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Mui, Wing-ki, and 梅詠琪. "Studies of Ga vacancy related defects in GaSb." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31226541.
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Ma, Shun-kit Martin. "The two gallium vacancy-related defects in undoped gallium antimonide." Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B31319658.
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Ma, Shun-kit Martin, and 馬信傑. "The two gallium vacancy-related defects in undoped gallium antimonide." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B31319658.
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Al-Abdulmalik, Dana A. "Evolution of vacancy-type defects in semiconductors : a positron annihilation study." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442881.
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CORONEL, SANCHEZ Edwin Danelli. "Optically detected magnetic resonance in nanodiamonds with single nitrogen-vacancy defects." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/24441.
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FACEPE
The control of the radiation-matter interaction, in our case of photons with quan- tum single emitters, as the nitrogen-vacancy (NV) defect in nanodiamonds, is crucial in the process of nano-devices fabrication. This is achieved taking advantage of the latest advances of the nano-optics to increase the interaction with single emitters for which ade-quate tools for precise interaction control has been developed. In this dissertation, we use a home-made inverted optical confocal microscope and coherent manipulation of spin states to study single NV defect in nanodiamonds. The NV defect in nanodiamonds presents optical properties that depend on the spin state of its optically active electrons, which makes them interesting for applications in nanomagnetometry, quantum informa- tion processing and nanobiothermometry. In particular, the negatively charged NV defect (NV-) exhibits single photon emission and long coherence times even at room tempera- ture. Furthermore, it has a paramagnetic ground state and can be optically polarized and read out, in an experimental technique known as Optically Detected Magnetic Resonance (ODMR). In this technique, the intensity of the fluorescence emitted by a nanodiamond depends on the spin configuration of the electronic ground state, from which an electronic transition is excited. In order to study these defects, nanodiamonds were deposited on a photolitographically structured antenna on a coverslip by spin coating and placed on the microscope. The microscope allows to both, the detection of the fluorescence and its exci- tation, by a CW laser emitting at 532 nm. The fluorescence emitted by the nanodiamond is centered around 650 nm with a zero phonon line at 637 nm. The collected fluores¬cence is sent to two avalanche photodiodes (APDs), that are in a configuration known as Hanbury-Brown and Twiss (HBT) interferometer. In it, we can verify whether the col- lected emission comes from an individual emitter, analyzing the second order correlation function g(2)(r): if g(2)(r) < 0.5 we have an emission from single photons generated by a single NV- defect in diamond. Working whit single emitter we could radiate a microwave field over the nanodiamond, which allows us to determine the resonance frequency for spin transitions in the ground state. At resonance one observes a drop in the fluorescence emitted by the nanodiamond. We explore the fact that the resonance frequency of the spin transition depends on the local magnetic field to measure the Zeeman effect gener- ated by the magnetic field of a permanent magnet (NdFeB). Finally, we realized coherent manipulation via an appropriate sequence of pulses of microwave and laser, observing Rabi oscillations. Thus, we can measure the inhomogeneous coherence time (T2*) given by the damping of Rabi oscillations.
O controle da interação radiação-matéria, em nosso caso de fotons com emissores quânticos individuais, como os defeitos de nitrogenio-vacancia (NV) em nanodiamantes, e crucial no processo da fabricacao de nano-dispositivos. Isto e conseguido aproveitando-se os ultimos avanços em nano-óptica para aumentar a interacao com emissores unicos, para os quais ferramentas adequadas para o controle preciso da interacao foi desenvolvido. Nesta dissertacao, descreveremos o uso de um microscopio confocal invertido e mani- pulacao coerente dos estados de spin de um defeito individual NV num nanodiamante. Os defeitos NV em nanodiamantes apresentam propriedades opticas que dependem do estado de spin dos seus eletrons opticamente ativos, o que os tornam interessantes para aplicacoes em nanomagnetometria, processamento de informaçao quantica e nanobioter- mometria. Em particular, defeitos NV negativamente carregados (NV-) exibem emissao de fótons unicos e longos tempos de coerência, mesmo a temperatura ambiente. Alem disso, tem um estado fundamental paramagnetico e o sistema pode ser opticamente pola¬rizado e lido, usando-se uma técnica experimental conhecida como Ressonância Magnetica Detectada Opticamente (ODMR). Nesta técnica, a intensidade de fluorescencia emitida pelo nanodiamante depende da configuracao de spin do estado eletrónico fundamental, a partir do qual a transicao eletrónica e excitada. Para estudar esses defeitos NV, nan- odiamantes foram depositados ao longo de uma antena, fotolitograficamente estruturada sobre um coverslip, usando spin coating e colocados sobre o microscopio. O microscopio permite a detecçao da fluorescencia do defeito e sua excitacao e feita por um laser CW emitindo em 532 nm. A fluorescencia emitida pelo nanodiamante ocorre em torno dos 650 nm com uma linha zero fonon em 637 nm. A fluo-rescencia coletada e enviada a dois foto-diodos de avalanche, que estao em configuraçao interferometrica do tipo Hanbury-Brown and Twiss (HBT). Nela, podemos garantir se a emissao coletada provem de um emissor individual, analisando a funcão de correlacão de segunda ordem (T): se g(2)(r) < 0, 5 comprovamos a emissão de fotons ónicos por um unico defeito NV- no nanodiamante. Trabalhamos entãao com um unico defeito NV- como emissor. Irradiando um campo de microondas sobre o nanodiamante, nos permite determinar a frequência de ressonância com a transicao de spin no estado fundamental, evidenciado por uma diminuto da flu- orescencia emitida pelo nanodiamante. Usamos o fato de que a frequencia de ressonancia da transiçao do spin depende do campo magnetico local para observar o efeito Zeeman gerado pelo campo magnetico de um ima (Nd-Fe-B). Finalmente, realizamos manipulacao coerente atraves de uma adequada sequencia de pulsos de microondas e laser, observando oscilações de Rabi. Assim, pudemos medir o tempo de coerência inhomogeneo (T2*) dado pelo amortecimento das oscilacões de Rabi.
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Chen, Haiyan. "Probing Defects and Electronic Processes on Gadolinia-doped Ceria Surfaces Using Electron Stimulated Desorption." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10427.
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Probing Defects and Electronic Processes on Gadolinia-doped Ceria Surfaces Using Electron Stimulated Desorption
Haiyan Chen
133 Pages
Directed by Professor Thomas M. Orlando
Polycrystalline gadolinia-doped ceria (GDC) has been widely investigated as a promising low temperature solid oxide fuel cell (SOFC) electrolyte and as part of composite electrodes. In this thesis, electron stimulated desorption (ESD) has been used to probe the defect related electronic properties of GDC surfaces and the interactions of water and molecular oxygen with these surfaces.
In particular, the electron irradiation induced surface charging of GDC has been found to be dependent on the incident electron energy: negative at lower energy and positive at higher energy. Trapping of electrons and holes by the gadolinium aggregated, oxygen vacancy rich grain boundaries has been considered as the origin of surface charging. Depending on the sample treatment, there can be various defects, hydroxyl groups, chemically adsorbed water molecules, or water dimers on GDC surfaces. Water and molecular oxygen interact primarily with defect sites.
Systematic investigations of electron stimulated O+ desorption have yielded activation energies relevant to oxygen vacancy production on ceria surfaces, and to surface positive charge dissipation related to ionic conduction of GDC. Highly efficient electron stimulated O+ desorption from GDC surfaces has been attributed to the lowered charge density on oxygen ions coordinated with oxygen vacancy clusters and thus may be used as a probe for surface defect types.
Electron stimulated desorption of O2+ from GDC surfaces during molecular oxygen adsorption has shown the ability of ESD to detect chemically adsorbed O2. The velocity distributions of O2+ can be used to probe intermediate adsorption species such as O2, as well as the positive charge of the surface.
Overall, this thesis has demonstrated that ESD can provide important information on the kinetics and dynamics of surface charging, charge transport, adsorption and reactions occurring at defective insulating metal oxides materials. The abilities to probe the defects and their roles in surface processes make ESD a valuable technique for surface chemistry and catalysis studies.
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Persson, Gulda Maria Christina Margareta. "Defects in Hard-Sphere Colloidal Crystals." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10695.
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Colloidal crystals of \(1.55 \mu m\) diameter silica particles were grown on {100} and flat templates by sedimentation and centrifugation. The particles interact as hard spheres. The vacancies and divacancies in these crystals are not in equilibrium, since no movement of single vacancies is observed. The lack of mobility is consistent with the extrapolation of earlier simulations at lower densities. The volume of relaxation of the vacancy has a plausible value for these densities as the volume of formation is approaching the volume in a close-packed crystal. The volume of relaxation for the divacancy is smaller than that of two vacancies, so that the association of two vacancies into a divacancy requires extra volume, and hence extra entropy. The mean square displacement of the nearest neighbors of the vacancies is an order of magnitude larger than that of the nearest neighbors of particles. The mobility of the divacancies is consistent with the extrapolation of older simulations and is similar to that associated with the annihilation of the vacancy-interstitial pair. The volume of motion of the divacancies is \(\Delta V_m = 0.19V_o (V_o\): close-packed volume) and the entropy of motion is \(\Delta S_m = 0.49k_BT\). Dislocation-twin boundary interactions can be observed by introducing strain via a misfit template. The dislocations formed are Shockley partials. When a dislocation goes through the boundary, two more dislocations are created: a reflected dislocation and one left at the boundary, both with the same magnitude Burgers vector. The dislocations relieve a total of about a third of the misfit strain. The remaining strain is sufficiently large to move the dislocation up to the boundary and close to sufficient to move the dislocation through the boundary. A small amount to extra strain energy is needed to cause nucleation of the two additional dislocations after a waiting time.Engineering and Applied Sciences
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Fuchs, Franziska [Verfasser], and Vladimir [Gutachter] Dyakonov. "Optical spectroscopy on silicon vacancy defects in silicon carbide / Franziska Fuchs. Gutachter: Vladimir Dyakonov." Würzburg : Universität Würzburg, 2016. http://d-nb.info/1112040560/34.
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Lopez, Nicolas A. "All-optical method of nanoscale magnetometry for ensembles of nitrogen-vacancy defects in diamond." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103712.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-65).
The Nitrogen-Vacancy (NV) defect in diamond has shown considerable promise in the field of small scale magnetometry due to its high localization and retention of favorable optical properties at ambient conditions. Current methods of magnetometry with the NV center achieve high sensitivity to fields aligned with the defect axis; however, with most present methods transverse fields are not directly measurable. The all-optical method of NV magnetometry provides a means to detect transverse fields by monitoring changes in the overall fluorescence profile. In this work the all-optical method is extended to ensembles of non-interacting NV centers. By establishing an external bias field aligned with the (1, 1, 1) axis, the magnitude of an unknown transverse field can be unambiguously identified through the measurement of the signal curvature. The angular orientation can be determined up to a two-fold degeneracy by observing the change in signal curvature produced when the bias field is shifted off-axis. The magnetometry method explored in this thesis thus provides good sensitivity to transverse fields, while reducing to a minimum the experimental apparatus required to operate the magnetometer.
by Nicolas A. Lopez.
