In this study, the reactive rf magnetron sputtering was used to deposit Ba(Zr0.1,Ti0.9)O3 (BZT) ferroelectric thin films on ITO/Glass substrate, and MFM structure was fabricated. The effects of various sputtering parameters on the characteristics of thin films, such as the oxygen concentrations, substrate temperature, rf power and chamber pressure were discussed, and then the optimal sputtering parameters were determined. The annealing process of rapid thermal annealing (RTA) and conventional thermal annealing (CTA) were used to promote the ferroelectric characteristics. The physical characteristics of BZT thin films were obtained by the analyses of SEM, XRD patterns and AFM morphologies. The surfaces, cross-section, crystallization and surface roughness of thin films were discussed. To investigate the electrical properties, the capacitance-voltage (C-V), current-voltage (I-V) and P-E hysteresis characteristics of BZT thin films were measured by the HP4284A impedance analyzer, HP4156C semiconductor parameter analyzer and computerized radiant technology (RT66), respectively. Furthermore, characteristics of the MFM structure were discussed. From the experimental results, the dielectric constant with optimal sputtering parameters was about 84, and the leakage current of thin film was about 6 ¡Ñ 10-8 A/cm2 when the applied electrical field of thin film was at 0.4 MV/cm. The remanent polarization (Pr) and coercive field (Ec) were 2.87 £gC/cm2 and 259 kV/cm from the P-E hysteresis loops, respectively. In addition, the ferroelectric characteristics of the thin film could be improved after rapid thermal annealing at 550¢J for 3 minutes. The remanent polarization (Pr), coercive field (Ec) and saturated polarization (Ps) were 3.42 £gC/cm2, 266 kV/cm and 6.99 £gC/cm2, respectively.

In this study, the electrical properties of [Al/(Bi4Ti3O12+V2O5 ) /Ba(Zr0.1Ti0.9)O3/Silicon¡AMFIS ]structure using annealed-BZT films would be improved for the nonvolatile FeRAM device applications. The radio-frequency magnetron sputtering was used to deposit BTV ferroelectric films on Mo/Ti/SiO2/Si and BZT/Si substrates, respectively, and MFMIS and MFIS structures would also be fabricated. The various sputtering parameter effects of BTV films such as the oxygen concentrations, rf power and deposition time would be discussed. Besides, the electrical and physical properties of as-deposited BZT films for (BTV/BZT/Si¡AMFIS) structure would be improved by different rapidly thermal annealing temperature. The physical characteristics of BTV films and annealed-BZT films for various sputtering parameters were obtained from the XRD pattern and SEM morphology. Besides, the memory window, dielectric constant and leakage current of MFM and MFIS structure using BTV films and annealed-BZT films would be found from the HP4284A, RT66A and HP4156C. From the experimental result obtained, the maximum dielectric constant of BTV films for 40 % oxygen concentration and 130W power were 10.79. The leakage current density was about 10-5A/cm2, as the applied electrical field of 200 kV/cm. In addition, the coercive field (Ec) and remanent polarization (2Pr) were 750 kV/cm and 12 £gC/cm2 from the P-E curves, respectively. Finally, the maximum memory window and lower leakage current density of [Al/(Bi4Ti3O12+V2O5) /Ba(Zr0.1Ti0.9)O3/Silicon¡AMFIS) structure would be found and they were 25V and 10-8A/cm2, respectively.

