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Coteau, Michele Denise de. "Impurity gettering at extended defects in silicon." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333296.
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Nakamura, Daisuke. "Bulk growth and extended-defect analysis of high-quality SiC single crystals." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136293.
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Lotharukpong, Chalothorn. "Defect characterisation in multi-crystalline silicon." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:a803fada-2296-41c3-9d96-864c186957a2.
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Electron beam induced current (EBIC) and atom probe tomography (APT) were used in this study to determine electrical activities and impurity compositions at extended defects in multicrystalline silicon (mc-Si) samples. The results provide, for the first time, information regarding the chemical species present at defects whose electrical activity has previously been measured. A new APT specimen fabrication process was developed with the ability to select a specific defect for APT analysis. Development of the APT specimen fabrication process proceeded by first selecting and optimising the preferential etching for nano-scale defect delineation. Three etchants were evaluated, namely Secco, Sirtl and Dash, from which the Secco etch was selected. Three parameters were optimised to produce etch pits with geometries that meet the requirements imposed by APT specimen fabrication methods. The optimum parameters were 0.05M potassium dichromate concentration, 20°C etch temperature, and 30sec etch time. In the second stage, marking techniques were developed in order for the defects to be located throughout the APT specimen fabrication process. However, it became apparent that the conventional APT specimen fabrication method could not be used to fabricate APT specimens containing selected defects in a mc-Si sample. This led to the development of a novel APT specimen fabrication approach which allowed APT specimens to be fabricated, reproducibly, containing grain boundaries and isolated dislocations. In order to evaluate accurately iron contamination in mc-Si, four atom probe parameters were optimised to maximise detection sensitivity: the evaporation rate, the laser beam energy, the pulse repetition rate and the specimen temperature. The optimisation process can be divided in to two parts. In the first part, a matrix of pre-sharpened single-crystal silicon specimens was subjected to a variety of experimental parameters. The optimised parameters were determined to be 0.3% evaporation rate, 0.5nJ beam energy, 160kHz repetition rate and 55K specimen temperature. The second part was to determine the iron detection efficiency –the percentage of detected Fe ions that can be correctly identified as Fe– and sensitivity using these parameters to analyse a specially prepared iron calibration specimen. The values were determined to be a detection efficiency of about 35% and sensitivity of 54ppm or 2.70x1018 atom/cm3. The APT specimen fabrication process and the optimised APT analysis parameters were used to analyse four extended defects in mc-Si samples subjected to three different processing conditions, namely gold-contaminated, as-grown and phosphorus diffusion gettering (PDG). The important aspects of the analysis are listed below: • Gold was not detected at the grain boundary and its associated dislocations in the gold-contaminated specimen. The binding enthalpy of gold to such defects is thus less than 0.63eV. • Iron was not detected in any specimen. • Copper was observed at the grain boundary in the as-grown specimen in the form of individual atoms as well as clusters with diameters ranging between 4nm and 9nm. The electrical activity of the grain boundary was about 58%. • Nickel and carbon were detected at the grain boundary in the post-PDG specimen with the former having platelet structures with diameters and thicknesses ranging between 4nm-7nm and 2nm-4nm, respectively. The recombination strength of the defect was about 22%. • Two nickel clusters were found at the isolated dislocation in the post-PDG specimen. The clusters were spherical with an average diameter of 10nm. The distance between the two clusters was 35nm. The recombination strength of the defect was about 4%.
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BARBISAN, LUCA. "Extended defects in heteroepitaxial structures on silicon by Molecular Dynamics simulations: applications to SiGe and cubic SiC." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/366130.
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Il numero di transistor per unità di area che possono essere posizionati su un wafer a semiconduttore dipende dalla capacità del wafer di dissipare tale energia termica. I materiali con elevata conducibilità termica e temperatura di fusione, come il silicio, sono quelli ideali. Le basse correnti di dispersione che si possono ottenere con l'ossido di Si e il nitrato di Si (i suoi composti nativi con l'aria) e l'elevata conducibilità termica hanno consentito una densità di transistor superiore rispetto ad altri semiconduttori. Anche se il silicio domina ancora il ramo principale della tecnologia dei semiconduttori, ci sono aree in cui la bassa mobilità, la bassa velocità di saturazione e il bandgap indiretto hanno permesso lo sviluppo di altri semiconduttori. Essendo il costo della materia prima molto superiore a quello del Si, sono state sviluppate alcune tecniche per ridurre tali costi. Un modo per mantenere il vantaggio termico di un substrato di silicio e ridurre il costo della materia prima dei semiconduttori che non sono Si consiste nell'utilizzare un sottile film di semiconduttore cresciuto sopra un substrato di Si spesso (etero-epitassia). L'eteroepitassia garantisce costi inferiori mantenendo un substrato termicamente efficiente, ma d'altro canto implica che il semiconduttore deve essere cresciuto su un substrato con un parametro reticolare diverso.
Le tecnologie epitassiali oggi più diffuse sono l'epi-crescita delle leghe di gruppo III-V e II-VI (soprattutto per l'amplificazione a radiofrequenza e le tecnologie laser) e l'epitassia di semiconduttori di gruppo IV come le leghe SiC e SiGe e il Ge puro. I semiconduttori del gruppo IV hanno il vantaggio non trascurabile di avere costi di fabbricazione inferiori rispetto ai primi. Ovviamente garantiscono prestazioni migliori in termini di proprietà elettroniche rispetto al Si. Il principale ostacolo alla realizzazione di tali dispositivi deriva dal fatto che il disadattamento reticolare induce la formazione di difetti dannosi durante la crescita epitassiale. Tali difetti ostacolano la possibilità di un'applicazione industriale ed estensiva di semiconduttori del gruppo IV diversi dal Si. In genere, i difetti generati sono bordi di grano, dislocazioni, errori di impilamento (stacking fault) e altri difetti estesi. Esiste un forte interesse accademico nella comprensione dei difetti nei sistemi epitassiali. In particolare, due sistemi presentano allo stesso tempo interessanti prospettive applicative e difficili sfide di modellazione teorica: il silicio-germanio e carburo di silicio cubico. Sono infatti semiconduttori attraenti che possono essere facilmente integrati nell'attuale architettura basata su silicio. La loro epitassia su Si è stata studiata per anni, ma le densità dei difetti sono ancora troppo alte in quei sistemi. In questa tesi, affronteremo il problema della modellazione dell'evoluzione di difetti estesi tramite simulazioni di dinamica molecolare. Affronteremo alcuni dei problemi aperti sull'evoluzione dei difetti in entrambi i materiali in esame. I nostri risultati forniranno informazioni sufficienti per far luce sui problemi specifici della formazione e dell'evoluzione di stacking fault multipli in SiC cubico e la formazione di array ordinati di dislocazioni di Lomer in Ge cresciuto su Si.Silicon has dominated semiconductor history for almost half a century. Even if the first transistor was made using germanium and other semiconductors show better electronic properties in terms of higher mobility, higher saturation velocity, and larger energy gap. It is the material used to build almost the 97% of all semiconductor-based electronic de- vices. The reason is straightforward; it is the most economical technology to make inte- grated circuits. It has been possible to fabricate integrated circuits with constantly increasing number of transistors on a single chip. The first that analyzed this trend was Gordon Moore in 1965, and he suggested that the trend was due to a constant exercise in cost reduction. The manufacturing cost for a square millimeter of Si remained constant at about 1$ for many decades, while the number of transistors and other elements