La dégradation induite par éclairement (Light Induced Degradation : LID), s'exprimant par la perte de qualités électriques, est devenu un problème récurrent dans les modules photovoltaïques de silicium de qualité métallurgique (compensé en dopants). Compte tenu des nombreuses impuretés présentes dans ce matériau, la compréhension des mécanismes mis en jeu est très complexe et reste incomplète. Pour cette raison, les seuls mécanismes identifiés à ce jour sont liées à l'action de complexes BO2i. Les travaux réalisés durant cette thèse sur différentes qualités de plaquettes de silicium de type p, ont mis en évidence la participation d'une autre réaction, activée thermiquement à 0.68 eV. D'après nos résultats cette réaction, associée aux complexes CiOi, n'est pas systématique. Elle semble agir si les échantillons ont une concentration en carbone substitutionnel supérieure ou égale à celle du dopage net et s'ils sont soumis à des températures T ≥ 50°C. Cette réaction, intervenant dans la LID, est donc indépendante du degré de compensation du matériau. Nous avons également mis en évidence un phénomène de dégradation à l'obscurité (DID : Degradation In Dark), conduisant à des pertes électriques analogues à celles obtenues par la LID. Cette DID, apparaissant uniquement par chauffe, semble faire intervenir des réactions similaires à celles de la LID. Son étude permet de supposer que des impuretés primaires (lacunes, auto-interstitiel) participent également à ces phénomènes. / Light induced degradation (LID), leading to a deterioration of electrical properties, has become a recurring problem in photovoltaic modules based on metallurgical grade silicon. Due to the many impurities present in the material (compensated by dopants), the mechanisms involved in this phenomenon are very complex and not very well understood. For this reason, the only reactions identified are related to the action of BO2i complexes.Works carried out during this thesis on different grades of p-type silicon wafers have highlighted the involvement of another thermally activated reaction at 0.68 eV. According to our results, this reaction, associated with CiOi complexes, is not systematic. It seems to act if the samples have a substitutional carbon concentration greater than or equal to the net doping and if they are subjected to temperatures T ≥ 50° C. We also highlighted the emergence of a phenomenon of degradation in the dark (DID), leading to similar electrical losses to those obtained by LID. This DID, appearing only by heating, seems to involve similar reactions to LID. Its study allows us to assume that the primary impurities (vacancies, self-interstitials) are also involved in these phenomena.

abstract: Nickel-Copper metallization for silicon solar cells offers a cost effective alternative to traditional screen printed silver paste technology. The main objective of this work is to study the formation of nickel silicide contacts with and without native silicon dioxide SiO2. The effect of native SiO2 on the silicide formation has been studied using Raman spectroscopy, Rutherford backscattering spectrometry and sheet resistance measurements which shows that SiO 2 acts as a diffusion barrier for silicidation at low temperatures of 350°C. At 400°C the presence of SiO2 results in the increased formation of nickel mono-silicide phase with reduced thickness when compared to samples without any native oxide. Pre and post-anneal measurements of Suns Voc, photoluminescence and Illuminated lock in thermography show effect of annealing on electrical characteristics of the device. The presence of native oxide is found to prevent degradation of the solar cells when compared to cells without any native oxide. A process flow for fabricating silicon solar cells using light induced plating of nickel and copper with and without native oxide (SiO2) has been developed and cell results for devices fabricated on 156mm wafers have been discussed. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2016