Les écoulements turbulents de gaz denses, qui sont d’un grand intérêt pour un large éventail d'applications, sont le siège de phénomènes physiques encore peu connus et difficiles à étudier par des approches expérimentale. Dans ce travail, nous étudions pour la première fois l’influence des effets de gaz denses sur la structure de la turbulence compressible à l’aide de simulations numériques. Le fluide considéré est le PP11, un fluorocarbure lourd, dont le comportement thermodynamique a été représenté à l’aide de différentes lois d’état, afin de quantifier la sensibilité des solutions aux choix de modélisation. Nous avons considéré d’abord la décroissance d’une turbulence homogène isotrope compressible. Les fluctuations de température sont négligeables, alors que celles de la vitesse du son sont importantes à cause de leur forte dépendance de la densité. Le comportement particulier de la vitesse du son modifie de manière significative la structure de la turbulence, conduisant à la formation de shocklets de détente. L’analyse de la contribution des différentes structures à la dissipation d’énergie et à la génération d’enstrophie montre que, pour un gaz dense, les régions de forte dilatation jouent un rôle similaire à celles de forte compression, contrairement aux gaz parfaits, dans lesquels le comportement est fortement dissymétrique. Ensuite, nous avons mené des simulations numériques pour une configuration de canal plan en régime supersonique, pour plusieurs valeurs des nombres de Mach et de Reynolds. Les résultats confirment la validité de l’hypothèse de Morkovin. L’introduction d’une loi d’échelle semi-locale prenant en compte le variations de densité et viscosité, permet de comparer les profils des grandeurs turbulentes (contraintes de Reynolds, anisotropie, budgets d’énergie) avec ces observés en gaz parfait. Les variables thermodynamiques, quant à elles, présentent une évolution très différente pour un gaz parfait et pour un gaz dense, la chaleur spécifique élevée de ce dernier conduisant à un découplage des effets dynamiques et thermiques et à un comportement proche de celui d’un fluide incompressible avec des propriétés variables. / Dense gas turbulent flows, of great interest for a wide range of engineering applications, exhibit physical phenomena that are still poorly understood and difficult to reproduce experimentally. In this work, we study for the first time the influence of dense gas effects on the structure of compressible turbulence by means of numerical simulations. The fluid considered is PP11, a heavy fluorocarbon, whose thermodynamic behavior is described by means of different equations of state to quantify the sensitivity of solutions to modelling choices. First, we considered the decay of compressible homogeneous isotropic turbulence. Temperature fluctuations are found to be negligible, whereas those of the speed of sound are large because of the strong dependence on density. The peculiar behavior of the speed of sound significantly modifies the structure of the turbulence, leading to the occurrence of expansion shocklets. The analysis of the contribution of the different structures to energy dissipation and enstrophy generation shows that, for a dense gas, high expansion regions play a role similar to high compression ones, unlike perfect gases, in which the observed behaviour is highly asymmetric. Then, we carried out numerical simulations of a supersonic turbulent channel flow for several values of Mach and Reynolds numbers. The results confirm the validity of the Morkovin' hypothesis. The introduction of a semi-local scaling, taking into account density and viscosity variations across the channel, allow to compare the wall-normal profiles of turbulent quantities (Reynolds stresses, anisotropy, energy budgets) with those observed in ideal gases. Nevertheless, the thermodynamic variables exhibit a different evolution between perfect and dense gases, since the high specific heats of the latter lead to a decoupling of dynamic and thermal effects, and to a behavior close to that of variable property incompressible fluids.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-06-03T23:23:31Z No. of bitstreams: 1 ArmandoMonteMendes_DISSERT.pdf: 6303230 bytes, checksum: 90f6b4372d141b15db0fbf05e1726b17 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-06-07T00:00:37Z (GMT) No. of bitstreams: 1 ArmandoMonteMendes_DISSERT.pdf: 6303230 bytes, checksum: 90f6b4372d141b15db0fbf05e1726b17 (MD5) / Made available in DSpace on 2016-06-07T00:00:37Z (GMT). No. of bitstreams: 1 ArmandoMonteMendes_DISSERT.pdf: 6303230 bytes, checksum: 90f6b4372d141b15db0fbf05e1726b17 (MD5) Previous issue date: 2015-01-28 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Materiais cer?micos ferroel?tricos com estrutura perovskita (ABO3) s?o largamente utilizados em componentes de mem?ria no estado s?lido (FeRAM?s e DRAM?s) bem como em capacitores de m?ltiplas camadas, especialmente na forma de filmes finos. Quando dopados com ?ons de zirc?nio, materiais ? base de BaTiO3 formam uma solu??o s?lida conhecida como titanato zirconato de b?rio (BaTi1-xZrxO3). Tamb?m chamado de BZT, esse material pode sofrer significativas mudan?as em suas propriedades el?tricas diante de pequenas varia??es do teor de zirc?nio na rede cristalina. O presente trabalho consiste no estudo dos efeitos dos par?metros de deposi??o de filmes finos de BaTi0,75Zr0,25O3 pelo m?todo de spin-coating sobre sua morfologia e propriedades f?sicas, utilizando um planejamento experimental do tipo Box-Behnken. A resina utilizada no processo de deposi??o foi sintetizada