Dissertations / Theses: 'Crystals – Defects'

1

Pourmatin, Hossein. "Computational Multiscale Methods for Defects: 1. Line Defects in Liquid Crystals; 2. Electron Scattering in Defected Crystals." Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/458.

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In the first part of this thesis, we demonstrate theory and computations for finite-energy line defect solutions in an improvement of Ericksen-Leslie liquid crystal theory. Planar director fields are considered in two and three space dimensions, and we demonstrate straight as well as loop disclination solutions. The possibility of static balance of forces in the presence of a disclination and in the absence of ow and body forces is discussed. The work exploits an implicit conceptual connection between the Weingarten-Volterra characterization of possible jumps in certain potential fields and the Stokes-Helmholtz resolution of vector fields. The theoretical basis of our work is compared and contrasted with the theory of Volterra disclinations in elasticity. Physical reasoning precluding a gauge-invariant structure for the model is also presented. In part II of the thesis, the time-harmonic Schrodinger equation with periodic potential is considered. We derive the asymptotic form of the scattering wave function in the periodic space and investigate the possibility of its application as a DtN non-reflecting boundary condition. Moreover, we study the perfectly matched layer method for this problem and show that it is a reliable method, which converges rapidly to the exact solution, as the thickness of the absorbing layer increases. Moreover, we use the tight-binding method to numerically solve the Schrodinger equation for Graphene sheets, symmetry-adapted Carbon nanotubes and DNA molecules to demonstrate their electronic behavior in the presence of local defects. The results for Y-junction Carbon nanotubes depict very interesting properties and confirms the predictions for their application as new transistors.

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Benedetti, Cesare. "Defects in thermosensitive colloidal crystals." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/4322/.

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Poly-N-Isopropylacrylamide (PNIPAM) colloidal particles form crystal phases that show a thermosensitive behaviour and can be used as atomic model systems. This polymer has both hydrophilic and hydrophobic character and has interesting stimuli-responsive properties in aqueous solution, of which the most important is the temperature response. Above a certain temperature, called Lower Critical Solution Temperature (LCST), the system undergoes a volume phase transition (VPT). Above the LCST, the water is expelled from the polymer network and the swollen state at low temperature transforms into a shrunken state at high temperature. The thermoresponsive behaviour of PNIPAM can be influenced by pH and ionic strength, as well as by the presence of copolymers, such as acrylic acid. In a system formed both by particles of PNIPAM and PNIPAM doped with acrylic acid, one can control the size ratio of the two components by changing the temperature of the mixture, while keeping particle interactions relatively the same. It is therefore possible to obtain thermoresponsive colloidal crystal in which temperature changes induce defects whose formation processes and dynamics can be analysed in an optical microscope at a convenient spatial and temporal scale. The goal of this thesis project was to find the conditions in which such a system could be formed, by using characterization techniques such as Static Light Scattering, Dynamic Light Scattering and Confocal Laser Scanning Microscopy. Two PNIPAM-AAc systems were available, and after characterization it was possible to select a suitable one, on the basis of its low polydispersity and the lack of a VPT, regardless of the external conditions (system JPN_7). The synthesis of a PNIPAM system was attempted, with particles of dimensions matching the JPN_7 system and, unlike JPN_7, displaying a VPT, and one suitable candidate for the mixed system was finally found (system CB_5). The best conditions to obtain thermoresponsive crystal were selected, and the formation and healing of defects were investigated with CLSM temperature scans. The obtained results show that the approach is the correct one and that the present report could represent a useful start for future developments in defect analysis and defect dynamics studies.

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Paturi, Naveen Kumar. "Analysis of photonic crystal defects for biosensing applications." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4861.

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Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains viii, 70 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 55-57).

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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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Kurz, GuÌˆnter. "Hydrodynamics of defects in nematic liquid crystal films." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313591.

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Glanville, Matthew J. "Kinematics of continuously distributed defects in crystals." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394747.

