<p>The photovoltaics (PV) research community is currently pursuing many approaches to reduce the cost of PV and increase the energy conversion efficiency. Single-crystalline silicon (sc-Si) solar cells are able to achieve high efficiency but have a higher cost relative to other technologies. It may be possible to drastically reduce the cost of sc-Si PV by fabricating solar cells which are an order of magnitude thinner than conventional solar cells, i.e. thinner than 30 microns. Aside from new fabrication paradigms, ultra-thin sc-Si solar cells require advanced light-trapping techniques to enhance the absorption of long-wave radiation which is otherwise transmitted through the cell. In this thesis, a novel process flow for the fabrication of ultra-thin sc-Si solar cells in the laboratory was designed and implemented with the aim of testing light-trapping structures in the context of actual ultra-thin sc-Si devices. The process flow uses 10 micron thick sc-Si membranes, 0.95 cm in diameter, fabricated on silicon-on-insulator wafers using double-sided processing. The best fabricated device incorporated a back surface field, a white paint diffuse rear reflector and a silicon nitride antireflection coating. It achieved a fill factor, efficiency, short circuit current and open circuit voltage of 0.67, 9.9%, 27.9 mA cm^-2 and 0.53 V respectively. Simulations suggest the device efficiency can approach 15.4% without light-trapping and 16.5% with a diffuse rear reflector as a light trapping structure. This process flow is intended to be used as a platform on which to test further light-trapping structures with the continuation of this project.</p> / Master of Applied Science (MASc)

<p>Preparing silicon wafers is a tedious multi-step process that includes etching, polishing, and cleaning. The minimum wafer thickness attainable in current high volume wafer production processes is generally 160 to 300 μm, and the kerf loss for these processes is up to 40% of the total volume. Thin silicon wafers (~30 to 100μm) are very expensive to produce and the wafering process is not cost effective due to the high amount of material loss (more than 80% at these dimensions) during the process and the risk of breakage of the wafers during wafering. In this thesis, a new method called Vapour-Liquid Interface Growth (VLIG) is proposed. VLIG is capable of directly growing a sheet of single crystal silicon without wafering with a thickness of about 30 to 50μm. The features of the process are 1) low temperature operation; 2) the resulting silicon sheet is easily detachable and self-supporting; 3) the resulting sheet has uniform thickness and is single crystal. The system operates in a supersaturated growth solution of an indium-silicon melt. A seed line in a substrate facing down is employed. A layer of single crystal silicon grows on the seed line at the melt surface due to surface segregation during the super cooling process. The grown silicon can grow laterally due to the limited thickness of the melt depth that minimizes growth in the vertical growth direction. The grown silicon can be easily peeled off from the seed line substrate due to the presence of a gap between the grown silicon sheet and the oxide layer on the seed line substrate. The self-supporting silicon sheet now comprises a very thin silicon substrate or sheet.</p> <p>VLIG silicon sheet is characterized by X-ray diffraction to determine the crystallinity. Hall Effect measurements are performed to measure the electrical properties. VLIG silicon sheet is (111) oriented single crystal and it exhibits the same orientation as the substrate. The growth temperature is from 975 to 850^oC, and the VLIG silicon is p-type doped with indium. The resistivity is 4.181x10^-3 ohm-cm, and the doping level is around 5.3.0x10¹⁸ /cm3. The measured mobility is ranging from 280 cm²/V.s. In this study, VLIG demonstrates the potential of growing thin sheet of single crystal silicon with qualities that feasible for photovoltaic application.</p> / Master of Applied Science (MASc)

