The cores of early UK graphite moderated research and production nuclear fission reactors operated at temperatures below 150°C. Due to this low temperature their core graphite contains significant amounts of stored (Wigner) energy that may be released by heating the graphite above the irradiation temperature. This exothermic behavior has lead to a number of decommissioning issues which are related to long term "safe-storage", reactor core dismantling, graphite waste packaging and the final disposal of this irradiated graphite waste. The release of stored energy can be modeled using kinetic models. These models rely on empirical data obtained either from graphite samples irradiated in Material Test Reactors (MTR) or data obtained from small samples obtained from the reactors themselves. Data from these experiments is used to derive activation energies and characteristic functions used in kinetic models. This present research involved the development of an understanding of the different grades of graphite, relating the accumulation of stored energy to reactor irradiation history and an investigation of historic stored energy data. The release of stored energy under various conditions applicable to decommissioning has been conducted using thermal analysis techniques such as Differential Scanning Calorimetry (DSC). Kinetic models were developed, validated and applied, suitable for the study of stored energy release in irradiated graphite components. A potentially valid method was developed, for determining the stored energy content of graphite components and the kinetics of energy release. Another parameter investigated in this study was dedicated in the simulation of irradiation damage using ion irradiation. Ion bombardment of small graphite samples is a convenient method of simulating fast neutron irradiation damage. In order to gain confidence that irradiation damage due to ion irradiation is a good model for neutron irradiation damage the properties and microstructure of various grades of ion irradiated nuclear graphite were also investigated. Raman Spectroscopy was employed to compare the effects of ion bombardment with the reported effects of neutron irradiation on the content of the defects. The changes of the of defect content with thermal annealing of the ion irradiated graphite have been compared with the annealing of neutron irradiated nuclear graphite.

No description available.

Title: Dynamics of structural defects in CdTe-based semiconductors Author: RNDr. Marek Bugár Institute: Institute of Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. Ing. Eduard Belas CSc.; Institute of Physics, Charles University in Prague Abstract: The work was aimed at investigation of the effect of annealing on structural, electrical and optical properties of CdZnTe epitaxial substrates and CdTe-based and CdZnTe-based X-ray and gamma-ray detectors. The first part of the work is focused on investigation of structural properties of one type of second phase defects - inclusions - present in the material, which degrade the material quality. Consequent annealing experiments were aimed at reduction of these defects. In case of CdZnTe substrates, an annealing treatment leading to increase of the infrared transmittance was investigated. On the other hand, annealing experiments on the detectors of high-energetic radiation were focused on preservation of the high-resistive state. Moreover, the work contains detailed measurements of transport properties of CdTe taken directly at high temperatures. Key words: CdTe, annealing, inclusions, detectors, defects

I introduce the concept of modular materials and give a brief overview of their history and widespread occurrence in many areas of chemistry. I then discuss some of the many applications in which modular materials may find a use and link them to the following chapters. Chapter 1 describes the layered superatomic material Re₆Se₈Cl₂ and the induction of superconducting behavior in its single crystals through a current annealing technique. We suggest that this superconductivity arises through electron doping, as a result of dissociation of the apical Cl atoms from the clusters. Chapters 2-4 explore other types of superatomic materials and their properties, centered on the well-studied Co₆X₈ unit, where X is a chalcogen. Chapter 2 describes a Co₆Te₈-C₇₀ co-crystal that exhibits multiple phase changes with temperature, each giving rise to unique electronic, thermal, and structural properties. Chapter 3 describes a series of “solid solutions” of Co₆Se₈ and Cr₆Te₈ units. By varying the ratios of the component superatoms, transport properties of the crystals can be tuned, and unexpected behavior arises as a result of structural heterogeneity. Chapter 4 presents another study of Co₆Se₈ co-crystallized with rod-shaped C₁₄₀ fullerenes. The packing and electronic properties are found to be greatly affected by the degree of solvent inclusion. Chapters 5-6 examine another class of cluster-based materials: atomically precise gold nanoparticles. In Chapter 5 the cluster Au₂₁ is shown to self-assemble depending on the surface “hook” ligands, with corresponding differences in electronic transport. Chapter 6 discusses an interesting phase transition and thermally-induced hysteresis observed in crystals of the Au₁₀₃ cluster, also related to the surface ligand configuration. Chapters 7-8 take a different approach to modular materials, in the form of organic polymers. Using the robust, electroactive pigment molecule PDI as a common building block, we synthesize extended networks that are found to be exceptional pseudocapacitive energy storage materials. Chapter 7 introduces the honeycomb-shaped PDI-triptycene polymer, establishes its pseudocapacitive nature, and explores the role of cyclization in tuning its behavior. Chapter 8 expands upon the concept by combining PDI with hexaazatrinaphthalene to create a “contorted” network with best-in-class energy storage performance. In addition to in-depth kinetic analyses to elucidate the mechanism of storage, we fabricate two-electrode cells to demonstrate the material’s potential in real-world devices.

