ultraviolet Raman spectroscopy. TEM and Xray spectroscopy were used to study metal-induced crystallization and layer exchange for aluminum/ germanium (Al/Ge). Only two samples definitively exhibited both Ge crystallization and layer exchange, and neither process was complete in either sample. The results were finally considered as inconclusive since no reliable path towards layer exchange and crystallization was established. Plan-view TEM images of indium arsenide (InAs) quantum dots with gallium arsenide antimonide (GaAsSb) spacer layers revealed the termination of some threading dislocations in a sample with spacer-layer thicknesses of 2nm, while a sample with 15-nm-thick spacer layers showed a dense, cross-hatched pattern. Cross-sectional TEM images of samples with 5-nm and 10-nm spacer-layer thicknesses showed less layer undulation in the latter sample. These observations supported photoluminescence (PL) and Xray diffraction (XRD) results, which indicated that GaAsSb spacer layers with 10-nm thickness yielded the highest quality material for photovoltaic device applications. a-Si/c-Si samples treated by hydrogen plasma were investigated using high-resolution TEM. No obvious structural differences were observed that would account for the large differences measured in minority carrier lifetimes. This key result suggested that other factors such as point defects, hydrogen content, or interface charge must be affecting the lifetimes. / Dissertation/Thesis / Doctoral Dissertation Physics 2020

The work is devoted to problems of electron microscopy, focusing on the scintillation detector, which is located in chamber separating the field from different pressures. Using of the CAD and CAE was created 3D model of the detector, which took place on calculations focused to influence of the performance of different types of air pumps at gas flow between the chambers. The results of individual variants are compared in graphic form and evaluated.

The interaction of emotion and memory is necessary for establishing a cognitive map including current context and past experiences, which is used by prefrontal cortex to regulate the internal state and guide goal directed actions and decision making. The amygdala, hippocampus and anterior cingulate cortex (ACC) play critical roles in these processes, but the organization of pathways between them is largely unknown in primates. This issue was addressed using neural tracers in rhesus monkeys to label the bidirectional pathways between amygdala and hippocampus and the unidirectional pathway from hippocampus to ACC. The amygdala sent a robust projection to hippocampus that formed large and closely spaced dual synapses on spines from the same dendritic segment, suggesting a strong influence. Further, amygdalar axon boutons innervated some disinhibitory calretinin neurons in CA1, suggesting enhanced excitatory influence. In contrast, in CA3 the amygdala pathway innervated calretinin and some of the powerful parvalbumin inhibitory neurons, which may help enhance memory of affective events. The reverse pathway from hippocampus densely and mainly targeted the ventro-medial part of the amygdala, including the basolateral (BL) and paralaminar basolateral (PLBL) nuclei. Hippocampal terminations formed synapses mostly on spines vii of presumed excitatory neurons. Some hippocampal terminations innervated inhibitory neurons in BL and PLBL and showed a rank of preference, by targeting mostly calretinin, and then calbindin and least parvalbumin inhibitory neurons. This pattern of innervation may allow contextual information represented by hippocampus to influence affective processes in the amygdala. The hippocampus sent strong projections to ACC (A32, A24a and A25) and targeted particularly A25, suggesting a role in affective and autonomic regulation. About 90% of hippocampal terminations in A25 innervated excitatory neurons, suggesting strong excitatory effects. The hippocampal pathway had a close relationship with postsynaptic D1 receptors in A25, especially in the deep layers. Dopamine has a strong influence in goal-directed actions, rewards, and attention in prefrontal cortex in primates, and may facilitate contextual information from the hippocampus to A25 to influence emotional regulation. The pathways studied were distinct, and suggest specific roles in emotional memory by the amygdala in hippocampus, in flexible learning and forgetting fear based on context transmitted from hippocampus to the amygdala, and in the synthesis of current context and past experience carried out by the hippocampal pathway to ACC to influence adaptive goal directed behavior. / 2021-09-27T00:00:00Z