Recently, there has been a dramatic increase in the amount of data transmission within short range local area networks (LAN). Multimode fibre (MMF) is widely used in local area networks because of its coupling and alignment along with the low cost of related components. Graded index MMF has become common due to the reduction in pulse spreading; however, as demands for high bandwidth increase towards a future gigabit rate network, the typical MMF using conventional transmission methods will not be suitable. Meanwhile, this increasing demand for high speed data transmission will soon reach the Shannon capacity limit of single mode fibres. After multiple input and multiple output (MIMO) technology was successfully used in wireless communication, the researcher realised that the same idea could also be applied to an optical fibre network. Optical MIMO techniques are gaining interest in order to create parallel channels over orthogonal modes in a MMF or a few mode fibre (FMF). This approach could lead to a significant increase in the bandwidth distance product and be employed in the next 40Gb/s or even 100Gb/s optical fibre transmission systems. Generally speaking, optical MIMO appears to be the best solution to the bandwidth limitation problem in either short distance MMF or long distance FMF systems. This thesis focuses on designing a simple, cost-effective, and energy efficient optical MIMO system based on MMFs. This proposed system can be realised by combining radial offset launching and annular multi-segment detectors. First, in the initial work, we performed a theoretical and numerical study of the key impairments of MMFs, and the mode propagation in an MMF was analysed mathematically. The variation in electrical field intensity for linearly polarised (LP) modes in the core region of an MMF and the analytical solutions for power coupling coefficients in either radial offset launching or centre launching were presented. In addition, the modal time delays, impulse response, and transfer function were all introduced. Subsequently, the near field intensity pattern (NFP) was simulated at the output facet of the MMF, which indicated that the overall NFP suffered from blurring when it contained mode mixing, and that the intensity pattern was particularly sensitive to the random phase. According to the spatial distribution of the NFP, the annular detector can be exploited more efficiently. All of the results were calculated and plotted using the MATLAB program. Secondly, the optical MIMO model in the multimode fibre was briefly summarised, including the MIMO channel matrix H expression, a mathematical expression of optical MIMO capacity, MIMO channel estimation and an equalization method. Two metrics can be used to characterise the MIMO channel performance: condition number and crosstalk at each receiver. The numerical results demonstrated that the new type of annular multi-segment detector exhibits superior performance compared to the conventional multiple single mode fibre (SMF) detectors, making them attractive for future optical MIMO systems. Finally, the core work of this thesis can be divided into two parts: the modelling of a 10Gb/s intensity modulation direct detection (IM-DD) optical MIMO MMF system; and the modelling of an advanced 10Gb/s coherent differential phase shift keying (DPSK) MIMO FMF system. In both simulation systems, the important transmission parameters of intra-group mode mixing, modal dispersion, chromatic dispersion, and mode attenuation were considered and discussed in detail. In the IM-DD optical MIMO system, the optimization of the transceiver can be based upon the laser spot size and the power flux distribution emitted by the transmitter. Results from the simulation showed that the intra-group mode mixing had a limited impact on system performance, and due to its inability to compensate for linear impairments, the IM-DD optical MIMO was not favourable for long distance transmission systems. Nevertheless, the new type of optical fibre FMF seems to be the most promising candidate for use in long haul transmission systems. Therefore, the well-known DPSK modulation format in conjugation with the coherent detection deployed in FMF was studied. Both heterodyne and intradyne detection schemes were analysed followed by mathematical derivation and numerical simulation; the results illustrated that similar system performances can be achieved in both schemes. Meanwhile, the coherent DPSK simulation results also demonstrated that the linear impairments were almost compensated by the frequency domain MIMO equalization process, which resulted in system performance being independent to transmission distance for up to 10km. This advantage proved that the coherent optical DPSK MIMO system can be employed in long haul networks. As with an IM-DD optical MIMO system, optimization of a coherent MIMO system was also possible. However, in contrast to the optimization of an IM-DD MIMO system, a trade-off had to be made between sufficient spatial diversity at the transceiver and differential modal delay caused by modal dispersion; consequently, the numerical results showed that the proposed coherent optical DPSK MIMO gained reasonable good results without using any active device, such as a spatial light modulator and a mode converter. In conclusion, this proposed optical MIMO system provided easy implementation and integration and is feasible for use in future optical communication systems.