has grown exponentially with time. The number of transistors for units of area that can be placed on a semiconductor wafer depends on the capacity of the wafer to dissipate such thermal energy. Materials with elevated thermal conducibility and melting temperature, like silicon, are the ideal ones. The low leakage currents that can be achieved with Si oxide and Si nitrate (its native composite with air) and the elevated thermal conducibility allowed a transistor density higher than with other semiconduc- tors. Even if Si still dominates the main branch of semiconductor technology, there are areas where the low mobility, the low saturation velocity, and the indirect bandgap per- mitted other semiconductors to develop. Being the raw material cost much higher than Si one, some techniques have been developed to reduce such costs. A way to maintain the thermal advantage of a silicon substrate and reduce the raw material cost of semi- conductors that are not Si consists of using a thin semiconductor film grown on top of a thick Si substrate (hetero-epitaxy). Hetero-epitaxy guarantees lower costs maintaining a thermally efficient substrate, but on the other side implies that the semiconductor has to be grown on a substrate with a different lattice parameter. Today’s more diffused epitaxial technologies are the epi-grow of group III-V and II-VI alloys (especially for radio frequency amplification and laser technologies) and the epitaxy of group IV semiconductors like the SiC and SiGe alloys and the pure Ge. Group IV semiconductors have the non-negligible advantage of having cheaper fabrication costs than the formers. They, of course, guarantee better performances in terms of electronic properties than Si. The main obstacle in realizing such devices stems from the fact that the lattice mismatch induces the formation of detrimental defects during epitaxial growth. Such defects hinder the possibility of an industrial, extensive appli- cation of group IV semiconductors other than Si. Typically, the generated defects are grain boundaries, misfit dislocations, stacking faults, and other extended defects. A strong academic interest exists in the comprehension of defects in epitaxial systems. In particular, two systems present at the same time exciting application perspectives and hard theoretical modeling challenges: silicon germanium and cubic silicon carbide. They indeed are attractive semiconductors that can be easily integrated into the actual silicon-based architecture. Their epitaxy on Si has been studied for years, but defect densities are still too high in those systems. In this Thesis, we will deal with the problem of modeling extended defects evolution via molecular dynamics simulations. We will tackle some of the open problems about defect evolution in both the materials under consideration. Our results provided enough information to shed light on the specific problems of the formation and evolution of multiple stacking faults in cubic SiC and the formation of ordered arrays of Lomer dislocation in Ge grown on Si.
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Bonjour, Filipe. "Extended defects in curved spacetimes." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4966/.
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This Thesis is concerned with three particular aspects of extended cosmic strings and domain walls in cosmology: their dynamics, gravitation and interaction with a black hole. In Chapter 3, we study the dynamics of an abelian-Higgs cosmic string. We find its equations of motion from an effective action and compare, for three test trajectories, the resulting motion with that observed in the Nambu-Gotō approximation. We also present a general argument showing that the corrected motion of any string is generically antirigid. We pursue the investigation of the dynamics of topological defects in Chapter 5, where we find (from integrability conditions rather than an effective action) the effective equations governing the motion of a gravitating curved domain wall. In Chapter 4 we investigate the spacetime of a gravitating domain wall in a theory with a general potential V(ɸ). We show that, depending on the gravitational coupling e of the scalar ɸ, all nontrivial solutions fall into two categories interpretable as describing respectively domain wall and false vacuum-de Sitter solutions. Wall solutions cannot exist beyond a value (^4)(_3)ɛmax, and vacuum-de Sitter solutions are unstable to decaying into wall solutions below ɛmax at ɛmax we observe a phase transition between the two types of solution. We finally specialize for the Goldstone and sine-Gordon potentials. In Chapter 6 we consider a Nielsen-Olesen vortex whose axis passes through the centre of an extremal Reissner-Nordstr0m black hole. We examine in particular the existence of piercing and expelled solutions (where the string respectively does and does not penetrate the black hole's horizon) and determine that while thin strings penetrate the horizon — and therefore can be genuinely called hair — thick strings are expelled; the two kinds of solution are separated by a phase transition.
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Elsner, Joachim. "Surfaces and extended defects in Wurtzite GaN." [S.l. : s.n.], 1998. http://deposit.ddb.de/cgi-bin/dokserv?idn=961023716.
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Olivier, Ezra Jacobus. "Analysis of the extended defects in 3C-SiC." Thesis, Nelson Mandela Metropolitan University, 2008. http://hdl.handle.net/10948/730.
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The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.
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Eberlein, Thomas Andreas Georg. "Point and extended defects in Group IV semiconductors." Thesis, University of Exeter, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398963.
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Fujita, Naomi. "Modelling of point and extended defects in Group IV semiconductors." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/90563.
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In this thesis first-principles calculations of point and extended defects in diamond and silicon are reported. In single crystal diamond grown by chemical vapour deposition (CVD) dislocations are observed as mixed-type 45° and edge-type dislocations lying along <100> with 1/2<110> Burgers vectors. Results are presented on the core structures, core energies and electrical properties of both types of dislocations and their interaction with nitrogen is investigated. Then the focus turns to the brown diamond problem. Despite concerted research efforts, the origin of the brown colouration of diamond is still under discussion. Recently, the attention was drawn to vacancy-related defects. Experiments on type IIa diamonds indicate that the brown colour is caused by vacancy-type extended defects, however the shape and size of these defects remained unclear. In this work, the structural, electrical and optical properties of large spherical vacancy clusters and thin vacancy disks are investigated by means of density functional theory and the calculations are compared with recent experimental measurements on brown diamond. High pressure high temperature treatment (HPHT) of brown type Ia diamonds above 2000°C results in the loss of the brown colour and the formation of nitrogen-vacancy defects. The generation of such defects requires a source of mobile vacancies during the annealing process. It is suggested that the vacancy cluster model described in this thesis can explain the observed annealing behaviour since the break-up of the clusters leads to a supersaturation of mobile vacancies which readily complex with substitutional nitrogen atoms present in the material. Therefore, the effect of HPHT treatment of brown type Ia diamond is investigated by studying the formation energies of common and rare defects and estimates of their equilibrium concentrations at different annealing stages are given. Finally, an open problem also involving nitrogen, but in a different group IV semiconductor is considered. In Czochralski-silicon, nitrogen-related shallow thermal donors are formed between 500 and 750°C. Until now the exact chemical composition and atomic structure of these defects are not well established. Here, it is shown that NO and NO_2 belong to the family of nitrogen-oxygen related shallow thermal donors. Based on the law of mass action the equilibrium defect concentrations are predicted. Finally, the theoretical results are compared to recent Fourier transform infrared (FTIR) spectroscopy measurements.
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Cristiano, Filadelfo. "Extended defects in SiGe device structures formed by ion implantation." Thesis, University of Surrey, 1998. http://epubs.surrey.ac.uk/843871/.
