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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.
421

Efetividade de corte das pontas do sistema CVDentUS : estudo in vitro /

Lima, Luciana Monti. January 2003 (has links)
Orientador: Lourdes Aparecida Martins dos Santos-Pinto / Banca: Evaldo José Corat / Banca: Celso Luiz de Angelis Porto / Resumo: A tecnologia CVD (Chemical Vapor Deposition) aplicada à confecção de pontas odontológicas diamantadas possibilitou aderência do diamante à haste metálica suficiente para suportar o efeito do ultra-som, surgindo então uma técnica alternativa para corte de tecido dentário. O objetivo deste estudo in vitro foi avaliar a efetividade dos corte realizados com as pontas CVD cilíndrica e esférica para ultra-som (pontas CVDentUSÒ), em esmalte e dentina de dentes permanentes, variando-se o sentido de movimento (frontal e lateral). Foram utilizados 40 terceiros molares, num total de 80 preparos cavitários confeccionados por meio de um dispositivo padronizador. Os cortes foram realizados com 30 movimentos consecutivos da ponta sobre a superfície dentária, correspondendo a 27 segundos de utilização das pontas CVDentUSÒ. A profundidade e largura dos preparos cavitários foram analisadas em microscopia eletrônica de varredura e medidas por meio de uma análise cefalométrica modificada no programa Radiocef 4.0 (Radiocef Memory Ltda). A análise estatística pelo teste não paramétrico de Kruskal-Wallis ao nível de significância de 5% mostrou que as maiores médias de largura e profundidade foram observadas nos preparos de dentina, sendo a ponta esférica responsável por cavidades mais profundas e a cilíndrica por cavidades mais largas, não havendo influência dos sentidos de movimento da ponta. / Abstract: The CVD (Chemical Vapor Deposition) technology applied in dental diamond burs manufacture allowed to the diamond to have enough adherence to the metallic stem supporting the ultrasound effect. This technique is bringing back an alternative method to cut dental tissue. The aim of this in vitro study was to evaluate the cutting effectiveness of cylindrical and round CVD-coated diamond burs for ultrasound (CVDentUSÒ system), in enamel and dentine of permanent teeth, changing the movement sense (frontal and lateral). Forty third molars were used, in a total of 80 cavity preparations made using a standard device. The cuts were made with 30 consecutive movements of the bur on the dental surface, corresponding to 27 seconds of CVDentUSÒ tips use. The depth and width of the cavity preparations were analyzed by scanning electronic microscopy and the measures were made using a modified cefalometric analysis in a Radiocef 4.0 program (Radiocef Memory Ltda). The statistical analysis applying Kruskal-Wallis non-parametric test, at 5% significance level, showed that the largest width and depth averages were observed in dentine cavities, being the round bur responsible for deeper cavities and the cylindrical for wider cavities. The movement senses had no influence on cavity size. / Mestre
422

Contribuição para a sintese de diamante nanocristalino com dopagem de boro / Contribution towards the synthesis of boron doped nanocrystalline diamonds

Manne, Gustavo Andre Mogrão 10 October 2008 (has links)
Orientadores: Vitor Baranauskas, Alfredo Carlos Peterlevitz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T10:56:53Z (GMT). No. of bitstreams: 1 Manne_GustavoAndreMograo_M.pdf: 4900447 bytes, checksum: 96ac39c8d4903a68da74c3db411b33b1 (MD5) Previous issue date: 2008 / Resumo: Esta tese apresenta um estudo do crescimento e caracterização do diamante nanocristalino crescido por deposição química a partir da fase vapor (diamante CVD), com a introdução de boro durante o crescimento. Nosso objetivo foi de produzir amostras com boas propriedades para emissão de elétrons para o vácuo por efeito do campo elétrico (FEE). As amostras foram caracterizadas por Microscopia Eletrônica de Varredura de Emissão por Campo (FESEM), micro-espectroscopia Raman e emissão de elétrons por campo elétrico. Os resultados destas caracterizações são apresentados e discutidos. / Abstract: This thesis presents a study of the growth and characterization of nano crystalline diamonds produced by the hot-filament chemical vapor deposition (CVD) with the introduction of boron during the growth process. Our objective was to produce samples with good electrical properties for field induced emission of electrons (FEE) to the vacuum. Characterization of the samples by electron microscopy, Raman micro-spectroscopy, and Field Emission measurements are presented and discussed. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica
423

Filament carburization during the hot-wire chemical vapour deposition of carbon nanotubes

