[pt] O Método dos Elementos Discretos (Discrete Element Method - DEM) é uma técnica numérico computacional capaz de simular o comportamento macroscópico de um material via solução das equações do movimento de seus constituintes. Para uma correta predição deste comportamento são informados, como dados de entrada, as características mecânicas dos elementos: os chamados microparâmetros. Contudo, não existe uma receita que determine estes microparâmetros baseados somente nas respostas macroscópicas do material simulado, necessitando de um passo adicional conhecido como Calibração. Tentativa e erro, um método ineficiente por conta de seu fator de escala desfavorável, é o mais comumente utilizado nesta etapa. Este trabalho propõe uma nova abordagem utilizando-se do método de otimização global Generalized Simulated Annealing, minimizando-se a área quadrática normalizada entre as curvas experimentais e calculadas de tensão-deformação axial e deformações volumétrica-axial simultaneamente. Foram efetuadas comparações via ensaio triaxial para dados sintéticos e reais cujos resultados demonstram o aproveitamento e aplicabilidade da técnica proposta. / [en] The Discrete Element Method (DEM) is a numerical computational technique that simulates the macroscopic material behaviour by solving the equations of motion of its constituents. For a correct prediction of this behaviour, are set as input data the mechanical characteristics of the elements, the so-called microparameters. However, there is no recipe for determining these microparameters based solely on the macroscopic responses of the simulated material. It is required an additional step known as Calibration. The method widely used in this calibration is trial and error, although is an inefficient method due its unfavorable scale factor. This work proposes a new approach using the Generalized Simulated Annealing global optimization method, minimizing the normalized quadratic area between the experimental and calculated curves of the axial stress-strain and volumetric-axial deformations curves simultaneously. Comparison is done using triaxial tests for both synthetic and real data whose results demonstrate the usefulness and applicability of the proposed approach.

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Intermediate band (IB) materials have attracted considerable research interest since they can dramatically enhance the near infrared light absorption and lead to applications in the fields of so-called intermediate band solar cells or infrared photodetectors. Hyperdoping Si with deep level impurities is one of the most effective approaches to form an IB inside Si. In this thesis, titanium (Ti) or chalcogen doped Si with concentrations far exceeding the Mott transition limits (~ 5×10^19 cm-3 for Ti) are fabricated by ion implantation followed by pulsed laser annealing (PLA) or flash lamp annealing (FLA). The structural and electrical properties of the implanted layer are investigated by channeling Rutherford backscattering spectrometry (cRBS) and Hall measurements. For Si supersaturated with Ti, it is shown that Ti-implanted Si after liquid phase epitaxy shows cellular breakdown at high doping concentrations during the rapid solidification, preventing Ti incorporation into Si matrix. However, the out-diffusion and the cellular breakdown can be effectively suppressed by solid phase epitaxy during FLA, leading to a much higher Ti incorporation. In addition, the formed microstructure of cellular breakdown also complicates the interpretation of the electrical properties. After FLA, the samples remain insulating even with the highest Ti implantation fluence, whereas the sheet resistance decreases with increasing Ti concentration after PLA. According to the results from conductive atomic force microscopy (C-AFM), the decrease of the sheet resistance after PLA is attributed to the percolation of Ti-rich cellular walls, but not to the insulator-to-metal transition due to Ti-doping. Se-hyperdoped Si samples with different Se concentrations are fabricated by ion implantation followed by FLA. The study of the structural properties of the implanted layer reveals that most Se atoms are located at substitutional lattice sites. Temperature-dependent sheet resistance shows that the insulator-to-metal transition occurs at a Se peak concentration of around 6.3 × 10^20 cm-3, proving the formation of an IB in host semiconductors. The correlation between the structural and electrical properties under different annealing processes is also investigated. The results indicate that the degrees of crystalline lattice recovery of the implanted layers and the Se substitutional fraction depend on pulse duration and energy density of the flash. The sample annealed at short pulse durations (1.3 ms) shows better conductivity than long pulse durations (20 ms). The electrical properties of the hyperdoped layers can be well-correlated to the structural properties resulting from different annealing processes.:Chapter 1 Introduction 1 1.1 Shallow and Deep level impurities in semiconductors 1 1.2 Challenges for hyperdoping semiconductors with deep level Impurities 2 1.3 Solid vs. liquid phase epitaxy 5 1.4 Previous work 7 1.4.1 Transition metal in Si 7 1.4.2 Chalcogens in Si 10 1.5 The organization of this thesis 15 Chapter 2 Experimental methods 18 2.1 Ion implantation 18 2.1.1 Basic principle of ion implantation 18 2.1.2 Ion implantation equipment 19 2.1.3 Energy loss 20 2.2 Pulsed laser annealing (PLA) 23 2.3 Flash lamp annealing (FLA) 24 2.4 Rutherford backscattering and channeling spectrometry (RBS/C) 27 2.4.1 Basic principles 27 2.4.2 Analysis of the elements in the target 28 2.4.3 Channeling and RBS/C 29 2.4.4 Analysis of the impurity lattice location 31 2.5 Hall measurements 31 2.5.1 Sample preparation 32 2.5.2 Resistivity 32 2.5.3 Hall measurements 33 Chapter 3 Suppressing the cellular breakdown in silicon supersaturated with titanium 34 3.1 Introduction 34 3.2 Experimental 35 3.3 Results 36 3.4 Conclusions 42 Chapter 4 Titanium-implanted silicon: does the insulator-to-metal transition really happen? 44 4.1 Introduction 44 4.2 Experimental section 45 4.3 Results 47 4.3.1 Recrystallization of Ti-implanted Si 47 4.3.2 Lattice location of Ti impurities 48 4.3.3 Electrical conduction 50 4.3.4 Surface morphology 52 4.3.5 Spatially resolved conduction 53 4.4 Discussion 55 4.5 Conclusion 56 Chapter 5 Realizing the insulator-to-metal transition in Se hyperdoped Si via non-equilibrium material processing 57 5.1 Introduction 57 5.2 Experimental 59 5.3 Results 60 5.4 Conclusions 65 Chapter 6 Structural and electrical properties of Se-hyperdoped Si via ion implantation and flash lamp annealing 67 6.1 Introduction 67 6.2 Experimental 68 6.3 Results 69 6.4 Conclusions 76 Chapter 7 Summary and outlook 78 7.1 Summary 78 7.2 Outlook 81 References 83 Publications 89

