Esta pesquisa engloba o estudo e desenvolvimento de novas heteroestruturas semicondutoras, tomando como base as estruturas SOI (Silicon-On-Insulator - silício sobre isolante) obtidas pela técnica Smart Cut, estudadas nestes últimos anos no Departamento de Engenharia de Sistemas Eletrônicos da Escola Politécnica da Universidade de São Paulo (EPUSP). Esta técnica combina a solda direta para a união de lâminas e a implantação iônica (I/I) de íons leves para a separação de camadas especificadas. São essenciais na preparação destas estruturas SOI, processos de I/I, limpeza e ativação das superfícies das lâminas e recozimentos em fornos a temperaturas moderadas. Estudamos também, diferentes métodos para a obtenção de novas heteroestruturas, basicamente combinando as técnicas de fabricação da estrutura SOI e os métodos de formação do carbeto de silício (SiC), que chamaremos de heteroestruturas SiCOI (Silicon Carbide-On-Insulator). O método usado para a formação do SiC depende, em cada caso, das características desejadas para o filme que, ao mesmo tempo, estão relacionadas com a aplicação à qual estará destinado. Analisamos três métodos de obtenção do material SiC com características específicas diferentes. A metodologia proposta aborda as seguintes tarefas: Tarefa 1: Obtenção de estruturas SOI pelo método convencional utilizado em trabalhos anteriores e melhoramento das características superficiais da estrutura resultante. Tarefa 2: partindo de uma lâmina de Si previamente coberta por uma camada isolante, fabricar a heteroestrutura SiC/isolante/Si, onde a camada de SiC é crescida pelo método de deposição química de vapor assistida por plasma (PECVD). O filme obtido por deposição PECVD é amorfo e portanto são necessárias etapas de cristalização posteriores ao crescimento. Tarefa 3: partindo de uma estrutura SOI, fabricar a heteroestrutura SiC/SiO2/Si, onde a camada de SiC é obtida por implantação de íons de carbono (C+) na camada ativa de Si da estrutura SOI para sua transformação em SiC. Tarefa 4: partindo de uma estrutura SOI, fabricar a heteroestrutura SiC/SiO2/Si, onde a camada de SiC é obtida por conversão direta da camada ativa de Si da estrutura SOI em SiC como resultado da carbonização do Si usando exposição a ambiente de hidrocarbonetos. Como resultado deste trabalho foram obtidas estruturas SOI Smart Cut com valor médio de rugosidade superficial dentro dos valores esperados segundo a bibliografia consultada. Durante o desenvolvimento de heteroestruturas SiC/isolante/Si obtidas utilizando a técnica de PECVD obtivemos filmes com boas características estruturais. Os recozimentos feitos em ambiente de N2 aparentemente trazem resultados satisfatórios, conduzindo à completa cristalização dos filmes. Nas análises feitas para a fabricação de heteroestruturas SiC/isolante/Si utilizando I/I de carbono confirma-se a formação de c-SiC depois de realizado o recozimento térmico. / In this work we study new semiconductors heterostructures, based on SOI (Silicon-On- Insulator) structures obtained by \"Smart-Cut\" process, that were studied in the last years at Departamento de Engenharia de Sistemas Eletrônicos da Escola Politécnica da Universidade de São Paulo (EPUSP). This technique combines high-dose hydrogen ion implantation (I/I) and direct wafer bonding. To produce SOI structures some processes are essential: I/I process, cleaning and activation of the surfaces, and conventional thermal treatments at moderated temperatures. We also investigate different methods to obtain new heterostructures, basically combining SOI technologies and silicon carbide (SiC) growth processes, which will be called as SiCOI (Silicon Carbide-On-Insulator) heterostructures. The utilized methods to obtain the SiC are related, in each case, with the desired film\'s characteristics, which at the same time are associated with the final application. We analyze three methods to obtain SiC material with specific different characteristics. The proposed methodology approaches the following tasks: Task 1: Fabrication of SOI structures by the conventional technology previously used by us, and the improvement of superficial characteristic of the final structure. Task 2: Fabrication of SiC/insulator/Si heterostructures from Si substrate previously covered with an insulator capping layer, where the SiC layer is deposited by plasma enhanced chemical vapor deposition (PECVD). The PECVD film is amorphous and therefore, a thermal annealing step is necessary for crystallization. Task 3: Fabrication of SiC/SiO2/Si heterostructures from SOI structure, where the SiC layer is synthesized through a high dose carbon implantation into the thin silicon overlayer of a SOI wafer. Task 4: Fabrication of SiC/SiO2/Si heterostructures from SOI structure, where the SiC layer is achieved by direct carbonization conversion of the silicon overlayer of a SOI wafer In this work we have obtained Smart Cut SOI structures with surface roughness similar to the previous reported. We also obtained SiC/insulator/Si heterostructures with good structural characteristics using PECVD technique. The investigated N2 thermal annealing appears to be suitable for the crystallization of all the amorphous films deposited by PECVD. We have shown the possibility of using carbon ion implantation and subsequent thermal annealing to form c-SiC for SiC/insulator/Si heterostructures.

