In this thesis, we present our original theoretical investigations of SiC microstruc-tures for extreme light control in the Reststrahlen band of Silicon Carbide (SiC), that occurs in the Mid-IR spectral regime. In this frequency regime, most of the light will be reflected from bulk SiC, due to the extreme permittivity response of SiC. However, we demonstrate that it is possible to control light to be absorbed or ultra refracted within the microstructures constructed from SiC in the Reststrahlen band of SiC. In particular, we show that this high reflective behaviour of SiC can be over-come via different mechanisms: by achieving a Photonic Crystal (PC) band-edge reflectionless condition in a SiC terminated one-dimensional (1D)-PC, by tailoring the effective phonon-polariton gap in SiC-based effective metamaterials, or by cou-pling to cavity modes in SiC structures made of rectangular-cross-section pillars. Furthermore, we demonstrate that by varying the thickness of SiC layers and filling ratio throughout SiC 1D-PC structures or by using SiC pillars of different size in a pyramid arrangement, we can achieve a broad absorption bandwidth with the SiC microstructures. This absorption control provides insight for the design of efficient thermal emitters, which can be used in thermal conversion devices. Moreover, us-ing the concept of Bloch impedance, we find that translucent spectral regions can exist in SiC 1D-PCs. This possibility is highly desirable for constructing optical components in the Mid-IR spectrum where suitable bulk highly refractive materials are rare. In addition, we also present a complete theory of propagation in lossy 1D-PCs, by systematically extending the comprehensive theory for lossless 1D-PCs. Relying on this theory, we report superbending of light, beyond 90 0 in a judiciously designed superprism constructed with a SiC 1D-PC. Since, the findings reported in this thesis are in principle applicable to any polar material, we believe that our work will inspire the design of a variety of absorptive/emissive and ultra-refractive devices across the THz/Mid-IR spectrum.

La filière solaire thermodynamique, et plus précisément la technologie des centrales à tour, est l'une des ressources d'énergies renouvelables les plus prometteuses. Le travail de thèse s’inscrit dans le cadre général de l’augmentation des rendements de centrales solaires à tour où l’augmentation de l'efficacité et de la température du récepteur joue un rôle clé. L’originalité de la thèse réside dans l’étude du rôle des sélectivités spectrale et directionnelle sur le rendement de récepteurs surfaciques à haute température. L’objectif poursuivit a été d’améliorer simultanément la géométrie, le matériau, la rugosité et la microstructuration des récepteurs surfaciques pour créer une sélectivité permettant l’augmentation des rendements. La première étape a consisté à l’élaboration d’un modèle approché d’une centrale solaire pour quantifier l’influence du rendement du récepteur sur le rendement de la centrale. Dans un second temps, un modèle de récepteur détaillé incluant la résolution précise des transferts radiatifs (grâce à la méthode Monte Carlo) a été développé pour déterminer le gain en rendement que l’on peut obtenir grâce à la sélectivité spectrale et directionnelle. Ensuite, la modification des propriétés radiatives des surfaces par des microstructures unipériodiques et bipériodiques a été étudiée dans l'objectif d'augmenter la sélectivité spectrale du récepteur. Cette étape a nécessité la résolution des équations de Maxwell par la méthode RCWA. La microstructure retenue et qui offre le meilleur potentiel possède un relief pyramidal bipériodique. L’optimisation de la période et de la hauteur de ce relief permet d’obtenir une absorptivité solaire maximale égale à 0,98. / Concentrated solar power (CSP) technology is an alternative for renewable thermal energy generation and a promising source of energy. Managing the optical properties of a cavity solar receiver to create spectral and directional selectivities is a solution to improve receiver and solar power plant efficiencies in order to reduce cost. The two main steps of the development are to quantify the potential gain that may result from theoretical selectivities and then the optimization of microstructuration to increase as possible the spectral selectivity. At first, a calculation code was built in order to quantify the influence of receiver on the global solar power plant efficiency. Then a parametric study which takes into account thegeometry, the material, the roughness and the microstructure of the receiver was conducted. At last, an optimization of microstructuration with uniperiodic and biperiodic structures was studied. As a conclusion the best structure is a biperiodic pyramidal relief which offers a huge gain of absorptivity.