This study aims to validate and develop applications for a novel impedance-based process analytical technology for monitoring the attributes of the product during the entire freeze-drying process (from pre-freezing and annealing to primary and then secondary drying). This measurement approach involves the application of foil electrodes, mounted externally to a conventional glass freeze-drying vial, and coupled to a high-impedance analyser. The location of the electrodes on the outside, rather than the inside of the vial, leads to a description of the technology as a through-vial impedance spectroscopy (TV-IS) technique. The principle observation from this approach is the interfacial-polarization process arising from the composite impedance of the glass wall and product interface. For a conventional glass vial (of wall thickness ~ 1 mm and cross sectional diameter ~ 22 mm) it was shown that the process is manifest within the frequency range 101 to 106 Hz, as a single, broad band peak which spans 2-3 decades of the imaginary part spectrum. Features of the interfacial-relaxation process, characterised by the peak amplitude, C″Peak, and peak frequency, fpeak, of the imaginary capacitance spectra and the equivalent circuit elements that model the impedance spectra (i.e. the solution resistance (R) and solution capacitance (C) were monitored along with the product temperature data during the cycle(s), for a variety of surrogate formulations comprising lactose, sucrose, mannitol or maltodextrin solutions, during the freezing, re-heating, annealing and primary drying stages of freeze drying). It was shown that the parameters, fpeak and R, are strongly coupled to each other and change as a function of the temperature of the solution and its phase state, whereas C″Peak is strongly coupled to the amount of ice that remains during the drying process. Both log fpeak and log R have a linear dependence on the temperature of the solution, provided there was no phase change in the solution. The crystallization process (ice onset, solidification and equilibration to shelf temperature) is characterized well by both log fpeak and log R, whereas the parameter R demonstrates most clearly the formation of eutectic crystallization during freezing. In contrast it was the parameter C which was most sensitive to the detection of the glass transition during re-heating. During primary drying, it was shown that C″peak, is dependent on the amount of ice remaining and therefore provides a convenient assessment of the rate of drying and primary drying end point. The impedance changes during annealing provide a mechanistic basis for the modifications in ice structure which result directly in the observed decrease in primary drying times. The principal observation on annealing of a 10% w/v solution of maltodextrin, was the minimal changes in the glass transition (recorded at ~−16 °C) during the re-heating and cooling step (post-annealing). This result alone appears to indicate that a maximum freeze concentration was achieved during first freezing with no further ice being formed on annealing. The phenomenon of devitrification (and the production of more ice, and hence larger ice crystals) was therefore discounted as the mechanism by which annealing impacts the drying time. Having excluded devitrification from the mechanism of annealing enhanced drying, it was then possible to conclude that the decrease in the electrical resistance (that was observed during the annealing hold time) must necessarily result from the simplified structure of the unfrozen fraction and the improved connectivity of ice crystals that may be the consequence of Ostwald ripening. The application of through vial impedance measurement approach provides a non-invasive, real time monitoring of critical process parameters which subsequently leads to an improved understanding of the mechanisms and effects of different parameters, providing a reliable basis for process optimization, along with improved risk management to ensure optimum quality of the formulation and optimization of the freeze drying process.

