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The increasing energy demand, combined with the use of harmful non-renewable energy sources calls for the search of alternative methods to cover our energy need.Renewable energy can be harvested in different ways, through the movement of wind and water, biomass, or directly from the rays of the sun, as in the case of photovoltaic (PV) devices. Whilst crystalline silicon (c-Si) is the most common absorber used for solar cells, other technologies are emerging. Solar cells with copper indium gallium diselenide (CIGS) as an absorber have the possibility of being flexible, which is an advantage due to the many more application possibilities that appear compared to the rigid and heavy c-Si solar cells. CIGS solar cells have some long-term stability issues, especially regarding ingression of atmospheric species through the front contact layer. This calls for further research in the front contact of the CIGS solar cell, exploring alternative materials to prevent degradation. The front contact of a solar cell must be both optically transparent and conduct electricity. Transparent conductive oxides (TCO) are materials characterized by the ability to conduct electricity, while also possessing a certain degree of optical transparency. The combination of conductivity and transparency makes TCOs ideal as front contacts in solar cells. A very common TCO for front contacts in CIGS solar cells is aluminum-doped zinc oxide (AZO) due to its low cost, good electrical conductivity and optical transparency. Because of its low resistance to degradation in humid environments more robust TCO alternatives, such as indium-doped tin oxide (ITO), are being investigated. Indium-doped tin oxide possesses similar electrical and optical properties as AZO, but better stability in humid environments.The ITO was deposited through RF magnetron sputtering, on a glass substrate to be able to measure optical properties. Initially, experiments focusing on oxygen content in the deposition atmosphere were done, together with a reproducibility experiment. This gave useful information about sputtering parameters and stability of the deposition. Thereon, an experiment was done varying three parameters: oxygen content in deposition atmosphere, sputtering power and temperature of substrate. A statistical software was used to analyze the data, identifying the effects of the changing parameters. The best performing samples were made with an oxygen content of 0,4-0,6 vol%. A high sensibility for oxygen in the system was also observed, as a result of the initial reproducibility experiments. This led to the introduction of a sacrificial deposition step after the machine had been shut down. Optimal substrate temperature was around 150°Cand it was not possible to go higher due to sensibility of the underlying solar cell layers.A lower threshold for the film thickness, located somewhere between 125 and 175 nm, was observed. Films with thickness below this threshold experienced a large resistivityincrease. Further depositions with higher oxygen content are advised to see if the properties of the films further improve.

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No description available.

[pt] Como motivação, apresentaremos alguns problemas que ilustram a conexão entre a teoria da probabilidade e algumas equações diferenciais parciais. Suas soluções mesclam os dois assuntos e provocam a suspeita de que alguns processos estocásticos e operadores diferenciais caminham juntos. Em seguida, exibiremos a teoria das difusões de Itô. Mostraremos algumas de suas características, como a propriedade de Markov e cada um destes processos possuirá o que chamaremos de gerador infinitesimal da difusão. Este será um operador diferencial de segunda ordem cujo estudo detalhado revela características do processo. Apresentaremos também a fórmula de Dynkin. Com essas ferramentas probabilísticas, encontraremos uma representação estocástica para a solução do problema de Dirichlet para operadores diferenciais elípticos, generalizando as soluções dos problemas inicialmente propostos. / [en] Firstly, for motivation purposes, we briefly present a few problems mixing notions of probability theory and of partial differential equations (PDE). In discussing the solution to such problems it will become apparent that some stochastic process and differential equations walk together. Next, we introduce a class of stochastic processes called the Ito diffusions, and some of its features such as the Markov property. Each such process has an associated linear operator the, so called, infinitesimal generator. This operator acts as a second-order differential operator on smooth functions, and controls the LOCAL behavior of these diffusions. We discuss these features together with Dynkin s formula a convenient relation derived from the infinitesimal generator, which informs us about the AVERAGE behavior of the diffusion. Finally, we apply these probabilistic tools to find a formula for the solution of the Dirichlet problem for a somewhat general linear elliptic second order PDE. This formula connects the solution of the PDE to the aggregated/average behavior and associated (Ito) diffusion. This type of stochastic representation generalizes the solution method of the problems firstly discussed.