The research shows a novel approach for the Magnetic Anomaly Differentiation and Localization Algorithm, which simultaneously localizes multiple magnetic anomalies with weak total field signatures (tens of nT). In particular, it focuses on the case where there are two homogeneous targets with known magnetic moments. This was done by analyzing the magnetic signals and adapting Independent Component Analysis (ICA) and Simulated Annealing (SA) to solve the problem statement. The results show the groundwork for using a combination of fastICA and SA to give localization errors of 3 meters or less per target in simulation and achieved a 58% success rate. Experimental results experienced additional errors due to the effects of magnetic background, unknown magnetic moments, and navigation error. While one target was localized within 3 meters, only the latest experimental run showed the second target approaching the localization specification. This highlighted the need for higher signal-to-noise ratio and equipment with better navigational accuracy. The data analysis was used to provide recommendations on the needed equipment to minimize observed errors and improve algorithm success. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

Thermische Ausheilprozesse werden bei der Transistorformation im Wesentlichen eingesetzt, um die durch die Ionenimplantation entstandenen Kristallschäden auszuheilen und die eingebrachten Dotanden zu aktivieren. Besonders kritisch sind dabei die finalen Aktivierungsprozesse, bei denen die Source/Drain-Gebiete der Transistoren gebildet werden. Im Zuge der kontinuierlichen Skalierung der CMOSFET-Technologie ist es außerdem erforderlich, möglichst flache, abrupte Dotierungsprofile mit maximaler elektrischer Aktivierung zu erhalten, um die bei diesen Bauelementeabmessungen immer stärker auftretenden Kurzkanaleffekte zu unterdrücken und gleichzeitig eine höhere Leistungsfähigkeit der Transistoren zu gewährleisten. Zur maximalen Aktivierung bei minimaler Diffusion der eingebrachten Dotanden müssen dazu während der finalen Ausheilung extrem kurze Ausheilzeiten bei sehr hohen Temperaturen bewerkstelligt werden. Mit dem derzeitig angewandten Ausheilverfahren, der schnellen thermischen Ausheilung (RTA), bei der die minimale Ausheilzeit im Bereich von 1 s liegt, sind diese Vorgaben nicht mehr realisierbar. Nur durch den Einsatz von neuartigen thermischen Ausheilprozessen mit Ausheilzeiten im Millisekundenbereich können diese Forderungen erreicht werden. Das Thema der vorliegenden Arbeit ist die wissenschaftliche Untersuchung der neuartigen Ausheilprozesse und die experimentelle Realisierung von Integrationsmöglichkeiten in die planare Hochleistungs-SOI-CMOSFET-Technologie. Dazu wird zunächst die Notwendigkeit der Einführung der neuartigen Ausheilprozesse erläutert. Anschließend wird basierend auf experimentellen Untersuchungen der Einfluss der Kurzzeitausheilung auf die Diffusion und Aktivierung der Dotierstoffe für eine p- und n-Dotierung analysiert. Des Weiteren werden zwei unterschiedliche Technologien der Kurzzeitausheilung, die Blitzlampen- und Laser-Ausheilung, und deren Einfluss auf das Transistorverhalten sowohl auf Wafer- als auch auf Mikroprozessorebene untersucht. Der Schwerpunkt der vorliegenden Arbeit liegt auf der experimentellen Untersuchung zur Integration der Kurzzeitausheilung in den Herstellungsprozess von Hochleistungs-SOI-CMOSFETs. Zwei verschiedene Ansätze werden dabei näher betrachtet. Zum Einen wird der Einfluss der Kurzzeitausheilung als zusätzlicher Ausheilschritt im Anschluss an die herkömmliche RTA und zum Anderen als alleiniger Ausheilschritt ohne RTA untersucht. Die Ergebnisse der durchgeführten Experimente zeigen, dass durch die zusätzliche Kurzzeitausheilung nach Ansatz 1 ohne eine Veränderung des Herstellungsprozesses ein verbessertes Transistorverhalten erreicht werden kann. Demgegenüber ist die Integration der Kurzzeitausheilung nach Ansatz 2 nur durch eine Anpassung der Transistorarchitektur und eine Optimierung der Implantationsparameter für die Halo-, Source/Drain-Erweiterungs- und Source/Drain-Gebiete möglich. Ein Hauptaugenmerk bei der Herstellung diffusionsarmer p-MOSFETs nach Ansatz 2 liegt in der Implementierung von Si1-xGex-Source/Drain-Gebieten, um die Erhöhung der Leistungsfähigkeit durch diese Verspannungsquelle auch bei diesen Transistortypen zu gewährleisten. Die dazu durchgeführten experimentellen Untersuchungen zeigen, dass bei diffusionsarmen p-MOSFETs mit Si1-xGex in den Source/Drain-Gebieten des Transistors, die Wahl der richtigen Implantationsspezies von entscheidender Bedeutung ist. Abschließend erfolgt eine Gegenüberstellung der Ergebnisse von optimierten, diffusionsarmen n- und p-MOSFETs mit Transistoren der 45 nm-Technologie. Letztere basieren auf einem Prozess mit einer kombinierten Ausheilung von RTA und Kurzzeitausheilung. Dabei wird gezeigt, dass im Gegensatz zur herkömmlichen RTA-Ausheilung eine weitere Miniaturisierung der planaren Transistorstruktur mit Hilfe der Kurzzeitausheilung möglich ist.

