L’utilisation des ultrasons pour l’imagerie présente plusieurs avantages : elle est extrêmement sure car ellen'utilise pas de radiations ionisantes et ne présente pas d'effets néfastes sur la santé. D’autre part, elle donne desrésultats d’excellente qualité avec un coût relativement faible. Historiquement, les matériaux piézoélectriques et leurscomposites ont été très tôt utilisés pour la génération d’ultrasons. Les transducteurs fabriqués à partir de ces matériauxdominent actuellement le marché des sondes ultrasonores. Cependant, pour certaines applications, ils ne peuvent pasêtre utilisés pour des raisons de dimensionnement et de limitations dues aux propriétés des matériaux. Une solutionpeut être apportée par l’utilisation des transducteurs ultrasonores capacitifs micro-usinés dits CMUTs. Ces dernierssuscitent un intérêt croissant dans le milieu de l’imagerie ultrasonore et sont considérés comme une alternativepotentielle et viable aux transducteurs piézoélectriques. Cette nouvelle technologie CMUTs est caractérisée par uneplus large bande passante, une sensibilité élevée, une facilité de fabrication et une réduction des coûts de production.Cette thèse est consacrée à la mise en place d’un certain nombre d’outils théoriques et expérimentaux permettant lamodélisation/conception, la fabrication et la caractérisation de transducteurs CMUTs à membrane circulaire pourl’émission des ultrasons. Nous commençons par développer des outils de simulation à base de calculs par élémentsfinis, permettant la compréhension et la modélisation du comportement électromécanique des CMUTs pour laconception et le dimensionnement des cellules élémentaires et des réseaux. Nous proposons par la suite un nouveauprocédé de fabrication de transducteurs CMUTs basé sur le collage anodique d’une couche de silicium monocristallind’épaisseur fixe d’une plaquette de SOI sur un substrat de verre. L’évolution du procédé de fabrication est détailléepour chaque étape technologique en soulignant à chaque fois les améliorations/modifications apportées pour unefiabilité et une répétitivité accrue associées à une connaissance des limites de faisabilité. Dans la dernière partie de cetravail, on s’intéresse à la mise en œuvre de plusieurs plateformes expérimentales permettant différentescaractérisations électromécaniques statiques et dynamiques des dispositifs CMUTs fabriqués / The use of ultrasound imaging has several advantages: it is extremely safe because it does not use ionizingradiation and has no adverse effects on health. It gives excellent quality results with a relatively low cost. Historically,piezoelectric materials and their composites have been early used for ultrasound generation. Transducers made fromthese materials dominate currently the ultrasonic probes market. However, for some applications, they can’t bebecause of design and limitation reasons due to material properties. A solution can be provided by the use ofcapacitive micromachined ultrasonic transducers CMUTs. A growing interest in the field of the ultrasound imaging isshown to this technology considered as a potential and viable alternative to piezoelectric transducers andcharacterized by a wide bandwidth, high sensitivity, ease of manufacture and reduce production costs. This thesis isdevoted to the establishment of a number of experimental and theoretical tools for the modeling/design, fabricationand characterization of circular membrane CMUTs transducers for ultrasound transmission. We begin by developingsimulation tools based on finite elements method in order to understand/model the CMUTs electromechanicalbehavior for the design and dimensioning of elementary cells and networks. Thereafter, we introduce a new CMUTtransducers fabrication process based on the anodic bonding a fixed thickness single crystal silicon layer of a SOIwafer on a glass substrate. The process evolution is detailed for each technological step highlighting everyimprovements/changes introduced for increased reliability and repeatability associated with an increased knowledgeof feasibility limits. In the last part of this work, we focus on the implementation of several experimental platformsallowing different static and dynamic electromechanical characterizations of the fabricated CMUTs devices.