Acoustic levitation utilizes general principles of ultrasonics to trap particles in midair without external support. This is done by creating an array of ultrasonic transducers to propagate sound waves to a focused point in space. In order to optimize the particle trap it is necessary to design transducers that can produce enough sound to create pressure pockets. In this work I examine the fundamental principles of acoustics by testing the sound pressure levels (SPL) of a known transducer in both air and water mediums. A comparison between domed and bimorphed transducers are also examined. Experimentation was performed on the feasibility of implementing a domed transducer array. Methods are described to fabricate a piezoelectric thin film made from poly(vinylidene difluoride) (PVDF). These films were analyzed for β-phase concentration, as well as transmission, resolution, and contrast. An additional study into the use of Indium Tin Oxide (ITO) as a conductive dielectric layer of a transducer is also examined. These studies are designed to test if spin coating can provide the necessary conditions to fabricate transparent, piezoelectric PVDF films. Included are the research and experiments that I conducted to determine the transparency of PVDF. I performed analysis on the transmission, absorption, and scatter of fabricated PVDF films. My results show that it is possible to fabricate PVDF films that are both transparent and piezoelectric.

No description available.

Diese Arbeit gibt einen tiefgehenden Einblick in verschiedene Aspekte von auf (In,Ga)N/GaN Heterostrukturen basierenden Leuchtdioden (LEDs), mittels Molekularstrahlepitaxie entlang der Achse von Nanodrähten (NWs) auf Si Substraten gewachsen. Insbesondere wurden die Wachstumsparameter angepasst, um eine Koaleszierung der Nanodrähte zu vermindern. Auf diese Weise konnte die durch die NW-LEDs emittierte Intensität der Photolumineszenz (PL) um einen Faktor zehn erhöht werden. Die opto-elektronischen Eigenschaften von NW-LEDs konnten durch die Verwendung von Indiumzinoxid, anstatt von Ni/Au als Frontkontakt, verbessert werden. Zudem wurde demonstriert, dass auch selektives Wachstum (SAG) von GaN NWs auf AlN gepufferten Si Substraten mit einer guten Leistungsfähigkeit von Geräte vereinbar ist und somit als Wegbereiter für eine neue Generation von NW-LEDs auf Si dienen kann. Weiterhin war es möglich, strukturierte Felder von ultradünnen NWs durch SAG und thermische in situ Dekomposition herzustellen. In den durch die NW-LEDs emittierten Elektrolumineszenzspektren (EL) wurde eine Doppellinenstruktur beobachtet, die höchstwahrscheinlich von den kompressiven Verspannungen im benachbarten Quantentopf, durch die Elektronensperrschicht verursachten, herrührt. Die Analyse von temperaturabhängigen PL- und EL-Messungen zeigt, dass Ladungsträgerlokalisierungen nicht ausschlaggebend für die EL-Emission von NW-LEDs sind. Die Strom-Spannungs-Charakteristiken (I-V) von NW-LEDs unter Vorwärtsspannung wurden mittels eines Modells beschrieben, in das die vielkomponentige Natur der LEDs berücksichtigt wird. Die unter Rückwärtsspannung aktiven Transportmechanismen wurden anhand von Kapazitätstransientenmessungen und temperaturabhänigigen I-V-Messungen untersucht. Dann wurde ein physikalisches Modell zur quantitativen Beschreibung der besonderen I-V-T Charakteristik der untersuchten NW-LEDs entwickelt. / This PhD thesis provides an in-depth insight on various crucial aspects of light-emitting diodes (LEDs) based on (In,Ga)N/GaN heterostructures grown along the axis of nanowires (NWs) by molecular beam epitaxy on Si substrates. In particular, the growth parameters are adjusted so as to suppress the coalescence of NWs; in this way the photoluminescence (PL) intensity emitted from the NW-LEDs can be increased by about ten times. The opto-electronic properties of the NW-LEDs can be further improved by exclusively employing indium tin oxide instead of Ni/Au as top contact. Furthermore, the compatibility of selective-area growth (SAG) of GaN NWs on AlN-buffered Si substrates with device operation is demonstrated, thus paving the way for a new generation of LEDs based on homogeneous NW ensembles on Si. Ordered arrays of ultrathin NWs are also successfully obtained by combining SAG and in situ post-growth thermal decomposition. A double-line structure is observed in the electroluminescence (EL) spectra emitted by the NW-LEDs; it is likely caused by compressive strain introduced by the (Al,Ga)N electron blocking layer in the neighbouring (In,Ga)N quantum well. An in-depth analysis of temperature dependent PL and EL measurements indicates that carrier localization phenomena do not dominate the EL emission properties of the NW-LEDs. The forward bias current-voltage (I-V) characteristics of different NW-LEDs are analysed by means of an original model that takes into account the multi-element nature of LEDs based on NW ensembles by assuming a linear dependence of the ideality factor on applied bias. The transport mechanisms in reverse bias regime are carefully studied by means of deep level transient spectroscopy (DLTS) and temperature dependent I-V measurements. The physical origin of the detected deep states is discussed. Then, a physical model able to describe quantitatively the peculiar I-V-T characteristics of NW-LEDs is developed.