This dissertation documents the development and demonstration of a new laser crystallization process called spot-beam annealing (SBA). The SBA method is a partial-melting-based laser-annealing method, which converts as-deposited amorphous Si films into high-mobility TFT-enabling polycrystalline films. SBA builds on the thermally additive utilization of multiple short-lived low-energy ultra-high-frequency pulses, achieved via substantially overlapped scanning of a small spot beam to incrementally and gradually heat and partially melt the beam-irradiated region. After a brief review of other laser crystallization technologies, the conceptual framework for the SBA process is introduced, and various possible implementation schemes and development paths are discussed. In the present work, the SBA method is implemented using a new class of ultra-high-frequency (>100 MHz), low-pulse energy (<1 𝜇J), short-pulse-duration (<1 ns) UV fiber lasers. The first half of the thesis (chapters 4 and 5) presents, the simulation- and calculation-based studies of the SBA process. A simple but relevant one-dimensional thermal analysis identifies the "dwell time" (associated with the overall intensity temporal profile defined by the collection of those pulses that irradiate a point in the film) as a key SBA parameter. Provided that a sufficient number of multiple shots are involved in irradiating the point in the film, this parameter dictates the overall thermal and transformation cycle of heating, primary melting, and solidification that enables the ultra-short-pulse-based SBA method to mimic the physical conditions encountered previously only using pulsed lasers with pulse duration in the range of tens to hundreds of nanoseconds; the precise range needed for optimally generating laser-annealed polycrystalline materials on glass and plastic substrates. Additionally, we also identify and examine an important differentiating feature of the SBA method, namely the highly transient temperature spikes that arise from the individual pulses incident onto a point on the film during overlapped scanning. By simultaneously considering the preliminary experimental results that are presented in this thesis (chapters 6 and 7), we suggest that these periodic temperature spikes, the specific degree of which depends on the temporal profile and energy density of individual pulses, can potentially play a key role in dictating certain important details of melting and solidification transitions encountered in SBA. In particular, we identify and elaborate on how the temperature fluctuations can affect how explosive crystallization of a-Si films is manifested in a different manner than has previously been observed. In addition, we point out how the fluctuations can control the degree to which the melting scenarios in SBA can deviate from the grain-boundary-melting-dominated 2-D transition scenario (as for instance encountered in pulsed-laser irradiation of columnar-grained polycrystalline films), where lateral melting is exclusively initiated at grain boundaries and propagates predominantly laterally into the superheated and defect-free interior of the grains. In the second half of the thesis, the experimental results that are obtained from a recently constructed research SBA system are presented, characterized, and evaluated. Specifically, the examination of single-scan and multiple-scan exposed Si films conducted using OM, AFM, and TEM material characterization techniques reveals that the method is capable of not only generating uniform polycrystalline Si films consisting of ordered grains with tight grain-size distribution around the beam wavelength, but it can furthermore be configured to produce polycrystalline films with an enhanced level of ordering as manifested in the films with a highly parallel ridge (HPR) pattern.