Nos últimos anos, avanços consideráveis foram alcançados no estudo da usinabilidade de materiais frágeis tais como cristais semicondutores, vidros ópticos, cerâmicas, etc. em função da demanda por processos mais rápidos de fabricação de superfícies com formas complexas para aplicações nos campos da óptica e eletrônica. A ductilidade apresentada por monocristais de silício durante a usinagem tem sido explicada através das Teorias de Mecânica de Fratura. Recentemente, algumas teorias novas foram apresentadas para justificar esta ductilidade. Foi proposto que a ductilidade de monocristais semicondutores seria provavelmente o resultado final de uma transformação de fase induzida por pressão/tensão durante o corte. Neste trabalho, a diferença entre os modos dúctil e frágil no Torneamento com Ferramenta de Ponta Única de superfícies de silício monocristalino foram investigadas através da técnica de espalhamento Raman. Nas condições que proporcionam o regime dúctil, existem sempre uma amorfização superficial nas amostras, denunciadas através da ativação de uma banda óptica Raman mais larga em 470 cm-1. Esta fase amorfa pode ser considerada resultante da transição de fase a qual o silício pode ter sofrido. Por outro lado, para as condições onde o modo frágil é predominante, somente um pico óptico agudo de fonon em 521.6 cm-1 está presente no espectro Raman. Baseado nas medições que determinados parâmetros de corte, tais como a profundidade de corte e a espessura crítica do cavaco, apresentaram este estudo propõe que o regime dúctil não deve possuir uma faixa definida e fixa de valores para os parâmetros críticos mas, ao invés disso, estes seriam dependentes da extensão da camada transformada induzida por pressão/tensão gerada pela interação entre a ponta/aresta da ferramenta de corte com a peça durante a usinagem. Esta proposta se baseia na comparação entre os valores obtidos e os medidos por outros autores que mostram que a extensão da fase amorfa observada após processos de deformação mecânica (p.e., indentação, riscamento, polimento, nanoretificação e torneamento com ferramenta de ponta única de diamante) encontram-se na mesma faixa de valores encontrados para os parâmetros críticos (100-200 nm). Finalmente, foi demonstrado, através de observações da topografia de ambos, cavacos e superfícies geradas, realizadas com MEV e MFA, que este tipo de análise pode oferecer explicações significativas sobre os mecanismos de remoção de material em ação durante a usinagem e também sobre o estado microscópicos da ferramenta de diamante. / In recent years, considerable progress has been made on the study of the machinability of fragile materials such as semiconductors crystals, optical glasses, ceramics, etc., because of the demand for faster fabrication processes of complex surface shapes for optoelectronic applications. The ductility presented by single crystal silicon during machining has been explained by fracture mechanics theories. Recently, some new theories have been presented in order to give another justify to this ductility. It was proposed that semiconductors single crystal ductility is likely the end result of a pressure/stress induced phase transformation during cutting. In this work, the difference between ductile and brittle mode single-point diamond turning on the surface of machined silicon samples were investigated using Raman scattering. In the ductile mode conditions of machining, there are always an amorphization of the surface samples, denounced by the activation of the broad Raman optical band at 470 cm-1. This amorphous phase can be considered resulted from the phase transiton which silicon might have suffered. Contrary to the findings, in the brittle mode conditions, only the sharp optical phonon peak at 521.6 cm-1 is present in Raman spectra. Based on the observation that certain cutting parameters such as cutting depth and critical chip thickness, e.g., the point where ductile-to-brittle transition occurs, somehow presents values in the same range (100-200 nm) that the amorphous phase layer depth extension after mechanical deformation. (p.e., indentation, scratching, polishing, nanogrinding and single point diamond turning) observed in the literature, it is propposed that the ductile regime has not a definite range of values for the critical parameters but instead, it is dependent of the extension of the phase transformed layer induced by pressure/stress generated by the tool tip/edge interaction with workpiece during machining. Finally, it is shown that observation of topography and morphology of chip and the surface generated through SEM and AFM can offer very significant explanation of the material removal mechanisms in action during the current machining cut and diamond tool state.

