Stoichiometric polyelectrolyte-surfactant complexes represent a type of comb-shaped polymers, in which every polymer chain unit has an electrostatically bound "side chain". These complexes are water-insoluble. In the solid state they assemble spontaneously into mesogenic structures. The [X,Y]-ionenes ([(CH2)XN+(CH3)2(CH2)YN+(CH3)2]nBr-2n) investigated formed stoichiometric complexes with alkyl sulfates. The ionene alkyl sulfate complexes display mesogenicity, i.e. optically isotropic dry complexes underwent lyotropic and thermotropic phase transitions to the optically anisotropic phase (and vice versa) under controlled relative humidity. The optically anisotropic phases exhibited hexagonal textures as revealed by polarizing microscopy. A new feature is the lyotropic transition brought about by the uptake of water through the gas phase. The complexes were all sensitive to both humidity and temperature. In principle, the effects can be applied to measure humidity.

Size effects in out-of-plane bending stiffness of honeycomb cellular materials were studied using analytical mechanics of solids modeling, fabrication of samples and mechanical testing. Analysis predicts a positive size-effect relative to continuum model predictions in the flexure stiffness of a honeycombed beam loaded in out-of-plane bending. A method of determining the magnitude of that effect for several different methods of constructing or assembling square-celled and hexagonal-celled materials, using both single-walled and doubled-walled construction methods is presented. Hexagonal and square-celled honeycombs, with varying volume fractions were fabricated in Nylon 12 using Selective Laser Sintering. The samples were mechanically tested in three-point and four point-bending to measure flexure stiffness. The results from standard three-point flexure tests, did not agree with predictions based on a mechanics of solids model for either square or hexagonal-celled samples. Results for four-point bending agreed with the mechanics of solids model for the square-celled geometries but not for the hexagonal-celled geometries. A closed form solution of an elasticity model for the response of the four-point bending configuration was developed, which allows interpretation of recorded displacement data at two points and allows separation the elastic bending from the localized, elastic/plastic deformation that occurs between the loading rollers and the specimen’s surface. This localized deformation was significant in the materials tested. With this analysis, the four-point bending data agreed well with the mechanics of solids predictions. / text

A new broadband beamformer composed of nested arrays (NAs), multi-dimensional (MD) filters, and multirate techniques is proposed for both linear and planar arrays. It is shown that this combination results in frequency-invariant response. For a given number of sensors, the advantage of using NAs is that the effective aperture for low temporal frequencies is larger than in the case of using uniform arrays. This leads to high spatial selectivity for low frequencies. For a given aperture size, the proposed beamformer can be implemented with significantly fewer sensors and less computation than uniform arrays with a slight deterioration in performance. Taking advantage of the Noble identity and polyphase structures, the proposed method can be efficiently implemented. Simulation results demonstrate the good performance of the proposed beamformer in terms of frequency-invariant response and computational requirements. The broadband beamformer requires a filter bank with a non-compatible set of sampling rates which is challenging to be designed. To address this issue, a filter bank design approach is presented. The approach is based on formulating the design problem as an optimization problem with a performance index which consists of a term depending on perfect reconstruction (PR) and a term depending on the magnitude specifications of the analysis filters. The design objectives are to achieve almost perfect reconstruction (PR) and have the analysis filters satisfying some prescribed frequency specifications. Several design examples are considered to show the satisfactory performance of the proposed method. A new blind multi-stage space-time equalizer (STE) is proposed which can separate narrowband sources from a mixed signal. Neither the direction of arrival (DOA) nor a training sequence is assumed to be available for the receiver. The beamformer and equalizer are jointly updated to combat both co-channel interference (CCI) and inter-symbol interference (ISI) effectively. Using subarray beamformers, the DOA, possibly time-varying, of the captured signal is estimated and tracked. The estimated DOA is used by the beamformer to provide strong CCI cancellation. In order to alleviate inter-stage error propagation significantly, a mean-square-error sorting algorithm is used which assigns detected sources to different stages according to the reconstruction error at different stages. Further, to speed up the convergence, a simple-yet-efficient DOA estimation algorithm is proposed which can provide good initial DOAs for the multi-stage STE. Simulation results illustrate the good performance of the proposed STE and show that it can effectively deal with changing DOAs and time variant channels. / Graduate / 0544 / imanmoaz@uvic.ca