Oliphant, Clive Justin January 2008 (has links)
Magister Scientiae - MSc / This study reports on the changes in the structural properties of a tungsten-filament when exposed to a methane / hydrogen ambient for different durations at various filament-temperatures. / South Africa
424

Growth And Characterization of Si-Ge-Sn Semiconductor Thin Films using a Simplified PECVD Reactor

January 2020 (has links)
abstract: The realization of Silicon based photonic devices will enable much faster data transmission than is possible today using the current electronics based devices. Group IV alloys germanium tin (GeSn) and silicon germanium tin (SiGeSn) have the potential to form an direct bandgap material and thus, they are promising candidates to develop a Si compatible light source and advance the field of silicon photonics. However, the growth of the alloys is challenging as it requires low temperature growth and proper strain management in the films during growth to prevent tin segregation. In order to satisfy these criteria, various research groups have developed novel chemical vapor deposition (CVD) reactors to deposit the films. While these reactors have been highly successful in depositing high crystal quality high Sn concentration films, they are generally expensive set-ups which utilize several turbomolecular/cryogenic pumps and/or load-lock systems. An more economical process than the state-of-the art to grow group IV materials will be highly valuable. Thus, the work presented in this dissertation was focused on deposition of group IV semiconductor thin films using simplified plasma enhanced CVD (PECVD) reactors. Two different in-house assembled PECVD reactor systems, namely Reactor No. 1 and 2, were utilized to deposit Ge, GeSn and SiGeSn thin films. PECVD technique was used as plasma assistance allows for potentially depositing the films at growth temperatures lower than those of conventional CVD. Germane (GeH4) and Digermane (Ge2H6) were used as the Ge precursor while Disilane (Si2H6) and tin chloride (SnCl4) were used as the precursors for Si and Sn respectively. The growth conditions such as growth temperature, precursor flow rates, precursor partial pressures, and chamber pressure were varied in a wide range to optimize the growth conditions for the films. Polycrystalline Ge films and SiGeSn films with an Sn content upto 8% were deposited using Reactor No. 1 and 2. Development of epitaxial Ge buffers and GeSn films was accomplished using a modified Reactor No. 2 at temperatures <400oC without the aid of ultra-high vacuum conditions or a high temperature substrate pre-deposition bake thereby leading to a low economic and thermal budget for the deposition process. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020
425

Achieving controllable continuous variable damping within a semi-active hydro-pneumatic suspension system

De Wet, Benjamin January 2020 (has links)
The compromise between ride comfort and handling for a passive suspension system is a well-known and often researched problem. Semi-active suspension systems offer significant improvements to this compromise. One example of a semi-active system, that can change both spring and damper characteristics between two discrete values is the 4-state semi-active hydro-pneumatic suspension system. This system can switch between a ”ride comfort mode” (soft spring and low damping) and a ”handling mode” (stiff spring and high damping) within 100ms, improving both ride comfort and handling. The discrete 4S4 could be improved upon further by adding continuous variable damping. Work on this topic showed great promise but also posed its challenges in achieving this in a safe and controllable manner. In order to make continuous variable damping a reality a new configuration for the 4S4 is proposed. This new configuration incorporates a blow-off damper in parallel with a proportional flow control valve. The system ensures that, in the highly non-linear closing region of the proportional flow control valve, adequate damping for handling is maintained and uncontrollable peak pressure differences are avoided. Experimental work conducted showed that the system was capable of achieving the required spring and variable damping characteristics in a safe and controllable manner. The experimental data was used for parametrizing and validating a physics based mathematical model of the suspension system. The mathematical model incorporates the: pressure drop vs: flow characteristics for both the blow-off and proportional valves, response time for the on-off valves as well as the gas pressure vs: flow characteristic incorporating the compressibility of the oil and thermal properties of the gas. This model can be used to make informed decisions on further prototype development or in full vehicle simulations. The system makes continuous variable damping possible ranging from the optimal damping characteristic for handling to the low damping characteristic required for ride comfort. The system also shows a significant reduction in friction. / Dissertation (MEng)--University of Pretoria, 2020. / VDG / University of Pretoria / Mechanical and Aeronautical Engineering / MEng / Unrestricted
426

Moderní řezné nástroje ze slinutých karbidů / Modern cutting cemented carbide tools

Vopařil, Josef January 2009 (has links)
This thesis is focused on cutting tools made of cemented carbides. It contains analysis of cemented carbides for uncoated and coated cutting tools. It contains examples of modern tools for turning, milling and drilling. Practical part of this thesis evaluates and compares cutting properties of two types of spiral drills.
427