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Petrovskyi, Mykhailo Vasylovych, Михайло Васильович Петровський, and Михаил Васильевич Петровский. "Electrodynamic properties of defects in photonic crystals." Thesis, Sumy State University, 2017. http://essuir.sumdu.edu.ua/handle/123456789/64229.

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Now the electrodynamic systems of terahertz range devices are being improved due to the rapid development of synthetic material media possessing the property of periodicity in several directions which are call photonic crystals. The implementation of field interaction of photonic crystals with electron beams or dielectric waveguides is based on the formation of linear disturbances of their periodicity, these disturbances having strongly expressed waveguide properties.

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Bergugnat, Jean-Baptiste. "Strain and lattice rotation fields of deformed polycrystals." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17899.

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KHELLAF, ABDALLAH. "LATTICE DEFECT STUDIES OF HIGH QUALITY SINGLE CRYSTAL PLATINUM AND PALLADIUM." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184115.

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An improved quenching technique is described. This technique allows samples to be quenched at slow quenching rates without introducing unwanted dislocations during quench. High quality platinum single crystals 1 mm in diameter have been quenched from temperatures between 900°C and 1550°C using this technique. The data have been analysed and discussed using a sink model for vacancy loss proposed by Emrick. The formation energy was found to be (1.30 ± 0.03) eV. The entropy of formation and the concentration of vacancies at the melting point have been determined to be respectively (0.42 ± 0.11)k and (9.4 ± 0.7)10⁻⁴. High purity palladium single crystals have also been quenched using the same technique. Due to the need for a temperature scale, measurements of the electrical resistance of an ultra pure palladium single crystal have been made to a temperature within 100°C of the melting point. These, along with measurements of the liquid palladium resistivity, are reported. The results are discussed and compared to previously reported values.

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Yoon, C. S. "Ultrasonic studies of molecular crystals." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382520.

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Lewis, Alexander. "Defects in liquid crystals : mathematical and experimental studies." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:56930aaf-43a5-46bb-9987-109b22950a97.

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Nematic liquid crystals are mesogenic materials that are popular working materials for optical displays. There has been an increased interest in bistable liquid crystal devices which support two optically distinct stable equilibria. These devices typically exploit a complex geometry or anchoring conditions, which often induces defects in the equilibria. There remains a great deal to be understood about the structure of the defects and how they stabilize multiple equilibria in modern devices. This thesis focuses on four problems: the first three explore the effect of confinement and defects on nematic equilibria in simple geometries, with the aim of exploring multistability in these geometries; the fourth problem concerns the fine structure of point defects, essential for future modelling of nematic equilibria in more complex geometries. Firstly, we study nematic liquid crystals confined to two-dimensional rectangular wells using the Oseen-Frank theory. Secondly, we study equilibria within a semi-infinite rectangular domain with weak tangential anchoring on the surfaces. Thirdly, we study nematic equilibria within two-dimensional annuli. We derive explicit expressions for the director fields and free energies of equilibria within these geometries and discuss the stability of the predicted states. These three problems are motivated by the experimental work on colloidal nematic liquid crystals, which we interpret in the context of our results. Finally, we study the fine structure and stability of the radial hedgehog defect in the Landau-de Gennes theory with a sixth order bulk potential, relevant to the observability of global biaxial phases in a model with higher order potential terms.

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Horton, Robert. "The thermodynamics of charged defects in ionic crystals." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24548.