Contrairement aux nanotubes de carbone qui sont des semi-conducteurs dits " à petit gap " et dont les propriétés électroniques sont complétement contrôlées par leur géométrie, les nanotubes hétérogènes mono-parois BxCyNz suscitent un grand intérêt scientifique du fait de leurs propriétés électroniques modulables. La synthèse de tels nanotubes hétérogènes permettrait en effet de moduler ce " gap " en agissant sur leur composition chimique et non sur leur géométrie. Les nanotubes BxCyNz qui résultent de la substitution de certains atomes de carbone dans le réseau graphénique par des hétéroatomes (B et/ou N) peuvent trouver de nombreuses applications notamment dans la réalisation de matériaux photoluminescents, les dispositifs à émission de champ ou encore les nanotransistors à haute température... Ce travail porte sur la synthèse de cette nouvelle génération de nanotubes par arc électrique. Cette technique présente l'avantage de réaliser la substitution in-situ des atomes de carbone par les hétéroatomes. Elle a été menée en utilisant une approche originale basée sur la corrélation des caractéristiques du plasma (champs de température et de concentration des différentes espèces) avec la morphologie et la composition des nanostructures carbonées caractérisées par différentes techniques (HRTEM, EDX, XPS, EELS). Ces résultats permettent une meilleure compréhension des phénomènes impliqués dans la croissance des hétéronanotubes aux échelles macroscopique et microscopique, et également de la structure et de l'environnement chimique des dopants dans le réseau graphénique de nanoformes carbonées obtenues tels que des nanotubes dopés au bore et ou à l'azote, et des couches de graphènes dopées. / In opposition to carbon nanotubes which are semi-conductors with so-called "small gap" and which electronic properties are entirely determined by their geometry, single-wall heterogeneous carbon nanotubes BxCyNz yield to great scientific interest due to their tunable electronic properties. Successfully synthesising these heterogeneous nanotubes would indeed allow tuning this gap by acting on their chemical composition instead of their geometry. BxCyNz nanotubes resulting from the substitution of some carbon atoms in the graphene lattice by heteroatoms (B and/or N) could have numerous applications, in particular in photo-luminescent materials, field emission devices, or high operating temperature nano transistors... This work is dedicated to the synthesis of this new generation of nanotubes by electric arc. This technique offers the advantage to perform in-situ substitution of carbon atoms by the heteroatoms. It was carried out using an original approach based on the correlation of plasma characteristics (temperature and concentration fields of the various species) with the morphology and the composition of the carbon nanostructures characterized by various techniques (HRTEM, EDX, XPS, EELS). These results bring a better understanding of the phenomena involved in the growth of heteronanotubes in plasma conditions and also of the structure and chemical environment of the doping elements in the graphene lattice of carbon nanoforms such as boron- or nitrogen-doped nanotubes, and doped graphene layers.