Σκοπός αυτής της διπλωματικής εργασίας είναι η θεωρητική μελέτη φωτοβολταϊκών πλαισίων χρησιμοποιούμενων σε διαστημικές εφαρμογές, περιγράφοντας την τεχνολογία και τη λειτουργία τους, καθώς και την ιστορική εξέλιξη τους τις τελευταίες δεκαετίες από το 1950 έως σήμερα. Στα πλαίσια αυτά περιγράφονται οι ηλιακές συστοιχίες για διαστημικές εφαρμογές, οι συνηθισμένοι τύποι ημιαγωγικών υλικών για τα πλαίσια, όπως το πυρίτιο Si και το αρσενιούχο γάλλιο GaAs και οι απαιτήσεις των. Αρχικά, μελετάται ποιες παράμετροι επηρεάζουν την απόδοση των φωτοβολταϊκών κυττάρων στο διάστημα και επιπλέον οι επιπτώσεις της διαστημικής ακτινοβολίας και θερμοκρασίας στην λειτουργία των πλαισίων. Στη συνέχεια παρουσιάζονται τα προηγμένα ηλιακά κύτταρα πυριτίου Si και τα υψηλής απόδοσης άμορφου πυριτίου που παρουσιάζουν βελτιωμένη ενεργειακή απόδοση του πλαισίου. Οι βέλτιστες παράμετροι των δομών για τις διαστημικές εφαρμογές, φαίνεται πλέον να επιτυγχάνονται με τα ευρέως χρησιμοποιούμενα ηλιακά κύτταρα πολυεπαφών multijunction MJ, που είναι κύτταρα ιδιαιτέρου τρόπου σχεδιασμού. Οι παράμετροι επηρεασμού της απόδοσης τους αναλύονται καθώς και οι επιπτώσεις των εξωτερικών συνθηκών. Μεγάλης σημασίας θεωρείται ο σχεδιασμός της ηλιακής συστοιχίας στο διάστημα και οι απαιτήσεις σχεδίασης για αξιόπιστη απόδοση και μεγάλη διάρκεια ζωής. Στη μελέτη αυτή αναλύουμε και τις δομές εκείνες που μπορούν να βελτιώσουν την απόδοση των διαστημικών ηλιακών κυττάρων. Οι πιο ελπιδοφόρες και πιο πολλά υποσχόμενες δομές είναι αυτές των μεταμορφικών «metamorphic» και ανεστραμμένων μεταμορφικών «inverted-metamorphic» ηλιακών κυττάρων σε σχέση με τα κλασικά "latticed matched" ηλιακά κύτταρα και αυτες οι δομές θα συνεχίσουν να βρίσκονται στο επίκεντρο για τις επόμενες δεκαετίες. Επιπλέον προϊόν της παρούσας διπλωματικής εργασίας, είναι η πειραματική μελέτη της συμπεριφοράς ενός φωτοβολταϊκού πλαισίου μονοκρυσταλλικού πυριτίου m-Si ισχύος αιχμής 80 W σε πραγματικές συνθήκες λειτουργίας στη γη, υπό την επίδραση διαφόρων εξωτερικών παραγόντων, όπως προσπίπτουσα ακτινοβολία, θερμοκρασία και γωνία κλίσης. Με στόχο την εκτίμηση της ενεργειακής απόδοσης και της ανίχνευσης της βέλτιστης τιμής αυτής πραγματοποιήθηκαν μετρήσεις με την βοήθεια του PVPM στη διάρκεια του έτους 2009 – 2010. Συγκεκριμένα περιλαμβάνονται δυο περίοδοι μετρήσεων: α) Απρίλιος 2009 έως Ιούλιος 2009, όπου πραγματοποιήθηκαν μετρήσεις ανά μια ώρα για όλες τις γωνίες κλίσης 0, 10, 20, 30, 40, 50, 60, 70, 80ο (μια ημέρα κάθε εβδομάδα) με την βοήθεια της ρυμθιζόνεμης βάσης και β) Αύγουστος 2009 έως Μάρτιος 2010, όπου πραγματοποιήθηκαν ολοήμερες μετρήσεις ανά 5 λεπτά, κάθε εβδομάδα με την βοήθεια φορητού υπολογιστή σε συγκεκριμένη κλίση 38ο, που αντιστοιχεί στο γεωγραφικό πλάτος της περιοχής της Πάτρας. Όλα αυτά οδηγούν σε μια ολοκληρωμένη εικόνα της ενεργειακής συμπεριφοράς και απόδοσης του φωτοβολταϊκού πλαισίου μας καθώς και των συνθηκών που οδηγούν σε βέλτιστες φωτοβολταϊκές ιδιότητες Η ετήσια αποδιδόμενη ενέργεια υπολογίστηκε ελαφρώς υψηλότερη από μετρήσεις γενικά αναφερόμενες από το ΚΑΠΕ. Αυτό θεωρούμε ότι οφείλεται στο γεγονός ότι η διάταξη μας δεν κατέγραφε μετρήσεις καθ όλη τη διάρκεια του έτους με αποτέλεσμα να μην είναι ακριβής η διάρκεια της ημέρας και η τιμή της προσπίπτουσας ηλιακής ακτινοβολίας. Μέσω του PVsyst προγράμματος προσπαθήσαμε να προσομοιώσουμε την ενεργειακή απόδοση του πλαισίου μονοκρυσταλλικού πυριτίου