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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

Évaluation environnementale de systèmes de construction de cloisons résidentielles : réflexions sur l'adaptabilité et la flexibilité

Patenaude, Mario 08 1900 (has links)
L’introduction du développement durable apporte de nouvelles préoccupations environnementales au niveau de la construction et de la rénovation résidentielles, une industrie qui représente un marché économique important au Canada. En plus d’engendrer plusieurs impacts sur l’environnement, la conception actuelle ne permet pas d’accommoder le changement initié par l’évolution des pratiques, les avancées technologiques, mais également par l’évolution des patrons de vie des occupants. Dans un premier temps, la revue de littérature dresse le portrait de l’industrie de la construction, rénovation et démolition (CRD) au Canada, ainsi que le profil de gestion des débris de CRD. Ensuite, une analyse documentaire traite de différents outils de conception développés pour améliorer la performance du secteur : 3RV-E, écoconception, écoconstruction et LEED®. De plus, la recension des écrits permet également de cerner les concepts d’adaptabilité et de flexibilité au niveau du bâtiment et dans les approches et mouvements émergents en architecture. Cette démarche nous amène à établir l’hypothèse que l’intégration des critères d’adaptabilité et de flexibilité au niveau du logement aurait pour effet d’améliorer l’adéquation entre les besoins évolutifs des occupants et les nouvelles considérations environnementales. Au niveau méthodologique, l’analyse du cycle de vie simplifiée par l’Eco-indicator99 encadre l’analyse environnementale de l’ossature de trois types de construction de cloison. De cette évaluation, on conclut que c’est la construction traditionnelle à ossature de bois qui produit le moins d’impacts. Dans l’ordre suivant la proposition de construction de cloison à ossature d’aluminium, plus adaptable et flexible, et finalement la construction à ossature d’acier qui est le système le plus dommageable. Par contre, en intégrant le facteur temporel, cette analyse démontre que l’intégration de l’adaptabilité et de la flexibilité procure plusieurs cycles de vie et de rénovation au produit et à ses composantes. Finalement, ces concepts offrent également le potentiel de diminuer les impacts générés par la construction et la rénovation, un constat qui mériterait d’être abordé dans une approche plus systémique. / The introduction of sustainable development brings new environmental concerns on an important Canadian market industry: construction and residential renovation. Not only does the current concept have a considerable impact on the environment, it also can’t follow up with the development of practices, technologies and occupants’ lifestyle. First, a literature review draws a picture of the construction, renovation and demolition industry (CRD) in Canada and it outlines the CRD rubbles management profile. Then a documentary analysis drafts different concept tools that were developed to improve the industry’s performance. They are 3RV-E, ecodesign, sustainable construction and LEED®. The papers review also explores the adaptability and flexibility concepts on the construction sector and on the emerging architectural trend. This approach brings us to the hypothesis that the integration of the adaptability and flexibility criteria to the housing sector will improve the adequacy between the progressive needs of the occupants and the new environmental issues. On a methodological perspective, the simplified lifecycle analysis performed with the Eco-indicator99 overviews the environmental analysis of three types of partition construction. The outcome of this evaluation is that the one with the less environmental impact is the traditional construction with a wooden framework, followed by the construction with an aluminum framework which is adaptable and flexible, and in third place, the construction with a steel framework which is the most harmful to the environment. On the other hand, adding the time factor to this analysis demonstrates that the integration of the adaptability and flexibility criteria brings a number of renovation and life cycles to the product and its components. In the end, these concepts present us with a potential of reducing the impacts of construction and renovation on the environment and that’s an assessment that would need to be approached systematically.
112

[en] ANALYSIS OF EXISTING BUILDINGS IN RIO DE JANEIRO WITH APPLICATION OF CERTIFICATION FOR SUSTAINABILITY / [pt] ANÁLISE DE EDIFÍCIOS DE APARTAMENTOS EXISTENTES NO RIO DE JANEIRO COM APLICAÇÃO DE CERTIFICAÇÃO PARA SUSTENTABILIDADE

MARINA DO REGO MONTEIRO F BACELLAR 21 May 2018 (has links)
[pt] O conceito da construção sustentável surge após discussões por todo o mundo acerca da possibilidade de desenvolvimento de forma sustentável. Paralelamente à adoção de práticas de sustentabilidade em novos projetos de empreendimentos, surge a necessidade de tornar sustentáveis edificações já existentes. Com isto, observa-se a dificuldade de se encontrar critérios de sustentabilidade para construções existentes aplicáveis no cenário brasileiro. O presente estudo desenvolve-se com uma inicial introdução dos principais certificados, selos e qualificações sustentáveis existentes no Brasil. Na sequência elaborados estudos de caso em duas edificações de diferentes características - ano de construção, bairros, entre outros - na cidade do Rio de Janeiro, nos quais foram analisados e aplicados os critérios de avaliação que constituem o Selo Casa Azul criado a adotado pela CAIXA. Como último passo indicados os obstáculos que cada edificação apresentou para atingir melhores resultados de acordo com o Selo. / [en] The study of the main certifications, seals and qualifications applied in Brazil and in the world reveals the advantages of these certificates for buildings that seek to encourage the practice of sustainability in the city of Rio de Janeiro. Over the next two decades there has been an impasse between developed countries and those who advocated environmental preservation, since the former believed in capitalist economic development only by changing raw materials. Finally, in the 1980s the term sustainable development was created, whose definition consisted in the defense of a development able to meet current needs without harming the possibility of future generations to meet their own needs. Due to this growing concern with the environment, the construction sector needed to adapt to new requirements, changing methods and creating means to control and supervise sustainable practices, through environmental certificates such as LEED, AQUA-HQE, Selo Casa Azul and Qualification Qualiverde.
113