pelo m?todo dos precursores polim?ricos (Pechini) e foi subsequentemente dividida em tr?s parcelas cada qual teve sua viscosidade ajustada para 10, 20 e 30 mPa?s por meio de um viscos?metro rotativo. As resinas foram depositadas em substratos de Pt/Ti/SiO2/Si pelo m?todo de spin-coating em 15 diferentes combina??es de viscosidade, velocidade de rota??o (3000, 5500 e 8000 rpm) e n?mero de camadas depositadas (5, 8 e 11 camadas) previstas no planejamento e ent?o calcinadas a 800?C por 1h. A fase cristalina dos filmes foi determinada por difra??o de Raios-X (DRX) e indexada com a carta JCPDS 36-0019. Morfologia da superf?cie e tamanho de gr?o foram observados por meio de microscopia de for?a at?mica (AFM) indicando filmes bem densificados e tamanho m?dio de gr?o em torno de 50nm. Imagens da se??o transversal dos filmes foram obtidas por interm?dio de microscopia eletr?nica de varredura com emiss?o de campo (MEV-FEG), indicando espessuras bem uniformes variando de 140-700 nm entre amostras. Medidas de capacit?ncia foram realizadas ? temperatura ambiente com a ajuda de um analisador de imped?ncia. Os filmes apresentaram valores de constante diel?trica de 49-277 a 100KHz e baixa perda diel?trica. O planejamento indicou efeitos n?o significativos das intera??es entre os par?metros de deposi??o sobre a espessura dos filmes. A metodologia de superf?cies de resposta possibilitou uma melhor observa??o dos efeitos das vari?veis. / Ferroelectric ceramics with perovskite structure (ABO3) are widely used in solid state memories (FeRAM?s and DRAM's) as well as multilayered capacitors, especially as a thin films. When doped with zirconium ions, BaTiO3-based materials form a solid solution known as barium zirconate titanate (BaTi1-xZrxO3). Also called BZT, this material can undergo significant changes in their electrical properties for a small variation of zirconium content in the crystal lattice. The present work is the study of the effects of deposition parameters of BaTi0,75Zr0,25O3 thin films by spin-coating method on their morphology and physical properties, through an experimental design of the Box-Behnken type. The resin used in the process has been synthesized by the polymeric precursor method (Pechini) and subsequently split into three portions each of which has its viscosity adjusted to 10, 20 and 30 mPa?s by means of a rotary viscometer. The resins were then deposited on Pt/Ti/SiO2/Si substrates by spin-coating method on 15 different combinations of viscosity, spin speed (3000, 5500 and 8000 rpm) and the number of deposited layers (5, 8 and 11 layers) and then calcined at 800 ? C for 1 h. The phase composition of the films was analyzed by X-ray diffraction (XRD) and indexed with the JCPDS 36-0019. Surface morphology and grain size were observed by atomic force microscopy (AFM) indicating uniform films and average grain size around 40 nm. Images of the cross section of the films were obtained by scanning electron microscopy field emission (SEM-FEG), indicating very uniform thicknesses ranging from 140-700 nm between samples. Capacitance measurements were performed at room temperature using an impedance analyzer. The films presented dielectric constant values of 55-305 at 100kHz and low dielectric loss. The design indicated no significant interaction effects between the deposition parameters on the thickness of the films. The response surface methodology enabled better observes the simultaneous effect of variables.

We have examined three problems involving steady flows of Navier-Stokes fluids. In each problem non-classical effects are considered. In the first two problems, we consider fluids which have bulk viscosities which are much larger than their shear viscosities. In the last problem, we examine steady supersonic flows of a Bethe-Zel'dovich-Thompson (BZT) fluid over a thin airfoil or turbine blade. BZT fluids are fluids in which the fundamental derivative of gasdynamics changes sign during an isentropic expansion or compression. In the first problem we consider the effects of large bulk viscosity on the structure of the inviscid approximation using the method of matched asymptotic expansions. When the ratio of bulk to shear viscosity is of the order of the square root of the Reynolds number we find that the bulk viscosity effects are important in the first corrections to the conventional boundary layer and outer inviscid flow. At first order the outer flow is found to be frictional, rotational, and non-isentropic for large bulk viscosity fluids. The pressure is found to have first order variations across the boundary layer and the temperature equation is seen to have two additional source terms at first order when the bulk viscosity is large. In the second problem, we consider the reflection of an oblique shock from a laminar flat plate boundary layer. The flow is taken to be two-dimensional, steady, and the gas model is taken to be a perfect gas with constant Prandtl number. The plate is taken to be adiabatic. The full Navier-Stokes equations are solved using a weighted essentially non-oscillatory (WENO) numerical scheme. We show that shock-induced separation can be suppressed once the bulk viscosity is large enough. In the third problem, we solve a quartic Burgers equation to describe the steady, two-dimensional, inviscid supersonic flow field generated by thin airfoils. The Burgers equation is solved using the WENO technique. Phenomena of interest include the partial and complete disintegration of compression shocks, the formation of expansion shocks, and the collision of expansion and compression shocks. / Ph. D.