Moderní řezné nástroje ze slinutých karbidů / Modern cutting cemented carbide tools

Štefek, Jaromír January 2010 (has links)
This thesis deals with modern cutting cemented carbide tools. In the first section are stated several basic innovations already used tools for basic machining operations, which is turning, milling and drilling. It continues with analysis of single materials for production of cemented carbides, non coated as well as coated and with comparing of their properties. There are listed the basic cutting properties of the cutting tools after that. The penultimate point of the work is optimization of the basic machining operations, namely roughing and finishing, for a given application, which is in this case turning on the lamp stand. Finally, everything is summed up and evaluated in the conclusion.
428

Synthese von Übergangsmetallformiaten und deren Verwendung zur Metallisierung

Abylaikhan, Akerke 29 September 2005 (has links)
In der vorliegenden Arbeit werden M(II)-Formiat-Komplexe mit M=Cu, Ni, Zn beschrieben. Das themogravimetrische Verhalten dieser Komplexe wird vorgestellt. TG-MS-Untersuchungen geben erste Hinweise auf das Metallisierungsverhalten obiger Spezies. Die Charakterisierung der entsprechenden Komplexe erfolgte durch die Elementaranalyse, IR-Spektroskopie sowie in einzelnen Fällen durch die Einkristallröntgendiffraktometrie.
429