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A generic methodology is developed in this thesis to calculate the thermodynamic contribution due to high concentrations of charged defects in ionic crystals. The aim of this methodology is to allow atomistic defect behaviour, such as correlation between defects, to be included in higher-level simulation techniques, for example, when calculating phase diagrams (using CALPHAD) or obtaining charge-concentration profiles through techniques such as solving the Poisson-Boltzmann equation. A number of Monte Carlo methods (specific-heat integration (SHI), Wang-Landau sampling (WL) and nested sampling (NS)) have been applied to a model of a simple solid-electrolyte system. This is an example of a system wherein defects in ionic crystals play a central role in the behaviour. The methods are then used to calculate the thermodynamic properties of the model; for example, it is shown that one can readily obtain the Helmholtz free energy. These properties can in turn be used to parameterise simple regular-solution approaches that allow the provision of a continuum-level description of the free energy. The thermodynamic description obtained from these Monte Carlo methods is compared to those given by more-traditional defect models, such as ideal-solution theory and Debye-Hückel theory, and it is shown that the thermodynamic behaviour of our model system agrees with such a description in the correct limits. The SHI, NS, and WL methods are compared in terms of computational efficiency and ease of implementation, and suggestions are made concerning the applicability of the methods in different regimes. Finally, some suggestions are made as to extensions and further applications of the work.

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De, Luca Gino. "Computational modelling of nematic liquid crystal defects in devices and fiber processing." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103377.

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This thesis uses multiscale computational modelling to find the fundamental principles that govern defects forming during the operation of new electro-optical devices and the processing of spider silk fibers. The generalized approach developed in this thesis bridges engineering devices and biological processes based on liquid crystalline materials.
Three types of defects are encountered: inversion walls, lines and points. Inversion wall defects are found in the electro-optical device when a nematic thin film undergoes a temperature-induced surface anchoring transition. Point defects naturally occur in the tubular extrusion duct of spiders, while line defects present close topological connections with point defects and are widespread in many high-performance industrial fibers. Three models are used in this thesis and their usage is dependent on the characteristics of the defects studied.
In the case of inversion wall defects, computational modelling is used to verify, complement and analyze experimental measurements made with fluorescence confocal polarizing microscopy by our collaborator at the Georgia Institute of Technology. The various simulation results agree and explain very well experimental observations and provide a thorough understanding of the wall defects behavior. A computational technique is developed to enable the precise determination of the interaction between the liquid crystal and the device substrate. Understanding the behavior of wall defects and estimating interfacial properties are indispensable to the development and optimization of the electro-optical device as they affect properties like temperature of operation, switching voltages and response time.
Computational modelling is also used to investigate the behavior of nematic point defects confined in cylindrical cavities as observed along spiders' spinning apparatus, and to examined textural connections with other well know structures seen in industrial fibers. The various scenarios investigated include: interactions between point defects, topological transformations between point, line and ring defects as well as interactions between ring defects. The simulation results agree and complement previous investigations but also offer a new fundamental understanding on the nature and stability of defects in cylindrical cavities. Understanding the behavior of nematic point and line defects in cylindrical geometries is important as they play a fundamental role in the processing of natural and industrial high-performance fibers.

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BOUFELFEL, ALI. "DE HAAS - VAN ALPHEN EFFECT IN QUENCHED PLATINUM CRYSTALS." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184187.

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The oscillatory de Haas-van Alphen (DHVA) magnetization has been studied in Pt crystals containing more than 100 ppm vacancies. Magnetic fields as high as 75 kG were used. The oscillations were observed at temperatures as low as 0.45 k, and found to be strongly attenuated by the vacancies in this concentration range. The emphasis of this work is on the measurement of this attenuation for the purpose of studying conduction electron scattering due to single vacancies. Dingle (scattering) temperatures due to vacancies are reported for four cyclotron orbits with the field in a (110) plane, along with a new measurement of the cyclotron effective mass (m* = 2.31 ± 0.03) for the electron orbit 33° away from <100>. Vacancies were generated by quenching Pt single crystals from temperatures as high as 1730 °C in air, using a technique which minimizes the induced strain. The vacancy contribution to the electron scattering rate was separated by measuring the Dingle temperature in both quenched and annealed specimens which had been subjected to the same quenching process. The results suggest that there is only a moderate variation in this scattering rate over the s-p-like electron sheet of the Fermi surface. However, the scattering rate for the d-like open hole sheet, which contacts the Brillouin zone, is about 49% larger than that for the electron sheet. This anisotropy is attributed mainly to the lattice distortion around a vacancy and to the difference between the hole and electron wave-function symmetries.