In this work we present a theoretical and computational study of the mechanism of ferroelectricity in multiferroic hexagonal manganite LuMnO3. Some structural and electronic properties are described in both paraelectric (PE) and ferroelectric (FE) phases. As theoretical and computation tool was employed the Full Potential Linear Augmented Plane Wave method, based on Density Functional Theory and embodied in WIEN2k computer code. The crystal structure of both PE and FE phases was optimized using two different types of exchange and correlation potentials. The local density approximation (LDA) and generalized gradient approximation (GGA). The lattice parameters from GGA calculation were obtained in better agreement with experimental than LDA result. Also, were analyzed two different GGA parameterizations: the so-called Perdew - Burke - Ernzerhof (PBE) and Wu - Cohen (WC). Comparing them, the result from GGA-PBE calculation is in better agreement with the experimental. After the structural optimization, the atomic positions were fully relaxed. In this step, was utilized the GGA with the PBE parameterization. The electronic properties were calculated from these optimized and relaxed structures and using the Tran and Blaha modified Becke-Johson potential. From these calculations were obtained an indirect band gap of 0,3 eV and a direct band gap of 1,6 eV in the PE and FE phases, respectively. The valence electronic density maps were obtained along the c axis of the phases PE and FE. It was observed when leave of the PE to the FE phase, the ionic character of Lu-O bonds was changed. By careful analysis of the calculated partial density of states, we showed that the loss of ionicity of the chemical bond is associated with the rehybridization of the 5dz2 - Lu with 2pz - O orbitals. This description corroborates with the model in which the mechanism of ferroelectricity of the hexagonal manganites is related with the rehybridization of the dz2 - Y or - Lu orbitals with 2pz - O s orbitals that are along the crystalline c axis. / No presente trabalho foi realizado um estudo teórico e computacional sobre o mecanismo da ferroeletricidade na manganita hexagonal multiferróica LuMnO3. Foram obtidas algumas das propriedades estruturais e eletrônicas desse composto nas fases paraelétrica (PE) e ferroelétrica (FE). Como ferramenta teórica e computacional foi utilizado o método de cálculo de estrutura eletrônica denominado de Full Potential Linearized Augmented Plane Wave que é baseado na Teoria do Funcional da Densidade e implementado no código computacional WIEN2k. Foi realizada a otimização dos parâmetros de rede usando duas diferentes aproximações para o potencial de troca e correlação. A aproximação da densidade local (LDA) e a do gradiente generalizado (GGA). Os parâmetros de rede obtidos com o cálculo GGA foram mais próximos do experimental do que aqueles obtidos usando a aproximação LDA. Para o cálculo usando a aproximação GGA foram testadas duas formas de parametrização: Perdew - Burke - Ernzerhof (PBE) e Wu - Cohen (WC). Nesse caso, o resultado obtido com a parametrização PBE é a que melhor se compara com o resultado experimental. Após a otimização dos parâmetros de rede, foram relaxadas as posições atômicas. Nessa etapa do cálculo, foi utilizada a aproximação GGA-PBE. Para o cálculo da estrutura eletrônica, foi usado o potencial modificado de troca de Becke-Johnson (mBJ). Com ele foi possível obter um band gap indireto de 0,3 eV na fase PE e um band gap direto de 1,6 eV na fase FE. Foram obtidos mapas de densidade eletrônica valência ao longo do eixo c cristalino das fases PE e FE. Observou-se, saindo da fase PE para a FE, que o caráter iônico da ligação Lu - O foi alterado. A análise da densidade de estados parciais mostrou que a perda da ionicidade da ligação química está associada à rehibridização dos orbitais 5dz2 do Lu com os orbitais 2pz do O. Esta descrição corrobora com o modelo em que o mecanismo da ferroeletricidade das manganitas hexagonais está associado à rehibridização dos orbitais dz2 do átomo R (Lu ou Y) com os orbitais 2pz dos átomos de oxigênio que estão ao longo do eixo cristalino c.