Dental erosion has been defined as a chemical process that involves the dissolution of enamel and dentine by acid(s) not derived from bacteria when the surrounding aqueous phase is under-saturated with tooth mineral. Clinically however, dental erosion hardly ever occurs exclusively from the other modes of tooth wear such as abrasion and attrition. Hence the term erosive wear has been proposed and used to describe erosion-facilitated wear.With the prevalence of erosive wear being reported to be on the rise among children and adolescents in many countries, a plethora of oral health products such as dentifrices and mouth rinses had been put forward with claims of increasing the resistance of the enamel and / or dentine from being demineralised. However, the efficacy of these oral health products is still widely questionable as the studies carried out were mainly in vitro and / or in situ studies and the contradictory results were reported by different groups of researchers.The above mentioned discrepancies are often due to non-standardised in vitro and in situ study designs of erosion studies. Parameters such as type of acid used, concentration of acid used, duration of acid exposure, inclusion or exclusion of abrasion in the study model, ex vivo or in vivo acid challenge, ex vivo or in vivo treatment with oral health product and the nature of pellicle on the specimen are often varied.The availability of an detection tool which could be used to measure demineralisation on natural tooth surface in vivo would exclude many of the inevitable variability in in situ and in vitro study design, such as the simulation of the intra oral conditions in which the erosion challenge and intervention take place and the nature of the pellicle formed on the specimens. Hence with an in vivo detection tool, it is hopeful that the efficacy of any interventions would be evaluated more accurately and its results expounded to a wider context. It would be useful if the tool was sensitive to the very early stages of the erosion process as this would entail shorter and more economical study designs. Arising from the problems discussed above, potential non-invasive assessment methods that could be used clinically to measure demineralisation were explored and it was found that two optical methods, Optical Coherence Tomography (OCT) and Quantitative Light-induced Fluorescence (QLF) were potential methods for the tasks.The studies described in this thesis were divided into three main big sections; the first being the in vitro validation work of the two optical methods (Chapter 5 and 6), the second, validation of these methods in situ (Chapter 7) and finally the assessment of the efficacy of a high fluoride dentifrice on early enamel erosion using these two methods (Chapter 8).In the in vitro validation (Chapter 5), it was demonstrated that both QLF and OCT were able to detect erosion-interval related changes in natural surface samples eroded with orange juice for 60 minutes. However, results of Multiple Linear Regression and Paired t test suggest that QLF was more sensitive than OCT in the detection of demineralisation changes in this particular experimental setting. QLF demonstrated a R2 value of 0.590 while the best of the OCT outcome measure demonstrated a R2 value of 0.319.Further in vitro study (Chapter 6) was performed to explore the use of a moistened-exposed surface as a reference method for both OCT and QLF as it was felt that it would be beneficial if a coated reference area which posts as an additional step for error could be done away with. Results of this study showed that the moistened-exposed surface could be used a reference method for QLF only but not for OCT. Furnished with the findings of the above mentioned in vitro validation studies, an in situ validation of both the optical methods was performed (Chapter 7). It was found that OCT and QLF were able to longitudinally measure in situ demineralisation on polished and natural surfaced enamel which were subjected to 150 minutes of in vivo exposure to orange juice. Similar to the results of the in vitro study, QLF was found to be more sensitive than OCT in the detection of demineralisation changes on natural surfaced enamel. The last in situ study (Chapter 8) was to evaluate whether there was a protective effect of treating human enamel with a high-concentrated fluoride dentifrice during an active erosion phase and whether OCT and QLF were able to detect the protective effect. It was found that treating natural surface enamel with a 5000ppm NaF dentifrice increased its resistance against concurrent in vivo erosive challenge with an orange juice challenge. QLF was able to detect the protective effect of the 5000ppm NaF dentifrice on natural surface enamel against early in vivo erosion with an orange juice challenge regime while OCT did not.

This master’s thesis deals with light induced degradation problems. In theoretical section it describes essentials of PN junction function and next light induced degradation mechanisms of solar cells and its symptoms at solar cell operation. In practical section it deals with set of measurements of solar cells since production of the silicon wafer to the complete solar cell. Selected cells are submitted to light induced degradation, measured dependencies are then evaluated. Degraded samples are subsequently recovered by two ways at high temperature treatment. The issues are evaluated.