S.B.
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Caulfield, John Christopher. "Transition-metal dichalcogenides and the scanning tunnelling microscope : the creation and imaging of vacancy defects." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286294.
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Chatzidrosos, Georgios [Verfasser]. "A perfect imperfection: Quantum magnetometry and applications using nitrogen-vacancy defects in diamond / Georgios Chatzidrosos." Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2021. http://d-nb.info/1241739544/34.
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Purser, Carola Midori. "Magnetic Resonance Detection using Nitrogen-Vacancy Centers in Diamond." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1560279273608591.
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Nagy, Roland [Verfasser], and Jens [Akademischer Betreuer] Anders. "Silicon vacancy defects in 4H-silicon carbide semiconductor for quantum applications / Roland Nagy ; Betreuer: Jens Anders." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1201646154/34.
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Ngetich, Geoffrey. "The defect level of carbon vacancy carbon antisite pair in 4H-SiC photo induced electron paramagnetic resonance." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/ngetich.pdf.
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Maurer, Peter. "Coherent control of diamond defects for quantum information science and quantum sensing." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11431.
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Quantum mechanics, arguably one of the greatest achievements of modern physics, has not only fundamentally changed our understanding of nature but is also taking an ever increasing role in engineering. Today, the control of quantum systems has already had a far-reaching impact on time and frequency metrology. By gaining further control over a large variety of different quantum systems, many potential applications are emerging. Those applications range from the development of quantum sensors and new quantum metrological approaches to the realization of quantum information processors and quantum networks. Unfortunately most quantum systems are very fragile objects that require tremendous experimental effort to avoid dephasing. Being able to control the interaction between a quantum system with its local environment embodies therefore an important aspect for application and hence is at the focus of this thesis.Physics
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Maiti, Debtanu. "Defect Laden Metal Oxides and Oxynitrides for Sustainable Low Temperature Carbon Dioxide Conversion to Fuel Feedstocks." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7694.
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The current energy and environmental scenario in the world demands acute attention on sustainable repurposing of waste CO2 to high value hydrocarbons that not only addresses the CO2 mitigation problem, but also provides pathways for a closed loop synthetic carbon cycle. Difference in the scales of global CO2 emissions (about 40 Gtpa, 2017) and the carbon capture and sequestration (CCS) facilities (estimated cumulative 40 Mtpa, 2018) provokes active research on this topic. Solar thermochemical (STC) and visible light photocatalysis are two of the most promising routes that have garnered attention for this purpose. While STC has the advantages of high CO2 conversion rates, it operates at high temperatures (more than 1000 °C) limiting its industrial implementation. Photocatalysis, on the contrary, is plagued by the poor quantum efficiency and conversion rates, although its exhibits the benefits of low temperature operation. Thus, any significant progress towards low temperature STC and visible light photocatalytic CO2 reduction is a giant leap towards a greener and sustainable energy solution. This dissertation is an effort towards improving both the STC and photocatalytic CO2 reduction.
Reverse water gas shift - chemical looping (RWGS-CL) is a modified STC approach that has the potential for low temperature CO2 conversion. RWGS-CL process uses mixed metal oxides like perovskite oxides (ABO3) for the conversion to CO, a potential feedstock for subsequent hydrocarbon production. Generation of oxygen vacancy defects on these perovskite oxides is a key step of RWGS-CL and thus, oxygen vacancy formation energy has been found to be a key descriptor for this process. Using density functional theory based calculations, this intrinsic material property has been used towards rational design of better catalysts. Highest rate of CO2 conversion at the low temperatures of 450 °C was demonstrated by earth abundant perovskite oxide via RWGS-CL. This low temperature and stable CO2 conversion process enables thermal integration with subsequent Fischer Tropsch processes for the hydrogenation of CO to hydrocarbons. Parallel to the developments on materials discovery, another crucial parameter that deserves attention is the surface termination effects of the perovskite oxides. Hence, the site specificity of the bulk and surface oxygen vacancies have been probed in detail towards elucidating the CO2 conversion performance over these materials. In the view of recent progress on the growth of selective crystal facets and terminations, this study opens new avenues for enhanced CO2 conversion performance not only through bulk composition variation, but also via exposing desired crystal facets.
Type-II semiconductor heterojunctions (staggered type) are promising candidates for efficient photocatalytic reactions, not only because of their capabilities of electronic density of states tuning, but also their ability to segregate the excited electrons and holes into different materials thereby restricting exciton recombination. Metal oxynitride heterojunctions have recently demonstrated promising activity on visible light water splitting. Elucidating the structure-function relationships for these materials can pave the way towards designing better CO2 conversion photocatalysts. This dissertation focuses on unravelling the roles of material composition, anion vacancy defects and lattice strain towards modulating the electronic density of states of lateral and vertical heterojunctions of (ZnO)X(AlN)1-X and (ZnO)X(GaN)1-X. The heterojunctions consist of periodic potential wells that allows for restricting interlayer charge transport. Increased ZnO concentration was explicitly shown to decrease the band gap due to N 2p and Zn-3d repulsion. Biaxial and vertical compressive strain effected increased band gap while tensile strain reduced the same. Oxygen vacancies was found to have different effect on the electronic state of the materials. When present in charged state (+2), it promotes mid gap state formation, while in neutral state it revealed increased electronic densities near the valence band and conduction band edges. These fundamental site specific material property tuning insights are essential for designing better photocatalysts for future.
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Kasper, Christian Andreas [Verfasser], Vladimir [Gutachter] Dyakonov, Björn [Gutachter] Trauzettel, and Volker [Gutachter] Behr. "Engineering of Highly Coherent Silicon Vacancy Defects in Silicon Carbide / Christian Andreas Kasper ; Gutachter: Vladimir Dyakonov, Björn Trauzettel, Volker Behr." Würzburg : Universität Würzburg, 2021. http://d-nb.info/1233968130/34.
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Wiktor, Julia. "Identification of equilibrium and irradiation-induced defects in nuclear ceramics : electronic structure calculations of defect properties and positron annihilation characteristics." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4050.
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Durant l'irradiation en réacteur la fission des atomes d'actinides entraine la création de grandes quantités de défauts, qui affecte les propriétés physiques et chimiques des matériaux dans le réacteur, en particulier les matériaux combustibles ou de structure. Une des méthodes non destructives pouvant être utilisées pour caractériser les défauts induits par irradiation, vides ou contenant les produits de fission, est la spectroscopie d'annihilation de positons (SAP). Cette technique expérimentale consiste à détecter le rayonnement généré lors de l'annihilation du paire électron-positon dans un échantillon et en déduire les propriétés de la matière étudiée. Les positons peuvent être piégés dans les défauts de type lacunaire dans les solides, et en mesurant leur temps de vie et les distribution de moment du rayonnement d'annihilation, on peut obtenir des informations sur les volumes libres et les environnements chimiques des défauts. Dans ce travail, des calculs de structure électronique des caractéristiques d'annihilation de positons ont été effectués en utilisant la théorie de la fonctionnelle de la densité à deux composants (TCDFT). Pour calculer les distributions de moment rayonnement d'annihilation, nous avons implémenté les méthodes nécessaires dans le code de calcul libre ABINIT. Les résultats théoriques ont été utilités pour contribuer à l'identification des défauts d'irradiation dans deux céramiques nucléaires, le carbure de silicium (SiC) et le dioxyde d'uranium (UO2)During in-pile irradiation the fission of actinide nuclei causes the creation of large amounts of defects, which affect the physical and chemical properties of materials inside the reactor, in particular the fuel and structural materials. Positron annihilation spectroscopy (PAS) can be used to characterize irradiation induced defects, empty or containing fission products. This non-destructive experimental technique involves detecting the radiation generated during electron-positron annihilation in a sample and deducing the properties of the material studied. As positrons get trapped in open volume defects in solids, by measuring their lifetime and momentum distributions of the annihilation radiation, one can obtain information on the open and the chemical environments of the defects. In this work electronic structure calculations of positron annihilation characteristics were performed using two-component density functional theory (TCDFT). To calculate the momentum distributions of the annihilation radiation, we implemented the necessary methods in the open-source ABINIT program. The theoretical results have been used to contribute to the identification of the vacancy defects in two nuclear ceramics, silicon carbide (SiC) and uranium dioxide (UO2)
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Chen, Junbo. "Effect of Defects and Photoexcited Electrons on CO2 Reduction using Supported Single Atom Catalysts." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/1266.
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Excessive CO2 emissions can negatively impact society and our planet. Reduction of CO2 is one potential avenue for its abatement. One of the most significant challenges to reducing CO2 is its extremely stable linear form. Experimentally, Cu/TiO2 has shown promise for CO2 photocatalytic reduction. Dispersed atomic catalysts can achieve high catalytic efficiency on a per atom basis. Active sites also typically having lower coordination number, and therefore may be more reactive. Using density functional theory and experimental techniques, we have investigated the role of surface oxygen vacancies (Ov) and photoexcited electrons on supported single atom catalysts and CO2 reduction. Cu atoms with Ov have shown to aid in the process of bent, anionic CO2 formation. In the first step involving CO2 dissociation (CO2* --> CO* + O*), a single Cu atom in Ov lowered the activation barrier to 0.10 - 0.19 eV, which could enable fast reduction of CO2 even at room temperature, in agreement with experimental findings. A photoexcited electron model was shown to readily promote Cu binding to the surface vacancy, and CO2 adsorption and direct dissociation. Finally, we briefly compare our results to calculations of supported single Pt atoms to determine how metals besides Cu may behave as photocatalysts for CO2 reduction, and we found a single Pt with Ov can promote CO2 dissociation. Our results show that tailoring TiO2 surfaces with defects in conjunction with atomic catalysts may lead to useful catalysts in the photoreduction of CO2.
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He, Chenwei. "Experimental study of the interaction of vacancy defects with Y, O and Ti solutes to better understand their roles in the nanoparticles formation in ODS steels." Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2057/document.