Le système binaire aluminium-iridium, du diagramme de phases aux surfaces atomiques / The Al-Ir binary system, from the phase diagram to atomic surfaces

Kadok, Joris 16 November 2016 (has links)
Un alliage métallique complexe (CMA) est un composé intermétallique dont la maille élémentaire est constituée d’un nombre important d’atomes formant bien souvent des aggrégats de haute symmétrie. De la complexité de ces composés peuvent découler des propriétés physico-chimiques intéressantes pour divers domaines d’application. Le système binaire aluminium-iridium est un système qui présente de nombreux composés intermétalliques dont la moitié sont des CMA. Malgré l’étude approfondie dont ce système a fait l’objet dans la littérature, certaines incertitudes demeuraient irrésolues, nous amenant ainsi à réexaminer le diagramme de phase Al-Ir. Nous avons également exploré les systèmes ternaires dits "push-pull" Al-Au-Ir et Al-Ag-Ir, propices à la formation de phases CMA selon certains auteurs. Au total, une centaine d’échantillons ont été préparés par fusion à l’arc puis analysés par diverses techniques de caractérisations: diffraction des rayons X (XRD), microscopie électronique à balayage (SEM), analyse dispersive en énergie (EDS) et analyse thermique différentielle (DTA). Quatre nouveaux composés intermétalliques ont ainsi été identifiés: Al2.4Ir, Al72Au2.5Ir29.5, Al3AuIr et Al11SiIr6, ce dernier étant issu d’une manipulation accidentelle. La structure cristallographique de chacun de ces composés a été résolue, révélant Al2.4Ir et Al72Au2.5Ir29.5 comme étant des CMA possédant une centaine d’atomes dans la maille. Des calculs basés sur la théorie de la fonctionnelle de la densité (DFT) sont venus apporter des précisions concernant la stabilité des composés Al3AuIr et Al11SiIr6. Pour le système Al-Ir, une variante structurale de deux CMA déjà connus de la littérature a également pu être mise en évidence. Les structures cristallographiques de la variante de Al2.75Ir et de celle de Al28Ir9 ont ainsi été approchées, présentant 240 et 444 atomes dans leur maille respective. Les propriétés de surface comptent parmi les aspects les plus intéressants des CMA, par exemple pour la catalyse hétérogène. En l’absence de monocristaux de taille macroscopique, nous avons étudié la possibilité de former des composés de surface par dépôt de Ir sur une surface Al(100) suivi de recuits. Des caractérisations par diffraction d’électrons lents (LEED), spectroscopie de photoélectrons excités par rayons X (XPS) et microscopie à effet tunnel (STM) supportés par ces calculs ab initio ont révélé qu’à partir de 320°C, le composé Al9Ir2 se formait en surface mais également dans une partie du volume du substrat / A complex metallic alloy (CMA) is an intermetallic compound whose unit cell contains a large number of atoms oftenly forming highly-symmetric clusters. From the complexity of these compounds can arise physical and chemical properties interesting for various fields of application. The aluminium-iridium binary system exhibits numerous intermetallic compounds of which half of them are actually CMAs. Despite this system being extensively studied in the literature, some uncertainies remained unsolved, leading us to reinvestigate the Al-Ir phase diagram. In addition, the "push-pull" systems Al-Au-Ir and Al-Ag-Ir, favorable for the formation of CMA according to the literature, have been explored. Thus, near a hundred of samples have been prepared by arc-melting before being analyzed with different characterizations techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and differential thermal analysis (DTA). From this study, 4 new intermetallic compounds could be identified: Al2.4Ir, Al72Au2.5Ir29.5, Al3AuIr and Al11SiIr6, the latter being the result of a fortuitous manipulation. The crystallographic structure of each of these compounds has been solved, revealing Al2.4Ir and Al72Au2.5Ir29.5 to be two CMAs with around one hundred of atoms in their unit cell. Calculations based on the density functional theory (DFT) brought further details about the stability of the two other Al3AuIr and Al11SiIr6 compounds. In the Al-Ir binary system, a structural variant of two well-known CMAs has been also unveiled. The crystallographic structures of the Al2.75Ir and Al28Ir9 variant have been approached, revealing 240 and 444 atoms in their respective unit cell. The CMAs oftently exhibit interesting surface properties. In order to study the Al-Ir compound surfaces, iridium adsorption on Al(100) surface followed by annealing has been investigated. The characterizations by lowenergy electrons diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling miscoscopy (STM) supported by ab initio calculations revealed that, from 320 C, the Al9Ir2 compound is formed at the surface but also in the substrate bulk
114

Ferramenta de apoio ao desenvolvimento de projetos no âmbito da sustentabilidade na construção / Support tool for design process in the context of sustainable construction