υπολογιστικά τόσο με τα πειραματικά μετεωρολογικά δεδομένα όσο και με τα μετεωρολογικά δεδομένα μέσω του προγράμματος Meteonorm και να την συγκρίνουμε με την πειραματική και επιπλέον να βρούμε την βέλτιστη απόδοση του ανάλογα με την κλίση και τον προσανατολισμό του. Η εξομοίωση με δεδομένα του προγράμματος Meteonorm 6.1 έδωσε τη διαφορά της αποδιδόμενης ενέργειας κάθε περίπτωσης, μεταξύ αυτής και της προηγούμενης μεθόδου. / The purpose of this thesis, is the theoretical study of solar modules used in space applications, together with the description of their technology and operation, and the historical development in recent decades from 1950 to today. In this context we analyzed the solar arrays for space applications, the requirements of materials for solar cells and the common types of semiconductor materials for modules, such as silicon Si and gallium arsenide GaAs. Initially, we studied what external factors affect the performance of solar cells in space and also the effects of space radiation and temperature. Further, we described the advanced silicon solar cells and the high-efficiency amorphous silicon solar cells, that improve the energy efficiency significant. For the optimal solution for space applications, we then analyzed thoroughly the most widely used in space multijunction MJ solar cells and their design, the performance parameters and the effects of external factors. To summarize the theoretical study, we studied the design of the solar array in space and the design requirements for reliable performance and longevity. Finally, there are many ways we can improve the performance of space solar cells. The most promising methods are those of metamorphic «metamorphic» and reverse metamorphic «inverted-metamorphic» solar cells compared to the classic "latticed matched" solar cells and will continue to be in the forefront for decades to come. Additional to the subject of this thesis, is the experimental study of the behavior of a photovoltaic monocrystalline silicon module m-Si 80 W peak power at real operation conditions under the influence of various external factors such as incident radiation, temperature and tilt. In order to estimate the energy efficiency we took measurements with the help of PVPM in the year 2009 - 2010. Specifically, it consists of two measurement periods: a) April 2009 to July 2009, when measurements were taken every hour for all angles 0, 10, 20, 30, 40, 50, 60, 70, 80 every week with the help of special structure and b) August 2009 to March 2010, when measurements were made all day, every five minutes, each week with a notebook in a particular inclination 38ο, corresponding to the latitude of the region of Patras. All these help us to gain a comprehensive idea of their behavior and performance of our photovoltaic modules. We also observed variation in the results in comparison with CRES databases due to the fact that we could not continuously conduct every day of the year. Using PVsyst we tried to verify our experimental results and find the best solutions for the tilt and orientation of the PV modules. With the program PVsyst we tried to simulate the performance of monocrystalline silicon solar cell using computational frameworks and to compare them with the experimental results. Finally it was also simulated with the data given from the database of the program Meteronorm 6.1 so as to compare both methods.