Thermal deposition approaches for graphene growth over various substrates

Pang, Jinbo 07 March 2017 (has links)
In the course of the PhD thesis large area homogeneous strictly monolayer graphene films were successfully synthesized with chemical vapor deposition over both Cu and Si (with surface oxide) substrates. These synthetic graphene films were characterized with thorough microscopic and spectrometric tools and also in terms of electrical device performance. Graphene growth with a simple chemo thermal route was also explored for understanding the growth mechanisms. The formation of homogeneous graphene film over Cu requires a clean substrate. For this reason, a study has been conducted to determine the extent to which various pre-treatments may be used to clean the substrate. Four type of pre-treatments on Cu substrates are investigated, including wiping with organic solvents, etching with ferric chloride solution, annealing in air for oxidation, and air annealing with post hydrogen reduction. Of all the pretreatments, air oxidation with post hydrogen annealing is found to be most efficient at cleaning surface contaminants and thus allowing for the formation of large area homogeneous strictly monolayer graphene film over Cu substrate. Chemical vapor deposition is the most generally used method for graphene mass production and integration. There is also interest in growing graphene directly from organic molecular adsorbents on a substrate. Few studies exist. These procedures require multiple step reactions, and the graphene quality is limited due to small grain sizes. Therefore, a significantly simple route has been demonstrated. This involves organic solvent molecules adsorbed on a Cu surface, which is then annealed in a hydrogen atmosphere in order to ensure direct formation of graphene on a clean Cu substrate. The influence of temperature, pressure and gas flow rate on the one-step chemo thermal synthesis route has been investigated systematically. The temperature-dependent study provides an insight into the growth kinetics, and supplies thermodynamic information such as the activation energy, Ea, for graphene synthesis from acetone, isopropanol and ethanol. Also, these studies highlight the role of hydrogen radicals for graphene formation. In addition, an improved understanding of the role of hydrogen is also provided in terms of graphene formation from adsorbed organic solvents (e.g., in comparison to conventional thermal chemical vapor deposition). Graphene synthesis with chemical vapor deposition directly over Si wafer with surface oxide (Si/SiOx ) has proven challenging in terms of large area and uniform layer number. The direct growth of graphene over Si/SiO x substrate becomes attractive because it is free of an undesirable transfer procedure, necessity for synthesis over metal substrate, which causes breakage, contamination and time consumption. To obtain homogeneous graphene growth, a local equilibrium chemical environment has been established with a facile confinement CVD approach, inwhich two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises facetted grains despite initially nucleating as round islands. Upon clustering these grains facet to minimize their energy, which leads to faceting in polygonal forms because the system tends to ideally form hexagons (the lowest energy form). This is much like the hexagonal cells in a beehive honeycomb which require the minimum wax. This process also results in a near minimal total grain boundary length per unit area. This fact, along with the high quality of the resultant graphene is reflected in its electrical performance which is highly comparable with graphene formed over other substrates, including Cu. In addition the graphene growth is self-terminating, which enables the wide parameter window for easy control. This chemical vapor deposition approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates which suffer from transfer. Moreover, this growth path shall be applicable for direct synthesis of other two dimensional materials and their Van der Waals hetero-structures.:Contents Quotation v Kurzfassung vii Abstract xi Contents xiii Acronyms xvii 1 Aims and objectives 1 2 Introduction 5 2.1 Carbon allotropes 6 2.1.1 Hybridized sp 2 carbon nanomaterials 6 2.1.2 Graphene 7 2.2 Properties of graphene 8 2.2.1 Crystalline structure 8 2.2.2 Electrical transport 10 2.2.3 Optical transparency 11 2.2.4 Other properties 12 2.3 Graphene deposition methods 13 2.3.1 Synthesis approaches 13 2.3.2 Chemical vapor deposition 14 2.3.3 Substrate selection 15 2.3.4 Substrate pretreatments 16 2.3.5 Carbon feedstock 17 2.3.6 Thermal chemical vapor deposition 17 2.3.7 Plasma chemical vapor deposition 18 2.3.8 Transfer protocol 19 2.4 Chemical vapor deposition for graphene growth 21 2.4.1 Thermodynamics 22 2.4.2 Arrhenius plots 22 2.4.3 Activation energy 24 2.4.4 Growth kinetics 25 2.4.5 Reaction mechanisms over Cu 27 2.4.6 Reaction mechanisms over Ni 29 2.4.7 Reaction mechanisms over non-metals 31 2.4.8 Reaction mechanisms of free-standing graphene 35 2.5 Summary 35 2.6 Scope of the thesis 36 3 Experimental setup and