Amorphous alloys possess attractive combinations of mechanical properties (high elastic limit, ~2%, high fracture toughness, 20-50 MPa.m1/2, etc.) and exhibit mechanical behavior that is different, in many ways, from that of the crystalline metals and alloys. However, fundamental understanding of the deformation and fracture mechanisms in amorphous alloys, which would allow for design of better metallic glasses, has not been established on a firm footing yet. The objective of this work is to understand the deformation and fracture mechanisms of amorphous materials at various length scales and make connections with the macroscopic properties of glasses. Various experimental techniques were employed to study the macroscopic behavior and atomistic simulations were conducted to understand the mechanisms at the nano level. Towards achieving these objectives, we first study the toughness of a Zr-based bulk metallic glass (BMG), Vitreloy-1, as a function of the free volume, which was varied by recourse to structural relaxation of the BMG through sub-Tg annealing treatment. Both isothermal annealing at 500 K (0.8Tg) for up to 24 h and isochronal annealing for 24 h in the temperature range of 130 K (0.65Tg) to 530 K (0.85Tg) were conducted and the impact toughness, Γ, values were measured. Results show severe embrittlement, with losses of up to 90% in Γ, with annealing. The variation in Γ with annealing time, ta, was found to be similar to that observed in the enthalpy change at the glass transition, ΔH, with ta, indicating that the reduction of free volume due to annealing is the primary mechanism responsible for the loss in Γ with annealing. Having established the connection between sub-atomic length scales (free volume) and macroscopic response (toughness), we investigated further the affects of relaxation on intermediate length scale behavior, namely deformation induced by shear bands, by employing instrumented indentation techniques. While the Vickers nano-indentation response of the as-cast and annealed glasses do not show any significant difference, spherical indentation response shows reduced shear band activity in the annealed BMG. Further, relatively high indentation strain was observed to be necessary for shear band initiation in the annealed glass, implying an increased resistance for the nucleation of shear bands when the BMG is annealed. In the absence of microstructural features that allow for establishment of correlation between properties and the structure, we resort to atomistic modeling to gain further understanding of the deformation mechanisms in amorphous alloys. In particular, we focus on the micromechanisms of strain accommodation including crystallization and void formation during inelastic deformation of glasses. Molecular dynamics simulations on a single component system with Lennard-Jones-like atoms suggest that a softer short range interaction between atoms favors crystallization. Compressive hydrostatic strain in the presence of a shear strain promotes crystallization whereas a tensile hydrostatic strain was found to induce voids. The deformation subsequent to the onset of crystallization includes partial re-amorphization and recrystallization, suggesting important mechanisms of plastic deformation in glasses. Next, a study of deformation induced crystallization is conducted on two component amorphous alloys through atomistic simulations. The resistance of a binary glass to deformation-induced-crystallization (deformation stability) is found to increase with increasing atomic size ratio. A new parameter called “atomic stiffness” (defined by the curvature of the inter-atomic potential at the equilibrium separation distance) is introduced and examined for its role on deformation stability. The deformation stability of binary glasses is found to increase with increasing atomic stiffness. For a given composition, the internal energies of binary crystals and glasses are compared and it is found that the energy of glass remains approximately constant for a wide range of atomic size ratios unlike crystals in which the energy increases with increasing atomic size ratio. This study uncovers the similarities between deformation and thermal stabilities of glasses and suggests new parameters for predicting highly stable glass compositions.