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Emotional responses, whether approach or withdrawal motivated, are fundamental factors in all food-related experiences. In this research project four experiments were completed with the goal of contributing to the growing body of research related to food and emotions. Implicit (unstated) measures of attention, emotional expression, and motivational behavior tendencies were assessed as additional supportive information for explicit (cognitive) measures of acceptability and emotional response to food and attributes of food with quality and safety concerns. Differences in explicit responses were evaluated using a 9-point hedonic scale, check-all-that-apply (CATA) emotion term questionnaire, and a six basic emotion intensity ratings scale. Implicit responses of emotion, attention and motivational behaviors were measured using automated facial expression analysis (AFEA), eye-tracking technology, electrocardiography (ECG) and electroencephalography (EEG). An initial study on light-induced milk oxidation flavor quality indicated reliable explicit measures of emotion and consumer acceptability, while AFEA showed a wide range of facial expression. In a following study, five different control breakfast meal videos were created; three were matched with a nearly identical video that contained one of three food concerns, food spoilage quality, hygiene quality and safety. Explicit measures provided solid support for the expected explicit response differences between food concerning and control breakfast meal types. Implicit measures of heart rate, facial motor expressions and frontal cortex asymmetries (brain activity) were only minimally informative across each measure or conclusive across meal types. The use of time series statistical analyses illustrated temporal changes in emotions when compared to a control condition, which was not evident using traditional analysis of variance approaches. A visual attention study investigated use of eye tracking as an indicator of the emotional responses elicited. Eye tracking technologies, as well as the other implicit measures (ECG, EEG, and AFEA), encountered similar limitations pertaining to participant variability due to personal preferences and characteristics, as well as a need for standard methodologies with food as stimuli and appropriate control conditions. With further research in this area of study, implicit measures of emotion, attention and motivational behaviors may provide additional valuable information to more traditional explicit affective methodologies for a greater understanding of the overall consumer food experience. / Ph. D.

La réalité d’amélioration de la qualité par le design de procédé (QdB) ainsi que l’apprentissage et le contrôle des variables critiques devient de plus en plus prédominant dans le milieu pharmaceutique. En effet, les risques associés à la mentalité d’analyse traditionnelle sur le produit fini uniquement et l’avènement des techniques d’analyse de procédés (PAT) ouvrent la voie à un contrôle plus complet et en temps réel de la qualité, tel que recommandé par les instances règlementaires. Ceci implique des économies d’échelle pour l’industrie étant donné la réduction des efforts (temps et argent) associés à l’analyse laboratoire par les techniques conventionnelles. Les appareils spectroscopiques constituent une technologie très utile pour l’analyse d’une formulation étant donné qu’ils sont généralement non-invasifs et non-destructifs. Dans le cadre de ce projet de recherche, il sera question de l’évaluation et du développement de la technique light-induced fluorescence spectroscopy (LIFS) afin de déterminer en-ligne la faible concentration d’un ingrédient actif dans une étape de mélange. Pour se faire, il sera tout d’abord nécessaire d’établir des modèles de calibration et d’évaluer l’impact des facteurs environnementaux et physico-chimiques sur les performances de ceux-ci, ainsi que sur le phénomène de photoblanchiment. Suite à une analyse de sensibilité, il sera possible d’élaborer un modèle optimisé et robuste. La méthodologie pour atteindre ces objectifs est la suivante : détermination des longueurs d’onde d’opération (excitation et émission); acquisition de spectres en mode dynamique, mais aussi en mode statique en faisant varier les paramètres de concentration, d’humidité, de taille de particule et de pression appliquée; traitement des données par analyse multivariée; établissement d’un modèle de calibration et validation de celui-ci par des essais à l’échelle pilote. La technologie LIFS, mais surtout son utilisation comme PAT, est très novatrice. De plus, les instruments développés antérieurement n’ont pas donné les résultats escomptés, ce qui renforce la pertinence de continuer les efforts de développement. Plus encore, le phénomène de photoblanchiment est encore mal défini et très peu d’études ont été faites sur des mélanges de poudres. En établissant de façon claire l’impact des différents facteurs sur la justesse, la précision, la répétabilité et la robustesse du modèle et de l’appareil, il sera possible de développer une technologie fiable permettant de quantifier des molécules fluorescentes en faible concentration dans un mélange particulaire.