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Les conditions sévères de fonctionnement des réacteurs du futur, Génération-IV, -haute température et fortes irradiations-nécessitent le développement de matériaux adaptés. Les aciers ODS (Oxide Dispersion Strengthened) sont des candidats très compétitifs pour le gainage du combustible en raison de leurs excellentes propriétés de gonflement et de fluage. Ces atouts majeurs sont induits par la fine dispersion de nanoparticules d’oxydes (Y, O, Ti) obtenue par co-broyage de poudres de la matrice et d’oxyde dont les conditions sont à optimiser pour maitriser la distribution en taille et composition de ces nanoparticules. Dans l’objectif de mieux comprendre le mécanisme de formation de ces nanoparticules à l’échelle atomique, la présente thèse met à profit l’utilisation de la spectroscopie d’annihilation de positons (PAS) et de la spectrométrie de masse d’ions secondaires pour étudier l’interaction des défauts lacunaires avec des solutés Y, O et Ti et évaluer leur rôle dans la formation des nanoparticules. Les irradiations avec des ions He ont été effectuées pour révéler les propriétés des défauts lacunaires et les implantations d’Y, Ti, O ont été réalisées pour étudier les interactions de ces éléments Y, Ti, O avec les lacunes dans la matrice de fer. La distribution des défauts en profondeur indique la présence de défauts lacunaires avec une taille plus petite dans la région où la concentration d’Y, Ti, O est la plus élevée. Cet effet est plus prononcé pour O, Y et Ti respectivement. Il est expliqué par la formation de V-X (X=O, Y, Ti) complexes qui réduisent la probabilité de la mobilité et d’agglomération des défauts lacunaires. Les recuits des échantillons implantés Y et O révèlent que des complexes O-lacune sont mobiles à température ambiante, et que l’yttrium ne diffuse pas jusqu’à 550°C alors que des complexes Y-lacunes sont encore détectés comme cela est attendu par des résultats théoriques. Un modèle des premières étapes de la nucléation des nanoparticules est proposé en utilisant les résultats obtenus dans cette thèseThe severe operating conditions of the future nuclear reactor, Generation-IV, -high temperature and high irradiation damage-, require the adapted materials development. Oxide-dispersion strengthened (ODS) alloy is one of the most potential candidates expected to be used for fuel cladding material because of their outstanding swelling and creep properties. Their excellent properties are induced by the fine dispersion of oxide nanoparticles (Y, O, Ti), obtained by mechanical alloying of steel and oxide powders and which has to be better mastered. But the atomic scale clustering mechanism of these nanoparticles is not yet cleared. In this context, the present thesis using positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry (SIMS) sheds light on the interaction of vacancy defects with Y, O and Ti solutes to better understand their roles in the nanoparticles formation. The He irradiations have been performed to reveal the vacancy defects properties and Y, Ti, O implantations realized to study the Y, Ti, O-vacancy interactions in bcc Fe matrix. In all cases, the defects depth distribution shows a lower size of vacancy defects in the region where the concentration of the incident ions Y, Ti and O is the highest. This effect of the ions on the damage formation is more pronounced for respectively O, Y and Ti. It is explained by the formation of V-X (X=O, Y, Ti) complexes which reduce the mobility and agglomeration probability of the vacancy defects. The annealing of the Y and O implanted samples reveals that some O-vacancy complexes are mobile at room temperature and Y doesn’t diffuse up to 550°C whilst Y-vacancy complexes remain as it is expected from theory. A model of the first steps of the ODS nanoparticles nucleation is proposed by using the results obtained in this thesis
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Agarwal, Sahil. "Defect Studies In Metals, Alloys, and Oxides By Positron Annihilation Spectroscopy and Related Techniques." Bowling Green State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1626713209028374.
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Fugate, Elizabeth Anne. "Understanding the Role of Lattice Defects and Metal Composition Ratio on the Photochemistry of CuFeO2 toward Solar Energy Conversion." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu157788103637799.
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Alves, Horacio Wagner Leite. "Níveis profundos associados a vacância e nitrogênio em diamante." Universidade de São Paulo, 1985. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-01042014-092413/.
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Neste trabalho estudamos a estrutura eletrônica de defeitos pontuais em diamante , os quais introduzem níveis profundos na faixa proibida deste material. Utilizamos o modelo de aglomerado molecular dentro de dois formalismos: o Método do Espalhamento Múltiplo X (MS- X), que é um método de primeiros princípios e o método \"Complete Neglect of Differential Overlap\" (CNDO/ BW), que é semi-empírico. Foi empregado um tratamento adequado para os orbitais de superfície em cada um dos dois formalismos . Foram estudados dois sistemas: o Nitrogênio substitucional e a vacância simples. Para o Nitrogênio, analisamos as possíveis distorções associadas a este centro, procurando interpretar os resultados experimentais. A vacância simples mostrou-se ser um sistema bastante semelhante à vacância simples em Silício: em ambos os casos observa - se uma distorção Jahn-Teller. O modelo adotado mostrou- se capaz de descrever satisfatoriamente as estruturas eletrônicas dos dois centros estudados, fornecendo resultados quantitativos que são comparados com a experiência .In this work we studied the electronic structure of point defects in diamond. To do this we used the molecular cluster model within two formalisms: the first-principles X Scattered wave method MS-X ) and the semiempirical Complete Neglect of Differential Overlap (CNOO/BW) method. In each case, an adequate surface orbitals treatment was utilized. We studied the following systems: the substitutional Nitrogen and the simple neutral vacancy. For the substitutional Nitrogen. We analyzed the possible distortion related to this center trying to interprete the experimental results. For the simple neutral vacancy in diamond. The results showed to be similar to the simple Silicon vacancy picture: In both cases we observed a Jahn-Teller distortion (lowering the symmetry of the center). The adopted model showed to be able to describe satisfactorily their electronic structures, and quantitative results are given, which are compared with the experimental data.
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Razumovskiy, Vsevolod. "Thermodynamic and kinetic properties of Fe-Cr and TiC-ZrC alloys from Density Functional Theory." Doctoral thesis, KTH, Materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-96285.
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The complete and accurate thermodynamic and kinetic description of any systemis crucialfor understanding and predicting its properties. A particular interest is in systemsthat are used for some practical applications and have to be constantly improved usingmodification of their composition and structure. This task can be quite accuratelysolved at a fundamental level by density functional theory methods. Thesemethods areapplied to two practically important systems Fe-Cr and TiC-ZrC.The elastic properties of pure iron and substitutionally disordered Fe-Cr alloy are investigatedas a function of temperature and concentration using first-principles electronicstructurecalculations by the exact muffin-tin orbitals method. The temperature effectson the elastic properties are included via the electronic, magnetic, and lattice expansioncontributions. It is shown that the degree of magnetic order in both pure iron andFe90Cr10 alloy mainly determines the dramatic change of the elastic anisotropy of thesematerials at elevated temperatures. A peculiarity in the concentration dependence ofthe elastic constants in Fe-rich alloys is demonstrated and related to a change in theFermi surface topology.A thermodynamic model for the magnetic alloys is developed from first principles andapplied to the calculation of bcc Fe-Cr phase diagram. Various contributions to the freeenergy (magnetic, electronic, and phonon) are estimated and included in the model. Inparticular, it is found that magnetic short range order effects are important just abovethe Curie temperature. The model is applied for calculating phase equilibria in disorderedbcc Fe-Cr alloys. Model calculations reproduce a feature known as a Nishizawahorn for the Fe-rich high-temperature part of the phase diagram.The investigation of the TiC-ZrC system includes a detailed study of the defect formationenergies and migration barriers of point defects and defect complexes involvedin the diffusion process. It is found, using ab initio atomistic simulations of vacancymediateddiffusion processes in TiC and ZrC, that a special self-diffusion mechanism isoperative for metal atom diffusion in sub-stoichiometric carbides. It involves a noveltype of a stable point defect, a metal vacancy ”dressed” in a shell of carbon vacancies.It is shown that this vacancy cluster is strongly bound and can propagate through thelattice without dissociating.QC 20120604
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Pentecoste, Lucile. "Etude de la formation de défauts lacunaires dans un cristal de tungstène par accumulation d’hélium." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2040/document.
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Le tungstène sera soumis à des conditions extrêmes de température et de bombardement de particules en tant que paroi des cibles du divertor dans le réacteur de fusion nucléaire ITER. De hauts flux d’ions légers impacteront la surface du tungstène et sont susceptibles de générer des défauts dans le cristal. Cette étude vise à étudier les premières étapes de la formation des défauts lacunaires dans le cristal de tungstène soumis à un faible flux d’ions de faible énergie afin de comprendre le rôle de l’accumulation de l’hélium, un des produits de la réaction de fusion du deutérium et du tritium. Pour cette étude, une source plasma ICP-RF a été développée et qualifiée afin de réaliser des implantations d’hélium dans des conditions parfaitement contrôlées. Les implantations d’hélium ont été réalisées pour plusieurs conditions de fluence, d’énergie et de température, sur des échantillons de tungstène polycristallins. La spectroscopie d’annihilation des positons a été utilisée pour caractériser les défauts lacunaires, les analyses par réactions nucléaires, pour quantifier l’hélium implanté et la spectrométrie de thermodésorption pour caractériser les interactions de l’hélium dans le cristal. Les résultats montrent que pour une énergie de 320 eV à température ambiante, une fluence incidente limite est atteinte à partir de laquelle une saturation de l’hélium implanté apparaît et la formation de lacunes de grande taille débute. L’étude de l’influence de l’énergie et de la température montre l’importance de la répartition de l’hélium en profondeur et de sa mobilité dans le cristal sur la taille et la diversité des défauts formés. Les implantations sont simulées par dynamique moléculaire. Les résultats obtenus par l’approche numérique sont comparés aux résultats expérimentaux afin de mieux comprendre les mécanismes élémentaires mis en jeuTungsten will be exposed to severe plasma conditions such as high temperature and high particle bombardment as a target of the divertor in the nuclear fusion reactor ITER. High fluxes of light ions will impact its surface and can generate defects in the crystal. This study means to observe the first steps of the vacancy-type defects formation in the tungsten crystal subject to low ion flux of low kinetic energy in order to understand the influence of the accumulation of helium, one of the nuclear reaction products. For the experiments, an ICP-RF plasma source was developed and characterized to perform helium implantations under perfectly controlled conditions. Helium implantations were performed under various conditions of fluence, energy and substrate temperature on polycrystalline tungsten samples. Positron annihilation spectroscopy was used to characterize vacancy-type defects, nuclear reaction analysis to quantify implanted helium and thermal desorption spectrometry to characterize the interactions of helium in the crystal. Results show that, for a kinetic energy of 320 eV and at room temperature, a saturation of the helium implanted quantity is reached for a limit incident fluence and that large vacancy defects starts to form. Study of the kinetic energy and the surface temperature influences show the importance of the depth distribution and the mobility of the helium in the crystal on the size and the diversity of the generated defects. Implantations are performed by molecular dynamic simulations. Results obtained by the numerical approach are compared to experimental ones in order to get a better understanding of the atomic scale mechanisms
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Sidibe, Moussa. "Etude du comportement du tungstène sous irradiation : applications aux réacteurs de fusion." Phd thesis, Université d'Orléans, 2014. http://tel.archives-ouvertes.fr/tel-01068634.