Neste trabalho foram estudadas as microestruturas, dureza, e resistência ao impacto em aço alta resistência e baixa liga (ARBL) na ZAC. O processo de soldagem foi por arco submerso, utilizando corrente de 600A, tensão de 25V, velocidade de soldagem de 25,5; 24; 20,94; e 19,5 cm/min. Utilizou-se chapa de aço USI-SAC-50. Os quatro aportes de calor produzidos 3,53; 3,75; 4,24; 4,61 kJ/mm, permitiram variações microestruturais na região de granulação grosseira da ZAC, promovendo variações nas medidas de durezas e nos resultados do ensaio de impacto medido à -25ºC e -10ºC. Quando realizado o tratamento térmico de alívio de tensões a 580ºC por 1 hora, as morfologias das microestruturas e medidas de dureza na região grosseira da ZAC, praticamente foram iguais, independente do aporte de calor. Os resultados do ensaio de impacto realizado à -25ºC, com e sem tratamento térmico, não sofreram alterações significativas para os valores das energias absorvidas na ZAC. Já a -10ºC a mudança foi mais significativa. O aspecto da morfologia da fratura na região de granulação grosseira da ZAC, após o ensaio de impacto, foi coerente para os quatro aportes de calor utilizados na soldagem. / It was studied in this report the microstructure, hardness and impact resistance in High Strength Low Alloyed (HSLA) steel in HAZ. The submerged are weld metals were made, using corrent of 600A, are voltage of 25V and travel speed of 25,5; 20,9; 24; and 19,5 cm/min. The USI-SAC-50 steel was used in present report. Four different heat input 3,53; 3,75; 4,24 and 4,61 kJ/mm were used to weld, produced significant changes in the coarse heat affected zone (HAZ) microstructure morphology, and this effect promoted changes on the hardness and the impact results at -25°C and -10°C. Using stress reliev treatment at 580°C for one hour, has changed the microstructure morphology in the coarse heat affected zone and the hardness measurements becames quite similar, therefore independent of the heat input. At -25°C the impact results has shown no variations with the stress reliev heat treatment. However, there were significant changes in the impact results at -10°C. After the impact test, the aspect of morphology facture in the coarse heat affected zone (HAZ), was coherent for the four different heat input, were used to weld.

The average size of hot-work tools has gradually increased over the past years.This affects the effective temperature cycle tools experience during hardening,as large dimensions prevent uniform and rapid cooling, and thereby the resulting microstructures and properties. In order to avoid the formation of coarse structures or cracking during heat treatment it has become common practise to lower the austenitising temperature below that recommended by the steel manufacturer.In this work, therefore, the effects of austenitising at temperatures lower thancommonly recommended are investigated. Three 5% Cr hot-work tool steelsalloyed with Mo and V were heat treated, resulting microstructures andtempering carbides were studied and transformation characteristics determined for different austenitising temperatures and different cooling rates. The temperatures and cooling rates have been chosen to be representative for heat treatments of different sizes of tools. Bainite rather than martensite formed during slow cooling regardless of austenitising temperature. A lowered austenitising temperature produced largeramounts of both bainite and retained austenite while a higher caused graingrowth. Carbon partitioning during the bainitic transformation resulted in anincrease of the carbon content in the retained austenite of at least 0.3 wt.%. The austenitising temperature influences also the type and amount of tempering carbides that precipitate, which affects the properties of the steel. Higher austenitising temperatures favour the precipitation of MC carbides during tempering. The Mo rich M2C type carbides were proven to be more prone to coarsening during service at 560°C-600°C, while V rich MC carbides preserve their fine distribution. A best practice heat treatment needs to balance the increase of grain size with increasing austenitising temperatures, with the possibility to form more tempering carbides. Higher austenitising temperatures also give less retained austenite, which can affect dimensional stability and toughness negatively after tempering