Submitted by Elóy Esteves Gasparin null (eloygasparin@gmail.com) on 2018-01-11T16:00:01Z No. of bitstreams: 1 Dissertação_Versão_Final_Elóy_Esteves_Gasparin.pdf: 1930199 bytes, checksum: 9e07c05152e38b9d557c7ac3cc3b6da7 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-01-11T18:38:30Z (GMT) No. of bitstreams: 1 gasparin_ee_me_ilha.pdf: 1930199 bytes, checksum: 9e07c05152e38b9d557c7ac3cc3b6da7 (MD5) / Made available in DSpace on 2018-01-11T18:38:30Z (GMT). No. of bitstreams: 1 gasparin_ee_me_ilha.pdf: 1930199 bytes, checksum: 9e07c05152e38b9d557c7ac3cc3b6da7 (MD5) Previous issue date: 2017-12-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Devido à alta demanda da substituição de fontes de energia que utilizam combustíveis fósseis por fontes de energia renovável, a ciência atual busca maximizar a eficiência das fontes renováveis para que sejam economicamente competitivas no mercado. Grande parte da liderança brasileira neste campo se deve à fonte hidráulica, que impacta negativamente o meio ambiente e as populações ribeirinhas. Assim, outras fontes renováveis como a eólica e a solar têm aumentado sua participação na matriz energética do país. Diante deste contexto, sistemas fotovoltaicos com alta eficiência podem aumentar a participação da energia solar na matriz interna de energia elétrica do Brasil. Os sistemas fotovoltaicos flutuantes são 11% mais eficientes do que os sistemas instalados em terra devido às menores temperaturas de operação. Para determinar se a umidade relativa do ar tem influência na eficiência das plantas flutuantes, neste trabalho, a partir de uma análise numérica, avaliou se a eficiência de conversão de energia é influenciada pela distância entre a superfície da água e o módulo fotovoltaico flutuante. Além disso, estudou dois tipos diferentes de módulos fotovoltaicos (monocristalinos e flexíveis) durante as quatro estações do ano, avaliando suas peculiaridades. A Planta Fotovoltaica de Rosana/SP foi utilizada como base para formulação dos modelos físicos, que resultaram em um modelo matemático solucionado através do Método de Volumes Finitos nos softwares FLUENT® e MECHANICAL® do pacote ANSYS®. As quatro distâncias simuladas (100, 300, 600 e 900mm) determinaram que os modelos físico e matemático adotados não captaram de forma conclusiva se as temperaturas de operação dos módulos diminuem com a aproximação da superfície da água. A potência gerada por um módulo monocristalino é 38,8% maior do que a gerada por um módulo flexível, no entanto os monocristalinos são dez vezes mais sensíveis à temperatura de operação. Para a mesma capacidade (25kW), a geração efetiva de energia da planta de módulos flexíveis é 9,1% maior devido à área de incidência receber 63,3% mais irradiação solar. As menores eficiências elétricas ocorrem no Verão/Primavera, entretanto, as plantas geram 30% mais energia em relação ao Outono/Inverno. Na atualidade, os módulos monocristalinos possuem melhor aplicabilidade do que os flexíveis, pois possuem maior eficiência elétrica, mesmo utilizando estruturas de suporte mais robustas. / Due to the high demand for the replacement of energy sources that use fossil fuels by renewable energy sources, the current science seeks to maximize the efficiency of renewable sources to them be economically competitive in the market. Much of the Brazilian leadership in this field is due to the hydraulic source, which negatively impacts the environment and the riverine populations. Thus, other renewable energy sources such as wind and solar energies have increased their participation in the country's energy matrix. Given this context, photovoltaic systems with high efficiency can increase the participation of solar energy in the internal matrix of electric energy of Brazil. Floating photovoltaic systems are 11% more efficient than onshore systems due to lower operating temperatures. To determine if the relative humidity of the air influences the efficiency of the floating plants; in this work, based on a numerical analysis, it was evaluated whether the energy conversion efficiency is influenced by the distance between the water surface and the floating photovoltaic module. In addition, it was studied two different types of photovoltaic modules (monocrystalline and flexible) during the 4 seasons of the year, evaluating its peculiarities. The Rosana/SP Photovoltaic Plant was used as the basis for the formulation of the physical models, which resulted in a mathematical model solved through the Finite Volume Method in the FLUENT® and