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The use of SiGe/Si heterostructures in the fabrication of electronic devices results in an improvement of the device performances with respect to bulk silicon. Ion implantation has been proposed as one of the possible technologies to produce these structures and, thus, the aim of this work is to develop an ion beam technology to fabricate strained SiGe heterostructures. The formation of extended defects in SiGe alloy layers formed by high dose Ge+ ion implantation followed by Solid Phase Epitaxial Growth (SPEG) has been investigated by transmission electron microscopy. Rutherford backscattering spectroscopy has also been used to determine the chemical composition and the crystalline quality of the synthesised structures. In addition, X-ray diffraction has been used to evaluate the strain level in selected samples. Two different structures have been studied in this project. The first consisted of "all-implanted" layers, where the Ge+ implants were followed in some cases by additional implants of Si+ and/or C+ ions, prior to SPEG, to investigate methods to inhibit defect formation. The second was achieved by capping the ion beam synthesised SiGe alloy layer by the deposition of a thin film of silicon, in order to realise structures compatible with device dimensions. Single crystal device worthy SiGe alloy layers have been achieved by implantation of Ge+ ions at energies ranging from 70 keV to 400 keV, where the only extended defects observed are EOR defects at a depth correspondent to the a/c interface formed during the Ge+ implant. In some cases, "hairpin" dislocations have also been observed in the vicinity of the EOR defects and extending up to the surface. Both types of defects are annihilated after post-amorphisation with 500 keV Si+ and replaced with dislocation loops at a depth of about 1 fj,m. For each Ge+ implantation energy a critical value of the peak germanium concentration exists above which the structures relax through the formation of stacking faults or "hairpin" dislocations nucleated in the vicinity of the peak of the germanium concentration depth profile and extending up to the surface. A critical value of the elastic energy stored in the structures (~300 mJ/m2) has been determined above which ion beam synthesised SiGe alloys relax, independently of the implantation energy. This empirical approach has been found to successfully account for the results obtained in this work as well as in many other studies reported in the literature. "Hairpin" dislocations formed under different experimental conditions have been investigated by plan view TEM and have been found to have the same crystallographic orientation () and Burgers vector (b= a ). Their formation has been explained within a "strain relaxation model". For a regrowth temperature of 700° C, all samples investigated by XRD have been found to be almost fully strained, including samples containing relaxation-induced defects, indicating that, under these conditions, the energy transferred to the defects is very low. C+ co-implantation has been successfully used to reduce both relaxation-induced defects and EOR dislocation loops. It is noted that a mixed technology entailing both layer deposition and ion implantation to produce the Si/SiGe/Si device structures requires extra process steps to control surface contaminations, pre cleaning and/or native oxide formation, resulting in increased fabrication costs. In this work an " all-implanted" route to the synthesis of Si/SiGe/Si device structures is therefore described, which exploits all of the advantages given by ion implantation.
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Ziebarth, Benedikt [Verfasser], and Christian [Akademischer Betreuer] Elsässer. "Interactions between metallic impurities and extended defects in silicon from first-principles." Freiburg : Universität, 2015. http://d-nb.info/1119898811/34.
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Du, Yaojun. "The dynamics of Si small point defects and formation of Si extended structures." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1126900310.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xix, 133 p.; also includes graphics (some col.). Includes bibliographical references (p. 126-133). Available online via OhioLINK's ETD Center
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Amaku, Afi. "A study of the electrical properties of point and extended defects in silicon." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339355.
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Lymperakis, Liverios. "Ab-initio based multiscale calculations of extended defects in and on group III-nitrides." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=97581284X.
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Cristiano, Filadelfo. "Ion Implantation‐Induced extended defects: structural investigations and impact on Ultra‐Shallow Junction properties." Habilitation à diriger des recherches, Université Paul Sabatier - Toulouse III, 2013. http://tel.archives-ouvertes.fr/tel-00919958.
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This dissertation summarises my research activities in the field of Ion Implantation-Induced extended defects and of their impact on the properties of Ultra-Shallow source/drain junctions (USJs) in miniaturized MOS transistors. The most common method for the fabrication of source/drain regions consists in the localized doping of the substrate material by ion implantation, followed by thermal annealing to achieve electrical activation. The major problem related to the use of ion implantation is the formation of various defect types resulting from the precipitation of the large amounts of interstitials and vacancies generated during the implantation process and their interaction with dopant atoms during annealing. The various complex interactions between the defects and the implanted dopants are at the origin of the diffusion and activation anomalies that represent the major obstacles to the fabrication of USJs satisfying the ITRS requirements. The main results of my work will be presented in three parts. The first part is dedicated to the fundamental studies on the formation and evolution of implant-induced defects and on their impact on transient enhanced diffusion (TED). These studies contributed (i) to provide a unified description of implantation-induced defect evolution, explaining why, depending on the implant and annealing conditions, a given defect type is formed, dissolves during annealing or transforms into a larger defect with different crystallographic characteristics and (ii) to improve the existing models by extending them to all defect families, including a correct TED dependence on the defects' size distributions. In the second part, I will focus on the defect-dopant interactions causing dopant activation anomalies, due to their impact on the active dose and is some cases, also on the carrier mobility. In the case of p+-n junctions formed by Boron implantation, these anomalies are due to the formation of small Boron-Interstitial Clusters (BICs), which will be at the centre of all the studies presented in this part. Other investigated defect-dopant interactions include the formation of Fluorine-related Si interstitial traps, used to reduce both B Transient Enhanced Diffusion and dopant deactivation, and the dopant trapping by implantation-induced defects. The progressive introduction of advanced processes and materials in the semiconductor industry during the last decade raised some specific questions related to the fabrication of USJs, including the formation of implant-induced defects during ultra-fast annealing, their evolution in the presence of the buried Si-SIO2 interface in SOI materials or the Boron activation stability in Germanium. We will address these issues in the third part of this presentation. Due to the increased difficulties to maintain the MOS miniaturization pace (as well as to the approaching of its physical limits), the general context of the MOS-related research domain has largely evolved over the last years. On the one hand, the continuous optimisation of advanced doping and annealing schemes for the fabrication of USJs will therefore have to deal with the increasingly important requirement of reducing power consumption in future device generations. On the other hand, the years 2000s have seen the emergence of the so-called "More-than-More" domain, consisting in the addition of novel functionalities to electronic devices based on (or derived from) Silicon MOS technology. The perspectives of my research activity within this "extended-CMOS" context will finally be presented at the end of the presentation.
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Verma, Lokesh. "Spatialized study of the coupling between extended defects and mobile species in the nuclear fuel." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0478.