Daniel Costa Reis 14 July 2015 (has links)
A indústria da construção, nomeadamente no setor da edificação, baseia-se essencialmente em métodos de construção tradicional. Esta indústria é caracterizada pela elevada quantidade de recursos que consome, pela quantidade de resíduos que produz, a sua implicação na economia dos países e à sua inter-relação com a sociedade. Esta realidade é de todo incompatível com os desígnios do desenvolvimento sustentável, nos quais se procura a correlação harmoniosa entre as vertentes ambientais, sociais e econômicas. O desafio da sustentabilidade colocado à atividade da construção tem motivado abordagens distintas, não só por parte das várias especialidades da engenharia, como também da arquitetura. Neste sentido, o presente trabalho propôs-se a desenvolver uma Ferramenta que, de uma forma coordenada e integrada permita orientar o desenvolvimento do projeto para soluções sustentáveis ao longo das várias fases do ciclo de evolução de um projeto. Foi desenvolvida recorrendo a uma pesquisa bibliográfica sobre o tema da gestão de projetos e sobre o sistema de certificação de sustentabilidade Leadership in Energy and Environmental Design (LEED). Para além disto, foram ainda incorporados alguns requisitos normativos, obtidos por meio de normas brasileiras ABNT, normas Americanas e normas Europeias. Pensa-se que da adequada aplicação desta ferramenta, os objetivos definidos pelo promotor da obra em termos de sustentabilidade, poderão ser mais facilmente atingidos pela equipa de projetista através da consideração antecipada de medidas e soluções de sustentabilidade nas diferentes fases de desenvolvimento do projeto permitindo assim, um melhor desempenho do edifício ao nível da construção sustentável. / The construction industry, particularly in the building sector, is based mainly on traditional construction methods. This industry is characterized by excessive consumption of resources, the amount of waste it produces, its implication in the economy of countries and their relationship with society. This reality is entirely incompatible with the aims of sustainable development, which seeks a harmonious relationship between the environmental, social and economic aspects. The sustainability challenge faced by the construction activity has motivated different approaches, not only by the various engineering specialties, but also by the architecture. In this sense, this paper aimed to develop a model in a coordinated and integrated manner to guide the development of the project to sustainable solutions throughout the various stages of the project life cycle. It was developed using a literature review about the topic of project management and sustainability assessment tool Leadership in Energy and Environmental Design (LEED). Furthermore, and to improve the effectiveness of the Model, it was been incorporated some standardisation requirements, obtained by Brazilian standards ABNT, American standards and European standards. Through proper application of this tool, the goals set by Owner of the work, in terms of sustainability, can be more easily achieved by the project design team through timely consideration of measures and sustainability solutions at different stages of project development. Allowing a better performance of the building in terms of the sustainable construction.
115

Investigation of diffusion and solid state reactions on the nanoscale in silicon based systems of high industrial potential : experiments and simulations

Parditka, Bence 18 December 2013 (has links)
La première partie de mes résultats concerne les phénomènes de diffusion induits par des effets de contrainte. Nous avons étudié ces effets d’un point de vu théorique, afin de comprendre le rôle de la contrainte dans la diffusion. Les résultats montrent que l’effet de contrainte ne semble pas induire d’effet mesurable sur le coefficient cinétique à l’interface, cependant le taux de mélange semble diminuer. La seconde partie concerne des mesures expérimentales, par EXAFS et GIXRF utilisées sur des empilements Ta/a-Si/Ni/a-Si/Ta/substrat permettant de suivre la formation des phases ainsi que la croissance, à une température donnée, et ce jusqu’à la formation de la phase Ni2Si et au delà. La troisième partie concerne le système Cu-Si. Nous avons suivi les premiers stades de la formation de la phase Cu3Si, en utilisant les techniques XRD, APT, SNMS, ainsi qu’un profilomètre et une mesure de résistance quatre points sur différents échantillons réalisés par pulvérisation. Dans le cas de l’empilement Cu/a-Si/substrat, la formation de phases a suivi une cinétique linéaire. Nous avons notamment mis en évidence la formation très rapide d’une phase qui apparait directement après le premier recuit très court, démontrant ainsi le rôle déterminant de la préparation des échantillons dans l’étude des processus de formation de phases. La quatrième partie s’intéresse au silicène : cette structure bidimensionnelle de silicium dite en « nid d’abeilles », réalisée sur un substrat d’argent et qui présente de grandes similitudes avec le graphène. En utilisant de façon complémentaire les techniques AES-LEED-STM, nous avons déterminé la limite de solubilité du silicium dans l’argent. / Diffusion and related solid state reaction phenomena have been studied in four different material couples. The first section of the results concerned the diffusion related stress effects. We analyzed the question theoretically, for planar model geometry, to find the role of stress in diffusion. We obtained that stress effects do not have any measurable effects on the kinetic coefficient of the interface shift. However, the intermixing rate decreases. The second section we performed EXAFS and GIXRF experiments on sandwich structured Ta/a- Si/Ni/a-Si/Ta/substrate samples and followed the phase formation and growth at a given temperature at which the Ni2Si phase has formed and continued to grow. The third section we obtained in the Cu-Si system. We followed the early stages of phase formation of the Cu3Si phase under different circumstances. We performed XRD, APT, SNMS, profilometer and 4 wire resistance measurements on sputtering deposited samples. We found that in case of the Cu/a-Si/substrate samples the phase formation was followed by a linear kinetics. Secondly, prior to the linear phase growth, we observed an extremely fast phase formation that appeared immediately after the very first and shortest annealing, which showed that the preparation sequence of the sample is a crucial point in phase formation processes. The fourth section deals with the silicene. It is the honeycomb structured formation of Si atoms with properties similar to graphene. We investigated the dissolution of Si into Ag. We performed a combination of AES, LEED, STM measurements. We determined the dissolution limit of Si in Ag from data obtained from the AES measurements.
116