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Olivier, Ezra Jacobus. "Analysis of the extended defects in 3C-SiC." Thesis, Nelson Mandela Metropolitan University, 2008. http://hdl.handle.net/10948/730.

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The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.

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Uddin, Salah. "Semi-analytical and numerical modeling of microsegregation for solidifying metallic alloys." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112587.

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In this study, two semi-analytical models of microsegregation were developed to predict the concentration fields of solute in the liquid and solid regions for dendritic solidification of binary metallic alloys. Both models assume that the growing dendrites are cylindrical in shape. This assumption is more realistic compared to the common assumptions of plate-like dendrites that most of the earlier researchers employed in their microsegregation modeling study. The solute redistribution profile, in the developing solid layer, necessary to determine the back diffusion parameter was derived from Fick's second law for the model without coarsening. The application of this parameter in a wide range of conditions and the use of its basic form in the model with coarsening was verified. The concept of coordinate transformation and enhancement of back-diffusion Fourier number were used in deriving the model which took into account the coarsening of dendrites. The models are then extended to deal with rapid solidification, peritectic transformations and multi-component systems and the results were compared with relevant experimental data. A good agreement between the model predictions and experimental results was found.
The second part of this study was focused on developing a fully numerical microsegregation model. The numerical model built upon a previously proposed phase change model which relied upon a coordinate transformation technique. The model was extended to deal with moving boundaries with solute diffusion. A suitable computational procedure was developed to solve the model equations which are strongly coupled to each other. To verify the accuracy of the present algorithm with regard to the capability of tracking the moving interfaces, analytical solution of the Stefan problem was used for verification purposes. A good agreement between the model predictions and the analytical solution was found. Evolution of concentration fields during solidification was calculated in the growing solid as well as in the shrinking liquid regions for rectangular, cylindrical and spherical dendrite geometries. The effects of various cooling conditions and relevant parametric values on microsegregation were analyzed and discussed.

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Jones, Christopher D. "Domains, defects, and de Vries: Electrooptics of smectic liquid crystals." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284490.

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Jensen, Katharine Estelle. "Structure and Defects of Hard-Sphere Colloidal Crystals and Glasses." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11052.

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Colloidal particles provide convenient and useful building blocks for creating ordered and disordered structures with length scales on the order of a micrometer. These structures are useful materials in their own right, and also serve as excellent scale models for exploring properties of atomic materials that would otherwise be inaccessible to direct experiment. In this dissertation, we explore structure formation in hard-sphere colloidal systems using templated sedimentation techniques, and then use colloidal crystals and glasses formed in this way to study the development of extended defects in single crystals and shear defects in glasses. We find that it is possible to form large, defect-free colloidal single crystals extremely rapidly by centrifugation onto a deterministic template. On non-deterministic templates, we find a critical deposition flux above which the material always crosses over to forming a glass. With this understanding of the effects of template and deposition flux, we designed and tested amorphous templates that allow us to make colloidal glasses by sedimentation under gravity, as well as more complex structures. In face-centered cubic colloidal single crystals grown on (100) templates, extended defects (dislocations and stacking faults) can nucleate and grow if the crystal exceeds a critical thickness that depends on the lattice misfit with the template spacing. We account for the experimental observations of the density of misfit dislocations using the Frank-van der Merwe theory, adapted for the depth-dependent variation of lattice spacing and elastic constants that results from the gravitational pressure. In the second part of the thesis, we report the first results of a detailed study of reversible and irreversible deformation of colloidal glasses. We show that shear defects exist and are active in both sheared and quiescent colloidal glasses and that these defects behave as Eshelby inclusions. We observe a decrease in the shear modulus of the glass, which corresponds to a small dilatation, which, in turn, lowers the activation barrier for shear.
Physics

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Brox, Andreas Sören Jonathan [Verfasser], and Tobias [Akademischer Betreuer] Schätz. "Topological defects in Coulomb crystals : : spectroscopy and dynamics of solitons." Freiburg : Universität, 2017. http://d-nb.info/1143461754/34.