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Les gaz de fission produits pendant l'irradiation d'un combustible nucléaire peuvent provoquer du gonflement et la libération de gaz de fission, qui peut affecter la performance du combustible. La théorie de la diffusion effective, qui est généralement utilisée dans la modélisation de l’irradiation de base du combustible nucléaire, ne permet pas de prédire le dégagement de gaz de fission intra-granulaire pendant les essais de recuit post-irradiation. Nous discutons et analysons trois des mécanismes possibles: le mouvement dirigé vers la surface du grain de bulles de gaz intra-granulaires pressurisées dans un gradient de lacunes, le mouvement brownien de ces bulles via des mécanismes de diffusion en volume et en surface, un scénario de mouvement de bulles de gaz avec les dislocations via le mécanisme de montée de dislocation. Un nouveau modèle spatialisé, BEEP, a été mis au point pour la migration des bulles de gaz et leur interaction avec les défauts ponctuels. Les analyses effectuées à l'aide du modèle BEEP montrent que ni le mouvement dirigé ou aléatoire, ni leur combinaison ne peuvent expliquer le relâchement important de gaz de fission obtenu lors du recuit post-irradiation dans notre expérience de référence. Il a été démontré que le mécanisme de montée peut constituer un mécanisme de relâchement de gaz important, cependant, le coefficient de diffusion de lacunes le long d’une dislocation, non connu, a été pris comme paramètre ajustable. Les travaux menés dans le cadre de cette thèse ont permis de mieux comprendre le relâchement des gaz de fission. Ce travail permet aussi de mieux cerner les questions aux quelles il serait utile de répondre aux plus basses échellesFission gases (Xe, Kr) produced during irradiation in a nuclear fuel can contribute to significant effects such as swelling and fission gas release which may affect the overall performance of the fuel. The effective diffusion theory, which is generally used in the modelling of base-irradiation of nuclear fuel, cannot predict the intra-granular fission gas release during post-irradiation annealing tests. From the several scenarios proposed, we discuss and analyze three such mechanisms: the directed movement of pressurized intra-granular gas bubbles in a vacancy concentration gradient towards the grain surface, the Brownian movement of these intra-granular bubbles via volume and surface diffusion mechanisms, a scenario of gas bubble movement along with the dislocations via the mechanism of dislocation climb. A new spatially resolved model, BEEP Model, has been developed for gas bubble migration and its interaction with point defects. Analyses done using the BEEP model show that neither of the directed or random movement, nor their combination, could explain the large fission gas release obtained during post-irradiation annealing in our reference experiment. The dislocation climb mechanism has been demonstrated as a prominent gas release mechanism, however, the values for diffusion of vacancies on the dislocations are not known and were chosen to allow gas release. The work carried out in this thesis has provided a better insight to the transport of intra-granular gas bubbles and its impact on fission gas release. This work also emphasized the questions that need to be answered at the lower scales
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Langhans, Frank [Verfasser], Matthias [Akademischer Betreuer] Bickermann, Matthias [Gutachter] Bickermann, and Peter [Gutachter] Wellmann. "Extended defects in PVT-grown AlN / Frank Langhans ; Gutachter: Matthias Bickermann, Peter Wellmann ; Betreuer: Matthias Bickermann." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156010926/34.
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Sun, Lixin Ph D. Massachusetts Institute of Technology. "Impact of extended defects on ion diffusion and reactivity in binary oxides : assessed by atomistic simulations." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121806.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 195-238).
Extended defects, such as dislocations, grain boundaries and surface step edges, are ubiquitous in nanomaterials that function in electrochemical devices and heterogeneous catalysts. The objective of this thesis is to advance the understanding of the influence of extended defects on ion diffusion and surface reactivity. The thesis investigates the interplay between extended defects and point defects and how this interplay alters ion diffusion and surface reactivity of binary oxides using multiple advanced computational modeling methods. The findings provide physics based insights into how to design the microstructure of materials in order to enhance the reactivity of materials in solid oxide fuel/electrolysis cells and catalysis. The work brings together computational techniques to address the chosen problems at suitable size and time scales.
In the first two studies, the goal is to resolve the distribution and transport kinetics of charged point defects, including both anions and cations, the latter being much slower than the former. The approach that is adapted for this problem area in this thesis is hybrid Monte Carlo and Molecular Dynamics simulations. The first study models an edge dislocation in reduced and doped ceria. The results showed that the dislocation redistributes point defects via elastic energy minimization and charged defect electrostatic association. The defect redistribution slows down oxide ion transport in the dislocation, contrary to the role of dislocations in accelerating atom migration in metals. The finding indicates that dislocations are detrimental for binary oxide solid electrolytes used for solid fuel cells, electrolyzers and membranes. In the second study, the interface between CeO₂ and Y₂O₃ was investigated.
The interface structural vacancies stabilizes and attract Ce³⁺ ions and oxygen vacancies. This leads to 1-2 orders of magnitude higher oxygen non-stoichiometry at the interface at low temperature and oxygen rich envirionments compared with that in bulk CeO₂. The interfacial enhanced oxygen capacity and the enhancement of electron polarons can be beneficial for catalyzing oxidation and reduction reactions and electron transport on ceria-based heterogeneous catalysts. The third study focuses on resolving whether dislocations could be sites to stabilize single atom catalysts, that are attractive for catalysis reactions but difficult to keep stable as single atoms at elevated temperatures. The approach here is density functional theory to compute defect formation energy at the core of an edge dislocation in Cu-CeO₂ in comparison to that in the bulk.
The result shows that dislocations can enrich Cu defects in an atomically-sized area and also stabilizes catalytically active cation species Cu¹⁺ and Ce³⁺. This result indicates that dislocations in Cu-CeO₂ have a great potential in anchoring single atom catalysts and enhance local reactivity. Lastly, a coupled quantum mechanics and molecular mechanics algorithm (QM/MM) is established and used to quantify the reactivity for oxygen evolution reaction (OER) at corners and edges of realistic nanoparticles. A 9.5-nm sized anatase titania nanoparticle was simulated by this approach. The reaction energies of oxygen evolution at the corners and edges are found 0.1 - 0.5 eV lower than on the facets since the former have a stronger adsorption of hydroxyl. However, some of the active sites are also prone to form electron polarons which can recombine with holes and compromise the high OER activity.
By considering both factors, the most active structures are found to be the (101) facets and the edges between {101} facets. This work provides insights for designing nanoparticle shapes for better photocatalysts and also demonstrates the potential of using the QM/MM method to simulate nanoparticles with realistic sizes.
by Lixin Sun.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
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Adepalli, Kiran Kumar [Verfasser], and Joachim [Akademischer Betreuer] Maier. "Influence of extended defects on the electrical properties of TiO2 (rutile) / Kiran Kumar Adepalli. Betreuer: Joachim Maier." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2013. http://d-nb.info/1037727789/34.
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Okumura, Hironori. "Formation Mechanism of Extended Defects in AlN Grown on SiC{0001} and Their Reduction by Initial Growth Control." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157592.
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Baker, Susan Colleen Rozanne. "The performance of children with Attention Deficit Hyperactivity Disorder on Griffiths Mental Development Scales - extended revised." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/388.
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Research has shown that Attention Deficit Hyperactivity Disorder (ADHD) is one of the commonest neurodevelopmental disorders which has a negative impact on a child. However, to date limited research has been conducted on learners, and specifically those learners with ADHD, within a National Education stream. Furthermore, running concurrently with this are new developments in education in South Africa. An inclusive educational policy favours the incorporation of all children into a mainstream scholastic setting, regardless of their diverse needs. In addition to educational changes for children with ADHD, many parents are presently unable to afford the medication commonly used to treat the disorder, resulting in both parents and teachers having to manage these children with limited professional support. It is widely accepted that early assessment and intervention are necessary in order to maximise a child’s potential. For this reason, the primary aim of this study was to explore and describe the developmental profile of children with ADHD on the Griffiths Mental Development Scales-Extended Revised (GMDS-ER). Further aims were to compare the performance of the clinical sample to a normal South African sample. In order to achieve these aims, a quantitative, exploratory-descriptive research design was employed. The sample (N = 38) of ADHD were selected by means of a non-probability, purposive sampling procedure, from various pre-school and primary schools in the Nelson Mandela Metropole. The normal sample (N = 38) was drawn from an existing database created during the revision of the Scales. Information was collated using the Conners 39 Item Teacher Rating Scale, biographical data, as well as the results of an assessment from the GMDS-ER. In this study the general performance of the ADHD sample on the GMDS-ER was found to be above average. Furthermore the performance of these children on the six Subscales of the GMDS-ER ranged from average to superior, with the poorest performance being on the Eye and Hand Co-ordination Subscale, and the best performance being on the Performance Subscale. Significant differences between the ADHD and normal sample were found on the General Quotient (GQ) as well as three of the six Subscales, namely, the Hearing and Speech, Eye and Hand Co-ordination and Performance Subscales. Generally, the results of the study suggest that a specific developmental profile for children with ADHD exists. Additionally, the study highlighted the success with which the GMDS-ER can be utilised on a specific clinical population.