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La fusion thermonucléaire est envisagée comme nouvelle source énergétique pratiquement inépuisable. Le projet ITER " International Thermonuclear Experimental Reactor " doit démontrer la faisabilité scientifique et la maitrise de la fusion thermonucléaire. Le tungstène (W) a été choisi pour recouvrir le " divertor ", un composant essentiel du réacteur ITER. Il sera soumis à des conditions extrêmes de fonctionnement : au bombardement neutronique, à d'intenses flux de chaleur et de particules (hélium, hydrogène). Ces conditions induiront dans le W des défauts et introduiront de l'hélium et de l'hydrogène, qui pourront conduire à des modifications de sa microstructure et de ses propriétés physiques, chimiques et mécaniques. L'objectif de ce travail est d'étudier, à l'échelle atomique, l'évolution de la microstructure du tungstène sous irradiation. Afin de simuler les atomes de recul générés par les irradiations aux neutrons, des échantillons de W ont été irradiés avec des ions lourds et/ou implantés avec de l'hélium. La nature des défauts a été étudiée à l'aide de la Spectroscopie d'Annihilation de Positons (PAS). Les résultats montrent que les irradiations aux ions lourds conduisent à la formation de monolacunes et de clusters lacunaires dont la taille et la concentration augmente avec la fluence. Des irradiations ou des recuits effectués à une température supérieure à 450 K conduisent à l'agglomération des défauts lacunaires essentiellement par migration des monolacunes. Pour des recuits à très hautes températures (1773 K), les observations MET montrent la présence de cavités nanométriques (∼10 nm). Les implantations avec les ions 4He 60 keV induisent dans le W une distribution de défauts complexes de type nHe-mv, ainsi qu'une faible concentration de monolacunes v. Une majorité de complexes He-v est formée pour la faible fluence et la fraction des défauts complexes (nHe-mv) augmente quand la fluence augmente. La nature et la distribution des défauts évolue en fonction de la température de recuit et dépend du ratio [He]/[v]. Le premier stade de recuit des défauts lacunaires (∼ 450 K) est masqué par la présence de l'hélium dans les défauts lacunaires. Pour un ratio [He]/[v] supérieur à 1, un stade d'agglomération des défauts est clairement observé à partir de 1623 K. Pour des conditions d'introduction de défauts et d'hélium proches de celles attendus dans les réacteurs de fusion (He/dpa allant de 0.03 à 8 appm He/dpa), la signature positon après irradiation est similaire à celle mesurée dans des échantillons seulement endommagés dans des conditions équivalentes mais sans introduire de l'hélium. Pour des rapports He/dpa allant de 0.3 à 8 appm He/dpa, les recuits révèlent des différences de distribution en taille et en concentration des défauts lacunaires. La présence d'hélium dans les amas lacunaires modifie les caractéristiques d'annihilation des positons et favorise la stabilisation des amas lacunaires.
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Belhabib, Tayeb. "Comportement thermique des défauts lacunaires induits par l’hélium et les gaz de fission dans le dioxyde d’uranium." Thesis, Orléans, 2012. http://www.theses.fr/2012ORLE2071/document.
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Dans les nouvelles centrales nucléaires dites 4ème génération, comme d’ailleurs les anciennes, le dioxyde d’uranium devra opérer dans des milieux hostiles de températures et d’irradiation avec la présence des produits de fission (PF) et des particules alpha (α). Le fonctionnement dans ces conditions extrêmes induira des déplacements d’atomes et dégradera les propriétés thermiques et mécaniques du combustible UO2. La compréhension du comportement des défauts lacunaires, des PF et de l’hélium est cruciale pour prévoir le comportement du dioxyde d’uranium au sein de ces futures installations nucléaires. La première partie de cette thèse est consacrée à l’étude des défauts lacunaires induits par l’implantation de krypton et d’iode (quelques MeV) dans l’UO2 polycristallin et leurs stades de recuits. L’analyse par spectroscopie d’annihilation de positons (PAS) a permis de mettre en évidence la création de défauts de Schottky VU-2VO dans le cas des implantations iode et la formation de clusters lacunaires contenant du gaz pour les implantations krypton. L’évolution en température de ces défauts générés dépend des paramètres d’implantation (nature des ions, énergie, fluence). Cette étude a montré les rôles importants que peuvent jouer les défauts lacunaires et la présence des gaz de fission dans l’évolution du matériau UO2. Ensuite, nous nous sommes intéressés à l’étude et à la caractérisation, par PAS et les techniques d’analyse par faisceau d’ions (NRA/C et RBS/C), du comportement de l’hélium dans l’UO2. Les mesures de NRA/C et RBS/C révèlent une localisation d’une grande fraction d’hélium dans les sites interstitiels octaédriques de la matrice UO2. La localisation de l’hélium reste stable dans ces sites pour T< 600°C, évoluent légèrement entre 600 et 700°C et devient aléatoire à 800°C. Les mesures PAS mettent en évidence trois stades d’évolution des défauts lacunaires : la recombinaison par migration des interstitiels d’oxygène, l’agglomération des défauts entre 600 et 800°C et leur dissociation et élimination lorsque la température augmente. Ces résultats suggèrent que le transport d'hélium est assisté par les défauts lacunairesIn the new fourth generation nuclear plants, as in the old ones, uranium dioxide must operate in hostile environments of temperature and irradiation with the presence of fission products (FP) and alpha particles (α). Operation in these extreme conditions will induce atoms displacements and degrade the thermal and mechanical properties of UO2 fuel. Understanding the behavior of induced vacancy defects, FP and helium is crucial to predict the uranium dioxide behavior in the future nuclear reactors. The first part of this thesis is dedicated to the study of vacancy defects induced by krypton and iodine implantation (a few MeV) in the UO2 polycrystalline and of their evolution under annealing. Analysis by positron annihilation spectroscopy (PAS) has highlighted the creation of Schottky defects VU-2VO in the case of iodine implantations and formation of vacancy clusters containing the gas for krypton implantation. The temperature evolution of these defects depends on the implantation parameters (nature of the ion energy, fluence). This study showed the important roles that can play vacancy defects and the presence of fission gases in the evolution of UO2 material. Then we were interested in the study of the helium behavior in UO2 its location and migration, agglomeration and interaction with vacancy defects by using PAS and ion beam analysis (NRA/C and RBS/C). The NRA/C and RBS/C characterizations showed a localization of a large helium fraction in the octahedral interstitial sites of the UO2 matrix. The helium location in these sites remains stable for T <600°C, changing slightly between 600 and 700°C and becomes random at 800°C. Positron annihilation spectroscopy reveals three stages of vacancy defects evolution : The recombination with oxygen interstitial migration, defects agglomeration between 600 and 800°C and their dissociation and elimination when the temperature increases. These results suggest that the He transport is assisted by the vacancy defects
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Lee, Donghun. "Atomic Scale Gate Electrode Formed by a Charged Defect: Scanning Tunneling Microscopy of Single Impurities in GaAs Semiconductors." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1274913629.
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Gérardin, Marie. "Etude du comportement thermique des gaz de fission dans l'UO₂ en présence de défauts d'irradiation." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2051/document.
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Lors de l’irradiation en réacteur, des gaz de fission tels que le xénon et le krypton sont produits. Ces gaz diffusent dans le combustible, mais peuvent également précipiter sous forme de bulles. En outre,les réactions de fission conduisent à la formation de défauts ponctuels (lacunes ou interstitiels) et sous forme d’amas (dislocations ou cavités). L’obtention de données expérimentales sur la migration des gaz de fission en présence de défauts est nécessaire afin d’améliorer la compréhension et la modélisation du comportement du combustible sous irradiation. La démarche mise en place dans ce travail a pour objectif d’étudier la diffusion thermique des gaz et de comprendre leur interaction avec les défauts d’irradiation. Elle repose sur la réalisation d’études à effets séparés couplant des irradiations/implantations aux ions à des techniques de caractérisation fines. La Spectroscopie d’Annihilation des Positons (SAP) complétée par la Microscopie Electronique en Transmission (MET)permet de caractériser les défauts (ponctuels et/ou sous forme d’amas) générés par l’irradiation et de suivre leur évolution en température. En parallèle, la modélisation des cinétiques de relâchement des gaz rares mesurées par désorption thermique couplée à la spectrométrie de masse, permet d’obtenir les coefficients de diffusion des gaz et de mettre en lumière les phénomènes de piégeage opérants. La synthèse de ces résultats expérimentaux nous amène à identifier les mécanismes de migration des gaz et à décrire leurs interactions avec les défauts d’irradiationDuring in-reactor irradiation, fission gases such as xenon or krypton are produced. In the fuel, those gases diffuse and precipitate to form bubbles. In addition, fission reactions induce small defects(vacancies and interstitials) and larger defects (cavities and dislocations) formation. Data acquire menton fission gases migration considering radiation-induced defects is thus necessary to better understand and improve models of in-pile fuel behavior. The experimental approach developed in this work aims to study thermal diffusion of rare gases and to understand their interaction with radiation-induced defects.To do this, separated effect studies were performed coupling ion implantations/irradiations to fine characterization techniques. Positron Annihilation Spectroscopy (PAS) coupled to Transmission Electron Microscopy (TEM) observations allows for defects characterizations (vacancies and/or cavities induced by ion implantation) and for their thermal behavior study. On the other hand, gas release measurements are performed by thermal desorption spectrometry. Simulation of gas kinetic release allows to determine diffusion coefficients and to lighten trapping mechanisms. The synthesis of those various experimental results brings us to identify gas migration mechanism and to describe their interaction with radiation-induced defects
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Markevich, Alexander. "Ab-initio calculations of diffusion barriers of small vacancy clusters in silicon." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2288.