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Access to clean water is essential for human health and dignity. The increasingly rapid population growth, combined with the emergence of resistant chemical compounds and more concentrated toxic residues in the effluent streams of treatment plants, point towards a decline in freshwater resources resulting in a global water crisis in the next decades. Current wastewater treatment plants rely on Advanced Oxidation Processes (AOPs) for the tertiary (or advanced) step of the treatment. Photocatalysis is one of such processes, by which semiconductors are exposed to radiation of specific wavelengths (traditionally UV) to generate Reactive Oxygen Species (ROS) that can degrade organic molecules through a chain of radical oxidation reactions. Anatase titania (TiO2) has been used for many decades as a photocatalyst. Its electronic band structure has a band gap of 3.2 eV, requiring radiation in the UV range to trigger its photocatalytic properties. One way to reduce the band gap energy and shift the absorption peak wavelength to the visible part of the spectrum (thus reducing operation costs) is by doping the photocatalyst particles with transition metal atoms. Iron (III) is a great candidate due to the placement of its conduction/valence bands within titania’s band gap, its atomic radius similar to titanium (IV) and its variety of oxidation states. However, iron-doped anatase titania synthesized by ordinary sol-gel methods shows a photodegradation efficiency that is much lower than undoped anatase. Previous studies have shown that this is caused by an inconspicuous iron oxide layer on the surface of the catalyst particle, forming a physical barrier to the mobility of charge carriers that trigger the formation of ROS radicals. Small changes to the synthesis protocol, namely slowing down the hydrolysis of the Ti precursor by lowering the solution’s pH and acid-washing the final product, have been shown to result in particles that are photoactive under visible radiation and boast an unobstructed reactive surface. In this work, the novel Fe-TiO2 photocatalyst is studied and characterized in terms of its particle size distribution, inner structure and composition using electron microscopy techniques. It is important to know the particle size profile arising from this novel synthetic method, as the presence of nanoparticles could pose a health risk whereas an abundance of oversized particles is undesirable from the perspective of chemical reaction engineering (low surface-to-volume ratio). Inner structure/composition analyses could reveal whether the iron content inside the photocatalyst segregates into iron oxides, which would hinder reaction rates by behaving as a recombination center for charge carriers. As well, gathering more information about the inner structure of the catalyst (such as degree of crystallinity) is desirable as that could help fine-tune the synthesis protocol in order to obtain optimal photocatalytic activity. The particle size distribution studies using scanning electron microscopy revealed that the catalyst samples contain a significant fraction of nanoparticles (31.55% smaller than 100 nm), even though those particles represent a very small fraction of total sample volume (0.00015%) and reactive area (0.03%). Moreover, oversized particles (bigger than 5 m) account for the biggest fraction of sample volume and reactive surface. It was suggested that the size distribution of the catalyst be shifted to intermediate particle sizes by introducing additional grinding and separation steps into the synthesis protocol. The inner structure studies were carried using a combination of scanning, transmission and scanning-transmission electron microscopy, as well as spectroscopy methods such as EDX and EELS to map composition. It was found that the original anatase lattice structure remained unchanged in terms of interplanar spacings and crystallographic orientations, indicating that the addition of iron impurities at the small concentrations used here (0.5at%) did not result in discernible changes to the lattice. The monocrystalline units of Fe-TiO2 (termed crystallites) often appear to be bound together by amorphous material. No segregation of Fe was observed inside the particles at this concentration, as shown by the apparent homogenous composition of the catalyst across crystalline and amorphous regions. The external iron oxide contamination layer observed in previous studies was theorized to form during the later steps of the sol-gel process due to the precipitation of the iron content in solution that failed to be incorporated into the TiO2 gel network. More in-depth studies must be carried to assess whether preferential segregation of iron within the catalyst could occur at higher dopant concentrations. / Graduate

The field of implantology is centred around interfacial interactions with the surrounding bone tissue. Assessing the suitability of novel engineering materials as implants for clinical application follows a preliminary workflow that can be simplified into three main stages: (i) implant design, (ii) in vitro compatibility, and (iii) in vivo compatibility. This thesis is subdivided to mirror each of these three themes, with a specific focus on the multiscale features of the implant itself as well as appositional bone tissue. In Chapter 3, a biomimetic approach to generate porous metallic implants is presented, using preferential seeding in a 3D Voronoi tessellation to create struts within a porous scaffold that mirror the trabecular orientation in human bone tissue. In Chapter 4, cytocompatible succinate-alginate films are generated to promote the in vitro activity of osteoblast-like cells and endothelial cells using a methodology that could be replicated to coat the interior and exterior of porous metals. In Chapter 5, two types of porous implants with graded and uniform pore size are implanted into rabbit tibiae to characterize the biological process of osseointegration into porous scaffolds. In Chapter 6, these same scaffolds are probed with high-resolution 2D and 3D methods using scanning transmission electron microscopy (STEM) and the first-ever application of plasma focused ion beam (PFIB) serial sectioning to observe structural motifs in biomineralization at the implant interface in 3D. This thesis provides new knowledge, synthesis techniques, and development of characterization tools for bone-interfacing implants, specifically including a means to: (i) provide novel biomaterial design strategies for additive manufacturing; (ii) synthesize coatings that are compatible with additively manufactured surfaces; (iii) improve our understanding of mineralization process in newly formed bone, with the ultimate goal of improving the osseointegration of implants. / Thesis / Doctor of Philosophy (PhD) / Metallic implants are widely used in dental and orthopedic applications but can be prone to failure or incomplete integration with bone tissue due to a breakdown at the bone-implant interface as defined by clinical standards. In order to improve the ability of the implant to anchor itself into the surrounding bone tissue, it is possible to use novel three-dimensional (3D) printing approaches to produce porous metals with an increased area for direct bone-implant contact. This thesis examines strategies to design porous implants that better mimic the structure of human bone, possible coating materials to accelerate early bone growth at the implant interface, and the microscale-to-nanoscale origins of bone formation within the interior of porous materials.

Methanation of CO2, a greenhouse gas component, using bimetallic catalysts is considered. Rh, Pd and Ru were combined separately with Co on silica support to form bimetallic catalysts with 5 % metal loading and atomic ratio to Co equal to 1. Pore volume of the silica was measured using physisorption analysis. The unreduced catalyst samples were characterized using XPS, TPR and SEM-EDS. XPS results showed low Rh, Pd, Ru and Co concentrations at the surface for the three bimetallic catalysts. The oxidation states of metals detected by XPS supported the likely presence of metals in their oxide form. Detection of alloys and/or bimetallic particles on the surface of the catalysts was difficult through the XPS results, but presence of bimetallic particles was confirmed in Ru-Co and Pd-Co catalysts through the TPR results. Surface segregation of cobalt was observed. This was supported and extended to other metals through the SEM-EDS results.

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