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Nedelkoski, Zlatko. "The atomic and spin-electronic structure of interfaces and extended structural defects in the Co-based full Heusler alloys." Thesis, University of York, 2017. http://etheses.whiterose.ac.uk/16736/.
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The atomic and spin-electronic structure of interfaces and extended structural defects in the Co-based full Heusler alloys is studied. Interfaces between a half-metallic Heusler alloy and metal or semiconductor are fundamental and determine the performance of spintronic devices such as spin valves or devices for spin injection applications. It is shown that for the Co2MnSi/Ag bulk-like terminated interfaces, the interfacial spin-polarisation significantly depends on the atomic plane termination. In addition, on the example of experimentally realised interface, part of a spin valve, it is demonstrated that there is an additional monolayer at the interface, which as shown by the density functional theory calculations can create significantly negative local spin-polarisation, detrimental for the device performance. It is demonstrated that the interfaces between the Heusler alloy and Si, suffer from large interfacial interdiffusion which leads to a gradual decrease of magnetic moment over 2-3 nm region in which the spin-polarisation is also significantly affected. It is shown that even sharp interfaces are not desirable since they lead to reversed spin-polarisation. However, it is demonstrated that the addition of thermodynamically stable Si-Co-Si monolayer provides very high spin-polarisation across all interface layers. An ideal candidate for spin injection applications is found to be the Co2FeAl0.5Si0.5/Ge interface which shows very minor and atomic plane selective interdiffusion that does not affect film’s half-metallic properties, absence of formation of any secondary phases and almost no interfacial strain. Based on models derived from electron microscopy observations, it is demonstrated that this interface retains very high interfacial spin-polarisation. Finally, the atomic structure of an extended structural defect observed in Co2FeAl0.5Si0.5 thin film is revealed by electron microscopy. The performed density functional theory modelling shows that these boundaries reverse the sign of spin-polarisation, hence their presence has to be minimised in order to achieve films with better properties.
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Flood, William Alan. "An extended functional analysis of off-task behavior in children with attention deficit-hyperactivity disorder (ADHD)." Scholarly Commons, 2001. https://scholarlycommons.pacific.edu/uop_etds/2649.
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A recent trend in the field of behavioral assessment and treatment has been the use of functional analyses. This assessment technique has been utilized with success to reduce self-injurious, stereotypic, and aggressive behavior in individuals with developmental disabilities. However, few studies have used an extended functional analysis to assess off-task behavior in children with Attention Deficit-Hyperactivity Disorder (ADHD). The present study evaluated the use of an extended functional analysis and subsequent interventions for three children with ADHD. Results suggested that automatic reinforcement and access to peer attention maintained the off-task behavior of the participants. Function-based interventions, one designed for automatic maintained behavior and two designed for peer-attention maintained behavior, were then evaluated. All of these interventions eliminated or reduced off-task behavior to low rates in all participants. Implications for the further development and use of this procedure with this population and target behavior are discussed.
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Parolin, Rosanne. "The effects of extended time on the mathematics performance of students with and without attention deficit hyperactivity disorder." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2006. http://proquest.umi.com/login?COPT=REJTPTU0NWQmSU5UPTAmVkVSPTI=&clientId=3739.
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Santisteban, Lopez Jose. "Dose response of extended release dexmethylphenidate and mixed amphetamine salts on sleep of youth with attention deficit/hyperactivity disorder." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121584.
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Background. Attention-Deficit/Hyperactivity Disorder (ADHD) is characterized by impulsivity, hyperactivity, and inattention, which affects 5-10% of school-age children. The first-line treatment for ADHD is stimulant medication, which increase levels dopamine (DA) and norepinephrine (NE). These medications are highly effective, but not always tolerated. Sleep side effects, such as insomnia, are reported for both stimulant classes and are usually, but not always, mild and transitory, which can lead to treatment discontinuation. Poor tolerability may limit efficacy by compromising the ability to prescribe effective doses. Few studies have assessed the comparative effectiveness of long-acting methylphenidate and amphetamine formulations in youth with ADHD, and it is unclear if there are differential effects of drug and/or dose on sleep. MAS increase NE and DA levels more than d-MPH and hence could be affecting sleep differently. Objectives. We sought to determine if there are significant differences in the dose-response effects of ER D-MPH and ER MAS on objective measures of sleep. Methods. Children, aged 10-17 (n=37), participated in a double-blind crossover study comparing two stimulants (extended release DMPH, MAS) at three doses (10, 20, 30 mg) and placebo. Each treatment session lasted one week, for a total protocol duration of eight weeks. Sleep was assessed in all conditions using actigraphy and questionnaires. Results. Sleep schedule measures showed a significant effect for dosage on sleep start time (F(1,36)=6.284, p<0.05), with a significantly later sleep start time when children were on 20mg or 30mg dosages, compared to placebo (p<0.05). Sleep duration revealed a significant dose effect on actual sleep duration (F(1,36)=8.112, p<0.05), with significantly shorter actual sleep duration for subjects receiving 30mg compared to those on placebo (p<0.05). There were no significant differences between medications. Conclusion. Higher dosages reduce sleep duration and lead to later sleep start times, regardless of medication.Contexte. Le Trouble Déficitaire de l'Attention et de l'Hyperactivité (TDAH) est caractérisé par l'impulsivité, l'hyperactivité, et l'inattention. Le TDAH se produit dans 5-10% des enfants scolaires. Le traitement de première ligne pour le TDAH sont les stimulants. Les stimulants augmentent les niveaux de dopamine (DA) et de norépinephrine (NE). Ces médicaments sont hautement efficaces, mais ne sont pas tolérés par tous les enfants. Les effets indésirables, comme l'insomnie, sont souvent reportés pour ces stimulants. Par contre, leurs effets sont habituellement, mais pas toujours, bénins et transitoires. En général, les enfants souffrant d'insomnie sévère cessent le traitment. La faible tolérance peut limiter l'efficacité en compromettant la possibilité de prescrire des doses plus efficaces. Peu d'études ont mesuré l'efficacité comparative du methylphenidate á action prolongée et de l'amphétamine á action prolongée chez les enfants avec un TDAH. De plus, il n'est pas clair s'il y a un effet différentiel de médicament et/ou de dose sur le sommeil. Les MAS augmentent les niveaux de NE et DA plus que les d-MPH, et donc pourraient avoir une incidence sur le sommeil d'une manière différente. Objectifs. Nous cherchons à déterminer s'il existe des différences significatives dans les effets de dose-réponse des d-MPH et MAS á actions prolongées sur des mesures objectives du sommeil. Méthodes. Les enfants, âgés 10-17 (n=37), ont participé dans une étude croisée à double insu comparant trois doses (10, 20, et 30mg) de d-MPH ou MAS au placebo. Chaque séance de traitement a duré une semaine, pour une durée totale de protocole de huit semaines. Le sommeil a été mesuré dans toutes les conditions avec actimétrie et questionnaires. Résultats. Les mesures d'horaire du sommeil ont montré un effet significatif de dose à l'heure de début de sommeil (F(1,36)=6.284, p<0.05); les enfants recevant 20mg ou 30mg on débuté leur sommeil significativement plus tard que ceux qui ont reçu le placebo (p<0.05). Un effet significatif de dose sur la durée réelle du sommeil (F(1,36)=8.112, p<0.05) a été découverte, avec une durée de sommeil plus courte quand les sujets ont reçu 30 mg comparé au placebo (p<0.05). Aucune différence entre les deux médicaments n'a été trouvée. Conclusion. Des doses plus élevées réduisent la durée du sommeil et conduisent à dormir plus tard, indépendamment de médicaments.