M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Pure Ti, Nb, Zr, Al and V powders were used as starting materials. Ti, Ti-6Al-4V and Ti-34Nb-25Zr materials produced by SPS were compared on the basis of density, microstructure, biocompatibility, tensile strength and corrosion resistance. In this study, powder metallurgy (PM) processing route was used to fabricate the alloys. The processing route was mechanical alloying (MA) and spark plasma sintering (SPS). Commercially pure metallic powders (Ti, Nb, Zr, V and Al) of different morphological features and different formulations were prepared. Powder mixing for ternary alloys with Ti as the matrix were conducted in a turbula mixer at a speed of 49 rpm. Followed by mechanical alloying of Ti, Ti-6Al-4V and Ti-34Nb-25Zr in a high energy ball mill for 5h at 500rpm, with a ball to powder ratio of 10:1. Spark plasma sintering of Ti, Ti-6Al-4V and Ti-34Nb-25Zr biomedical alloys was conducted using a hybrid spark plasma sintering furnace at a sintering temperature, heating rate, holding time and pressure of 1200°C, 100°C/min, 10min and 50MPa, respectively. Ti-34Nb-25Zr was fabricated in two ways, fully densified and porous samples. The fully densified sample was fabricated at a sintering temperature, heating rate and holding time and pressure of 1200°C, 100°C/min, 10min and 50MPa, respectively. Whereas, porous Ti-34Nb-25Zr was fabricated using NaCl space holder at a sintering temperature, heating rate, holding time and pressure of 750°C, 50°C/min, 5min and 50MPa, respectively. This was done to compare the solid and porous alloy biocompatibility behaviour. Microstructures, elemental compositions. Phase constitution of the sintered specimens were examined using a field emission scanning electron microscope (FE-SEM) equipped with energy dispersive x-ray spectrometer (EDS) and an x-ray diffractometer (XRD). The microstructure of Ti-34Nb-25Zr had pores and precipitates of niobium. Relative density, micro-hardness, biocompatibility and corrosion test was also conducted on the metallographically polished cross sections of sintered specimens. Ti, Ti-6Al-4V and Ti-34Nb-25Zr alloys made from the irregularly shaped Ti powders and sintered on the hybrid sintering machine yielded higher densifications reaching up to 100 % relative densities. Hardness values ranging from 300-600Hv at a load of 0.5kg. The corrosion resistance of the alloys was higher in the range of 2-4 nA/cm2 exhibiting a passive behaviour in simulated body fluids, such as Hank’s, 0.9wt.% NaCl and eagles minimum essential + 10% fetal bovine serum (E-MEM+ 10% FBS). Biocompatibility tests were conducted (cytotoxicity by WST-1 with SaOS-2 human osteosarcoma cells, protein adsorption and surface wettability). Fibronectin adsorption was less for solid Ti and Ti-34Nb-25Zr (<2ng/mm) compared to Ti-34Nb-25Zr porous and Ti-6Al-4V (4 ng/mm). Albumin adsorption was the highest on Ti substrate (3 ng/mm) than on the fully densified and porous Ti-34Nb-25Zr surfaces followed by less adsorption on Ti-6Al-4V. Surface wettability of Ti and Ti-6Al-4V showed a high contact angle of between 93-98° compared to 86° for the Ti-34Nb-25Zr solid alloy, indicating that Ti-34Nb-Zr alloys exhibited hydrophilic behaviour. The surface wettability results correlated well to less fibronectin adsorption on Ti-34Nb-25Zr solid alloy and excellent adsorption for Ti-6Al-4V. Solid and porous Ti-34Nb-25Zr showed less cell proliferation (0.06 and 0.02% cell viability) which was possibly linked to fibronectin adsorption results. Biocompatibility behaviour of Ti-34Nb-25Zr solid and porous alloys was poorer than Ti (0.20% cell viability) and Ti-6Al-4V (0.23% cell viability). There was poor protein adsorption and cell proliferation on all the alloy substrates.

No description available.