Die vorliegende Dissertation befasst sich mit dem RF- überlagerten DC-Sputtern von Indiumzinnoxid und aluminiumdotierten Zinkoxid. Bei dem dafür entwickelten synchron gepulsten RF/DC-Verfahren werden die zu untersuchenden Materialien gleichzeitig mit Hilfe eines RF- und eines PulsDC-Generators gesputtert. Ein wesentliches Resultat der Untersuchungen ist, dass durch RF- überlagertes DCSputtern Schichten abgeschieden werden können, die im Vergleich zum DC- bzw. PulsDC-Sputtern geringere spezifische Widerstände aufweisen. Dies ist auf eine Verringerung von Defekten in den abgeschiedenen Schichten zurückzuführen. Es konnte anhand der Untersuchungen gezeigt werden, dass fur die Abscheidung von Indiumzinnoxid und aluminiumdotiertem Zinkoxid die Substrattemperatur beim RF überlagerten DC-Sputtern gegenüber dem DC-Sputtern um bis zu 100°C verringert werden kann.

This thesis investigates large private companies in Sweden that have outsourced their information technology (IT). A considerable proportion of IT outsourcing (ITO) is unsuccessful. For IT service buyers, this could cause IT that does not fully work, entailing problems with the network, application, infrastructure and security, with serious consequences such as a loss of customers’ confidence and significantly increased costs. Therefore, the main research goal was to analyse and define ways to improve ITO for buyer organizations. This main research goal was accomplished through three research goals that are the followings: 1) To develop a method for risk assessment in IT outsourcing; 2) To identify the important factors in IT outsourcing relationship; and 3) To identify the success factors in IT outsourcing.                       The research strategies applied in conducting this research were design science research and survey research. To achieve the first research goal, a method was developed for assessing the ITO risks, including support for mitigating these risks. This method could help both researchers and practitioners in estimating the ITO risks and in this way improve ITO. An application based on the developed method was used to facilitate the testing of this method by several ITO decision makers in large companies concerning its usability, correctness and functionality. Moreover, a study was performed to explore ITO decision makers’ acceptance of the developed method and their use of it for assessing the ITO risks.             The second research goal investigated how to improve service buyers’ ITO relationship with their providers. A well-working ITO relationship is a critical determinant of successful ITO and is relevant to the whole ITO life cycle. This research goal was achieved by identifying and analysing the most important factors in ITO relationships, including a prioritized list of those factors that are highly recommended for use in creating and maintaining a good ITO relationship.                       The third research goal examined how to improve ITO by identifying and prioritizing the success factors (SFs) in ITO. This research identified the ITO SFs in large companies and provided a prioritized list of them to be applied in these companies with a description of the value that they could create from implementation during the ITO life cycle. Moreover, the SFs identified in large companies were compared with those identified in medium-sized companies, which could give an indication to the researchers in this field that company size matters in regard to the implementation order of the identified SFs.               