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Mestrado em Ciência e Engenharia de MateriaisEsta tese apresenta os resultados de um programa de investigação sobre a difusão da lacuna, bi-lacuna e tri-lacuna em silício utilizando simulações numéricas pelo método da teoria do funcional da densidade. Este método está implementado na forma de um programa informático referido como AIMPRO (Ab Initio Modelling PROgram). Para o cálculo dos pontos cela dos mecanismos de difusão foi usado o método “Nudged Elastic Band”. As condições fronteira dos problemas foram impostas recorrendo à utilização de agregados esféricos de silício com 275 atomos, cuja superfície foi saturada por ligações Si-H. As lacunas foram então introduzidas no centro destes agregados. Os valores calculados das barreiras de difusão para a lacuna simples e para a bi-lacuna são respectivamente 0.68 e 1.75 eV. Estes valores apresentam um acordo razoável com os obtidos experimentalmente e obtidos em outros cálculos anteriores. A barreira de difusão da tri-lacuna foi, de acordo com a literatura disponível, calculada pela primeira vêz. O mecanismo de difusão mais favorável apresenta uma barreira de 2.2 eV. No seguimento dos resultados para a lacuna e bi-lacuna, pensamos que este resultado sobrestima a barreira em cerca de 0.25 eV, colocando a nossa melhor estimativa em 1.9- 2.0 eV. Varias fontes de erro nos resultados são comentadas, assim como são sugeridas várias formas de as evitar. ABSTRACT: This work presents the results of a computational investigation into the diffusion of the single vacancy (V) and small vacancy clusters, divacancy (V2) and trivacancy (V3), in silicon. The calculations were performed principally using local density functional theory as implemented by the AIMPRO (Ab Initio Modelling PROgram) code. The Nudged Elastic Band Method was used for elucidating diffusion paths and obtaining the energy barriers for diffusion of the defects considered. Based on ab-initio calculations with H-terminated Si clusters with 275 host atoms, diffusion paths for neutral Vn (n = 1 to 3) defects were found. Calculated values of the activation energy for the diffusion of the Si vacancy and divacancy are 0.68 and 1.75 eV, respectively. These values are in a reasonable agreement with those derived from experimental and previous ab-initio modelling studies. The diffusion of trivacancy in Si has been modelled for the first time. The diffusion barrier of V3 along the proposed diffusion path was found to be about 2.2 eV. This result comes overestimated as the experimental data indicates that the values of diffusion barriers for divacancy and trivacancy in Si should be similar. Probable sources of the calculation errors have been considered and possible ways to surmount these difficulties are proposed.
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Asplet, William. "Etude des interactions entre les défauts lacunaires et les solutés Y,O, Ti pour mieux comprendre leur rôle dans la formation des nanoparticules d'oxydes dans les aciers ODS." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2056/document.
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Cette thèse est dédiée à l’étude des interactions entre les défauts lacunaires et les solutés (Y, Ti, O) pour mieux comprendre la formation des nanoparticules d’oxyde dans les aciers ODS (Oxide Dispersion Strengthened). Ces aciers sont envisagés comme matériau de structure dans la prochaine génération de réacteurs nucléaires fission et fusion. Leurs bonnes propriétés reposent essentiellement sur une répartition homogène de nanoparticules (YxTiyOz) de très faible taille. Cependant, l’obtention de cette répartition n’est pas encore maitrisée et le mécanisme de formation de ces nanoparticules n’est pas encore bien défini. Des modèles théoriques montrent que la présence de lacunes pendant l’étape de broyage pourrait impacter la formation de ces nanoparticules. Cette étude fait suite à la thèse de C. He et apporte de nouveaux résultats et de nouvelles interprétations et conclusions. Des implantations avec des ions Y, Ti, O ont été réalisées afin de simuler l’étape de broyage de ces aciers ODS. Elles ont permis d’introduire des défauts et les solutés désirés dans la matrice de fer α. Nous avons ensuite étudié les interactions entre les solutés et les défauts générés dans la matrice. La nature des défauts induits a été étudiée en fonction de l’ion implanté et de traitements thermiques après implantation par spectroscopie d’annihilation de positons (PAS) et corrélée avec les profils en profondeur des solutés obtenus par spectrométrie de masse des ions secondaires (SIMS). Les caractéristiques d’annihilation de certains défauts encore inconnues ont pu être déterminées. Les mesures SIMS ont montré que le titane ne migre pas entre 100 et 450°C et que l’oxygène présente un comportement complexe de migration et de piégeage dépendant de la température et de la microstructure des matériaux. Les résultats PAS montrent que les implantations ioniques conduisent à la formation de clusters lacunaires, de complexes lacunes-solutés et de dislocations dont la proportion change en fonction de la profondeur et de la nature de l’ion implanté. Les clusters de lacunes Vn et les dislocations sont détectés au-delà du pic d’implantation avec une fraction plus importante pour les dislocations indiquant que les défauts ont pu migrer pendant l’implantation. La proportion des complexes lacunes-solutés est maximale dans la zone d’arrêt des ions. Elle est en accord avec les énergies de liaison théoriques des complexes lacunes-soluté. La nature et la distribution des défauts formés évoluent en fonction de la température de recuit. Les clusters lacunaires Vn disparaissent entre RT et 300°C alors que les dislocations sont éliminées à partir de 400°C. Des phases oxydes sont détectées pour des recuits à 500 et 550°C en lien avec la contamination en oxygène. Des défauts dont la nature est non identifiée ont été mis en évidence pour des recuits réalisés entre 300 et 400°C dans les implantations O, Y et Y+OThis PhD thesis is dedicated to the study of interaction between vacancies and Y, Ti,O solutes for a better understanding of formation of oxide nanoparticles in ODS steel (Oxide Dispersion Strengthened). These ODS steels are considered as structural material for the next generation of fission and fusion nuclear reactors. Their good properties are induced by the fine dispersion of low size oxide nanoparticles. However, obtaining this distribution is not mastered and atomic scale clustering is not yet defined. Furthermore, it was shown by theoretical models that the presence of vacancy during mechanical alloying could affect the formation of these nanoparticles. This study follows upon on a previous study made by C.He, and bring new results, new interpretation and conclusions. Some implantations with Y, Ti, O ions with several energy have been made in order to simulate the mechanical alloying step used for ODS steel fabrication. Theses irradiations have induced defects and solutes into the iron matrix. Then we characterized samples using positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry (SIMS). The nature of defects was studied according to nature of the implanted ion and the annealing temperature by PAS and correlated to depth profiles of solutes obtained by SIMS. Annihilation characteristics of some defects still unknown were able to be determined thanks to positron lifetime measurements. SIMS analysis showed that titanium doesn’t migrate for annealing experiments between 100°C and 450°C and that oxygen show a complex behavior of migration and trapping dependent on the microstructure of the material. PAS results show that ionic implantations produce vacancy clusters, dislocations and solutes-vacancies complex. Their proportion changes as a function of depth and nature of these irradiations. Vacancy clusters and dislocations are detected deeper than the implantation peak with a higher fraction for the dislocations indicating that the defects were able to migrate during implantations. The fraction of vacancy-solutes complexes is the highest in the ion stopping zone and is in a good agreement with the theoretical binding energy of vacancies-solutes complex. The nature and the distribution of the defects evolve according to the annealing temperature. Vacancy clusters disappear between RT and 300°C while the dislocations are eliminated from 400°C. Oxide phases are detected for annealing at 500 and 550°C in relation with the oxygen contamination during these annealings. Some defects which the nature is not yet identified were highlighted for annealing between 300 and 400°C for Y, O and Y+O irradiations
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Stokes, Stephen J. "Atomistic modelling studies of fluorite- and perovskite-based oxide materials." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527142.
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Fast oxide-ion and proton conductors are the subject of considerable research due to their technological applications in sensors, ceramic membranes and solid oxide fuel cells (SOFCs). This thesis describes the use of computer modelling techniques to study point defects, dopants and clustering effects in fluorite-and perovskitetype ion conductors with potential SOFC applications. Bi2O3 related phases are being developed with the objective of high oxide-ion conductivities at lower operating temperatures than 1000°C, as in current generation SOFC electrolytes. Doped Bi2O3 phases have shown promise as materials capable of accomplishing this goal. First, the Y-doped phase, Bi3YO6, has been investigated including the ordering of intrinsic vacancies. The defect and dopant characteristics of Bi3YO6 have been examined and show that a highly mobile oxygen sub-lattice exists in this material. A preliminary structural modelling study of a new Re-doped Bi2O3 phase was also undertaken. A comprehensive investigation of the proton-conducting perovskites BaZrO3, BaPrO3 and BaThO3 is then presented. Our results suggest that intrinsic atomic disorder in BaZrO3 and BaThO3 is unlikely, but reduction of Pr4+ in BaPrO3 is favourable. The water incorporation energy is found to be less exothermic for BaZrO3 than for BaPrO3 and BaThO3, but in all cases the results suggest that the proton concentration would decrease with increasing temperature, in accord with experimental data. The high binding energies for all the dopant-OH pair clusters in BaPrO3 and BaThO3 suggest strong proton trapping effects. Finally, a study of multiferroic BiFeO3 is presented, in which the defect, dopant and migration properties of this highly topical phase are investigated. The reduction process involving the formation of oxygen vacancies and Fe2+ is the most favourable redox process. In addition, the results suggest that oxide-ion migration is anisotropic within this system.
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Belloir, Jean-Marc. "Spectroscopie du courant d’obscurité induit par les effets de déplacement atomique des radiations spatiales et nucléaires dans les capteurs d’images CMOS à photodiode pincée." Thesis, Toulouse, ISAE, 2016. http://www.theses.fr/2016ESAE0029/document.