Les Céramiques Ultra-Haute Température (UHTC) sont des matériaux prometteurs dans le cadre d'applications en conditions extrêmes comme les parties proéminentes de véhicules à rentrée atmosphérique ou les chambres de combustion de moteurs aéronautiques. La compréhension des mécanismes d'oxydation à haute température présente donc un intérêt majeur, car les réactions en milieu oxydant limitent fortement leur durée de vie. Les matériaux ZrB2-SiC, HfB2-SiC et HfB2-SiC-Y2O3 ont été soumis pendant des durées et températures variables (jusqu'à 2400°C) à des environnements contrôlés contenant de la vapeur d'eau. Les microstructures formées ont été décrites, et les mécanismes et cinétiques d'oxydation régissant leur comportement ont été analysés. L'importance de la stabilité et de la nature de la phase vitreuse formée durant l'oxydation a été soulignée. En complément de ces analyses microstructurales, une campagne d'essais utilisant la Fluorescence Induite par Laser (LIF) a permis, via la détection in situ de la molécule BO2, de comprendre plus finement la dynamique de la phase vitreuse lors de l'oxydation. Enfin, une modélisation de la croissance de couches oxydées sur un matériau monophasé a été effectuée. / Ultra-High Temperature Ceramics (UHTC) are promising materials for applications in extreme environments such as prominent parts of atmospheric re-entry vehicles or the combustion chambers of aeronautic engines. The understanding of oxidation mechanisms at high temperature is of great interest, because reactions in oxidizing atmosphere strongly shorten their lifetime. ZrB2-SiC, HfB2-SiC and HfB2-SiC-Y2O3 materials have been subjected to controlled water vapor-containing environments for different durations and temperatures (up to 2400°C). The microstructures developed by the oxidized materials have been described, and oxidation mechanisms and kinetics governing their behavior have been analyzed. The importance of the stability and nature of the vitreous phase formed during the oxidation has been emphasized. In order to complement these microstructural analyses, tests using Light-Induced Fluorescence (LIF) have been performed, allowing us to finely understand the dynamics of the vitreous phase during oxidation thanks to the in situ detection of the BO2 molecule. Finally, a modelling of the growth of oxidized layers on a single-phased material has been performed.

The objective of the proposed research is to develop low-cost, screen-printed 20% efficient silicon solar cells. In the first part of this thesis, a ~19% efficient, screen-printed cell was fabricated using the commercially-dominant aluminum back surface field (Al-BSF) cell structure. Device modeling was then used to determine that increasing the efficiency to 20% required improvements in both back surface passivation and rear reflectance. In the second part of this thesis, a passivated, transparent boron BSF (B-BSF) structure was proposed as a high-throughput method for realizing these improvements. The first step in fabricating the proposed B-BSF cell involved the successful development of a water-based, spin-on solution of boric acid as a low-cost, non-toxic and non-pyrophoric alternative to common boron diffusion sources such as boron tribromide. A review of the literature shows that a common problem with boron diffusion is severe bulk lifetime degradation, with Fe contamination being commonly speculated as the cause. An experimental study was therefore devised in which the impact of boron diffusion and subsequent cell process steps on the bulk lifetime and bulk iron contamination was tracked. From this study, a model for boron diffusion-induced Fe contamination was developed along with methods for gettering Fe from the substrate. A key achievement of this thesis was the discovery of a novel, negatively charged, aluminum-doped spin-on glass (SOG) which can, in a short thermal step, simultaneously getter Fe and provide stable, high-quality passivation of planar, boron-diffused Si surfaces. Since past attempts at achieving low-cost, high-efficiency, boron-diffused cells have suffered from bulk lifetime degradation and difficulties with passivating a boron-diffused Si surface, the Al-doped SOG provides a solution to both challenges. Since a high rear reflectance is important for achieving high-efficiencies, an experimental study of various reflectors was undertaken and a silver colloid material was found which exhibits both high electrical conductivity and Lambertian reflectance >95%. The work on boric acid diffusion, iron gettering, surface passivation and rear reflectors was successfully integrated into a 20.2% efficient, screen-printed, B-BSF cell fabricated on 300 µm thick, p-type float-zone (FZ) Si wafers. Both device theory and modeling was used to show that, due to its well-passivated surfaces, this cell would suffer a large loss in efficiency due to light-induced degradation (LID) if it were fabricated on commercial p-type Czochralski (Cz) Si substrates. Since n-type Si substrates do not suffer from LID, the p-type process was slightly tweaked and applied to n-type FZ wafers, resulting in 20.3% efficient cells on 190 µm thick wafers. Computer modeling shows that both the p-type and n-type cells can maintain efficiencies of 20% for wafers as thin as 100 µm.