MECHANICAL® softwares of the ANSYS® package. The four simulated distances (100, 300, 600 and 900mm) determined that the physical and mathematical models adopted did not capture in a conclusive way whether the operating temperatures of the modules decrease with the approximation of the water surface. The power generated by a monocrystalline module is 38.8% greater than that generated by a flexible module, however the monocrystalline is ten times more sensitive to the operating temperature. For the same capacity (25kW), the effective power generation of the flexible module plant is 9.1% higher due to the incidence area receiving 63.3% more solar irradiation. The lowest electrical efficiencies occur in the Summer/Spring season, but generate 30% more energy compared to Fall/Winter season. Currently, the monocrystalline modules have better applicability than the flexible ones because they have greater electrical efficiency, even using more robust support structures. / 130005/2016-9

Orientador: João Batista Campos Silva / Resumo: Devido à alta demanda da substituição de fontes de energia que utilizam combustíveis fósseis por fontes de energia renovável, a ciência atual busca maximizar a eficiência das fontes renováveis para que sejam economicamente competitivas no mercado. Grande parte da liderança brasileira neste campo se deve à fonte hidráulica, que impacta negativamente o meio ambiente e as populações ribeirinhas. Assim, outras fontes renováveis como a eólica e a solar têm aumentado sua participação na matriz energética do país. Diante deste contexto, sistemas fotovoltaicos com alta eficiência podem aumentar a participação da energia solar na matriz interna de energia elétrica do Brasil. Os sistemas fotovoltaicos flutuantes são 11% mais eficientes do que os sistemas instalados em terra devido às menores temperaturas de operação. Para determinar se a umidade relativa do ar tem influência na eficiência das plantas flutuantes, neste trabalho, a partir de uma análise numérica, avaliou se a eficiência de conversão de energia é influenciada pela distância entre a superfície da água e o módulo fotovoltaico flutuante. Além disso, estudou dois tipos diferentes de módulos fotovoltaicos (monocristalinos e flexíveis) durante as quatro estações do ano, avaliando suas peculiaridades. A Planta Fotovoltaica de Rosana/SP foi utilizada como base para formulação dos modelos físicos, que resultaram em um modelo matemático solucionado através do Método de Volumes Finitos nos softwares FLUENT® e MECHANICAL® do pacote A... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Due to the high demand for the replacement of energy sources that use fossil fuels by renewable energy sources, the current science seeks to maximize the efficiency of renewable sources to them be economically competitive in the market. Much of the Brazilian leadership in this field is due to the hydraulic source, which negatively impacts the environment and the riverine populations. Thus, other renewable energy sources such as wind and solar energies have increased their participation in the country's energy matrix. Given this context, photovoltaic systems with high efficiency can increase the participation of solar energy in the internal matrix of electric energy of Brazil. Floating photovoltaic systems are 11% more efficient than onshore systems due to lower operating temperatures. To determine if the relative humidity of the air influences the efficiency of the floating plants; in this work, based on a numerical analysis, it was evaluated whether the energy conversion efficiency is influenced by the distance between the water surface and the floating photovoltaic module. In addition, it was studied two different types of photovoltaic modules (monocrystalline and flexible) during the 4 seasons of the year, evaluating its peculiarities. The Rosana/SP Photovoltaic Plant was used as the basis for the formulation of the physical models, which resulted in a mathematical model solved through the Finite Volume Method in the FLUENT® and MECHANICAL® softwares of the ANSYS® package.... (Complete abstract click electronic access below) / Mestre