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Les imageurs CMOS représentent un outil d’avenir pour de nombreuses applications scientifiques de haut vol, tellesque l’observation spatiale ou les expériences nucléaires. En effet, ces imageurs ont vu leurs performancesdémultipliées ces dernières années grâce aux avancées incessantes de la microélectronique, et présentent aussi desavantages indéniables qui les destinent à remplacer les CCDs dans les futurs instruments spatiaux. Toutefois, enenvironnement spatial ou nucléaire, ces imageurs doivent faire face aux attaques répétées de particules pouvantrapidement dégrader leurs performances électro-optiques. En particulier, les protons, électrons et ions présents dansl’espace ou les neutrons de fusion nucléaire peuvent déplacer des atomes de silicium dans le volume du pixel et enrompre la structure cristalline. Ces effets de déplacement peuvent former des défauts stables introduisant des étatsd’énergie dans la bande interdite du silicium, et ainsi conduire à la génération thermique de paires électron-trou. Parconséquent, ces radiations non-ionisantes produisent une augmentation permanente du courant d’obscurité despixels de l’imageur et donc à une diminution de leur sensibilité et de leur dynamique. L’objectif des présents travauxest d’étendre la compréhension des effets de déplacement sur l’augmentation du courant d’obscurité dans lesimageurs CMOS. En particulier, ces travaux se concentrent sur l’étude de la forme de la distribution de courantd’obscurité en fonction du type, de l’énergie et du nombre de particules ayant traversé l’imageur, mais aussi enfonction des caractéristiques de l’imageur. Ces nombreux résultats permettent de valider physiquement etexpérimentalement un modèle empirique de prédiction de la distribution du courant d’obscurité pour une utilisationdans les domaines spatial et nucléaire. Une autre partie majeure de ces travaux consiste à utiliser pour la première foisla technique de spectroscopie de courant d’obscurité pour détecter et caractériser individuellement les défautsgénérés par les radiations non-ionisantes dans les imageurs CMOS. De nombreux types de défauts sont détectés etdeux sont identifiés, prouvant l’applicabilité de cette technique pour étudier la nature des défauts cristallins généréspar les effets de déplacement dans le silicium. Ces travaux avancent la compréhension des défauts responsables del’augmentation du courant d’obscurité en environnement radiatif, et ouvrent la voie au développement de modèles deprédiction plus précis, voire de techniques permettant d’éviter la formation de ces défauts ou de les faire disparaîtreCMOS image sensors are envisioned for an increasing number of high-end scientific imaging applications such asspace imaging or nuclear experiments. Indeed, the performance of high-end CMOS image sensors has dramaticallyincreased in the past years thanks to the unceasing improvements of microelectronics, and these image sensors havesubstantial advantages over CCDs which make them great candidates to replace CCDs in future space missions.However, in space and nuclear environments, CMOS image sensors must face harsh radiation which can rapidlydegrade their electro-optical performances. In particular, the protons, electrons and ions travelling in space or thefusion neutrons from nuclear experiments can displace silicon atoms in the pixels and break the crystalline structure.These displacement damage effects lead to the formation of stable defects and to the introduction of states in theforbidden bandgap of silicon, which can allow the thermal generation of electron-hole pairs. Consequently, nonionizingradiation leads to a permanent increase of the dark current of the pixels and thus a decrease of the imagesensor sensibility and dynamic range. The aim of the present work is to extend the understanding of the effect ofdisplacement damage on the dark current increase of CMOS image sensors. In particular, this work focuses on theshape of the dark current distribution depending on the particle type, energy and fluence but also on the imagesensor physical parameters. Thanks to the many conditions tested, an empirical model for the prediction of the darkcurrent distribution induced by displacement damage in nuclear or space environments is experimentally validatedand physically justified. Another central part of this work consists in using the dark current spectroscopy techniquefor the first time on irradiated CMOS image sensors to detect and characterize radiation-induced silicon bulk defects.Many types of defects are detected and two of them are identified, proving the applicability of this technique to studythe nature of silicon bulk defects using image sensors. In summary, this work advances the understanding of thenature of the radiation-induced defects responsible for the dark current increase in space or nuclear environments. Italso leads the way to the design of more advanced dark current prediction models, or to the development ofmitigation strategies in order to prevent the formation of the responsible defects or to allow their removal
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Dalponte, Mateus. "Redistribuição e ativação de dopantes em Si com excesso de vacâncias." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/15397.
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A redistribuição e ativação elétrica dos dopantes tipo n (As e Sb) e tipo p (Ga e In) em Si com excesso de vacâncias foram analisadas. As vacâncias foram geradas por implantação iônica de altas doses de oxigênio ou nitrogênio em alta temperatura, de acordo com procedimentos já estudados. Em seguida foram implantados os dopantes com dose de 5x1014 cm-2 a 20 keV na região rica em vacâncias. Dopagens idênticas foram realizadas em amostras de Si sem vacâncias e em SIMOX. Em seguida foram feitos recozimentos a 1000ºC por 10 s ou 15 min. Os perfis atômicos dos dopantes foram medidos com Medium Energy Ion Scattering e os perfis dos dopantes ativados, com Hall diferencial. A redistribuição e as propriedades elétricas de cada um dos dopantes no Si sem vacâncias foram bastante similares às observadas no SIMOX, porém várias diferenças foram observadas em relação às amostras com excesso de vacâncias. As vacâncias reduziram a ativação elétrica do As e do Sb, mas proporcionaram maior estabilidade da ativação após recozimentos longos. A redistribuição destes dopantes foi infuenciada pelo íon usado na geração das vacâncias, ou seja, nitrogênio ou oxigênio. O oxigênio proporcionou maior dose retida de As e o nitrogênio, maior dose retida de Sb. Já para o Ga e o In, as vacâncias tiveram papel fundamental na sua redistribuição, diminuindo a difusão para fora das amostras e garantindo maior dose retida. A ativação elétrica do Ga e especialmente a do In foram baixas, onde observamos forte influência do íon pré-implantado, principalmente o oxigênio.The redistribution and electrical activation of n type (As and Sb) and p type (Ga and In) dopants in Si with excess vacancy concentration were analyzed. The vacancies were formed by high dose ion implantation of oxygen or nitrogen at high temperature, following previously studied procedures. Dopants were implanted to a dose of 5x1014 cm-2 at 20 keV in the vacancy rich regions of the samples. Identical doping implantations were performed in bulk Si and SIMOX. Samples were then submitted to thermal annealing at 1000ºC for 10 s or 15 min. The dopants atomic profiles were obtained by Medium Energy Ion Scattering and the active dopant profiles, by differential Hall measurements. The redistribution and the electrical properties of each dopant in bulk Si were similar to those observed in SIMOX, but several differences were observed in the vacancy-rich samples. Vacancies reduced the electrical activation of As and Sb, although the activation was maintained stable after long annealing times. The redistribution of these dopants was, otherwise, dominated by the ion used in the vacancy generation, i.e., nitrogen or oxygen. The presence of oxygen resulted in larger As retained dose, while the presence of nitrogen, in larger Sb retained dose. Regarding the p type dopants, Ga and In, the vacancies played an important role in their redistribution, reducing their out-diffusion and allowing larger retained doses. Ga and especially In electrical activation was low, where strong influence of the pre-implanted ions was observed, especially oxygen.
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Li, Hongfei. "Density functional simulations of defect behavior in oxides for applications in MOSFET and resistive memory." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274924.
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Defects in the functional oxides play an important role in electronic devices like metal oxide semiconductor field effect transistors (MOSFETs) and resistive random-access memories (ReRAMs). The continuous scaling of CMOS has brought the Si MOSFET to its physical technology limit and the replacement of Si channel with Ge channel is required. However, the performance of Ge MOSFETs suffers from Ge/oxide interface quality and reliability problems, which originates from the charge traps and defect states in the oxide or at the Ge/oxide interface. The sub-oxide layers composed of GeII states at the Ge/GeO2 interface seems unavoidable with normal passivation methods like hydrogen treatment, which has poor electrical properties and is related to the reliability problem. On the other hand, ReRAM works by formation and rupture of O vacancy conducting filaments, while how this process happens in atomic scale remains unclear. In this thesis, density functional theory is applied to investigate the defect behaviours in oxides to address existing issues in these electronic devices. In chapter 3, the amorphous atomic structure of doped GeO2 and Ge/GeO2 interface networks are investigated to explain the improved MOSFET reliability observed in experiments. The reliability improvement has been attributed to the passivation of valence alternation pair (VAP) type O deficiency defects by doped rare earth metals. In chapter 4, the oxidation mechanism of GeO2 is investigated by transition state simulation of the intrinsic defect diffusion in the network. It is proposed that GeO2 is oxidized from the Ge substrate through lattice O interstitial diffusion, which is different from SiO2 which is oxidized by O2 molecule diffusion. This new mechanism fully explains the strange isotope tracer experimental results in the literature. In chapter 5, the Fermi level pinning effect is explored for metal semiconductor electrical contacts in Ge MOSFETs. It is found that germanides show much weaker Fermi level pinning than normal metal on top of Ge, which is well explained by the interfacial dangling bond states. These results are important to tune Schottky barrier heights (SBHs) for n-type contacts on Ge for use on Ge high mobility substrates in future CMOS devices. In chapter 6, we investigate the surface and subsurface O vacancy defects in three kinds of stable TiO2 surfaces. The low formation energy under O poor conditions and the +2 charge state being the most stable O vacancy are beneficial to the formation and rupture of conducting filament in ReRAM, which makes TiO2 a good candidate for ReRAM materials. In chapter 7, we investigate hydrogen behaviour in amorphous ZnO. It is found that hydrogen exists as hydrogen pairs trapped at oxygen vacancies and forms Zn-H bonds. This is different from that in c-ZnO, where H acts as shallow donors. The O vacancy/2H complex defect has got defect states in the lower gap region, which is proposed to be the origin of the negative bias light induced stress instability.
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Lhuillier, Pierre-Emile. "Etude du comportement de l'hélium et des défauts lacunaires dans le tungstène." Phd thesis, Université d'Orléans, 2010. http://tel.archives-ouvertes.fr/tel-00587482.
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Dans les réacteurs à fusion, le tungstène subira des contraintes sévères dont, l'irradiation neutronique induisant la création de défauts ponctuels, et l'implantation d'hélium. La compréhension du comportement synergique des défauts lacunaires et de l'hélium est cruciale pour modéliser le comportement des composants en tungstène des futurs réacteurs à fusion thermonucléaire.Cette étude utilise la spectroscopie d'annihilation des positons (PAS) pour déterminer la nature et l'évolution en température des défauts d'implantation et l'analyse par réaction nucléaire (NRA)couplée ponctuellement à la microscopie électronique pour suivre le comportement de l'hélium.Les défauts générés dépendent des paramètres d'implantation (nature des ions, énergie, fluence). Par implantation d'3He à 800 keV, des monolacunes ont été créées et sont mobiles entre 473 et 623 K.L'augmentation de la concentration initiale en monolacunes décale le seuil de migration vers les basses températures. Des implantations à fort dpa (Fe 10 MeV) génèrent des amas lacunaires. Les impuretés jouent un rôle prépondérant sur le comportement en température des défauts.Le comportement de l'hélium a été étudié sous trois conditions d'implantation différentes. Les implantations à basse énergie (0,32 keV) montrent la création de complexes hélium-lacune par mutation. Les implantations à 60 keV mettent en évidence la compétition entre la migration, à basse fluence et le piégeage de l'hélium, à haute fluence. Finalement, des implantations à haute énergie(500 keV) renseignent sur l'influence de la microstructure sur la distribution des bulles d'hélium.
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Rohr, Sven. "Hybrid spin-nanomechanical systems in parametric interaction." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY046/document.