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Ramanachalam, M. Swaminathan. "Correlation of defects and electrical properties in Si and ZnO." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19675.

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Hong, Liang, and 洪亮. "On nanoferroelectric domain structures and distributions of defects inferroelectrics." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44138763.

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Hutton, Keith Beveridge. "Characterisation of imperfections in single crystals of high purity synthetic quartz." Thesis, University of Strathclyde, 1990. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21289.

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The work described in this thesis is a study of imperfections in high purity, low dislocation content synthetic quartz single crystals which are grown on a commercial scale by the General Electric Company. Hydrogen and metal ion impurities in quartz were studied using low temperature transmission Fourier Transform Infrared Spectroscopy, (FTIR). Incorporation of impurities in quartz was investigated using crystals which were doped with Al, Fe, Cr, Co, Ti, P, Cu and K. Orientation of hydroxyl impurities was determined using polarised infrared spectroscopy. Deuterated quartz crystals were grown and studied as analogues to high purity crystals. X-ray diffraction topography was used to evaluate crystal quality and to perform a study of quartz which had been treated by electrodiffusion, or sweeping. Crystal lattice strain and sweeping damage was studied using double crystal topography at the Synchrotron Radiation Source, (SRS), at the Daresbury Laboratory. Metal ion impurities were sh own to incorporate interstitially into quartz crystals. The only exceptions were aluminium and iron, which incorporated substitutionally. All the impurities studied introduced hydrogen impurities such as hydroxyl ions and water molecules into quartz. A relationship between impurity concentration and hydrogen content was clearly indicated. The 3200 cm-1 broad absorption band characteristic of impure and fast grown synthetic quartz was strongly implicated as being due to interstitially incorporated water molecules. The major hydrogen impurities in quartz were sodium hydroxide molecules which were preferentially aligned along the X, Y and Z growth axes. Hydroxyl ions were not incorporated directly from the growth solution. Sweeping was shown to induce the formation of a negative space charge in treated quartz which gave rise to inhomogeneous lattice strain. The strain was gradually relieved upon prolonged exposure to x-rays. A mechanism for the production and relief of lattice strain has been proposed. Sweeping produced surface damage on mechanically polished crystals but not on those treated by chemical polishing using hydrofluoric acid. No further detrimental effects of sweeping were observed. Double crystal topographic studies revealed two possible bulk defects in Quartz. The first of these was a previously unreported planar defect parallel to the X-Y plane of quartz. The second was possibly a planar defect associated with the cellular growth cells in the (00.1) growth sector of quartz. The validity of these observations was put in doubt by the possibility of defect projection from the silicon monochromator which had been used in double crystal studies.

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Eddleston, Mark David. "Crystal form and defect analysis of pharmaceutical materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610090.

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Zhao, Xiaofang, and 赵晓芳. "The influence of defects on the domain structure and properties of ferroelectrics." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47031608.

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Stehr, Jan Eric, Xingjun Wang, Stanislav Filippov, S. J. Pearton, Ivanov Ivan Gueorguiev, Weimin Chen, and Irina Buyanova. "Defects in N, O and N, Zn implanted ZnO bulk crystals." Linköpings universitet, Funktionella elektroniska material, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-91343.