Metaheuristics are used to find feasible solutions to hard Combinatorial Optimization Problems (COPs). Constraint Satisfaction Problems (CSPs) may be formulated as COPs, where the objective is to reduce the number of violated constraints to zero. The popular puzzle Sudoku is an NP-complete problem that has been used to study the effectiveness of metaheuristics in solving CSPs. Applying the Simulated Annealing (SA) metaheuristic to Sudoku has been shown to be a successful method to solve CSPs. However, the ‘easy-hard-easy’ phase-transition behavior frequently attributed to a certain class of CSPs makes finding a solution extremely difficult in the hard phase because of the vast search space, the small number of solutions and a fitness landscape marked by many plateaus and local minima. Two key mechanisms that metaheuristics employ for searching are diversification and intensification. Diversification is the method of identifying diverse promising regions of the search space and is achieved through the process of heating/reheating. Intensification is the method of finding a solution in one of these promising regions and is achieved through the process of cooling. The hard phase area of the search terrain makes traversal without becoming trapped very challenging. Running the best available method - a Constraint Propagation/Depth-First Search algorithm - against 30,000 benchmark problem-instances, 20,240 remain unsolved after ten runs at one minute per run which we classify as very hard. This dissertation studies the delicate balance between diversification and intensification in the search process and offers a hybrid SA algorithm to solve very hard instances. The algorithm presents (a) a heating/reheating strategy that incorporates the lowest solution cost for diversification; (b) a more complex two-stage cooling schedule for faster intensification; (c) Constraint Programming (CP) hybridization to reduce the search space and to escape a local minimum; (d) a three-way swap, secondary neighborhood operator for a low expense method of diversification. These techniques are tested individually and in hybrid combinations for a total of 11 strategies, and the effectiveness of each is evaluated by percentage solved and average best run-time to solution. In the final analysis, all strategies are an improvement on current methods, but the most remarkable results come from the application of the “Quick Reset” technique between cooling stages.

Indiana University-Purdue University Indianapolis (IUPUI) / Computer Numerical Control (CNC) is widely used in many industries that needs high speed machining of the parts with high precision, accuracy and good surface finish. In order to avail this the generation of the CNC part program size will be immensely big and leads to an inefficient process, which increases the delivery time and cost of products. This work presents the automation of high-accuracy CNC tool trajectory planning from CAD to G-code generation through optimal NURBs surface approximation. The proposed optimization method finds the minimum number of NURBS control points for a given admissible theoretical cord error between the desired and manufactured surfaces. The result is a compact part program that is less sensitive to data starvation than circular and spline interpolations with potential better surface finish. The proposed approach is demonstrated with the tool path generation of an involute gear profile and a topologically optimized structure is developed using this approach and then finally it is 3D printed.

No description available.