Doped semiconductor systems have for decades provided an excellent platform to study novel concepts in solid state physics such as quantum hall effect, metal-to-insulator transition (MIT), weak localization and many body interaction effects. Doped Si, in particular and doped Ge has been studied extensively to study MIT as a function of dopant concentration or uniaxial stress. Spin transport phenomena have also been probed in bulk doped Si. All the previous studies involved bulk doped semiconductors where the dopants are spread through the bulk of the material. However spatial confinement of dopants in one or more dimensions may lead to a range of exotic quantum phenomena such as an absence of Anderson localization in one and two dimensions, hole-mediated (Nagaoka) ferromagnetism and new modes of quantum transport, when the Fermi energy lies at or close to centre of the band. Since many of these phenomena are inherent to lower dimensions, it has been hard to observe these experimentally in bulk doped crystals of Si and Ge. Recent advances in the monolayer doping techniques with atoms that closely pack on a surface, has made it possible to design a new class of 2D electron systems (2DES) in elemental semiconductors, such as Si and Ge, where the dopant (P) atoms are confined within a few atomic planes. The uniqueness of these systems lies not merely in the planar doping profile in bulk semiconductors that allow versatile designs of nanodevices, such as 1D wires, tunnel gaps and quantum dots, but also that it is now possible to study the interplay of wavefunction overlap and commensurability effects in 2D with unprecedented control. From an application perspective as well these systems are technologically important as they are aimed at being the building blocks of a solid state quantum computer. This thesis deals with investigating the electrical transport properties, both average (resistance) and dynamic (noise) of doped semiconductor systems in 2D delta layers, 1D wires and 0D quantum dots. We find that the 2D δ-layers shows suppressed low frequency noise and the Hooge parameter of delta doped Si is about five to six orders of magnitude lower when compared to bulk doped Si in metallic regime. At low temperatures, the noise arises in these systems due to universal conductance fluctuations. For 1D wires as well we find that the Hooge parameter is one of the lowest among various 1D systems including carbon nanotubes. We identify that charge traps in the Si/SiO2 are responsible for causing noise in δ-doped systems. Then we study the noise and transport in 2D delta layers as a function of doping density (and hence carrier density and interaction). Weak localization corrections to the conductivity and the universal conductance fluctuations were both found to decrease rapidly with decreasing doping in the Si:P and Ge:P delta layers, suggesting a spontaneous breaking of time reversal symmetry driven by strong Coulomb interactions. At low doping density we observe metal-like dependence of resistance on temperature at low temperatures, raising the possibility of a metallic ground state in 2D at 0 K in doped semiconductors. Finally we probe the low density devices (with broken time reversal symmetry) using superconducting Al as ohmic contacts. Anomalous increase in resistance below the superconducting transition temperature of Al and magnetoresistance with a sharp peak at 0 T is observed. Additionally we find that when the Al is superconducting, there exists a non-local resistance in low doped devices.

No description available.