CHALLENGES WHEN EXECUTING GREEN BUILDING PROJECTS IN SWEDEN : An interview study on project managers’ perceptions / UTMANINGAR I GENOMFÖRANDET AV GRÖNA BYGGPROJEKT I SVERIGE : En intervjustudie om projektledares uppfattningar

Becker, Tove, Gustafsson, Emma January 2020 (has links)
A sustainable development is required within the construction sector, in order to cope with an increasing population in a built environment that already suffers from high energy consumption. Green building certification systems, such as BREEAM and LEED, function as tools to support sustainability of buildings in the design, production, maintenance and operation. In green building projects, green requirements are added to the traditional project scope for the buildings in order to achieve certifications. Green buildings tend to be more complex than traditional buildings without high green requirements. Thereby, challenges can appear in these projects that do not exist within traditional building projects. To date, there is little published research exploring how the green requirements impact the execution of green building projects and what challenges they entail in such projects in the Swedish context. This master thesis examines project managers’ perceptions of the impact of green building certification systems on the execution of building projects in Sweden. Furthermore, the study identifies the main challenges that these project managers perceive within green building projects. In order to achieve the aim of this study, semi-structured interviews have been conducted with professionals with experience from green building projects. From the empirical findings, it could be concluded that the general perception among project managers is that the additional requirements that the certifications imply, do not impact the execution of building projects to a considerable extent. However, project managers within this study perceive deficiencies in the ability of BREEAM and LEED to consider Swedish conditions, which impacts the green aspect in the end product. To be able to carry out green building projects, the traditional way of working has been adapted to a certain extent, where set of activities have been organized differently compared to traditional projects. Moreover, four considerable challenges could be identified that the project managers perceive, which are connected to the high green requirements within green building projects in Sweden: (1) Conflict between green requirements and tenants’ requests/user comfort, (2) Lack of engagement among project members regarding green requirements, (3) Management of materials in building material databases and (4) Heavy administration and documentation. / I avsikt att möta en ökande befolkningsmängd i en bebyggd miljö med redan hög energikonsumtion, krävs en utveckling mot en mer hållbar byggnadssektor. Miljöcertifieringssystem, såsom BREEAM och LEED, används som verktyg för att främja hållbarhet i byggnaders projekterings-, produktions- och förvaltningsskeden. I gröna byggprojekt tillkommer miljökrav till traditionella byggprojekts omfattning för att dessa byggnader ska kunna uppnå miljöcertifieringar. På grund av dessa tillkommande miljökrav tenderar gröna byggnader att vara mer komplexa än traditionella byggnader och som en följd av detta kan utmaningar uppstå som inte förekommer i traditionella byggprojekt. Fram till idag har endast ett begränsat antal forskningsstudier utförda i Sverige påträffats, vilka studerar hur miljökraven påverkar genomförandet av gröna byggprojekt samt de utmaningar som uppstår i dessa projekt. Detta masterexamensarbete undersöker projektledares uppfattningar om miljöcertifieringssystems påverkan vid genomförandet av byggnadsprojekt i Sverige. Vidare syftar denna studie till att identifiera de huvudsakliga utmaningar som dessa projektledare ställs inför i gröna byggprojekt. För att uppfylla syftet av denna studie, har semistrukturerade intervjuer genomförts med yrkesverksamma som innehar erfarenhet av gröna byggprojekt. Från det empiriska resultatet kunde slutsatsen dras att den generella uppfattningen bland projektledare är att de ytterligare krav som certifieringssystemen medför, inte påverkar genomförandet av byggprojekt i någon större utsträckning. Däremot uppfattar projektledarna vissa brister gällande potentialen i BREEAM och LEED att kunna beakta svenska förhållanden, vilket påverkar slutproduktens miljöprestanda. För att kunna genomföra gröna byggprojekt har det traditionella arbetssättet i viss utsträckning anpassats, där olika arbetsprocesser organiserats på andra sätt jämfört med i traditionella byggprojekt. Vidare kunde fyra betydande utmaningar som projektledare i Sverige upplever kopplade till höga miljökrav i gröna byggprojekt identifieras, nämligen: (1) Målkonflikt mellan miljökrav och hyresgästers önskemål/användarkomfort, (2) Avsaknad av engagemang från projektmedlemmar gällande miljökrav, (3) Hantering av byggmaterial i materialdatabaser samt (4) Omfattande administration och dokumentation.
117

Dagvattenåtervinning i byggnader : Analys av effektivitet, kostnad och miljöcertifiering i system inom Norden / Stormwater recycling in buildings : Analysis of efficiency, cost and environmental certification in systems in the Nordic region