<p>The resonance of surface plasmons on metal nanoparticles can be excited at visible wavelengths. The extraordinary enhancement of a variety of optical phenomena in the vicinity of metal nanoparticles has been attributed to the strong fields generated under resonance conditions. As a result, extensive research has been carried out to incorporate the extraordinary optical properties of metal nanoparticles into optical devices and applications, ranging from spectroscopy (e.g, surface enhanced Raman, IR and Fluorescence), optical sensing and imaging, to photovoltaic cells, photonic crystals and optical switches. Particular effort has been directed towards producing stable dispersion of metal nanoparticles within soft dielectric matrices and their subsequent construction into different device geometries.</p> <p>This thesis describes a method to photolytically generate Ag nanoparticles within organosiloxane sols, which can subsequently be photopolymerized in the presence of photoinitiators and therefore, be patterned through a variety of photo-inscription processes. The mechanism of Ag nanoparticle growth and evolution is described in detail followed by the fabrication of periodic metallodielectric gratings through photomask and laser interference lithography. Studies also showed that three different forms of nonlinear light propagation, optical self-trapping, modulation instability and spatial self-phase modulation could be elicited in the Ag nanoparticle-doped systems. Detailed experimental examination of these phenomena elucidated significant differences in their dynamics in the metallodielectric systems compared to non-doped samples. These included variations in the dynamics of self-trapped beams such as the excitation of optical modes, critical thresholds for modulation instability and self-phase modulation. The potential of these nonlinear processes for the self-inscription of 3-D metallodielectric structures including cylindrical multimode waveguides and waveguide lattices has also been studied.</p> / Doctor of Philosophy (PhD)

This thesis describes a number of studies of microstructured optical resonators, designed with the aim of enhancing the performance of organic semiconductor lasers and exploring potential applications. The methodology involves the micro-engineering of the photonic environment in order to modify the pathways of the emitted light and control the feedback mechanism. The research focuses on designing new organic microstructures using established semi-analytical and numerical methods, developing fabrication techniques using electron-beam lithography, and optically characterising the resulting structures. Control of the feedback mechanism in conjugated polymer lasers is first investigated by studying Distributed Feedback or photonic crystal resonators based on a square feedback lattice. This study identified the diffraction to free space radiation as a major source of loss in current microstructured resonator designs. By cancelling the coupling to free space through the use of different feedback symmetries and diffraction orders, a threshold reduction by almost an order of magnitude is demonstrated. The introduction of mid-gap defect photonic states in an otherwise uniformly periodic structure was studied in Distributed Bragg Reflector (DBR) resonators. This enabled GaN diode pumped polymer lasers to be demonstrated, indicating that the transition from complex excitation sources to more compact systems is possible. Devices for potential applications in the field of optical communications are also explored by demonstrating a polymer DBR laser based on silicon. In this way, the potential for integrating conjugated polymers with silicon photonics is confirmed. Photonic crystal fibres, which have a periodic microstructure in the transverse direction, are explored as an alternative means for controlling the optical properties of organic lasers. Fluidic fibre organic lasers were demonstrated as efficient sources with good spectral purity. In these devices, mechanisms to tune the emission wavelength were explored and the origin of the frequency selection mechanism was investigated.

Les évolutions de microstructures du nouvel alliage chinois Ti B19 ont été étudiées au cours de divers traitements thermiques et des relations entre microstructures et propriétés mécaniques ont été établies. Les cinétiques de transformations isothermes ont été établies par des mesures de résistivité électrique. Les structures et microstructures ont été caractérisées par DRX synchroton, Microscopies Optiques et Electroniques (MEB, MET). Les cinétiques de transformation et les caractéristiques microstructurales. Les cinétiques de transformation isothermes ont été obtenues, analysées (loi JMAK), et cet ensemble de résultats a conduit à l'établissement du diagramme TTT de l'alliage TiB19. Enfin il a été montré que la vitesse de chauffage a une très forte influence sur les transformations mises en jeu, et qu'une pré déformation plastique accélère les cinétiques de transformation (introduction de nouveaux sites de germination). Enfin les cinétiques de transformation ont été caractérisées en refroidissement continu depuis le domaine monophasé bêta. Une première approche de la modélisation des cinétiques de transformation a été menée en utilisant le loi JMAK et le principe d'additivité de Scheil. Enfin les relations entre microstructures et propriétés sont discutés / The phase transformations and microstructure evolutions has been characterized for different thermal treatments, and the relationships between final microstrures and properties have been investigated in the new metastable Ti-B19 alloy. The isothermal phase transformation kinetics and the influence of different heat treatment phaths have been establisheb by using in-situ electrical Resistivity. The structures have been determined by synchrotron X-Ray Diffraction and the microstructures were observed by SEM and TEM. The results show that phase transformation kinetics and microstructure characteristics are strongly dependent on the aging temperature (ranging from 300 to 700°C). The global isothermal phase transformation phase transformation kinetics has been got and anallyzed with JMAK equation, and the TTT diagram of Ti-B19 alloy has been established. We have also shown that the heating rate has remarkable influence on the isothermal phase transformation behaviors and the pre-deformation accelerates the transformation kinetics. The microstructure evolutions during cooling are obviously dependent on the cooling rates. A first attempt has been made to calculate the transformation kinetics during cooling using JMAK law and Scheil principle. Finally, the relationship between mechanical properties and microstructure has been discussed