Im Bauwesen kommen verschiedene Kantenausführungsarten von Glas zum Einsatz. In Abhängigkeit ihrer Art erfüllen sie Anforderungen an den Schnittschutz, die Maßhaltigkeit und die Ästhetik. Nach DIN 1249-11 erfolgt die Einteilung entsprechend des äußeren Erscheinungsbildes in geschnittene (KG), gesäumte (KGS), maßgeschliffene (KMG), geschliffene (KGN) und polierte (KPO) Kanten. Die mechanische Festigkeit der Glaskante ist jedoch gesondert zu betrachten. Die charakteristische Biegezugfestigkeit von Glas ist maßgeblich von dessen Oberflächenzustand abhängig. Die Herstellung und Bearbeitung der Kante erfolgt durch einen Materialeingriff mit harten Schneid- und Schleifwerkzeugen. Dabei werden die Oberflächenbeschaffenheit verändert und das Bruchverhalten beeinflusst. Bisher regelt die europäische Normung Kantenfestigkeiten in der Bemessung in Form von Beiwerten, welche die charakteristische Biegezugfestigkeit pauschal oder in Abhängigkeit der Kantenausführungsart abmindern. Bestehende Untersuchungen zeigen jedoch wesentliche Unterschiede der Kantenfestigkeit in Abhängigkeit von Kantenausführungsart und Herstellungsprozess. Die Bemessungswerte der Kantenfestigkeit gelten als untere Grenze der auf dem Markt verfügbaren Qualitäten. Wissenschaftlich belegte Beurteilungen der visuellen Kantenqualität mit Einschätzung ihrer mechanischen Festigkeit liegen bisher nur für die geschnittene Kantenausführung vor. Für den industriellen Schneidprozess wurden auf Basis systematischer Untersuchungen Parameter detektiert, die sich positiv auf die Kantenfestigkeit auswirken. Es ist unbekannt, wie sich der Oberflächeneingriff durch Schleif- und Polierprozesse auf die mechanische Festigkeit der dabei hergestellten Kantenausführungsarten auswirkt und welche Ursachen dafür zu benennen sind. Zudem fehlen geregelte, einheitliche Methoden, um die Kantenqualitäten optisch und mechanisch zu erfassen. Im Rahmen dieser Arbeit wird eine Versuchsmethodik entwickelt, welche über mikroskopische Analysen und Bruchversuche die Erfassung vergleichbarer optischer und mechanischer Kennwerte ermöglicht. In einer Zusammenführung der Methoden erfolgt erstmalig die Charakterisierung bruchverursachender Fehlstellen und deren Rückführung auf den Entstehungsort im Herstellungsprozess. Anhand einer systematischen Untersuchung verschiedener Kantenausführungsarten eines Herstellers findet die Erprobung und Bewertung der entwickelten Versuchsmethodik statt. Anschließend werden Prozessanpassungen zur Fehlstellenreduzierung vorgenommen und in Bezug auf eine Steigerung der Kantenfestigkeit untersucht. Weitere Analysen des Herstellungsprozesses eines zweiten Herstellers erfolgen für verschieden polierte Kanten. Entsprechend der ermittelten bruchverursachenden Fehlstellen werden Hypothesen für zukünftige Untersuchungen abgeleitet. Die Erkenntnisse dieser Arbeit stellen die wissenschaftliche Grundlage für verfahrenstechnische Handlungsempfehlungen zur Herstellung von Glaskanten dar. Der aktuelle Stand bedeutender europäischer Bemessungsregeln wird für abschließende normative Empfehlungen einbezogen. Die gesäumte Kante ergibt sich beim ersten Hersteller als Kantenausführungsart mit der höchsten Kantenfestigkeit. Für die maßgeschliffene, geschliffene und polierte Kante ergeben sich im Vergleich zur geschnittenen und gesäumten Kante geringere Festigkeiten. Die Untersuchung der polierten Kantenausführung des zweiten Herstellers ergibt, verglichen mit der polierten Kante des ersten Herstellers, eine höhere Kantenfestigkeit. Daraus leitet sich der Einfluss der Maschinenkonfiguration als einflussreicher Prozessparameter ab. Die Analyse der bruchverursachenden Fehlstellen zeigt, dass höherfeste Kanten mit einer Reduzierung von mikroskopisch erfassbaren Fehlstellen für die geschnittene, gesäumte und polierte Kante korrelieren. Darüber hinaus gewährleisten die in dieser Arbeit entwickelten Fehlstellenanalysen eine Detektion festigkeitsmindernder Fehlstellen, die auf eine Einbringung nach der Herstellung hindeuten und somit die Notwendigkeit von Kantenschutzmaßnahmen nach sich ziehen. Definitionen allgemeingültiger Prozessparameter in Schleif- und Polierprozessen, die eine positive Auswirkung auf die Kantenfestigkeit bearbeiteter Kanten haben, sind bisher in der Literatur nicht vorhanden. Die in dieser Arbeit beschriebenen Ergebnisse dienen als Grundlage zur Optimierung der Prozessparameter für hohe Kantenfestigkeiten. Experimentelle Nachweise der mechanischen Festigkeit sind dabei unabdingbar. Die Kantenqualität ist in optische und mechanische Eigenschaften zu unterscheiden. Die optisch als am hochwertigsten geltende polierte Kante geht nicht zwangsläufig mit einer hohen Kantenfestigkeit einher, was eine in der Praxis weitverbreitete Annahme widerlegt. In diesem Kontext leistet die vorliegende Arbeit einen Beitrag zum Verständnis der Herstellungsprozesse und der Bemessung von Glasbauteilen, um den steigenden Anforderungen im konstruktiven Glasbau