Billstein, Tova, Värnqvist, Sara January 2019 (has links)
I samband med kommande klimatförändringar kommer antalet skyfall och perioder av torka att öka i världen vilket i sin tur ställer större krav på städers dagvattenhantering. Ett sätt att förbättra dagvattenhanteringen är att införa vattenåteranvändning i byggnader. Syftet med detta arbete är därför att utreda olika referensobjekt inom Norden som planerar att införa denna sorts teknik, eller som redan etablerat tekniken på marknaden. Arbetet ämnar även att utforska olika driftrelaterade frågor samt utreda vilken teknik som är mest lönsam utifrån faktorerna effektiv återvinning av dagvatten, projektkostnad samt poänggivande möjligheter inom olika miljöcertifieringssystem. För att besvara de formulerade frågeställningarna utfördes fem intervjuer baserat på en semistrukturerad intervjuteknik med individer insatta i de olika referensobjekten. Därutöver granskades ett flertal dokument som införskaffats från de olika företagen, både från intervjuobjekten men även från andra inblandade. En modell i programmeringsprogrammet MATLAB togs fram för att beräkna antalet dagar då det insamlade dagvattnet täcker behovet i byggnaderna övriga beräkningar gjordes i Excel där data inhämtats från SMHI:s hemsida över historisk data. Efter vidare undersökning framkom det att det inom Norden finns fem aktuella projekt varav ett är i projekteringsfasen, ett i byggnadsfasen och tre är i drift. Sergelhuset i Stockholm är det största projektet sett till takyta. Huset försörjer systemet flest antal dagar av året med tillräckligt dagvattenmängd för att täcka upp det dagliga vattenbehovet i byggnaden. Citypassagen i Örebro bedömdes vara minst kostnadseffektivt då projektet hade högst kostnader samtidigt som byggnaden hade minst antal dagvattenförsörjningsdagar. Då information saknas för Skanskas huvudkontor och Humlehuset kunde dessa referensobjekt inte jämföras på likartat sätt. Det framkom även att det vanligaste förekommande miljöcertifieringssystemet var LEED som tillämpats inom både Sergelhuset, Celsius och Skanskas huvudkontor. Samtliga projekt har ambitioner om att nå den högsta nivån, platinum, främst på grund av kommersiella skäl. Citypassagen hade ansökt om Miljöbyggnad och beräknas att certifieras enligt näst högsta nivån - Silver. / Due to future climate change, the number of downpours and periods of drought will increase which in turn will put greater demands on urban stormwater management. One way to improve stormwater management is to implement water recycling in buildings. The purpose of this essay is therefore to investigate projects in the Nordic region who are planning to implement this kind of technology or already have implemented it. The essay also aims to explore various connected operational issues and see which technology is most profitable based on the factors; efficient stormwater recycling, project cost and the possibility to give points in different environmental certification systems. In order to fulfil the purpose of the essay, five interviews were conducted based on a semi-structured interview technique with individuals familiar with the projects. In addition, several documents collected from the same individuals and others involved were also examined. A model in the programming software MATLAB was generated to enable calculation of the number of days the buildings were able to provide the storm water system with a volume of rainwater large enough to cover the daily need. Other calculations were performed in Excel where data over downpour has been obtained from SMHI’s website over historical data. Only five current projects could be found within the Nordic region, one of which is in the planning phase, one in the construction phase and three are in operation. Sergelhuset in Stockholm is the largest project based to roof area. The building provides the stormwater system with rainwater large enough to cover the water requirement during the highest number of days. Citypassagen in Örebro was the least cost-effective since the project had the highest costs while at the same time it had the least number of water supply days, only 69 days of the year the system was provided only with rainwater. Skanska's head office and Humlehuset were not included in the comparison since essential information was missing. It also emerged that the most common environmental certification system was LEED, which was used in both Sergelhuset, Celsius and Skanska's head office. All projects have ambitions to reach the highest level, platinum, mainly because of commercial reasons. Citypassagen has applied for Miljöbyggnad - level Silver.
118

Croissance et caractérisation de nanostructures de Ge et Si déposées sur des substrats d'oxyde cristallin à forte permittivité LaA1O3

Mortada, Hussein 29 October 2009 (has links) (PDF)
Les mémoires flash non volatiles - utilisées dans les ordinateurs, téléphones portables ou clés USB - peuvent être constituées de nanocristaux semiconducteurs (SC) insérées dans une matrice isolante. Elles nécessitent l'élaboration d'hétérostructures de type "oxyde/SC/oxyde/Si(00l)" et la maîtrise de chaque interface. Dans ce cadre, nous avons étudié les mécanismes de croissance initiale du Si et du Ge (SC) sur des substrats d'oxyde cristallins LaA1O3(001) à forte permittivité (high-k). Les propriétés chimiques et structurales ont été déterminées in-situ par photoémission X (XPS et XPD) et par diffraction d'électrons (RHEED et LEED) puis ex-situ par microscopies en champ proche (AFM) et en transmission (HRTEM). Le substrat LaAlO3(001) propre présente une reconstruction de surface c(2x2) attribuée à des lacunes d'O en surface. Les croissances de Si et Ge ont été réalisées par épitaxie par jet moléculaire (MBE), soit à température ambiante suivies de recuits, soit à haute température. L'épitaxie requiert des températures de dépôt supérieures à 550°C. Le mode de croissance est de type Volmer Weber caractérisé par la formation d'îlots cristallins de dimensions nanométriques et de forte densité. Ces îlots sont relaxés et présentent une interface abrupte avec le substrat. Quant aux îlots de Ge, ils ont majoritairement des orientations aléatoires avec néanmoins une relation d'épitaxie privilégiée, la même que celle du Si.
119