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Comprehensive characterization of defects formed in bulk ZnO single crystals co-implanted with N and Zn as well as N and O atoms is performed by means of optically detected magnetic resonance (ODMR) complemented by Raman and photoluminescence (PL) spectroscopies. It is shown that in addition to intrinsic defects such as Zn vacancies and Zn interstitials, several N-related defects are formed in the implanted ZnO. The prevailed configuration of the defects is found to depend on the choices of the co-implants and also the chosen annealing ambient. Specifically, co-implantation with O leads to the formation of (i) defects responsible for local vibrational modes at 277, 511, and 581 cm−1; (ii) a N-related acceptor with the binding energy of 160 ± 40 meV that is involved in the donor-acceptor pair emission at 3.23 eV; and (iii) a deep donor and a deep NO acceptor revealed from ODMR. Activation of the latter defects is found to require post-implantation annealing in nitrogen ambient. None of these defects are detected when N is co-implanted with Zn. Under these conditions, the dominant N-induced defects include a deep center responsible for the 3.3128 eV PL line, as well as an acceptor center of unknown origin revealed by ODMR. Formation mechanisms of the studied defects and their role in carrier recombination are discussed.

Funding Agencies|Swedish Research Council|621-2010-3971|

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Dai, Xuemin, and 戴學敏. "Experimental and theoretical studies of defects related emissions in ZnO crystals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B4163388X.

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Matsunaga, Katsuyuki. "Theoretical Study on Electronic States of Point Defects in Ionic Crystals." Kyoto University, 1997. http://hdl.handle.net/2433/77835.

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Dai, Xuemin. "Experimental and theoretical studies of defects related emissions in ZnO crystals." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B4163388X.

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Garces, Nelson Y. "Analysis of paramagnetic point defects in KH₂PO₄ and KTiOPO₄ crystals." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1778.

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Thesis (Ph. D.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains xii, 116 p. : ill. Includes abstract. Includes bibliographical references (p. 106-109).

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Hong, Liang. "On nanoferroelectric domain structures and distributions of defects in ferroelectrics." Click to view the E-thesis via HKUTO, 2010. http://sunzi.lib.hku.hk/hkuto/record/B44138763.

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Ó, Conbhuí Pádraig. "Micromagnetic modelling of imperfect crystals." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33133.

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In paleomagnetism, practical measurements are rarely made using perfect, isolated, single-phase, ferromagnetic crystals. Experimental observations are typically made using magnetic materials formed by a variety of natural processes. In this thesis, we will look at bridging the gap between current numerical modelling capability and experimental observations. First, we work towards micromagnetic modelling of multi-phase magnetic materials, including magnetostriction, embedded in a rocky matrix, along with crystal defects. We present a derivation of the Boundary Element Method formulation used by the micromagnetics package, MERRILL, and provide an extension of this from single-phase materials to multi-phase. After discussing issues with previous approaches to modelling magnetostriction, we derive and present a more robust and flexible approach. This model of magnetostriction is suitable for non-uniformmagnetizations, for multi-phase materials, and for arbitrary boundary conditions, and can be incorporated into MERRILL.We then outline a method for extending our model to materials embedded in an infinite elastic matrix of arbitrary elasticity. Finally, we present a method for modelling the magnetic response of a material due to crystal defects, along with a concrete example of a magneto-dislocation coupling energy at a magnetite-ilmenite boundary where stress due to lattice misfit is eased by regular edge dislocations. Second, we work towards being able to verify micromagnetic models against nano-scale experimental data. To do this, we present two techniques for simulating electron holograms from micromagnetic modelling results, a technique capable of imaging magnetic structures at the nano-scale. We also present example electron holograms of commonly occurring magnetic structures in nano-scale rock and mineral magnetism, and highlight some distinguishing features, which may be useful for interpreting experimental electron holography data.

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Ahmad, S. A. "Theoretical studies of the structures of defects in silicon germanium and other crystals." Thesis, University of Surrey, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354752.

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Blood, Arabella M. "A study of the electrical properties of defects in silicon." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298320.

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Vale, Renato Pessoa. "Defeitos em cristais formados por átomos de 4He." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277196.