Vacuum forming is a popular, cost effective method amongst large and small scale applications. The method is used to mold a material to the surface of a mold/pattern in order to create a negative copy for reproduction or an object in positive form. The prototype vacuum forming system developed and documented herein is of a membrane-seal type that consists of three (3) principle parts: radial platen, Hinged Frame and Platen Support Assembly, and a PVC surge tank. Each part is described in detail through design, manufacturing, and testing processes. The design supports functional versatility, small scale molding, and uses readily available materials. Functional prototype testing was performed with the thermoplastic KYDEX® and multiple objects for mold examples. Results include successful proof of concept, design pros and cons, and findings based on functional testing.

Wood composites are widely used in construction applications because of their superior dimensional and structural attributes over raw wood products. However, current wood composite manufacturing practices, which rely on thermal-curing of adhesives, are expensive, energy intensive, time consuming and are prone to manufacturing defects. Use of radiation curable adhesives (RCAs) could potentially answer all of these issues. Specifically, use of electron-beam (e-beam) radiation has been increasing in areas of research and industry where rapid, low-temperature polymerization is required and low energy consumption is desired. For e-beams to be used in wood composites, however, it must be determined whether or not the wood is structurally impacted by irradiation, and to what extent. Maple beams irradiated with a range of e-beam dosages were studied in three-point bend tests to assess the changes in bulk properties of the wood, and were further studied with infrared spectroscopy to identify chemical changes resulting from the radiation treatments. Also, dynamic mechanical analysis (DMA) was performed on maple veneers treated with the same doses of radiation to characterize changes in the viscoelastic properties. Furthermore, while RCAs and their curing have been studied, it is important to understand if the presence of wood will impede the polymerization of these adhesives, and to what extent. Maple veneers impregnated with one of two resins were cured with the same e-beam dosages and investigated by means of DMA and FTIR spectroscopy. Swelling tests were conducted to detect interaction between the resins and the wood, which would indicate good interfacial bonding in the composite matrix. Notable loss of strength was observed in the irradiated wood, especially at 180kGy. Monitoring the glass transition temperature (Tg) and activation energy (Ea) derived from DMA revealed that the most destructive trends in the wood began around 80kGy. Cure of resins in the composites was hindered by the presence of the wood, but both resins did eventually reach complete cure at doses higher than what the neat resins required. Interaction between the resins and the wood was evident. In the end, results indicate that there is a range of radiation dosages in which the resin in a wood composite can be cured without destroying the structural integrity of the wood.

The use of sunlight has always been a major goal in the design and operation of commercial buildings to minimize electrical consumption of artificial lighting systems. Glazing systems designed to allow optimal visible light transmission also allow significant unwanted direct solar heat gain caused by infrared light. Conversely, glazing systems that are designed to reflect unwanted direct solar heat gain significantly reduce the transmittance of visible light through windows. The goal of this research was to characterize the performance of water as gap-fill for double-glazing units in eliminating the compromises that exist in current glazing systems with respect to light and heat transmittance. An in situ test approach and computer simulations were conducted to measure the performance of water-filled glazing units against air-filled glazing units. The thermal transmittance and solar heat gain coefficient values obtained from both the field experiments and computer simulations, glazing units with air-fill proved better than the glazing units with non-flowing water-fill. However, the high convective coefficient and the high thermal mass of the water can be used to its advantage when it is allowed to flow at peak temperatures, thus, maintaining lower temperature swings indoor. This can lead to a reduction of about 50-70% direct solar heat and still maintain high visibility.

This thesis presents a novel policy assessment tool that serves as a decision support framework for analysis of energy policy problems involving multilevel, multidimensional and multi-stakeholder complexity. This new approach, The Energy Policy Assessment Technique (E-PAT), integrates System Dynamics Simulation and Multi-Criteria Evaluation models into a unified assessment framework. The E-PAT doubles as a systems-thinking model and a multi-criteria evaluation archetype. The E-PAT is designed for assessing policy issues, particularly those relating to energy planning in a national context. It is a suitable tool for evaluation and selection of optimal policies from competing and conflicting alternatives. To test its robustness and practical application, a case study on energy policy evaluation in Nigeria is carried out with this tool. A model of the Nigerian energy economy was constructed, and three proposed government policies for Sustainable Energy Development were evaluated relative to a Business-As-Usual case. The evaluation process identified ‘best’ policy options according to stakeholder viewpoints. The original contribution of this research is the creation of an integrated, transparent and comprehensive assessment tool, and the development of measurable Energy Sustainability Indicators (ESI), to aid policymakers in diverse policy analysis. The new tool is intended to support assessment of energy policies in relation to impacts on the economy, society and environment.