Made available in DSpace on 2015-03-03T15:16:24Z (GMT). No. of bitstreams: 1 CharlieSG_TESE.pdf: 3311987 bytes, checksum: 5f80153b1b46fc49c2f7148d8e447904 (MD5) Previous issue date: 2010-02-26 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this work we have developed a way to grow Fe/MgO(100) monocrystals by magnetron sputtering DC. We investigated the growing in a temperature range among 100 oC and 300 oC. Structural and magneto-crystalline properties were studied by different experimental techniques. Thickness and surface roughness of the films were investigated by atomic force microscopy, while magneto-crystalline properties were investigated by magneto-optical Kerr effect and ferromagnetic resonance. Our results show that as we increase the deposition temperature, the magneto-crystalline anisotropy of the films also increases, following the equation of Avrami. The best temperature value to make a film is 300 oC. As the main result, we built a base of magnetoresistence devices and as an aplication, we present measurements of Fe/Cr/Fe trilayer coupling. In a second work we investigated the temperature dependence of the first three interlayer spacings of Ag(100) surface using low energy electron diffraction. A linear expansion model of crystal surface was used and the values of Debye temperatures of the first two layers and thermal expansion coefficient were determinated. A relaxation of 1% was found for Ag(100) surface and these results are matched with faces (110) and (111) of the silver. iv / Neste trabalho foi desenvolvida a metodologia de deposi??o dos filmes monocristalinos de Fe/MgO (100) via magneto sputtering DC. Foi Investigado o crescimento de filmes na faixa de temperatura entre 100 oC e 300 oC. As propriedades estruturais e magnetocristalinas dos filmes foram estudadas por diferentes t?cnicas experimentais. A espessura e a rugosidade da superf?cie foram investigadas por microscopia de for?a at?mica (AFM). A t?cnica de espectroscopia de fotoel?trons excitados por raios-X (XPS) foi utilizada para determinar a pureza da composi??o dos filmes. E as propriedades magn?ticas foram investigadas por resson?ncia ferromagn?tica (FMR) e Efeito Ker Magneto-?ptico (MOKE). O resultados mostram que o aumento da temperatura de deposi??o gera um aumento da anisotropia magnetocristalina segundo um comportamento regido pela equa??o de Avrami. Como resultado principal, foi constru?da a estrutura base para a fabrica??o de dispositivos magnetoresistivos. E, como aplica??o s?o apresentadas as medidas do acoplamento entre uma tricamada de Fe/Cr/Fe/MgO. Em um segundo trabalho, foi investigado a depend?ncia com a temperatura dos primeiros tr?s espa?amentos entre camadas da Ag (100) via t?cnica de difra??o de el?trons. Utilizando um modelo de expans?o linear da superf?cie do cristal, foi determinada a temperatura de Debye, a varia??o percentual da dist?ncia interplanar e o coeficiente de expans?o t?rmica da superf?cie. A relaxa??o encontrada foi de 1% e os resultados s?o confrontados com as faces (110) e (111) da prata

In this work are discussed photovoltaic cells. There are also discussed basic concepts of radiation source for solar cells. Also mentioned the issue of semiconductors and even the history and evolution of the solar cells. A large part deals with possibilities of photovoltaic cells degradation. In one chapter is an attempt to bring some types of photovoltaic cells and a description of the production of these modules.The practical part deals with photovoltaic modules degradation and its evaluation. Following part compares measured values with the values provided by producer of photovoltaic modules.

Foram desenvolvidos sistemas de medidas visando a caracterização de células solares de sílico monocristalino. Para isso, foram determinadas as características I x V no escuro para diferentes níveis de iluminação. Curvas de resposta espectral e capacitância em função da tensão inversa aplicada foram também obtidas. Foi feita uma avaliação do comportamento dessas células em função da temperatura e realizadas medidas de profundidade de junção utilizando-se três métodos distintos. Os principais parâmetros, que determinam o desempenho dessas células, foram obtidos boa concordância com a teoria e com os resultados apresentados na literatura. / Systems of measurements were developed for the characterization of single crystal silicon solar cells. For that, the curves I x V were measured in the dark and for different intensity of illumination. Curves of spectral response and of capacitance as a function of the reciprocal of the voltage were also measured. The behavior of the cells as a function of temperature was analysed and also measurements of junction depth were made by three different methods. Values for the parameters that characterize the cells were obtained, showing a good agreement with theoretical values and also with already reported values.