Designing healthy communities: A walkability analysis of LEED-ND

Zuniga-Teran, Adriana A., Orr, Barron J., Gimblett, Randy H., Chalfoun, Nader V., Going, Scott B., Guertin, David P., Marsh, Stuart E. 12 1900 (has links)
Prevailing city design in many countries has created sedentary societies that depend on automobile use. Consequently, architects, urban designers, and land planners have developed new urban design theories, which have been incorporated into the Leadership in Energy and Environmental Design for Neighborhood Development (LEED-ND) certification system. The LEED-ND includes design elements that improve human well-being by facilitating walking and biking, a concept known as walkability. Despite these positive developments, relevant research findings from other fields of study have not been fully integrated into the LEED-ND. According to Zuniga-Teran (2015), relevant walkability research findings from multiple disciplines were organized into a walkability framework (WF) that organizes design elements related to physical activity into nine categories, namely, connectivity, land use, density, traffic safety, surveillance, parking, experience, greenspace, and community. In this study, we analyze walkability in the LEED-ND through the lens of the nine WF categories. Through quantitative and qualitative analyses, we identify gaps and strengths in the LEED-ND and propose potential enhancements to this certification system that reflects what is known about enhancing walkability more comprehensively through neighborhood design analysis. This work seeks to facilitate the translation of research into practice, which can ultimately lead to more active and healthier societies. (C) 2016 The Authors. Production and hosting by Elsevier B.V.
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Surface stress and large-scale self-organization at organic-metal interfaces / Oberflächenspannung und langreichweitige Selbstorganisation an Organik-Metall Grenzflächen