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Zhao, Yanfei. "Fundamental Solutions and Numerical Modeling of Internal and Interfacial Defects in Magneto-Electro-Elastic Bi-Materials." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1433529049.
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Ramadan, Amr Hazem Helmy [Verfasser], Souza Roger A. [Akademischer Betreuer] De, and Arne [Akademischer Betreuer] Lüchow. "Simulation studies of extended defects in the model system of the functional oxide strontium titanate / Amr Hazem Helmy Ramadan ; Roger A. De Souza, Arne Lüchow." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130590682/34.
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Müller, Julian [Verfasser], and Erdmann [Gutachter] Spiecker. "A Study on Microstructures and Extended Defects in Ni- and Co-Base Superalloys - Development and Application of Advanced TEM Techniques / Julian Müller. Gutachter: Erdmann Spiecker." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2016. http://d-nb.info/1111102503/34.
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Merabet, Amina. "Etude par microscopie électronique du silicium aux petites échelles : comportement mécanique et structure atomique des défauts." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0554/document.
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De récents travaux consacrés à l’étude des propriétés des matériaux aux petites échelles ont souligné des différences exceptionnelles dans le comportement mécanique des nano-objets par rapport aux matériaux massifs. Dans le cas du silicium, une transition fragile-ductile à température ambiante a été observée lorsque la taille des échantillons est réduite. Cependant, les défauts et les mécanismes à l’origine de ce changement de comportement n’ont pas été clairement identifiés. Ce travail repose sur l’étude post mortem de nanopiliers déformés, en utilisant différentes techniques de microscopie électronique. Les nanopiliers étudiés ont été préparés par gravure plasma et déformés en compression à température ambiante. Les résultats obtenus durant cette thèse, confirment la différence de comportement des nano-objets par rapport au matériau massif. Par ailleurs, une grande variété de défauts produits lors de la compression a été observée. L’orientation cristallographique de l’axe de sollicitation semble avoir un impact important sur les mécanismes à l’origine du comportement ductile observé. La comparaison entre images HRTEM expérimentales et simulées témoigne de la propagation simultanée de dislocations partielles et parfaites dans les plans {111}. De plus, des événements plastiques ont également été observés dans des plans {115}. Divers mécanismes de déformation possibles impliqués lors de la compression des piliers sont décrits à partir des observations microscopiques. Un modèle tenant compte de l’influence sur la mobilité des dislocations des interactions entre systèmes de glissement est proposé afin d’expliquer la transition fragile-ductile observé aux petites échellesSeveral recent works devoted to the study of the properties of materials at small scales have revealed exceptional differences in the mechanical behavior of nano-objects as compared to bulk material. In the case of silicon, a brittle-ductile transition at room temperature has been observed when the sample size decreases. However, the extended defects and mechanisms behind this behavioral change have not been clearly identified. This work is based on the post mortem study of deformed nanopillars, using different electron microscopy techniques. The studied nano-pillars of 100 nm in diameter were prepared by plasma etching (RIE) and deformed in compression at room temperature. The results obtained during this thesis confirm the difference in the behavior of nano-objects compared to bulk material. Moreover, a large variety of defects produced during plastic deformation has been observed. The crystallographic orientation of the deformation axis seems to have a significant impact on the mechanisms behind the observed ductile behavior. The comparison between experimental and simulated HRTEM images notably evidences the simultaneous propagation of partial and perfect dislocations in {111} planes. In addition, unexpected plastic events have also been observed in {115} planes. Various possible deformation mechanisms involved during the nano-compression of the pillars are described, based on the microscopic observations. Finally, a model considering the influence of interactions between various activated systems on the mobility of dislocations is proposed to explain the brittle-ductile transition observed at small scales in silicon
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Pokam, Kuisseu Pauline Sylvia. "Détachement des substrats ultra-minces des matériaux semi-conducteurs par implantation d’hydrogène à hautes énergies pour les applications photovoltaïques et électroniques." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2035/document.
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Cette thèse a été motivée par l’étude d’un procédé innovant de production de substrats ultra-minces (d’épaisseur variant de 15 μm à 70 μm), basé sur l’implantation d’hydrogène à haute énergie, dans notre cas comprise entre 1MeV et 2.5MeV. Une telle implantation suivie d’un traitement thermique approprié, conduit au détachement d’un film mince autoporté, appelé « substrat ultra-mince ». L’intérêt de ce procédé de détachement est purement économique, car il ne génère presque aucune perte de matière première. Nous l’avons particulièrement utilisé pour produire des substrats ultra-minces de silicium (100), pour la production des cellules PV bas-coûts. Dans le but d’élargir les champs d’applications du procédé, le détachement de substrats ultra-minces de deux autres matériaux (le Ge et le SiC) très utilisés en électronique a aussi été étudié. Ainsi, dans cette étude, les paramètres optimaux d’implantation (énergie et fluence) et de recuits conduisant au détachement de grandes surfaces de Si(100) ont tout d’abord été investigués. Ensuite, l’application technologique du procédé proposé a été validée par la réalisation des cellules solaires au moyen des substrats ultrafins de Si détachés (50 μm et 70 μm d’épaisseur). Les performances PV obtenues ont été assez proches de celles obtenues avec une cellule référence réalisée sur un substrat standard. Par la suite, une étude détaillée faite par TEM et par FTIR sur les défauts étendus à différents stades de recuits a permis de mettre en lumière la nature et la distribution spatiale des défauts précurseurs de la fracture dans le Si après implantation à haute énergie. Enfin, des essais de détachements réalisés avec le Ge et le SiC, lesquels ont été comparés au cas du Si, ont permis d’en savoir plus sur les critères de détachement. En effet, plus le matériau sera rigide, i.e. plus il aura un module d’Young élevé, plus la fluence et la température de recuit nécessaires pour le détachement seront élevéesThe motivation of this thesis was the study of an innovative process for the production of ultra-thin substrates (with thicknesses between 15 μm and 70 μm), based on the high energy hydrogen implantation, in our case in the range of 1 MeV to 2.5 MeV. Such an implantation followed by an appropriate thermal annealing, lead to the delamination of a freestanding thin layer, that we call “ultra-thin substrate”. The benefit of this delamination process is purely economic, since almost no raw material is lost. We have particularly used this process to produce ultra-thin (100) Si substrates, for the production of low-cost PV solar cells. In order to extend the process application fields, the delamination of ultra-thin substrates of two other materials (Ge and SiC) widely used in electronics has been also studied. In our work, the optimal implantation parameters (energy and fluence) and thermal annealing, leading to the delamination of large areas of Si (100) were first investigated. Subsequently, in order to validate the technological application of our process, solar cells have been performed with ultra-thin silicon substrates delaminated, with thicknesses of 50 μm and 70 μm. Results of PV performances obtained were quite close to those obtained with a reference solar cell achieved on a standard substrate. After that, in order to highlight the nature and the spatial distribution of fracture precursor defects after high energy hydrogen implantation in silicon, which had not yet done so far the subject of specific studies, characterizations have been carried out at different annealing stages, by means of TEM and FTIR. Finally, delamination results obtained with Ge and SiC, which were compared to the case of Si, helped us to learn more about delamination criteria. Indeed, we observed that, as the material rigidity increase, i.e. as the Young modulus is higher, the fluence and temperature require for the delamination will be also high
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Pingault, Timothée. "Etude pionnière combinant l’implantation d’hydrogène et la fracture induite par contrainte pour le détachement de couches ultra-minces de silicium pour le photovoltaïque." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2048/document.