Les mésophases hexagonales sont des systèmes quaternaires formés de tensioactifs et co-tensioactifs, eau salée et huile. Ces mésophases sont utilisées comme moules « mous » pour la synthèse de différents nanomatériaux tels que des nanostructures métalliques poreuses, des nanostructures de polymères conjugués et des nanocomposites métalliques-polymères. Contrairement aux matrices (ou moules) durs, qui nécessitent des réactifs chimiques corrosifs pour extraire les nanomatériaux synthétisés in situ, le processus d'extraction des nanomatériaux synthétisés dans les mésophases hexagonales est simple : les nanomatériaux peuvent être extraits simplement par lavage avec de l'éthanol ou du 2-propanol. Un autre intérêt à utiliser ces mésophases comme matrice de synthèse est qu’elles peuvent être gonflées en contrôlant le rapport huile / eau. Cette thèse est divisée en trois parties: 1) La synthèse de nanostructures métalliques poreuses dans la phase aqueuse des mésophases hexagonales et leur application dans les piles à combustible (oxydation de l'éthanol), 2) La synthèse de nanostructures de polymères conjugués dans la phase huile des mésophases hexagonales pour des applications en photocatalyse et en particulier pour la dégradation de polluants, 3) La synthèse combinée dans les phases huile et eau des mésophases hexagonales de nanocomposites métal-polymère. Plusieurs nanostructures métalliques telles que des nanoballes PdPt de porosité et composition contrôlées, des nanostructures poreuses cœur-coquille AuPd et AuPt, bimetalliques PtNi et trimétalliques AuPdPt ont été synthétisées par radiolyse dans la phase aqueuse des mésophases hexagonales. Les nanoballes PdPt de porosité et composition contrôlées ont été utilisées comme électro-catalyseurs pour l'oxydation de l'éthanol. L'effet de la taille des pores sur la surface électro-active des nanostructures métalliques et leur activité électrocatalytique pour l'oxydation de l'éthanol a été étudié. Les nanostructures poreuses cœur-coquille bimétalliques AuPd et AuPt, et trimétalliques AuPdPt ont été utilisées pour l'oxydation de l'éthanol et du glucose. Les nanoballes poreuses PtNi ont été utilisées pour l'évolution de H2 et la réaction de réduction de l’oxygène. Des nanostructures de polymères conjugués (poly(3-hexylthiophène), P3HT) ont été synthétisées dans la phase huile des mésophases hexagonales. Ces nanostructures de polymères ont une activité photocatalytique élevée sous UV et lumière visible. Le phénol et la rhodamine B ont été utilisés comme polluants modèles. Ces photocatalyseurs sont très stables même après plusieurs cycles photocatalytiques. L'ajout de molécules capteurs et l’étude du mécanisme montrent que les radicaux O2.− sont les principaux radicaux responsables de la dégradation du phénol. De manière très intéressante, l'activité photocatalytique de ces nanostructures de P3HT est fortement augmentée lorsqu'elles sont supportées sur une surface solide. Ce résultat ouvre de nouvelles perspectives pour des applications dans des réacteurs photocatalytiques et des surfaces autonettoyantes. Des résultats préliminaires sur la synthèse des nanocomposites Pt-PDPB (polydiphenylbutadiyne) sont également présentés dans cette thèse. / Soft hexagonal mesophases, which consist of quaternary systems (surfactants, brine, oil, and co-surfactant) are used as templates for the synthesis of different nanomaterials such as metal nanostructures, conjugated polymer nanostructures, and metal-polymer nanocomposites. Unlike hard templates, which need a harsh chemical reagent to extract nanomaterials after the synthesis, in soft template hexagonal mesophases, the extraction process of nanomaterials is simple, only by washing with ethanol or 2-propanol. Another interesting property of this class of template lies on its ability to be swollen by controlling the ratio of oil to water.This thesis is divided into three parts: 1) Radiolytic synthesis of metal nanostructures in the aqueous phase of hexagonal mesophases and their application in fuel cells (ethanol oxidation), 2) Synthesis of conjugated polymer nanostructures in the oil phase of hexagonal mesophases for photocatalytic degradation of pollutants, 3) Combined synthesis in the oil and water phases of hexagonal mesophases of metal-polymer nanocomposites.Several metal nanostructures such as PdPt nanoballs with controlled composition and porosity, AuPd and AuPt core shell, bimetallic PtNi and trimetallic AuPdPt porous nanoballs were synthesized by radiolysis in the aqueous phase of hexagonal mesophases. PdPt nanoballs with controlled porosity and composition were used as electrocatalysts for ethanol oxidation. The effect of the pore size on their electro active surface and their electrocatalytic activity towards ethanol oxidation were studied. AuPd and AuPt core-shell, and trimetallic AuPdPt porous nanoballs were used for ethanol and glucose oxidation. PtNi porous nanoballs were used for H2 evolution and oxygen reduction reaction. Conjugated polymer nanostructures namely P3HT (poly(3-hexylthiophene)) were synthesized in the oil phase of hexagonal mesophases. These polymer nanostructures are highly active for photocatalysis under UV and visible light. Phenol and rhodamine B were used as model pollutants. These photocatalysts are very stable even after repeated cycling. Addition of scavengers and mechanistic studies show that O2.− is the main radical responsible for degradation of phenol. Most interestingly, the photocatalytic activity of these P3HT nanostructures is highly enhanced when they are supported on a solid surface opening new perspectives in photocatalytic reactors and self-cleaning surfaces. Premiminary results on the synthesis of Pt-PDPB (polydiphenylbutadiyne) nanocomposites are also presented in this thesis.

After the experimental discovery of graphene at the beginning of the 21st century, many other interesting 2D materials have been discovered. However, the electrical and optical properties of these layers are greatly influenced by the composition and quality of the surrounding materials. In order to preserve the exceptional properties of thin films, attention has gradually been drawn to heterostructures from 2D composite materials. This thesis describes the preparation and characterization of heterostructures composed of graphene and hexagonal boron nitride. In addition, a specific focus will be placed on optimizing the production process of heterostructures by the dry thin film transfer process, prepared by micromechanical exfoliation. Characterization and quality of prepared layers are controlled by Raman spectroscopy, while morphology is examined by atomic force microscope (AFM). Furthermore, the electrical properties of the graphene-hBN device are discussed and the charge carrier of the graphene field-effect transistor is measured.