Pollinger, Florian January 2008 (has links) (PDF)
Anhand von Modellsystemen wurde in dieser Arbeit die Bedeutung elastischer Wechselwirkungen an Organik-Metall Grenzflächen, insbesondere für die Selbstorganisierte Ausbildung periodisch facettierter Strukturen, untersucht. Die Änderung der Oberflächenspannung während der Ausbildung der Grenzfläche zwischen 3,4,9,10-Perylentetracarbonsäuredianhydrid (PTCDA) und Ag(111) wurde mit der Biegekristalltechnik gemessen. Es ist bekannt, dass dieses System durch eine chemisorptive Bindung bestimmt wird. In der Tat stimmen Vorzeichen und Bedeckungsabhängigkeit mit Vorhersagen und Experimenten aus der Literatur zu chemisorptiv bestimmten Grenzflächen überein. Während der Einbau von Molekülen in große Domänen die Oberflächenspannung verringert, führt das Auftreten von fehlerhaften Domänengrenzen zu einer Erhöhung der Oberflächenspannung. Die absolute Änderung der Oberflächenspannung in der Höhe von (0.30 +- 0.10) N/m ist in der relativ schwachen Wechselwirkung des PTCDA Moleküls mit einem einzelnen Silberatom begründet. Es soll jedoch betont werden, dass dieser Wert einer Oberflächenspannungsänderung von (2.2 +- 0.2) eV pro Molekül entspricht, die damit in derselben Größenordnung wie die vermutete Bindungsenergie des Systems liegt. Daher zeigen diese Experimente, dass elastische Wechselwirkungen eine nicht zu vernachlässigende Rolle in dieser ganzen Materialklasse spielen können. Dadurch tragen die Experimente eine neue Sichtweise zum Verständnis dieser Grenzflächen bei. Ferner etablieren sie die Biegekristalltechnik auf dem ganzen Feld der Organik-Metall Grenzflächen, da die Ergebnisse in Einklang mit den wohlbekannten Eigenschaften des Systems liegen. Schon der Nachweis einer Durchbiegung der Probe ist speziell für die Grenzfläche PTCDA/Ag(111) von Bedeutung. Dieser Effekt ist der erste experimentelle Nachweis einer strukturellen Änderung in den obersten Substratatomlagen während der Adsorption von PTCDA auf Ag(111). Da eine solche Modifikation nicht zu vernachlässigende Konsequenzen für die Interpretation anderer experimenteller Ergebnisse hat, erscheinen weitere Studien mit anderen, quantitativeren strukturellen Methoden notwendig. Der Schwerpunkt dieser Arbeit lag jedoch auf der Untersuchung der Ausbildung der langreichweitigen, selbstorganisierten Ordnung der facettierten PTCDA/Ag(10 8 7) Grenzfläche. Der reziproke Raum dieser Grenzfläche wurde sowohl mit mittelnder hochauflösender Elektronenbeugung (SPA-LEED) als auch mit lokaler Elektronenbeugung in der Mikroskopie niederenergetischer Elektronen (LEEM) kartiert. Außerdem wurden diese reziproken Daten durch mikroskopische LEEM Realraumdaten komplementär ergänzt um die Morphologie der Grenzfläche zu charakterisieren. Für die gewählte Präparationsart, Adsorption der Moleküle auf das 550 K warme Substrat, wurden sechs verschiedene Facettentypen ((111), (532), (743),(954), (13 9 5) und (542)) beobachtet. Diese Facettentypen treten in homogenen, mikrometergroßen Gebieten auf der Oberfläche auf, wie Dunkelfeld-LEEM Aufnahmen zeigen. Wenn jedoch die ursprüngliche mesoskopische Orientierung der Oberfläche lokal von der Durchschnittsorientierung z.B. in Bezug auf die ursprüngliche Stufendichte abweicht, werden an dieser Stelle andere Facettentypen gebildet und damit das ansonsten regelmäßige Muster gestört. Sowohl der Grad der erreichten Ordnung der facettierten Grenzfläche als auch die gebildeten Facettentypen hängen somit stark von der ursprünglichen mesoskopischen Morphologie des sauberen Substrates ab. Um das Verständnis der kinetischen Prozesse zu verbessern wurde die Temperaturabhängigkeit der Ausbildung der Grenzfläche in einem Temperaturbereich zwischen 418 K und 612 K untersucht. Bei niedrigen Wachstumstemperaturen traten zusätzliche, steilere Facetten mit einem Neigungswinkel von 27° gegenüber der (111) Fläche auf. Weiterhin wurde mit facetten-sensitivem Dunkelfeld-LEEM die Größen- sowie die räumliche Verteilung ausgewählter Facettentypen bei den verschiedenen Temperaturen untersucht. Die Nukleationsdichte der Facetten zeigte dabei keine Temperaturabhängigkeit. Eine Diffusionslimitierung der Nukleation kann daher ausgeschlossen werden. Darüber hinaus wurden die Ausmaße der Facetten statistisch ausgewertet. Die absolute Facettengröße folgt einer exponentiellen Verteilung, was auf ein zufallsgetriebenes Wachstum und das Fehlen einer Wechselwirkung der Facetten untereinander hinweist. Während die Facettenlängen ebenso einer exponentiellen Verteilung unterliegen, ist die Breitenverteilung durch ein Maximum ausgezeichnet. Letztere Verteilung spiegelt den hohen Grad an lateraler Ordnung in dem System wieder. Diese Anisotropie hängt von der Temperatur ab und kann bei Substrattemperaturen über 478 K während des Wachstums beobachtet werden. Die Existenz eines Maximums in einer solchen Größenverteilung weist auf eine langreichweitige Wechselwirkung hin, die die strukturelle Ordnung induziert. Die Natur dieser langreichweitigen Wechselwirkung wurde mit drei komplementären in-situ Methoden untersucht, wobei jeweils neue Einblicke in die Ausbildung von facettierten Organik-Metall-Grenzflächen gewonnen werden konnten: Die Biegekristalltechnik, hochauflösende Beugung niederenergetischer Elektronen (SPALEED), sowie deren Mikroskopie (LEEM). Die Biegekristalltechnik wurde das erste Mal überhaupt auf ein facettierendes System angewendet. Unterhalb der kritischen Temperatur des Facettierungsüberganges ähnelt die Oberflächenspannungsänderung während der Bildung der PTCDA/Ag(10 8 7)-Grenzflächenbildung sowohl in funktionaler Abhängigkeit als auch in der Größenordnung der für die Referenzgrenzfläche PTCDA/Ag(111) beobachteten. Oberhalb der Übergangstemperatur beobachtet man jedoch für die ausfacettierte PTCDA/Ag(10 8 7) Grenzfläche mit (0.67 +- 0.10) N/m eine bedeutend größere Oberflächenspannungsänderung als in den vorherigen Fällen. Zudem ändert sich die Oberflächenspannung in klar unterscheidbaren Schritten mit einer eindeutig auflösbaren Feinstruktur aus positiven und negativen Spannungsänderungen. Diese einzelnen Phasen in der Änderung der Oberflächenspannung können Stufen in der Entwicklung der Strukturüberganges dieses Systems zugeordnet werden, die mit den strukturellen Charakterisierungsmethoden beobachtet wurden. Durch diese Identifikation werden morphologischen Objekten, also den Facetten, ein eigener besonderer Spannungscharakter zugeordnet. Somit werden aber auch Spannungsdomänen auf der Oberfläche identifiziert. Die Existenz dieser Spannungsdomänen ist nun aber die Vorraussetzung für die Anwendung von elastizitätsbasierten Kontinuumsbeschreibungen des Selbstordnungseffektes. Daher stellen diese Ergebnisse den ersten experimentellen Nachweis dar, dass diese Kontinuumsbeschreibungen der Selbstorganisation tatsächlich auch auf die gesamte Materialklasse der facettierenden Organik-Metall-Grenzflächen angewendet werden können. Zusammengefasst sind diese Ergebnisse starke Beweise dafür, dass elastische Wechselwirkungen der physikalische Ursprung der langreichweitigen Ordnung dieses Systems sind. Weiterhin legt die eindeutige Korrelation zwischen strukturellem Phasenübergang und Oberflächenspannungsänderung auch nahe, dass letzterer ebenso eine wichtige Rolle in der Kinetik des Systems spielt. Tatsächlich scheint das System zu versuchen die Gesamtänderung der Oberflächenspannung während der Grenzflächenbildung durch die Bildung von Facettentypen positiven und negativen Charakters zu begrenzen. Daher könnte die Art ihres Beitrags zur Oberflächenspannungsänderung darüber entscheiden, ob eine bestimmte Facettenorientierung gebildet wird oder nicht. Auch scheint das System sich bei hohen Bedeckungen unter anderem deshalb erneut umzufacettieren um der Bildung von