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La motivation de cette thèse est la production innovante de germes ultra-minces de silicium cristallin. L’utilisation de tels germes dans un procédé de fabrication de cellules solaires permettrait une réduction importante de la consommation de silicium, qui compte déjà pour 60% du coût de production des panneaux solaires de première génération. Dans le cadre de cette thèse, une méthode pionnière de détachement de germes minces a été mise en oeuvre. Dans cette méthode, une contrainte induite mécaniquement est guidée par des défauts étendus induits par l’implantation d’hydrogène. Par cette méthode, le détachement de germes minces d’environ 710nm d’épaisseurs a été obtenu. Le but est ensuite d’utiliser ces germes pour faire croitre du silicium cristallin avec des épaisseurs variables à souhait, soit une technique kerf-free : sans pertes. Cette étude présente ainsi les étapes menant à la mise en oeuvre de ce procédé : en premier lieu, un état de l’art des méthodes de détachement de films ultra-minces existants est réalisé. Celui-ci nous a ainsi guidés vers l’implantation d’hydrogène en tant que méthode viable du guidage de la fracture. Par la suite, différents tentatives de détachement de germes ultra-minces ont été réalisés puis caractérisés, notamment par MEB, MET, AFM et DRX. Dans de bonnes conditions de collage et de croissance de défauts, le détachement de germes ultra-minces de silicium cristallin a été réalisé. Par la suite, la croissance et la cristallisation de couches de silicium amorphe a été réalisée sur les germes détachés. Pour finir, certaines couches détachées ont été utilisées pour la production de cellules solaires prototypesThe goal of this thesis is to find an innovative way to produce ultra-thin crystalline silicon seeds. The use of such seeds in a solar cell production process could lead to a significant reduction of the silicon consumption, which cost alone is worth 60% of the total cost of a first generation solar panel. Within the context of this PhD thesis, a pioneer seed exfoliation method was implemented. This method use the defects induced by hydrogen implantation to guide a stress-induced spalling process. This method has allowed the exfoliation of 710nm-thick crystalline silicon seeds. These seeds will then be used for the growth of crystalline silicon layers of any desired thickness, hence a totally kerf-free method. This thesis work presents the steps leading to the implementation of this process: firstly, the state of the art of ultra-thin films exfoliation methods is reviewed, which guided us towards the use of hydrogen implantation as a crack guide. Then, different ultra-thin seeds exfoliation processes were tried and characterized, specifically by SEM, TEM, AFM and XRD. In the right conditions of bonding and defects growth, ultra-thin silicon seeds were successfully exfoliated. The growth and crystallization of amorphous silicon layers on these seeds were then studied. Finally, several exfoliated layers were used for the production of prototype solar cells
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Song, Xi. "Activation des dopants implantés dans le carbure de silicium (3C-SiC et 4H-SiC)." Thesis, Tours, 2012. http://www.theses.fr/2012TOUR4019/document.
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Ces travaux de thèse sont consacrés à l’étude de l’activation des dopants implantés dans le carbure de silicium. L’objectif est de proposer des conditions d’implantation optimisées pour réaliser le dopage de type n dans le 3C-SiC et de type p dans le 4H-SiC.Nous avons tout d’abord étudié les implantations de type n dans le 3C-SiC. Pour cela, des implantations de N, de P et une co-implantation N&P avec les recuits d’activation associés ont été étudiés. L’implantation d’azote suivie d’un recuit à 1400°C-30min a permis une activation proche de 100% tout en conservant une bonne qualité cristalline. Une étude sur les propriétés électriques des défauts étendus dans le 3C-SiC a également été réalisée. A l’aide de mesures SSRM, nous avons mis en évidence l’activité électrique de ces défauts, ce qui rend difficile la réalisation de composants électroniques sur le 3C-SiC.Nous avons ensuite réalisé une étude du dopage de type p par implantation d’Al dans le 4H-SiC, en fonction de la température d’implantation et du recuit d’activation. Nous avons pu montrer qu’une implantation à 200°C suivie d’un recuit à 1850°C-30min donne les meilleures résultats en termes de propriétés physiques et électriquesThis work was dedicated to the activation of implanted dopants in 3C-SiC and 4H-SiC. The goal is to propose optimized process conditions for n-type implantation in 3C-SiC and for p-type in 4H-SiC.We have first studied the n-type implantation in 3C-SiC. To do so, N, P implantations, N&P co-implantation and the associated annealings were performed. The nitrogen implanted sample, annealed at 1400°C-30 min evidences a dopant activation rate close to 100% while maintaining a good crystal quality. Furthermore, the electrical properties of extended defects in 3C-SiC have been studied. Using the SSRM measurements, we have evidenced for the first time that these defects have a very high electrical activity and as a consequence on future devices.Then, we have realized a study on p-type doping by Al implantation in 4H-SiC with different implantation and annealing temperatures. Al implantation at 200°C followed by an annealing at 1850°C-30min lead to the best results in terms of physical and electrical properties
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Pal, Terek. "Unapređenje kvaliteta alata za livenje pod pritiskom primenom tehnologija inženjerstva površina." Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2016. http://www.cris.uns.ac.rs/record.jsf?recordId=101472&source=NDLTD&language=en.
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Proučavane su koroziona postojanost i tendencija lepljenja različitihmaterijala u kontaktu sa tečnom Al–Si–Cu legurom. Ispitivanjem suobuhvaćeni čelik za rad na toplo, plazma nitrirani čelik i dupleksslojevi sa CrN, TiAlN, TiAlSiN i CrAlN prevlakama, različitog nivoapovršinske hrapavosti. Za ispitivanja pomenutih fenomenaprimenjena je metoda izvlačenja, koja je unapređena kako bi se povećalenjena tačnost i verodostojnost simulacije procesa livenja. Korozioniefekti su pojačani tako što su uzorci osim kratkog kontakta sa odlivkomzadržavani i u dužim periodima u kontaktu sa tečnom legurom (5 i 20min). Uprkos opštim stavovima, za ispitivane materijale jeustanovljeno da su sile izvlačenja uzoraka iz Al–Si–Cu odlivakanezavisne od njihovog hemijskog sastava. Uticaj hrapavosti je izraženkod uzoraka sa prevlakama kod kojih pri smanjenju hrapavosti dolazi dopovećanja sile izvlačenja. Sve ispitane prevlake su sklone mehaničkomlepljenju Al–Si–Cu legure za svoje površine, ali sa aspekta korozije utečnom metalu značajno prevazilaze performanse čelika i plazmanitriranog sloja. Duži kontakt livene legure sa površinama prevlakauzrokovao je niže vrednosti sila izvlačenja, što je posledicaoksidacije površina prevlaka. Ustanovljeno je da su ispitivaneprevlake inertne ka tečnoj leguri aluminijuma. Međutim, dolazi dooksidacije i korozije materijala podloge kroz greške rasta koje suprisutne u prevlakama. Stečena znanja o identifikovanimmehanizmima habanja i propadanja zaštitnih slojeva prevlakaposlužiće daljem razvoju dupleks slojeva namenjenih za zaštitu alataza livenje pod pritiskom.Corrosion resistance and soldering tendency of different materials in moltenAl–Si–Cu alloy were studied. Hot-working tool steel, plasma nitrided steel andduplex layers with CrN, TiAlN, TiAlSiN and CrAlN top coatings, which wereproduced to various degree of surface roughness, were covered by the study.An ejection test was employed for investigation of the concerned phenomena.The ejection test was improved in order to increase its accuracy and thereliability of process simulation. Samples were examined in both short andextended periods of contact (5 and 20 min) with liquid casting. Castingsolidification was extended in order to intensify the corrosion effects. Contraryto common findings, it was found that the ejection force of the investigatedmaterials does not depend on their chemical composition. For the coatedsamples, a pronounced dependence of the ejection force on the surfaceroughness was found. The ejection force increases with decrease in surfaceroughness. All investigated coatings are prone to mechanical soldering by Al–Si–Cu alloy. Still, their corrosion resistance substantially exceeds the corrosionresistance of steel and plasma nitrided layer. Longer exposure of coatedsamples to cast alloy induced lower ejection forces, which is a consequenceof coatings oxidation. It was found that the investigated coatings are inert toliquid aluminium. However, the underlying material undergoes oxidation andcorrosion through coating growth defects. The findings concerning the wearmechanisms of protective layers support further development of duplex layersintended for die casting tools protection.