Σκοπός αυτής της διπλωματικής εργασίας είναι να εμβαθύνουμε στη λειτουργία φωτοβολταϊκού πλαισίου μονοκρυσταλλικού πυριτίου και μέσα από τα αριθμητικά δεδομένα των μετρήσεων και των υπολογισμών, να αποφανθούμε πώς η λειτουργία σε πραγματικές συνθήκες μπορεί να επηρεάσει την παραγόμενη ισχύ του. Στα πλαίσια αυτά, πραγματοποιήθηκαν μετρήσεις ρεύματος και τάσης, στο χώρο του τμήματος των Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών, με φωτοβολταϊκό πλαίσιο μονοκρυσταλλικού πυριτίου ισχύος αιχμής 80 W. Οι μετρήσεις γίνονταν μια φορά την εβδομάδα κατά τη διάρκεια ενός έτους περίπου (2008-2009) και στόχος ήταν να διεξαχθούν μετρήσεις υπό διάφορες συνθήκες ακτινοβολίας και θερμοκρασίας και για αρκετές γωνίες κλίσης ώστε να αποκτήσουμε μια ολοκληρωμένη εικόνα της ενεργειακής του συμπεριφοράς. Στη διάρκεια των μετρήσεων αλλάζαμε την τιμή ενός μεταβλητού φορτίου, για να πάρουμε τη χαρακτηριστική ρεύματος τάσης του συγκεκριμένου πλαισίου και επιπλέον σημειώναμε την ακτινοβολία, τη θερμοκρασία του περιβάλλοντος, του κυττάρου και της πίσω όψης του, καθώς και της κλίσης τοποθέτησης. Ακόμα ελέγχαμε πώς επηρεάζει τη χαρακτηριστική καμπύλη I-V, και κατά συνέπεια την απόδοση, τυχόν φυσική σκίαση από παρακείμενο αντικείμενο. Ο προσανατολισμός των πλαισίων ήταν πάντα προς το Νότο, ώστε να έχουμε περισσότερες ώρες ηλιοφάνειας, μίας και η Ελλάδα είναι χώρα του βόρειου ημισφαιρίου. Κατά την επεξεργασία των μετρήσεων καταλήξαμε στην βέλτιστη κλίση τοποθέτησης του πλαισίου ανά εποχή και είδαμε πως η ακτινοβολία επιδρά θετικά στην απόδοση του σε αντίθεση με τη θερμοκρασία του κυττάρου που τη μειώνει όταν αυτή αυξάνεται. Τέλος, έγινε μια σύγκριση των τιμών που δίνει ο κατασκευαστής σε εργαστηριακό περιβάλλον με τις τιμές των μετρήσεων για να διαπιστώσουμε τις απώλειες που έχουμε όταν το μονοκρυσταλλικό πλαίσιο λειτουργεί σε πραγματικές συνθήκες. / The aim of this diploma thesis is to take a better look at the operation of a monocrystalline silicon photovoltaic module and through the numerical data of measurements and the calculations, to come to a conclusion about how the operation in real conditions can influence his produced power. Measurements of current and tendency have been made in the area of the department of Electrical and Computer Engineering using a monocrystalline silicon photovoltaic module of peak power 80 W. The measurements took place once a week for about a year (2008-2009) and our goal was to obtain measurements under various conditions of radiation and temperature and for some angles of bent so that we acquire a completed picture of its energy behavior. During the measurements we changed a variable load, in order to form the characteristic curve of current and tendency of the module and we also noted down the radiation, the environmental, the cell and the back side temperature of the module, as well as the bent of placement. Moreover, we checked how a possible natural shading from an adjacent object influences the characteristic I-V curve, and as a result the efficiency of the module. The orientation of the module was always South, in order to gain more hours of sunlight, since Greece is a country of the northern hemisphere. While processing the measurements, we found the optimal bent of placement per season for the module and we saw that the radiation affects positively its efficiency contrary to the cell temperature that decreases the efficiency when increased. Finally, we compare the electrical specifications in laboratorial environment that the constructor gives, with the measurements in order to realise the losses that we have when the monocrystalline module functions in real conditions.

Foram desenvolvidos sistemas de medidas visando a caracterização de células solares de sílico monocristalino. Para isso, foram determinadas as características I x V no escuro para diferentes níveis de iluminação. Curvas de resposta espectral e capacitância em função da tensão inversa aplicada foram também obtidas. Foi feita uma avaliação do comportamento dessas células em função da temperatura e realizadas medidas de profundidade de junção utilizando-se três métodos distintos. Os principais parâmetros, que determinam o desempenho dessas células, foram obtidos boa concordância com a teoria e com os resultados apresentados na literatura. / Systems of measurements were developed for the characterization of single crystal silicon solar cells. For that, the curves I x V were measured in the dark and for different intensity of illumination. Curves of spectral response and of capacitance as a function of the reciprocal of the voltage were also measured. The behavior of the cells as a function of temperature was analysed and also measurements of junction depth were made by three different methods. Values for the parameters that characterize the cells were obtained, showing a good agreement with theoretical values and also with already reported values.