characterization techniques 37 3.1 Experimental setup of chemical vapor deposition 37 3.2 Optical microscopy 39 3.3 Scanning electron microscopy 40 3.4 Atomic force microscopy 41 3.5 Transmission electron microscopy 42 3.5.1 Selected area electron diffraction 44 3.5.2 Dark field transmission electron microscopy 46 3.6 Raman spectroscopy 47 3.7 Ultraviolet-Visible spectrophotometry 49 3.8 Electrical transport measurements 49 4 CVD growth of graphene on oxidized Cu substrates 51 4.1 Motivation 52 4.2 Experimental protocol 53 4.3 Influence of Cu pretreatments on graphene formation 54 4.4 Influence of Cu oxidation on graphene growth 60 4.5 Effect of oxidation pretreatment on Cu surface cleaning 64 4.6 Summary 66 5 Chemo-thermal synthesis of graphene from organic adsorbents 67 5.1 Motivation 67 5.2 Experimental protocol 69 5.3 Influence of reaction temperature on graphene growth 75 5.4 Influence of reaction pressure on graphene growth 78 5.5 Influence of reaction flow rate on graphene growth 80 5.6 Summary 81 6 Monolayer graphene synthesis directly over Si/SiO x 83 6.1 Motivation 83 6.2 Experimental protocol 86 6.3 Influence of substrate confinement configuration 87 6.4 Time dependent evolution for graphene formation 91 6.5 Grain boundaries in graphene film 95 6.6 Bubble clustering of faceted graphene grains 98 6.7 Electrical and optical performance of graphene 100 6.8 Summary 102 7 Conclusions 103 8 Outlook 107 A Graphene synthesis over Cu and transfer to Si/SiO x substrate 111 B Chemo-thermal synthesis of graphene over Cu 115 C CVD graphene growth directly over Si/SiO x substrate 127 Bibliography 147 List of Figures 193 List of Tables 197 Acknowledgements 199 List of publications 203 Erklaerung 205 / Im Zuge dieser Doktorarbeit wurden großflächige und homogene Graphen-Monolagen mittels chemischer Gasphasenabscheidung auf Kupfer- (Cu) und Silizium-(Si) Substraten erfolgreich synthetisiert. Solche monolagigen Graphenschichten wurden mithilfe mikroskopischer und spektrometrischer Methoden gründlich charakterisiert. Außerdem wurde der Wachstumsmechanismus von Graphen anhand eines chemo-thermischen Verfahrens untersucht. Die Bildung von homogenen Graphenschichten auf Cu erfordert eine sehr saubere Substratoberfläche, weshalb verschiedene Substratvorbehandlungen und dessen Einfluss auf die Substratoberfläche angestellt wurden. Vier Vorbehandlungsarten von Cu-Substraten wurden untersucht: Abwischen mit organischen Lösungsmitteln, Atzen mit Eisen-(III)-Chloridlösung, Wärmebehandlung an Luft zur Erzeugung von Cu-Oxiden und Wärmebehandlung an Luft mit anschließender Wasserstoffreduktion. Von diesen Vorbehandlungen ist die zuletzt genannte Methode für die anschließende Abscheidung einer großflächigen Graphen-Mono-lage am effektivsten. Die chemische Gasphasenabscheidung ist die am meisten verwendete Methode zur Massenproduktion von Graphen. Es besteht aber auch Interesse an alternativen Methoden, die Graphen direkt aus organischen, auf einem Substrat adsorbierten Molekülen, synthetisieren konnen. Jedoch gibt es derzeit nur wenige Studien zu derartigen alternativen Methoden. Solche Prozessrouten erfordern mehrstufige Reaktionen, welche wiederrum die Qualität der erzeugten Graphenschicht limitieren, da nur kleine Korngrößen erreicht werden konnen. Daher wurde in dieser Arbeit ein deutlich einfacherer Weg entwickelt. Es handelt sich dabei um ein Verfahren, bei dem auf einer Cu-Substratoberfläche adsorbierte, organische Lösungsmittelmoleküle in einer Wasserstoffatmosphäre geglüht werden, um eine direkte Bildung von Graphen auf einem sauberen Cu-Substrat zu gewahrleisten.Der Einfluss von Temperatur, Druck und Gasfluss auf diesen einstufigen chemothermischen Syntheseweg wurde systematisch untersucht. Die temperaturabhängigen Untersuchungen liefern einen Einblick in die Wachstumskinetik und thermodynamische Größen, wie zum Beispiel die Aktivierungsenergie Ea, für die Synthese von Graphen aus Aceton, Isopropanol oder Ethanol. Diese Studien untersuchen außerdem die Rolle von Wasserstoffradikalen auf die Graphensynthese. Weiterhin wurde ein verbessertes Verständnis der Rolle von Wasserstoff auf die Graphen-synthese aus adsorbierten, organischen Lösungsmitteln erlangt (beispielsweise im Vergleich zur konventionellen thermischen Gasphasenabscheidung). Die direkte Graphensynthese mittels chemischer Gasphasenabscheidung auf Si-Substraten mit einer Oxidschicht (Si/SiOx ) ist extrem anspruchsvoll in Bezug auf die großflächige und einheitliche Abscheidung (Lagenanzahl) von Graphen-Monolagen. Das direkte Wachstum von Graphen auf Si/SiOx -Substrat ist interessant, da es frei von unerwünschten Übertragungsverfahren ist und kein Metall-substrat erfordert, welche die erzeugten Graphenschichten brechen lassen können. Um ein homogenes Graphenwachstum zu erzielen wurde durch den Kontakt zweier Si-Wafer, mit ihren Oxidflachen zueinander zeigend, eine lokale Umgebung im chemischen Gleichgewicht erzeugt. Diese Konfiguration der Si-Wafer ist nötig, um eine einheitliche Graphen-Monolage bilden zu können. Eine gründliche Untersuchung des abgeschiedenen Materials zeigt, dass trotz der anfänglichen Keimbildung von runden