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L'exploration du monde quantique au moyen d'objets macroscopiques constitue l'un des défis centraux de ces dernières décennies pour la recherche en physique. Parmi les systèmes proposés pour atteindre cet objectif, les systèmes hybrides, qui couplent un résonateur nanomécanique à un qubit unique, font figure de paradigme.L'excitation cohérente d'un oscillateur mécanique macroscopique par un unique spin électronique ouvrirait en particulier de nouvelles perspectives pour la création d'états quantiques arbitraires du mouvement.Dans ce manuscrit, nous considérons un système hybride constitué d'un oscillateur nanomécanique et du spin électronique d'un unique centre NV, couplés entre eux par une interaction magnétique. Nous nous concentrons sur le cas d'une interaction paramétrique où la vibration mécanique module l'énergie du qubit, et plus précisément sur le cas où le qubit ainsi forcé et l'oscillateur mécanique évoluent sur des échelles de temps comparables.Dans cette situation, nos observations montrent une synchronisation de la dynamique du qubit sur l'oscillation mécanique. Le phénomène est dans un premier temps abordé par une expérience-test qui remplace le mouvement mécanique par un champ radiofréquence en couplage paramétrique avec le spin. Cette première implémentation permet de dégager les propriétés essentielles de l'effet paramétrique, qui est dans un second temps observé sur l'expérience principale.Dans cette seconde expérience, un centre NV est attaché à l'extrémité d'un nanofil de carbure de silicium en vibration placé dans un fort gradient de champ magnétique. Le caractère bidimensionnel des déformations du nanofil octroie alors à la synchronisation des signatures vectorielles encore inédites, qui peuvent aussi être interprétées comme la manifestation d'un triplet de Mollow phononique, ainsi qu'il a été observé dans les premières expériences d'électrodynamique quantique.Finalement, nous explorons la robustesse de la synchronisation vis-à-vis du mouvement Brownien du résonateur, et démontrons la possibilité de protéger le qubit de cette source de décohérence additionnelle grâce à une excitation mécanique de faible amplitudeProbing the quantum world with macroscopic objects has been a core challenge for research in physics during the past decades. Proposed systems to reach this goal include hybrid devices that couple a nanomechanical resonator to a single spin qubit. In particular, the coherent actuation of a macroscopic mechanical oscillator by a single electronic spin would open perspectives in the creation of arbitrary quantum states of motion.In this manuscript, we investigate a hybrid system coupling a nanomechanical oscillator and a single electronic spin of a NV defect in magnetic interaction. We focus on the parametric interaction case, when the mechanical motion modulates the qubit energy, and in particular when the driven qubit and mechanical oscillators evolves on similar timescales. In that situation a synchronization of the qubit dynamics onto the mechanical motion is observed. The phenomenon is first explored on a test experiment where mechanical motion is replaced by a parametrically coupled RF field. It allows to establish the main properties of the phenomenon, which is subsequently investigated on the core experiment. It consists of a NV defect attached at the vibrating extremity of a silicon carbide nanowire, immersed in a strong magnetic field gradient. The bidimensional character of the nanowire deformations is responsible for novel vectorial signatures in the synchronization, which can also be viewed as a phononic Mollow triplet as observed in early quantum electrodynamics experiments. We finally explore the robustness of the synchronization against the Brownian motion of the resonator and demonstrate the possibility to protect the qubit against this additional decoherence source by applying a small coherent mechanical drive
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Schröder, Tim. "Integrated photonic systems for single photon generation and quantum applications." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16723.
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Im Rahmen der vorliegenden Dissertation wurden neuartige integrierte Einzelphotonenquellen (EPQ) und ihre Anwendung für die Quanteninformationsverarbeitung entwickelt und untersucht. Die Erzeugung von Einzelphotonen basiert auf einzelnen Defektzentren in nanometergroßen Diamantkristallen mit einzigartigen optischen Eigenschaften: Stabilität bei Zimmertemperatur ohne optisches Blinken. Diamantkristalle mit Größen bis unter 20nm wurden mit neuartigen „pick-and-place“ Techniken (z.B. mit einem Atomkraftmikroskop) in komplexe photonische Strukturen integriert. Zwei unterschiedliche Ansätze für die Realisierung der neuartigen EPQ wurden verfolgt. Beim ersten werden fluoreszierende Diamantkristalle in nano- und mikrometergroße Faser-basierte oder resonante Strukturen in einem „bottom-up“ Ansatz integriert, dadurch werden zusätzliche optische Komponenten überflüssig und das Gesamtsystem ultra-stabil und wartungsfrei. Der zweite Ansatz beruht auf einem Festkörperimmersionsmikroskop (FIM). Seine Festkörperimmersionslinse wirkt wie eine dielektrische Antenne für die Emission der Defektzentren. Es ermöglicht die höchsten bisher erreichten Photonenzählraten von Stickstoff-Fehlstellen von bis zu 2.4Mcts/s und Einsammeleffizienzen von bis zu 4.2%. Durch Anwendung des FIM bei cryogenen Temperaturen wurden neuartige Anwendungen und fundamentale Untersuchungen möglich, weil Photonenraten signifikant erhöht wurden. Die Bestimmung der spektralen Diffusionszeit eines einzelnen Defektzentrums (2.2µs) gab neue Erkenntnisse über die Ursachen von spektraler Diffusion. Spektrale Diffusion ist eine limitierende Eigenschaft für die Realisierung von Quanteninformationsanwendungen. Das Tisch-basierte FIM wurde außerdem als kompakte mobile EPQ mit Ausmaßen von nur 7x19x23cm^3 realisiert. Es wurde für ein Quantenkryptographie-Experiment implementiert, zum ersten Mal mit Siliziumdefektzentren. Des Weiteren wurde ein neues Konzept für die Erzeugung von infraroten EPQ entwickelt und realisiert.The presented thesis covers the development and investigation of novel integrated single photon (SP) sources and their application for quantum information schemes. SP generation was based on single defect centers in diamond nanocrystals. Such defect centers offer unique optical properties as they are room temperature stable, non-blinking, and do not photo-bleach over time. The fluorescent nanocrystals are mechanically stable, their size down to 20nm enabled the development of novel nano-manipulation pick-and-place techniques, e.g., with an atomic force microscope, for integration into photonic structures. Two different approaches were pursued to realize novel SP sources. First, fluorescent diamond nanocrystals were integrated into nano- and micrometer scaled fiber devices and resonators, making them ultra-stable and maintenance free. Secondly, a solid immersion microscope (SIM) was developed. Its solid immersion lens acts as a dielectric antenna for the emission of defect centers, enabling the highest photon rates of up to 2.4Mcts/s and collection efficiencies of up to 4.2% from nitrogen vacancy defect centers achieved to date. Implementation of the SIM at cryogenic temperatures enabled novel applications and fundamental investigations due to increased photon rates. The determination of the spectral diffusion time of a single nitrogen vacancy defect center (2.2µs) gave new insights about the mechanisms causing spectral diffusion. Spectral diffusion is a limiting property for quantum information applications. The table-top SIM was integrated into a compact mobile SP system with dimension of only 7x19x23cm^3 while still maintaining record-high stable SP rates. This makes it interesting for various SP applications. First, a quantum key distribution scheme based on the BB84 protocol was implemented, for the first time also with silicon vacancy defect centers. Secondly, a conceptually novel scheme for the generation of infrared SPs was introduced and realized.
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Guttman, Jeremy. "Polymer-based Tunnel Diodes Fabricated using Ultra-thin, ALD Deposited, Interfacial Films." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469125487.
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Berroudji, Sid-Ahmed. "Cinétiques de mise en ordre à courte distance et caractéristiques des lacunes et des autointerstitiels dans des alliages [gamma]-FeNiCr." Grenoble 1, 1988. http://www.theses.fr/1988GRE10095.
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Etude des cinetiques de mise en ordre dans les alliages fe::(59)ni::(25)cr::(16) et fe::(9)ni::(75)cr::(16) par mesure de resistivite electrique. Determination des caracteristiques des lacunes et autointerstitiels par les techniques de trempe a l'helium liquide, de mesure de resistivite lors des cycles alternes de chauffage et de trempe ou lors de cycles continus. Evaluation des enthalpies de formation, de migration et d'autodiffusion. Influence de la composition. Analyse des sursaturations dynamiques de defauts lors de l'irradiation. Determination des frequences de saut des autointerstitiels et de leur enthalpie en fonction de la composition chimique
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Huguenin, Denis. "Effets induits par irradiation électronique dans les alliages austénitiques Fe-Ni-Cr." Grenoble 1, 1989. http://www.theses.fr/1989GRE10034.
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Tsai, You-Sheng, and 蔡尤勝. "Orientation of the vacancy line defects on Si(100)." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/66729282645104305987.
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碩士國立中山大學
物理研究所
84
Using the local-orbital density-functional molecular-dynamics method, we have obtained relaxed Si(100) surfaces with vacancy line defects that are perpendicular and parallel to the surface dimer rows and their corresponding total energies. Our results show that the perpendicular line defects with two-dimer wide are most favorable with respect to the parallel line defects in agreement with scanning tunneling microscopy (STM) observations. This preference can be attributed mainly to the formation of troughs around the defect in the perpendicular case and the limited space that prevents the exposed second- layer atoms to form long dimer rows in the parallel case.
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Fuchs, Franziska. "Optical spectroscopy on silicon vacancy defects in silicon carbide." Doctoral thesis, 2015. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-124071.
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This work sheds light on different aspects of the silicon vacancy in SiC: (1) Defect creation via irradiation is shown both with electrons and neutrons. Optical properties have been determined: the excitation of the vacancy is most efficient at excitation wavelengths between 720nm and 800nm. The PL decay yields a characteristic excited state lifetime of (6.3±0.6)ns. (2) Defect engineering, meaning the controlled creation of vacancies in SiC with varying neutron fluence. The defect density could be engineered over eight orders of magnitude. On the one hand, in the sample with highest emitter density, the huge PL signal could even be enhanced by factor of five via annealing mechanisms. On the other hand, in the low defect density samples, single defects with photostable room temperature NIR emission were doubtlessly proven. Their lifetime of around 7ns confirmed the value of the transient measurement. (3) Also electrical excitation of the defects has been demonstrated in a SiC LED structure. (4) The investigations revealed for the first time that silicon vacancies can even exist SiC nanocrystals down to sizes of about 60 nm. The defects in the nanocrystals show stable PL emission in the NIR and even magnetic resonance in the 600nm fraction. In conclusion, this work ascertains on the one hand basic properties of the silicon vacancy in silicon carbide. On the other hand, proof-of-principle measurements test the potential for various defect-based applications of the vacancy in SiC, and confirm the feasibility of e.g. electrically driven single photon sources or nanosensing applications in the near futureIn dieser Arbeit werden verschiedene Aspekte der Silizium-Fehlstelle in SiC beleuchtet: (1) Die Erzeugung der Defekte durch Bestrahlung, sowohl mit Elektronen als auch Neutronen. Einige optische Eigenschaften wurden ermittelt: die Anregung der Fehlstelle ist im Bereich von 720nm bis 800nm am effizientesten. Das Abklingen der PL zeigt eine charakteristische Lebensdauer des angeregten Zustands von (6.3±0.6)ns. (2) Maßschneidern der Defektdichte meint die kontrollierte Erzeugung von Defekten durch variablen Neutronenfluss. Hier konnte die Defektdichte gezielt über acht Größenordnungen verändert werden. Auf der einen Seite, in der Probe mit der höchsten Defektdichte, konnte das ohnehin schon große PL Signal noch um den Faktor fünf durch Temperprozesse erhöht werden. Auf der anderen Seite konnten in den Proben mit geringer Defektdichte einzelne Defekte mit stabiler nahinfrarot Emission bei Raumtemperatur zweifelsfrei nachgewiesen werden. Ihre Lebensdauer von etwa 7ns bestätigt den Wert aus den transienten Messungen. (3) Auch die elektrische Anregung der Defekte in einer SiC LED Struktur konnte gezeigt werden. (4) Die Untersuchung zeigte zum ersten Mal, dass Silizium-Fehlstellen in SiC Nanokristallen bis hinunter zu einer Größe von ca. 60 nm existieren können. Die Defekte zeigen stabile PL Emission im Nahinfraroten und sogar Magnetresonanz in der 600 nm Fraktion. Zusammenfassend werden in dieser Arbeit zum Einen grundlegende Eigenschaften der Silizium-Fehlstelle in Siliziumkarbid herausgefunden. Zum Anderen können Messungen zur Machbarkeit von verschiedenen Anwendungen sowohl das Potenzial der Fehlstelle in SiC für defektbasierte Anwendungen aufzeigen, als auch die Umsetzbarkeit von z.B. elektrisch betriebenen Einzelphotonenquellen oder Nanosensoren in naher Zukunft bestätigen
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Tien, Li-Gan, and 田力耕. "Effect of vacancy defects and defects interaction on electrical properties of single-walled carbon nanotube." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/78507458848639643220.