fehlerhaften Domänengrenzen entgegenzuwirken, die mit einem Anstieg der Oberflächenspannung verbunden wären. Schließlich wurde im Rahmen dieser Arbeit noch das templatunterstützte Wachstum lateraler, heteroorganischer Nanostrukturen untersucht. Dabei wurde ein zweites, typisches molekulares Modellsystem, sogenannte "Selbstassemblierte Monolagen", auf der teilbedeckten PTCDA/Ag(10 8 7) Grenzfläche aufgewachsen. Mit Standardmethoden der Oberflächencharakterisierung konnte nachgewiesen werden, dass die grundlegenden Eigenschaften dieses Wachstumsprinzips im Experiment in der Tat erreicht werden. / The role of elastic interactions, particularly for the self-organized formation of periodically faceted interfaces, was investigated in this thesis for archetype organic-metal interfaces. The cantilever bending technique was applied to study the change of surface stress upon formation of the interface between 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and Ag(111). This system is known to form a chemisorptive bonding. Indeed, the sign and the coverage-dependence of the surface stress change are in agreement to models and previous measurements of chemisorptive systems in literature. While the adsorption of molecules into the large domains is associated with a negative, i.e. compressive stress change, the formation of domain boundaries in the molecular layer induces a stress change of opposite sign, increasing the surface stress. The magnitude of the surface stress change of (-0.30 +- 0.10} N/m reflects a relatively weak binding of a PTCDA molecule to each individual single silver atom. It is emphasized, however, that if normalized to the surface stress change per molecule, this value corresponds to a stress change of (-2.2 +- 0.2) eV per molecule which is in the order of the suspected binding energy of this system. Therefore, these experiments reveal elastic interactions to be of significant order of magnitude for this system class. Thereby, they add a new point of view to the understanding of these interfaces. Besides, since the results are in agreement with the well-known properties of this interface, they establish the cantilever bending technique in the field of organic-metal interfaces. The mere existence of a bending of the sample implies an interesting detail for the PTCDA/Ag(111) interface in particular. It is the first experimental evidence for a structural change in the topmost substrate layers upon adsorption of PTCDA on Ag(111). Since such a modification has significant implications for the interpretation of other experimental results, a further investigation with more quantitative structural methods appears necessary. The main focus of this work, however, was on the investigation of the formation of the long-range ordered, self-organized faceted PTCDA/Ag(10 8 7) interface. Reciprocal space maps of this interface were recorded both by spot profile analysis low energy electron diffraction (SPA-LEED) and low energy electron microscopy (LEEM) in selected area LEED mode. Complementary to the reciprocal data, also microscopic real-space LEEM data were used to characterize the morphology of this interface. Six different facet faces ((111), (532), (743), (954), (13 9 5), and (542)) were observed for the preparation path of molecular adsorption on the substrate kept at 550 K. Facet-sensitive dark-field LEEM localized these facets to grow in homogeneous areas of microscopic extensions. If the pristine mesoscopic orientation locally deviates from the average orientation, e.g. in pristine step density, locally different facet types are formed, distorting the otherwise regular mesoscopic pattern. Hence, the original mesoscopic orientation of the substrate strongly determines the degree of order of the faceted surface and the facet species formed. The temperature-dependence of the interface formation was studied in a range between 418 K and 612 K in order to learn more about the kinetics of the process. Additional steeper facets of 27° inclination with respect to the (111) surface were observed in the low temperature regime. Furthermore, using facet-sensitive dark-field LEEM, spatial and size distributions of specific facets were studied for the different temperatures. The nucleation density of the facets did not depend on temperature and can therefore be concluded not to be limited by diffusion. Moreover, the facet dimensions were statistically analyzed. The total island size of the facets follows an exponential distribution, indicating a random growth mode in absence of any mutual facet interactions. While the length distribution of the facets also follows an exponential distribution, the width distribution is peaked, reflecting the high degree of lateral order. This anisotropy is temperature-dependent and occurs starting above 478 K substrate temperature during growth. The peaked distribution indicates the presence of a long-range interaction which leads to the structural order of the self-organized grating. The origin of this long-range interaction was investigated combining three complementary in-situ methods, all providing new insights into the formation of faceted organic-metal interfaces: the cantilever bending technique, high-resolution low energy electron diffraction (SPA-LEED), and microscopy (LEEM). The cantilever bending technique was applied for the first time to a faceting system at all. Below the faceting transition temperature the surface stress change associated with the formation of the PTCDA/Ag(10 8 7) interface resembles in shape and magnitude the one observed for the reference interface PTCDA/Ag(111). But above the transition temperature the absolute surface stress change of (-0.67 +- 0.10) N/m observed for the faceted PTCDA/Ag(10 8 7) interface is considerably larger than for the previous cases. Moreover, the stress change happens in distinguishable stages with a clearly resolvable fine structure of regimes of positive and negative stress changes. These different regimes of surface stress change can be correlated to different stages of the structural phase transition observed by the structural in-situ methods. Thereby, morphological objects (i.e. the facets) are assigned to a specific stress character. Thus, domains of different stress character can be identified on the surface. These stress domains are the prerequisite to apply continuum descriptions of the self-ordering process based on elastic interactions. Hence, the results are the first experimental verification that these continuum descriptions are indeed also applicable to the whole system class of faceting organic-metal interfaces. In conclusion, the results provide strong evidence for elastic interactions being the physical origin of long-range order for this system. In addition, the clear correlation of structural phase transition and surface stress change regimes suggests surface stress to play also an important role for the kinetics of the system. Indeed, the system seems to try to limit the overall stress change during the interface formation by forming facets of positive and negative stress character. Hence, the selection of specific facets could depend on the corresponding stress character. Furthermore, the system seems willing to re-facet at high coverages in order to prevent imperfect domain boundaries which are associated with an increase of surface stress. Finally, template-assisted growth of lateral, heterorganic nanostructures has been explored. Therefore, self-assembled monolayers as a second archetype class of molecules were grown on partially covered PTCDA/Ag(10 8 7) interfaces. Indeed, using standard surface science techniques, the basic principle of this growth scheme was confirmed to be successful.

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