In summary, the research presented in this thesis contributes with: 1) a method for assessing the risks of outsourcing IT and, in the case that IT has been outsourced, suggested ways to mitigate them; 2) the important factors that could improve ITO relationships and 3) a prioritized list of success factors that could improve IT outsourcing. / Denna avhandling undersöker stora privata företag i Sverige som har outsourcat sin IT verksamhet. Som vi uppmärksammade har en stor del av IT-outsourcingen (ITO) misslyckats. För köparen av IT-tjänsten kan det leda till bristande IT funktionalitet med allvarliga konsekvenser som i värsta fall leder till förlorade kunder och betydande kostnadsökningar. Därför är det övergripande forskningsmålet är att analysera och fastställa hur ITO:n för köparen av IT tjänsten kan förbättras. För att lösa det övergripande forskningsmålet forskningen undersökte: 1) Utvecklingen av en metod för att bedöma riskerna med IT-outsourcing; 2) Identifiering av de viktiga faktorerna inom IT-outsourcingsrelationer; och 3) Identifiering av en lista över framgångsfaktorer i IT-outsourcing. De använda forskningsstrategierna för att genomföra forskningen var ”design science research" och kartläggning. För att uppnå först huvudforskningsmålet, har en metod tagits fram för att bedöma riskerna och vägleda hur man kan minska dem. Den här metoden kan hjälpa både forskare och de som utövar IT-outsourcing med att bedöma ITO-riskerna och på så sätt förbättra sina IT-outsourcing.  En programvara baserad på den metoden har utvecklats för att underlätta testningen av metoden vilket har genomförts med IT beslutsfattare på stora organisationer, beträffande användbarhet, korrekthet och funktionalitet. Dessutom har en studie utförts för att bedöma om programvaran kan accepteras av IT beslutsfattare och få reda på om de skulle använda metoden för att bedöma ITO riskerna. Det andra forskningsmålet har undersökt hur köparna av den outsourcade IT-tjänsten kan förbättra relationen med sina leverantörer. En bra ITO-relation är en avgörande faktor för en framgångsrik ITO och den är viktig för hela livscykeln. Forskningsmålet har uppnåtts genom analys för att hitta de viktigaste faktorerna ITO-relationsfaktorer, som studien rekommenderar för att skapa och underhålla en bra ITO relation. Det tredje forskningsmålet har undersökt hur ITO kan förbättras genom att identifiera och prioritera framgångsfaktorerna i ITO. Studien har identifierat framgångsfaktorerna i stora företag och tagit fram en lista med prioriterade framgångsfaktorer som bör implementeras i de undersökta företagen. Dessutom så har nyttan av dessa framgångsfaktorer beskrivits under ITO livscykeln. Dessutom har de identifierade framgångsfaktorerna från stora företag jämförts med framgångsfaktorerna som har identifierats för medelstora företag. Denna jämförelse ger en indikation till forskarna på det här området att prioriteringen av framgångsfaktorerna är beroende av företagsstorlek. Sammanfattningsvis, den beskrivna forskningen i den här uppsatsen bidrar med: 1) En metod för att bedöma risker och förslag på hur minska dessa risker; 2) En lista med de viktiga faktorerna för att förbättra ITO relationen inom IT-outsourcing och; 3) En prioriterad lista av framgångsfaktorer som kan förbättra IT outsourcing.