No presente trabalho produzimos microestruturas, através da técnica de fotopolimerização via absorção de dois fótons, dopadas com nanofios de ZnO, um material que vem sendo amplamente explorado devido as suas interessantes propriedades ópticas e elétricas. Para a fabricação das microestruturas, utilizamos um oscilador laser de Ti:safira que produz pulsos de aproximadamente 100 fs em 800 nm. A intensidade dos pulsos de femtossegundos é alta o suficiente para induzir a absorção¬ de dois fótons em torno do volume focal, localizando a polimerização a esta região. Portanto, através da varredura do feixe na resina polimérica fabrica-se a estrutura desejada. Neste trabalho, desenvolvemos uma metodologia para introduzir nanofios de ZnO às microestruturas fabricadas, a partir da mistura do pó de nanofios de ZnO à resina acrílica. A resina utilizada é uma combinação de duas resinas, o etoxilated(6)trimethylolpropane triacrylate (SR-499) e tris(2-hydroxy ethyl)isocyanurate triacrylate (SR-368). Como fotoiniciador utilizamos o Lucirin TPO-L (2,4,6-trimetilbenzoiletoxifenil phosphine oxide). As microestruturas produzidas foram caracterizadas pelas técnicas de microscopia óptica, microscopia eletrônica de varredura, espectroscopia de energia dispersiva, difração de Raios X e espectroscopia de espalhamento micro-Raman. Através destas técnicas, foi possível observar a presença dos nanofios nas microestruturas, bem como caracterizar suas propriedades morfológicas que se mostram adequadas para o desenvolvimento de microdispositivos. Observamos também a emissão de fluorescência das microestruturas excitadas por um e dois fótons. Sendo assim, a metodologia de fabricação descrita aqui pode ser usada como mais uma opção na concepção de novos dispositivos tecnológicos. / In this study we fabricated microstructures, using the two-photon polymerization technique, containing ZnO nanowires, a material that has been widely exploited due to their interesting optical and electrical properties. For the microstructures fabrication, we used Ti:Sapphire laser oscillator operating at 800 nm with 100 fs pulses. The intensity of the fs-pulses is high enough to induce two-photon absorption, confining the excitation and thus the polymerization to the focal volume. By scanning the beam across the resin the desired microstructure is fabricated. In this work, we developed a method to introduce ZnO nanowires in the fabricated microstructure by mixing the ZnO nanowires powder to the acrylic resin. The used resin is a combination of two compounds, etoxilated(6)trimethylolpropane triacrylate (SR-499) and tris(2-hydroxy ethyl)isocyanurate triacrylate (SR-368). As a photoinitiator we have used Lucirin TPO-L (2,4,6-trimetilbenzoiletoxifenil phosphine oxide).The produced samples were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction spectroscopy and micro-Raman scattering. From these techniques it was possible to observe the presence of nanowires in the microstructures, as well as to characterize the morphological properties, which has been shown to be interesting for developing microdevices. We have also observed fluorescent emission of the microstructures excites by one and two-photons absorption. Therefore, the methodology described here can be used as an alternative in the design of new optical devices.