gerecht zu werden.:1 Einleitung 2 Grundlagen zu Glaskanten 3 Wissensstand zur Kantenfestigkeit 4 Entwicklung einer Versuchsmethodik zur Erfassung der Kantenqualität 5 Systematische Analyse der Kantenqualität eines Herstellers 6 Einfluss von Prozessparametern auf die Kantenfestigkeit nach Kantenausführungsart 7 Diskussion der Ergebnisse 8 Bemessungsansätze für Glaskanten 9 Handlungsempfehlungen 10 Zusammenfassung und Ausblick 11 Literatur / In the building industry, different types of glass edges are used. Depending on their type, they fulfil requirements for cutting protection, dimensional accuracy, and aesthetics. According to DIN 1249-11, the classification is based on the visual appearance and includes cut (KG), arrissed (KGS), ground (KMG), smooth ground (KGN), and polished (KPO) edge finishing type. However, the mechanical strength of the glass edge requires additional consideration. The characteristic bending tensile strength of glass depends mostly on its surface condition. During production and processing the edge comes in contact with hard tools, which modifies the optical appearance and influences the strength. Presently, the European standardization regulates the edge strength in the design by general coefficients, which reduce the characteristic bending tensile strength depending on the edge finishing type. Existing studies show a large range of values in edge strength depending on the edge finishing and the manufacturer. The design edge strength considers the lower limits of the available glass edge finishing types. Scientifically based evaluation of the optical edge quality with assessment of the mechanical strength is available only for the cut edge. For the industrial cutting process, parameters have been determined on the basis of systematic investigations that show a positive influence on edge strength. It is still unknown how surface interferences by grinding and polishing processes affect the edge strength of processed glass edges and what are the underlying mechanisms. In addition, there is a lack of unified methods for assessing the mechanical edge quality. Within the scope of this work, a test methodology is developed that enables the determination of comparable optical and mechanical characteristics by means of microscopic analysis and destructive tests. A combination of different methods is used to characterize fracture-causing defects and to identify the location of their creation in the manufacturing process. The testing methods are approved and evaluated on the basis of a systematic examination of different edge types of one manufacturer. Subsequently, process adjustments for defect reduction are conducted and investigated with regard to an increase in edge strength. Moreover, the manufacturing process of various polished edge types of a second manufacturer are examined. Thereby, fracture-causing flaws are identified and hypotheses for future investigations are derived that form the basis for processing recommendations for the manufacturing of glass edges. The current status of relevant European design rules is finally discussed for normative recommendations. The arrised edge finishing type revealed the highest edge strength. For the ground, smooth ground, and polished edges, the edge strength is lower compared to the cut and arrised edges. The examination of the polished edge from the second manufacturer resulted in a higher edge strength compared to the polished edge from the first manufacturer. Therefore, the influence of the machine configuration is derived as an impacting process parameter. The analysis of fracturecausing defects has confirmed that a higher edge strength correlates with a reduction in microscopically detectable defects for the cut, arrised, and polished edge types. The defect analysis also enables the detection of strength-reducing defects that are introduced after production and require edge protection measures. Definitions of generally valid process parameters in grinding and polishing that positively affect the edge strength of machined edges are unknown. However, the results of this work enable manufacturers to optimize processes specific to their (manufacturing) process in order to ensure high values of edge strength. Nonetheless, experimental verifications are indispensable in this respect. Optical and mechanical properties of glass edges need to be considered separately. For example, the polished edge is considered to offer the highest optical quality. However, contrary to a widespread assumption, it does not necessarily display high edge strength. A better understanding of the manufacturing processes and the verification of edge strength are necessary for the design to meet the increasing demands in structural glass applications.:1 Einleitung 2 Grundlagen zu Glaskanten 3 Wissensstand zur Kantenfestigkeit 4 Entwicklung einer Versuchsmethodik zur Erfassung der Kantenqualität 5 Systematische Analyse der Kantenqualität eines Herstellers 6 Einfluss von Prozessparametern auf die Kantenfestigkeit nach Kantenausführungsart 7 Diskussion der Ergebnisse 8 Bemessungsansätze für Glaskanten 9 Handlungsempfehlungen 10 Zusammenfassung und Ausblick 11 Literatur