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Simulated annealing is a useful heuristic for finding good solutions for difficult combinatorial optimization problems. In some engineering applications the quality of a solution is based upon how tolerant the solution is to changes in the environment. The concept of simulated annealing is based upon the metallurgical process of annealing where a material is tempered by heating and cooling. Genetic algorithms have been used to evolve solutions to complex problems by imitating the biological process of evolution using crossover and mutation to modify the candidate solutions. In coevolution a candidate solution is composed of multiple species each of which provides a portion of the candidate solution. Those individuals of a species that, in collaboration with the individuals from the other species, are evaluated as providing the most fit solution are the preferred individuals of a species. This work investigated whether robustness, defined as the ability of a solution to tolerate changes to the problem environment, could be improved by defining a neighborhood of fitness functions that are centered in the neighborhood of the nominal objective function. Simulated annealing was used to manage the subsequent narrowing of the neighborhood of fitness functions. Two robustness measures were developed that used samples from the neighborhood of objective functions; one employed the minimum fitness value, and the other employed the average fitness value. Coevolutionary genetic algorithms were used to generate candidate solutions employing the robustness measures. This study used three benchmark functions to evaluate the effects of the robustness measures. The results indicated that the robustness measures could produce solutions that were robust and, often, globally optimal for benchmark functions employed in the testing. Future work includes applying this framework to a broader class of optimization problems, investigating new neighborhood strategies, and devising new robustness measures.

Master of Science / Department of Industrial & Manufacturing Systems Engineering / Jessica L. Heier Stamm / Communication is an integral part of emergency response, and improving the information dissemination network for crisis communication can save time, resources, and lives. This thesis focuses specifically on emergency response to a foreign animal disease (FAD) outbreak, an incident in which an animal disease that is not active domestically is introduced and being spreading in the U.S. In a FAD outbreak, timeliness of detection and response are critical. An outbreak of foot-and-mouth disease, a particularly significant FAD, could cripple the agriculture economy and every hour of poor communication could result in the loss of thousands of animals. Improving this and other such crisis communication networks is of high importance. There is a comparatively large amount of prior research that critiques past catastrophic events but very little that aims to quantitatively improve such networks. This research uses communication data from a FAD response exercise in Kansas to develop a reliable network model, contributing a general method for creating an information dissemination network from empirical communication data. The thesis then introduces a simulated annealing heuristic to alter the network structure, reducing the overall information transmission time by almost 90%. Both the application of simulated annealing in network design and the use of discrete event simulation to calculate the heuristic objective function are new contributions to the field of crisis communication and emergency response. This work begins by extracting data from communication logs, grouping the large numbers of stakeholders into more manageable clusters, and developing a simulation model framework that accurately depicts the flow of information in the actual network. Then a simulated annealing heuristic is used to alter the network structure. The goal is to identify an alternative network structure in which the time for information to reach all response participants is minimized. The resultant network structures are analyzed to reveal observations and recommendations for FAD response communication. This research finds that not only can such a network be improved significantly, but the quantitative results support the qualitative observations from early in the data extraction process. This paper adds original methods to the literature and opens the door for future quantitative work in the area of crisis communication and emergency response.

Les semi-conducteurs transparents de type oxyde, communément appelés TCO (Transparent Conducting Oxides) sont utilisés comme électrodes transparentes dans des nombreux d'applications telles que les cellules solaires, les écrans à cristaux liquides, les écrans tactiles et autres. Toutefois, les applications technologiques sont actuellement limitées puisque les TCO possédant des propriétés électriques et optiques satisfaisantes sont uniquement des semi-conducteurs de type n. Les oxydes de cuire de structures delafossite ACuO2 ou du type SrCu2O2, présentent des prometteuses avec un comportement de semi-conduction de type P et une faible absorption optique dans le spectre visible. Dans cette thèse, le systèm MOCVD (Dépôt chimique en phase vapeur du métal organique) a été utilisé pour le dépôt des couches minces de SrCu2O2. Cette phase est obtenue après quelques étapes de recuit sous oxygène puis argon, ou azote uniquement avec en particulier la nécessité de réalier des recuit rapaides. Les propriétés électriques et optiques mesurées pour la couche mince de SrCu2O2 ont un ordre de grandeur similaire à ce qui est publié dans la littérature.

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