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Kasper, Christian Andreas. "Engineering of Highly Coherent Silicon Vacancy Defects in Silicon Carbide." Doctoral thesis, 2021. https://doi.org/10.25972/OPUS-23779.
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In this work the creation of silicon vacancy spin defects in silicon carbide with predictable properties is demonstrated. Neutron and electron irradiation was used to create silicon vacancy ensembles and proton beam writing to create isolated vacancies at a desired position. The coherence properties of the created silicon vacancies as a function of the emitter density were investigated and a power-law function established. Sample annealing was implemented to increase the coherence properties of existing silicon vacancies. Further, spectral hole burning was used to implement absolute dc-magnetometryIn dieser Arbeit wird die Erzeugung von Silizium Fehlstellen in Siliziumkarbid mit vorhersagbaren Eigenschaften nachgewiesen. Neutronen- und Elektronenbestrahlung wurden zur Erzeugung von Ensembles von Silizium Fehlstellen verwendet, während isolierte Fehlstellen an einer gewünschten Position mit Hilfe eines Protonenstrahls erzeugt wurden. Die Kohärenz der erzeugten Silizium Fehlstellen wurde in Abhängigkeit der Emitterdichte untersucht und eine Gesetzmäßigkeit hierfür eingeführt. Um die Kohärenz der Silizium Fehlstellen zu erhöhen, wurden Annealing Experimente durchgeführt. Des Weiteren wurde spektrales Holeburning verwendet, um absolute DC-Magnetometrie nachzuweisen
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Huang, Cheng-Yen, and 黃丞言. "Studies of Oxygen Vacancy Defects and Magnetism in Co-Doped Cerium Oxide Nanoparticles." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/45604922345335992055.
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Webb, Geoffrey. "Ab-initio investigation of the antimony-vacancy complex and related defects in germanium." Diss., 2016. http://hdl.handle.net/2263/52849.
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Recent advances in computational technology and algorithms have made it feasible to accurately model the electronic structures of solids by means of density functional theory. The development of hybrid functionals have improved the accuracy of band gap calculations and made it possible to make qualitative predictions regarding the charge transition energy levels of defects in semiconductors.
The Sb-V defect (also known as the E-center) in germanium is a well-known defect, which have been the subject of many experimental and some theoretical studies. It has been found to have interesting annealing properties and the aim of this study is to investigate the electronic properties of the Sb-V defect theoretically. The vacancy defect in germanium (VGe), the antimony substitutional (SbGe) defect in germanium and the defect complex (Sb-V) arising from the combination of these two defects is explored in great detail and how they interact in proximity to one another is presented here. In addition, this work can be seen as a test for the effectiveness of the technique to model defects in semiconductors correctly.
The E-center defect was investigated using the HSE06 hybrid functional as implemented in the VASP code. A positive binding energy of 1.5 eV, 1.02 eV and 0.88 eV was found for the first, second and third nearest neighbor configurations respectively, between the Sb and the vacancy was predicted. No metastability was detected and the nearest-neighbor configuration had the lowest energy for all charge states. Four transition levels in the band gap were predicted, with energy level relative to the valence band maximum, lying at 0.52 eV (-2/-1), 0.40 eV (-1/0), 0.44 eV (0/+1) and 0.02 eV (+1/+2). The two mid-gap levels (-1/0) and (0/+1) had negative-U ordering with U= -0.04 eV.
iv
These findings were consistent with the current experimental model of the Sb-V complex in germanium whereby no metastability has been observed experimentally. The energy level of the (-2/-1) corresponded well with the experimental DLTS level in n-type material at 0.37 eV, though the correspondence for the other levels was not as good. Experimentally, no negative-U behavior was observed, but the predicted negative-U behavior was rather small and no deliberate experiments have been performed to investigate the presence of negative-U behavior in the Sb-V complex.Dissertation (MSc)--University of Pretoria, 2016.
National Research Foundation (NRF)
Physics
MSc
Unrestricted
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Griffith, John W. "Indium donor/metal vacancy defect complexes in Cadmium Telluride studied with Perturbed Angular Correlation Spectroscopy." Thesis, 2002. http://hdl.handle.net/1957/32627.
Full textAbstract:
Semi-insulating, powder samples of Cadmium Telluride (CdTe) have been
studied using ������In Time Differential Perturbed Angular Correlation (PAC)
Spectroscopy. The samples have been lightly doped (~10���� cm�����) with ������In atoms,
which occupy well-defined metal (Cd) lattice sites and act as probes of the local
environment. These substitutional donors form a single defect complex in CdTe.
This complex has been identified and characterized as a function of temperature.
Those indium probes that are not complexed occupy metal lattice sites with no
defect in the local vicinity.
Samples containing metal vacancy concentrations as large as 500 ppm have
been prepared by a high temperature anneal and quench. The defect complex
involves the trapping of a cadmium metal vacancy bound to the indium probe. The
electric field gradient (EFG) experienced by probe atoms has a coupling constant of
V[subscript Q]=61.5(5) MHz and is not axially symmetric, with the asymmetry parameter
given by ��=0.16(4). It is believed that this asymmetry results from a relaxation of
the chalcogen (Te) atoms adjacent to the metal vacancy, with the tellurium atom
shared by the probe atom and the vacancy providing the dominant contribution.
The fraction of complexed probe atoms increases as the sample
temperature is decreased, and is still increasing at room temperature. Complexed
fractions are reproducible on cycling within the temperature range 40 to 200��C.
The binding energy of the complex has been measured to be 0.15(2) eV and is
independent of metal vacancy concentration, which varies and is dependent on the
details of the quench.
In rapidly cooled samples, a non-equilibrium number of these defect
complexes is observed. This state equilibrates with a time constant of 45(5) hours
at 15��C, implying that at least one of the two constituents involved in the complex
has a significant diffusion rate at this temperature. Under the assumption that
vacancy diffusion mechanisms dominate at this temperature, it is found that the
cadmium vacancies overcome an energy barrier of 0.9(1) eV with a jump time of
20(2) minutes in CdTe at 15��C.Graduation date: 2002
49
McCrate, Joseph Michael. "Characterization of low density oxide surface sites using fluorescent probes." 2013. http://hdl.handle.net/2152/23078.
Full textAbstract:
Low density surface sites are believed to play an important role in processes occurring on oxide surfaces, including catalysis and particle and film nucleation. However, our understanding of the role and chemical nature of such sites play in these processes is limited by the inability to experimentally detect minority surface sites in many oxide systems. The research performed for this dissertation is focused on developing a surface science technique utilizing fluorescent molecules to titrate specific surface sites on planar fused silica surfaces in an ultra-high vacuum (UHV) environment. High sensitivity (low detection limit) is achieved by using derivatives of perylene, a high quantum yield fluorophore. High specificity is attained by employing perylene derivatives with functional groups designed to react chemically with and titrate various sites. In addition to titrating the well-studied hydroxyl sites with perylene-3-methanol (density ~ 10¹⁴ cm⁻²), which is used to establish the technique, the detection of strained siloxane sites (~ 10¹² cm⁻²), ) with perylene-3-methanamine and oxygen vacancy sites (~ 10¹¹ cm⁻²), ) with 3-vinyl perylene is demonstrated. Particle nucleation on oxides is suspected to involve defects that trap adatoms and form critical nuclei. Using this technique, the possible role strained siloxane and oxygen vacancy sites play in trapping adatoms during the nucleation of Ge nanoparticles on silica surfaces is examined.text
50
Chu, Yow-Lin, and 朱宥霖. "Effects of nitrogen-vacancy-related defects on optical and electrical properties of heavily Mg-doped GaN films." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/15466132004323546009.
Full textAbstract:
碩士國立彰化師範大學
光電科技研究所
94
We have employed the photoluminescence (PL), surface photovoltage spectroscopy (SPS), x-ray photoelectron spectroscopy (XPS), and secondary-ion-mass spectroscopy (SIMS) measurements to study the effects of nitrogen-related defects on optical and electrical properties of heavily Mg-doped p-type GaN (p-GaN) in this study. From the PL and SPS measurements, p-GaN of (NH4)2Sx treatment suggests that the (MgGa–VN)2+ (MgGa:Ga vacancies occupied by Mg; VN:nitrogen vacancies) complexes near the p-GaN surface region were transformed into the (MgGa-SN)0 (SN:N vacancies occupied by S) complexes after (NH4)2Sx treatment, which resulted in the reduction of the ~2.8eV PL intensity and the increase of the hole concentration near the p-GaN surface region. According to the observed results from XPS and SIMS measurements, we found that the formation of more nitrogen-vacancy- related defects created near the surface by reactive ion etching technique would lead to an increase in the surface band bending, a shift of the surface Fermi level toward the conduction-band edge, the reduction of the current flow at the metal/etched p-GaN interface, and an increase in the barrier height at the metal/etched p-GaN interface. In addition, from the SIMS measurements, it is suggested that the depth of the nitrogen- deficient near-surface region resulting from the dry-etch process is about 60 nm.