The demand for flat glass is high and increasing significantly in the building industry as a direct result of architectural requirements for lightness, transparency and natural light. Current architectural trends require glass in curvilinear forms for smooth free-form façades. Two principal challenges arise from this: to cost-effectively produce the desired curvature and; to ensure its safe performance after exposure to ageing. The recent availability of high strength glass provides an opportunity to address the first challenge by developing cold bent glass. Cold bending involves the straining of relatively thin glass components, at ambient temperatures, and is a low energy and cost effective manner of creating curvilinear forms. However, cold bending is not yet widely established as a reliable method. The aim of this thesis is to develop the understanding of cold bent glass during the bending process and to evaluate its post-ageing performance. This thesis, firstly, investigates the mechanical response of monolithic glass plates during the cold bending process. The stability of cold bent glass is investigated experimentally by bending it in double curved anticlastic shapes. A parametric numerical analysis involves different boundary conditions, geometrical plate characteristics and bending parameters. The principal outcome is that a local instability, now termed cold bending distortion, occurs when certain displacement limits are exceeded and could degrade the optical quality of the glass. An evaluation procedure is also formulated to set limits and aid designers/manufacturers to predict the mechanical response and the optical quality of the glass. Cold bent glass is subjected to permanent bending stresses throughout its service life and therefore, its strength degradation after ageing needs to be quantified. Analytical, experimental and numerical investigations are undertaken in this thesis to identify the most effective method for estimating glass strength (evaluation of destructive tests, required number of specimens, statistical analysis methods and sub-critical crack growth). The limited availability of naturally aged toughened glass and the absence of a reliable ageing standard impede the evaluation of its aged performance. Therefore, a parametric experimental investigation of artificial ageing methods on glass is undertaken in this thesis. A procedure for the evaluation of the strength of aged glass is finally, formulated to allow the selection of artificial ageing parameters that correspond to a target level of erosion. The knowledge on artificial ageing and strength prediction acquired above is finally implemented on different types of glass to determine their strength after ageing and assess their safe use in cold bending / load bearing applications. The investigation showed that fully toughened glass has a superior performance to chemically toughened or annealed glass. Overall, the research presented in this thesis demonstrates that high quality cold bent toughened glass can be created when certain applied displacement limits are respected. These can be used as a safe, cost-effective and energy efficient replacement to the more conventional hot bent glass. However, cold bending / load bearing applications in which the stressed glass surface is exposed to ageing, require glass with a relatively high case depth such as fully toughened or bi-tempered glass.

This work reports on the cobalt pyridinoporphyrazinate (CoTmtppa) as a platinum-group metal-free catalyst for hydrogen evolution and oxidation reactions with the possibility of use in hydrogen energy and hydrogen potentiometric sensing. A different interaction of CoTmtppa with various electrode substrates, highly oriented pyrolytic graphite (HOPG) and annealed gold (Au(111)), affects its electrocatalytic behaviour in hydrogen reactions. The formation of a hydride-type complex with the bonding of hydrogen atoms to cobalt centre is supposed to be the rate-determining step. In the case of hydrogen evolution, the maximum catalytic activity of mediator was reached at pH = 11,0, when the HOPG/CoTmtppa showed overpotential decrease by 300 mV and an almost 60-fold increase of current densities compared to HOPG. The electrocatalytic activity of Au(111)/CoTmtppa resulted in a further decrease of overpotential by 175 mV in comparison with HOPG/Co(I)Tmtppa. The electrochemical oxidation of hydrogen was found to depend on hydrogen source which was electrochemically generated on-site or molecular hydrogen supplied from an external source. In the case of electrochemically generated hydrogen, the maximum activity of HOPG/CoTmtppa was reached at pH = 2.1 and an additional it was observed 50 % increase in current...