Inseln facettierte Körner erzeugt werden. Aufgrund der Bestrebung der Graphenkörner ihre (Oberflächen-) Energie zu minimieren, wird eine Facettierung der Körner in polygonaler Form erzeugt, was darin begründet liegt, dass das System idealerweise eine Anordnung von hexagonal geformten Körnern erzeugen würde (niedrigster Energiezustand). Der Prozess ist vergleichbar mit der sechseckigen Zellstruktur einer Bienenstockwabe, welche ein Minimum an Wachs erfordert. Dieser Prozess führt auch zu einer nahezu minimalen Gesamtkorn-grenzlänge pro Flächeneinheit. Diese Tatsache zusammen mit der hohen Qualität der resultierenden Graphenschicht spiegelt sich auch in dessen elektrischer Leistungsfähigkeit wider, die in hohem Maße mit der auf anderen Substraten gebildeten Graphenschichten (inklusive Cu-Substrate) vergleichbar ist. Darüber hinaus ist das Graphenwachstum selbstabschliessend, wodurch ein großes Parameterfenster für eine einfache und kontrollierte Synthese eröffnet wird. Dieser Ansatz zur chemischen Gasphasenabscheidung von Graphen auf Si- Substraten ist leicht skalierbar und gegenüber der Abscheidung auf Metallsubstraten konkurrenzfähig, da keine Substratübertragung notig ist. Darüber hinaus ist dieser Prozess auch für die direkte Synthese anderer zweidimensionalen Materialien und deren Van-der-Waals-Heterostrukturen anwendbar.:Contents Quotation v Kurzfassung vii Abstract xi Contents xiii Acronyms xvii 1 Aims and objectives 1 2 Introduction 5 2.1 Carbon allotropes 6 2.1.1 Hybridized sp 2 carbon nanomaterials 6 2.1.2 Graphene 7 2.2 Properties of graphene 8 2.2.1 Crystalline structure 8 2.2.2 Electrical transport 10 2.2.3 Optical transparency 11 2.2.4 Other properties 12 2.3 Graphene deposition methods 13 2.3.1 Synthesis approaches 13 2.3.2 Chemical vapor deposition 14 2.3.3 Substrate selection 15 2.3.4 Substrate pretreatments 16 2.3.5 Carbon feedstock 17 2.3.6 Thermal chemical vapor deposition 17 2.3.7 Plasma chemical vapor deposition 18 2.3.8 Transfer protocol 19 2.4 Chemical vapor deposition for graphene growth 21 2.4.1 Thermodynamics 22 2.4.2 Arrhenius plots 22 2.4.3 Activation energy 24 2.4.4 Growth kinetics 25 2.4.5 Reaction mechanisms over Cu 27 2.4.6 Reaction mechanisms over Ni 29 2.4.7 Reaction mechanisms over non-metals 31 2.4.8 Reaction mechanisms of free-standing graphene 35 2.5 Summary 35 2.6 Scope of the thesis 36 3 Experimental setup and characterization techniques 37 3.1 Experimental setup of chemical vapor deposition 37 3.2 Optical microscopy 39 3.3 Scanning electron microscopy 40 3.4 Atomic force microscopy 41 3.5 Transmission electron microscopy 42 3.5.1 Selected area electron diffraction 44 3.5.2 Dark field transmission electron microscopy 46 3.6 Raman spectroscopy 47 3.7 Ultraviolet-Visible spectrophotometry 49 3.8 Electrical transport measurements 49 4 CVD growth of graphene on oxidized Cu substrates 51 4.1 Motivation 52 4.2 Experimental protocol 53 4.3 Influence of Cu pretreatments on graphene formation 54 4.4 Influence of Cu oxidation on graphene growth 60 4.5 Effect of oxidation pretreatment on Cu surface cleaning 64 4.6 Summary 66 5 Chemo-thermal synthesis of graphene from organic adsorbents 67 5.1 Motivation 67 5.2 Experimental protocol 69 5.3 Influence of reaction temperature on graphene growth 75 5.4 Influence of reaction pressure on graphene growth 78 5.5 Influence of reaction flow rate on graphene growth 80 5.6 Summary 81 6 Monolayer graphene synthesis directly over Si/SiO x 83 6.1 Motivation 83 6.2 Experimental protocol 86 6.3 Influence of substrate confinement configuration 87 6.4 Time dependent evolution for graphene formation 91 6.5 Grain boundaries in graphene film 95 6.6 Bubble clustering of faceted graphene grains 98 6.7 Electrical and optical performance of graphene 100 6.8 Summary 102 7 Conclusions 103 8 Outlook 107 A Graphene synthesis over Cu and transfer to Si/SiO x substrate 111 B Chemo-thermal synthesis of graphene over Cu 115 C CVD graphene growth directly over Si/SiO x substrate 127 Bibliography 147 List of Figures 193 List of Tables 197 Acknowledgements 199 List of publications 203 Erklaerung 205
430

Photo-physical properties of lead-tin binary Perovskite thin films

Mabiala, Floyd Lionel January 2021 (has links)
>Magister Scientiae - MSc / Organic-inorganic lead-based perovskite has exhibited great performance in the past few years. However, the lead (Pb) embedded in those compounds is a significant drawback to further progress, due to its environmental toxicity. As an alternative, tin (Sn) based-perovskites have demonstrated promising results in terms of electrical and optical properties for photovoltaic devices, but the oxidation of tin ion- from stannous ion (Sn2+) to stannic ion (Sn4+) presents a problem in terms of performance and stability when exposed to ambient conditions. A more feasible approach may be in a Pb-Sn binary metal perovskite in pursuit of efficient, stable perovskite solar cells (PSCs) with reduced Pb-content, as compared to pure Pb- or Sn-based PSCs. Here, we report on the deposition of a Pb-Sn binary perovskite by sequential chemical vapor deposition.

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