Cette thèse étudie l’intérêt de la mesure de la diffusion cohérente de rayons X dans le cadre de l’imagerie du sein à des fins de diagnostic. Aujourd'hui, la plupart des systèmes d'imagerie médicale par rayons X exploitent le rayonnement transmis à travers les tissus. C’est le cas pour la mammographie, qui est la modalité d’imagerie du sein la plus courante. L'apparition récente de détecteurs résolus en énergie, à base de semi-conducteurs notamment, permet cependant d'envisager l'exploitation en milieu clinique d'un autre phénomène : le rayonnement diffusé cohérent. La mesure de spectres de diffusion peut apporter de nouvelles informations liées à la structure moléculaire des tissus examinés pour mieux les caractériser et ainsi améliorer le diagnostic final. Deux modalités sont envisagées : la détection in vivo de tumeurs du sein, à la suite d’une mammographie présentant un résultat suspect ou l'analyse de biopsie.Le système de mesure de diffusé développé lors de cette thèse exploite les détecteurs résolus en énergie de type CdZnTe, ces derniers présentant des caractéristiques (résolution en énergie, sensibilité, résolution spatiale, compacité) prometteuses pour une utilisation en condition clinique. Il se base par ailleurs sur la pixellisation du détecteur afin de proposer une modalité d’imagerie permettant de caractériser les matériaux ou tissus traversés dans une direction sans translation ni rotation.Cette thèse propose ainsi une étude complète de ce système, articulée autour de trois grandes parties : modélisation puis simulation du système de mesure, développement du traitement des données mesurées par le détecteur afin d’imager et caractériser l’échantillon analysé et enfin, dimensionnement d’un banc expérimental plus complexe intégrant un détecteur complet et un système de collimation multifente. Ces trois parties font par ailleurs l’objet de validations expérimentales associées. / This thesis studies the interest of measuring the coherent scattering of X-rays for breast diagnosis imaging. Nowadays, most of X-ray-based medical imaging techniques use the information of X-rays attenuation through the tissues. It is the case for mammography, the most common breast imaging modality. The recent emergence of energy resolved detectors (based on semiconductors in particular) allows to consider using another phenomenon: the coherent X-ray scattering. Measurement of diffracted spectra can provide new information related to the molecular structure of the examined tissues, in order to improve their characterization and therefore improve the final diagnosis. Two modalities are considered: the breast cancer detection in vivo, following a suspicious mammography result, or biopsy analysis.The coherent scattering measurement system developed during this thesis work uses energy-resolved CdZnTe-based detectors, these detectors combining performances (energy resolution, sensitivity, spatial resolution, and compactness) promising for clinical application. This system is also based on the detector pixelation, which allows to provide an imaging modality capable of characterizing analyzed materials or tissues in one direction without any translation or rotation.A complete study of the measurement system is proposed in this thesis, structured in three main parts: modeling and simulation of the system, development of the processing of the data measured by the detector in order to image and characterize the analyzed sample and finally, designing of a new and more complex experimental setup based on a whole detector and multislit collimation system. An experimental validation is proposed for each of these three parts.