In the presented thesis, lead-free Ba(Ti0.8Zr0.2)O3-(Ba0.7Ca0.3)TiO3 (BZT-BCT) thin films were deposited on Pt/TiO2/SiO2/Si substrates using chemical solution deposition method and then the effect of process parameters were investigated to obtain optimum parameters of these lead-free thin films. The phase was selected near to the morphotropic phase boundary (MPH) to increase the number of polarization directions where rhombohedral and tetragonal phases exist together. In this study, the effect of sintering temperatures on microstructure, dielectric and ferroelectric properties were studied systematically. Among the various high-quality BZT-BCT thin films with uniform thickness, the optimum dielectric and ferroelectric responses were observed for films annealed at 800 oC for 1 h sintering time. The thickness was kept constant for all measurements as 500 nm (triple layered films). Therefore, the average grain sizes were found around 60 nm for samples sintered at 700,750 and 800 oC. BZT-BCT thin films sintered at 800 oC showed effective remnant polarization and coercive field values of 2.9 &micro / C/cm2 and 49.4 kV/cm, together with a high dielectric constant and low loss tangent of 365.6 and 3.52 %, respectively, at a frequency of 600 kHz due to pure perovskite phase showing full crystallization and minimum surface porosity obtained at this temperature.

At the interface of physics, mathematics, and computer science, Uncertainty Quanti cation (UQ) aims at developing a more rigorous framework and more reliable methods to characterize the impact of uncertainties on the prediction of Quantities Of Interest (QOI). Despite signi cant improvements done in the last years in UQ methods for Fluid Mechanics, there is nonetheless a long way to go before there can be talk of an accurate prediction when considering all the numerous sources of uncertainties of the physical problem (boundary conditions, physical models, geometric tolerances, etc), in particular for shock-dominated problems. This manuscript illustrates my main contributions for improving the reliability of the numerical simulation in Fluid Mechanics: i) the development of e cient and exible schemes for solving at low-cost stochastic partial di erential equations for compressible ows, ii) various works concerning variancebased and high-order analysis, iii) the design of some low-cost techniques for the optimization under uncertainty. The application of interest is the robust design of turbines for Organic Rankine Cycles (ORC). Some contributions to the numerical ow prediction of the thermodynamically complex gases involved in ORC will be presented. This manuscript is divided in two parts. In the rst part, some intrusive algorithms are introduced that feature an innovative formulation allowing the treatment of discontinuities propagating in the coupled physical/stochastic space for shock-dominated compressible ows. Then, variance and higher-order based decompositions are described, that could alleviate problems with large number of uncertainties by performing a dimension reduction with an improved control. Some ANOVAbased analyses are also applied to several ows displaying various types of modeling uncertainties, be it cavitation, thermodynamic or turbulence modeling. Two algorithms for handling stochastic inverse problems are then introduced for improving input uncertainty characterization by directly using experimental data. Finally, robust-optimization algorithms are introduced, that are e cient when dealing with a large number of uncertainties, relying on di erent formulations, i.e. with decoupled/ coupled approaches between the stochastic and the optimization solvers. The second part is devoted to the study of dense gas ow in ORC-cycles, which represent a highly demanding eld of application as far as ow simulation reliability is concerned. The numerical ingredients necessary for this kind of simulation are described. Then, some recent results are illustrated : i) high- delity turbine computations; ii) a feasibility study concerning the appearance and the occurrence of a Rarefaction Shock Wave, using experimental data and di erent operating conditions (in monophasic and two-phase ows); iii) a stochastic study concerning the thermodynamic model uncertainties. This set of research works has produced several papers in international journals and peer-reviewed conferences.