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Rodrigues, João Nuno Barbosa. "Extended Stone-Wales defects in graphene." Doctoral thesis, 2013. https://repositorio-aberto.up.pt/handle/10216/65933.
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Rodrigues, João Nuno Barbosa. "Extended Stone-Wales defects in graphene." Tese, 2013. https://repositorio-aberto.up.pt/handle/10216/65933.
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Godwyn, Martin. "A defence of extended cognitivism." Thesis, 2006. http://hdl.handle.net/2429/18440.
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This dissertation defends extended cognitivism: a recently emerging view in the
philosophy of mind and cognitive science that claims that an individual's cognitive
processes or states sometimes extend beyond the boundaries of their brain or their skin to
include states and processes in the world. I begin the defence of this thesis through a
background discussion of several foundational issues in cognitive science: the general
character of cognitive behaviour and cognitive processes, as well as the nature and role of
representation as it is standardly taken to figure in cognition. I argue in favour of the
widely held view that cognition is best characterised as involving information processing,
and that carriers of information (i.e., representations) are ineliminable components of the
most distinctively human and powerful forms of cognition. Against this background the
dissertation argues in stages for successively stronger claims regarding the explanatory
role of the external world in cognition. First to be defended is the claim that cognition is
often embedded in one's environment. I develop this claim in terms of what I call 'parainformation':
roughly, information that shapes how we tackle a cognitive task by enabling
the extraction of task-relevant information. Proceeding then to the defence of extended
cognitivism, I draw most significantly on the work of Andy Clark. In outline, and in
general following Clark, it is argued that states and processes occurring beyond the skin of
the cognitive agent sometimes play the same explanatory role as internal processes that
unquestionably count as cognitive. I develop this claim in two versions of differing
strength: firstly, in a general way without commitment to the representational character of
extended cognition, and secondly in a specifically representational version with special
attention to intentional explanation. Against each of these versions of extended
cognitivism are ranged a number of criticisms and objections, many of which stem from
the work of Fred Adams and Ken Aizawa. The dissertation examines these objections and
rejects each of them in turn.Arts, Faculty of
Philosophy, Department of
Graduate
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Goteri, Prakash L. N. S. "Quantum models for effects of extended defects on Ion-Channeling." Thesis, 1999. http://hdl.handle.net/2009/1011.
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Kansuwan, Panya. "The role of extended defects in solid-state mass transport." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3285749.
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Elsner, Joachim [Verfasser]. "Surfaces and extended defects in Wurtzite GaN / von Joachim Elsner." 1998. http://d-nb.info/961023716/34.
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Lymperakis, Liverios [Verfasser]. "Ab-initio based multiscale calculations of extended defects in and on group III-nitrides / Liverios Lymperakis." 2005. http://d-nb.info/97581284X/34.
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Allarie, Nicolas. "Shelf life extended: the longevity and continued relevance of the binational North American Aerospace Defense Command." 2016. http://hdl.handle.net/1993/31199.
Full textAbstract:
This thesis asks why the North American Aerospace Defense Command (NORAD) continues to exist and remain relevant in the defence of North America following the disappearance of the threat of the Soviet Union at the end of the Cold War. This thesis argues that NORAD’s binational nature is key to understanding the command’s continued role in continental defence. By employing the international relation theories of functionalism and neoliberal institutionalism as a lens of analysis to understand binational defence cooperation, NORAD’s origins as a binational defence command tasked with the air defence of North America, and its acquisition of its responsibilities for drug interdiction, the continental interior, and for maritime warning are analyzed. NORAD’s longevity and continued relevance can be attributed to the command’s binational nature, which has allowed the command to focus on and institutionalize specific functional-technical solutions to select issues of mutual concern in continental defence and security for Canada and the U.S.May 2016
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"Evaluation of Compound Semiconductors for Infrared Photo-Detection Applications." Doctoral diss., 2017. http://hdl.handle.net/2286/R.I.44103.
Full textAbstract:
abstract: In this dissertation research, conventional and aberration-corrected (AC) transmission electron microscopy (TEM) techniques were used to evaluate the structural and compositional properties of thin-film semiconductor compounds/alloys grown by molecular beam epitaxy for infrared photo-detection. Imaging, diffraction and spectroscopy techniques were applied to TEM specimens in cross-section geometry to extract information about extended structural defects, chemical homogeneity and interface abruptness. The materials investigated included InAs1-xBix alloys grown on GaSb (001) substrates, InAs/InAs1-xSbx type-II superlattices grown on GaSb (001) substrates, and CdTe-based thin-film structures grown on InSb (001) substrates.
The InAsBi dilute-bismide epitaxial films were grown on GaSb (001) substrates at relatively low growth temperatures. The films were mostly free of extended defects, as observed in diffraction-contrast images, but the incorporation of bismuth was not homogeneous, as manifested by the lateral Bi-composition modulation and Bi-rich surface droplets. Successful Bi incorporation into the InAs matrix was confirmed using lattice expansion measurements obtained from misfit strain analysis of high-resolution TEM (HREM) images.
Analysis of averaged intensity line profiles in HREM and scanning TEM (STEM) images of the Ga-free InAs/InAs1-xSbx type-II strained superlattices indicated slight variations in layer thickness across the superlattice stack. The interface abruptness was evaluated using misfit strain analysis of AC-STEM images, electron energy-loss spectroscopy and 002 dark-field imaging. The compositional profiles of antimony across the superlattices were fitted to a segregation model and revealed a strong antimony segregation probability.
The CdTe/MgxCd1-xTe double-heterostructures were grown with Cd overflux in a dual-chamber molecular beam epitaxy with an ultra-high vacuum transfer loadlock. Diffraction-contrast images showed that the growth temperature had a strong impact on the structural quality of the epilayers. Very abrupt CdTe/InSb interfaces were obtained for epilayers grown at the optimum temperature of 265 °C, and high-resolution imaging using AC-STEM revealed an interfacial transition region with a width of a few monolayers and smaller lattice spacing than either CdTe or InSb.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2017
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Urban, Arne. "Position-controlled selective area growth of Ga-polar GaN nanocolumns by molecular beam epitaxy." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-609E-3.
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