Les matériaux élastomères hyper élastiques offrent aux domaines des capteurs, des antennes radio fréquences et des soft robots de nouvelles opportunités en termes de déformabilité. Le but de ce travail est d'étudier un matériau élastomère hyper élastique appelé Ecoflex et de l'intégrer à des systèmes microfluidiques en exploitant ses caractéristiques mécaniques particulières.Dans un premier temps, les propriétés mécaniques de ce matériau ont été caractérisées par des expériences de soufflages membranaires. Par la suite des outils de modélisation mécanique basés sur le modèle phénoménologique de Mooney-Rivlin ont été étudiés et validés. Deux exemples d'applications ont été développés.Une première famille de système concerne des capteurs de grandes déformations. Ces capteurs électro fluidiques combinent les propriétés hyper élastiques de l'Ecoflex et les propriétés électriques du Galinstan qui est un métal liquide à température ambiante : une résistance électrique est formée par un canal moulé dans l'Ecoflex et rempli du liquide conducteur. Une déformation du capteur induit une modification de la géométrie du canal et donc une variation de résistance. Les caractérisations réalisées sur ces capteurs ont montré leur capacité à mesurer des étirements très importants avec un comportement réversible et sans rupture de contact électrique. Des taux d'élongation de 400 %, entrainant une variation de résistance de 800% ont ainsi été obtenus. Les résultats suivant la géométrie des capteurs sont discutés en utilisant des outils de modélisations.La deuxième famille de système concerne les laboratoires sur puce avec la fabrication de réservoirs déformables pouvant être intégrés à des composants fluidiques. Inspirés des tests de soufflage membranaire, ces réservoirs peuvent embarquer des volumes allant de quelques dizaines de microlitres à quelques millilitres de réactifs tout en ayant un encombrement minimum. L'élasticité des membranes permet de pressuriser naturellement le réservoir et une méthode simple de détection de la forme du réservoir permet de connaitre à tout moment le volume interne de celui-ci. Couplés à un système de vannes pneumatiques, ces réservoirs permettent d'injecter précisément un volume de fluide dans un réseau microfluidique. Différents exemples de composants ont été développés, allant du réservoir simple pour les caractérisations, à des cartes intégrants plusieurs réservoirs en vue d'effectuer des protocoles complexes, tel une dilution programmable ou un test ELISA. / Mechanical properties of hyper elastic elastomers provide new opportunities to captors, radio frequencies antennas and soft robots. This work is focused on the study of a hyper elastic material called Ecoflex and on its integration in microfluidic systems using its exceptional mechanical properties.First, material's mechanical properties were investigated during membrane blowing experiments. Simulations based on the phenomenological model of Mooney-Rivlin were developed and validated. These results were useful to the development of two applications.First application of hyper elastic system is an elongation sensor. Electro fluidic sensors combine Ecoflex's hyper elastic properties and Galinstan's electrical properties. Galinstan is a metallic alloy which is liquid at room temperature. A microchannel molded in the elastomer and filled with the liquid metal form an electrical resistance. Sensor's deformation induces a geometrical change into the channel and therefore a variation of the electrical resistance. Characterization tests performed on these sensors showed capabilities to measure large elongations and reversibly without loss of electrical contact. An elongation of the sensor's length by a factor 4 involves an increase of the electrical resistance by a factor 8 providing a good sensibility of the system. Results according to the sensor's geometry are discussed using simulation tools, analytical study and experimental data.Second application is the development of hyper elastic reservoirs integrated into microfluidic cards. Inspired from membrane blowing tests, they are able to store volumes from few microliters to milliliters of reagents without taking too much place on the microfluidic cards' surface. Membranes' elasticity naturally pressurizes the reservoir when it is filled and a simple optical edge detection method gives the internal volume in real time. Combined with pneumatic valves these reservoirs inject precise volumes into a microfluidic network. Different microfluidic systems were developed, a simple reservoir with two valves for the characterizations and cards with multiple reservoirs to realize complex protocols like on demand dilution or automated ELISA test.

The search for new and additional sources of energy -- from sun, wind, waves, and ocean currents -- is necessitating the development of structures in the open environment of the oceans as well as on land. The advantages of round or tubular members for use in such structures are shown; and to avoid the uncertainties of welded joints, two bolted connections are proposed and their feasibility explored.