Ziel dieser Doktorarbeit war es, den Einfluss von verschiedenen Parametern auf die spektroskopischen Eigenschaften von Lanthanid-basierten Aufkonversions-Materialien zu erforschen. Ein besonderer Fokus lag dabei auf hexagonalen Natrium-Yttrium-Tetrafluorid Kristallen, die mit dreifachgeladenen Yb und Er oder Tm Ionen kodotiert wurden. Eine wesentliche Voraussetzung für mögliche Anwendungen dieser Kristalle ist ein Verständnis aller ihrer wichtigen photophysikalischen Besonderheiten. Die erste Studie dieser Doktorarbeit untersuchte daher, wieso Nanokristalle viel weniger absorbierte in ausgesendete Photonen umwandeln als mikrokristalline Teilchen. Die Ergebnisse zeigten, dass man ungeschalte Kristalle aufgrund von Oberflächen-Lösch-Effekten in zwei Teile unterteilen kann, einen strahlenden Kern und eine Schale aus stark oder vollständig gelöschten oberflächennahen Lanthanid-Ionen, welche für Kristalle abnehmender Größe einen immer größeren Volumenanteil einnimmt. Die zweite Studie untersuchte exemplarisch, ob eine kompliziertere Partikelarchitektur, bestehend aus einem einfach-dotierten Er Kern und Yb als Schalenmaterial, diesen Effizienzverlust der Lumineszenz reduzieren kann. Die Ergebnisse zeigten jedoch, dass dies nicht der Fall ist. Eine weitere Studie untersuchte den Einfluss der Konzentration der Tm Ionen in Yb, Tm kodotierten Nanokristallen auf die spektroskopischen Eigenschaften dieser Materialien und zeigte, dass für eine maximale Emission im Lichtwellenbereich über 700 nm andere Tm Konzentrationen benötigt werden als für maximale Lichtemissionen in den unteren Lichtwellenbereichen. Die letzte Studie untersuchte den Einfluss eines zuvor berichteten Zersetzungsprozesses von exemplarisch ausgewählten Yb, Tm kodotierte Nanokristallen in wässrigen Dispersionen auf deren spektroskopische Eigenschaften. Mithilfe dieser Ergebnisse war es möglich, mehrere Emissionsbanden als Parameter für das Langzeit-Stabilitäts-Monitoring dieser Materialien zu identifizieren. / This PhD thesis investigated the influence of various parameters on the spectroscopic properties of so-called upconversion nanoparticles (UCNPs). A special emphasis was dedicated to hexagonal-phase sodium yttrium tetrafluoride crystals that were codoped with trivalent Yb and either Er or Tm ions. Such UCNPs can, however, experience no breakthrough in the field of UC nanotechnology before all of their important photophysical features are understood. The first study of this PhD thesis therefore investigated, why nanocrystalline upconverters with different surface chemistries convert less absorbed to emitted photons than their microcrystalline counterparts. The results revealed that upconverting crystals apparently have to be subdivided into two parts, with one being the luminescent core and the other being a completely dark shell that is quenched by surface effects and assumes an ever increasing volumetric content for small UCNPs. The second study exemplarily investigated, if a more complex particle nanostructure that consisted of a Er doped core, surrounded by a Yb doped shell, could overcome these efficiency losses, however, it concluded that it does not. Another study explored the influence of Tm doping concentrations of Yb, Tm codoped nanocrystals on their spectroscopic properties and concluded that different Tm doping concentrations are required for a maximum upconversion luminescence in the wavelength regions above 700 nm, than for the wavelength regions below that. The last study of this PhD thesis investigated the influence of a previously reported dissolution process of UCNPs in aqueous solutions on the spectroscopic properties of exemplarily chosen Yb, Tm codoped nanocrystals. These results were then utilized to identify several upconversion emission bands that can be used as a screening parameter for the long-term stability monitoring of UCNPs.

Stoichiometric polyelectrolyte-surfactant complexes represent a type of comb-shaped polymers, in which every polymer chain unit has an electrostatically bound "side chain". These complexes are water-insoluble. In the solid state they assemble spontaneously into mesogenic structures. The [X,Y]-ionenes ([(CH2)XN+(CH3)2(CH2)YN+(CH3)2]nBr-2n) investigated formed stoichiometric complexes with alkyl sulfates. The ionene alkyl sulfate complexes display mesogenicity, i.e. optically isotropic dry complexes underwent lyotropic and thermotropic phase transitions to the optically anisotropic phase (and vice versa) under controlled relative humidity. The optically anisotropic phases exhibited hexagonal textures as revealed by polarizing microscopy. A new feature is the lyotropic transition brought about by the uptake of water through the gas phase. The complexes were all sensitive to both humidity and temperature. In principle, the effects can be applied to measure humidity.

No description available.