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Orientadores: Silvio Antonio Sachetto Vitiello, Maurice de Koning
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Neste trabalho apresentamos um estudo feito sobre defeitos em um sólido quântico formado por átomos de 4He. Embora ainda não exista um mecanismo para explicar a fase supersólida deste sistema, ela tem sido frequentemente associada com a presença de desordem no cristal, que pode ocorrer com a existência de algum tipo de defeito. O método do trabalho reversível é aplicado para calcular a concentração de vacâncias e a energia livre de ligação entre estes defeitos pontuais. Inicialmente, esta metodologia é aplicada a um sólido quântico descrito por uma função de onda tipo Jastrow, para em seguida ser aplicada no nosso sistema de interesse. A função de onda sombra é utilizada para modelar o 4He sólido hcp, cujas configurações são amostradas através do método de Monte Carlo utilizando o algoritmo de Metropolis. Além da determinação das concentrações de monovacâncias e divacâncias, nossos resultados indicam que não existe uma tendência de se formar aglomerados deste defeito, que poderia levar a uma separação de fases. Posteriormente, utilizamos o método de Peierls-Nabarro para estudar defeitos lineares do tipo discordâncias. Para isto, determinamos as constantes elásticas do material, sendo esta a primeira estimativa teórica destas propriedades para o hélio sólido. Nosso modelo indica que estes defeitos lineares possuem uma tendência em se separar em pares de discordâncias parciais. Além disso, a resistência intrínseca da rede cristalina desempenha um papel importante na mobilidade destes defeitos. Portanto, um mecanismo para explicar a fase supersólida do 4He, que envolva a presença de discordâncias, deve levar em conta esta resistência
Abstract: In this work we present a study about defects in a quantum solid formed by atoms of 4He. Although there is no mechanism to explain the supersolid phase of this system, it has often been associated with the presence of disorder in the crystal, which can occur with the presence of some type of defect. The reversible work method is applied to calculate the concentration of the vacancies and the binding free energy between these point defects. Initially, this methodology is applied to a quantum solid described by a Jastrow wave function, to then be applied in our system of interest. A shadow wave function is used to model the hcp solid helium, whose con gurations are sampled by the Monte Carlo method using the Metropolis algorithm. Besides the determination of monovacancy and divacancy concentrations, our results indicate that there is not a tendency to form clusters of these defects, which could lead to a phase separation. Subsequently, we used the Peierls-Nabarro method to study linear defects like dislocations. With this purpose, we determined the elastic constants of material, this being the rst theoretical estimates of these properties for solid helium. Our model indicates that these linear defects have a tendency to separate into pairs of partial dislocations. Furthermore, the intrinsic resistance of the crystal lattice plays an important role in the mobility of these defects. Therefore, a mechanism to explain the supersolid phase of helium, which involves the presence of dislocations, should take account of this resistance
Doutorado
Física da Matéria Condensada
Doutor em Ciências

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35

Cramer, Loren Paul. "Defects in calcium fluoride generated by 157 NM laser and low-energy electrons." Online access for everyone, 2004. http://www.dissertations.wsu.edu/Dissertations/Fall2004/L%5FCramer%5F121704.pdf.

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36

Hung, Wing Wa. "FTIR and XPS of congruent and stoichiometric LiNbO3." HKBU Institutional Repository, 2003. http://repository.hkbu.edu.hk/etd_ra/442.

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37

Nazar, Faizan Q. "Electronic structure of defects in the Thomas-Fermi-von-Weizsäcker model of crystals." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/91552/.

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In this thesis, we establish a locality property for solutions to the Thomas-Fermi-von Weizsäcker (TFW) equations. This is a system of coupled PDEs that models the ground state electron density corresponding to a given nuclear arrangement. The locality property is a pointwise stability estimate for the TFW equations, that demonstrates the exponential response of the electron density to a perturbation of the nuclei. We show that this result holds for the TFW when using either the Coulomb or the Yukawa potential to treat the interaction of charged particles. We then use the locality result to prove several consequences for the TFW ground state, which includes generalising results from [14] regarding the neutrality of infinite systems and also showing the uniform convergence of ground states when passing to the limit from the Yukawa to the Coulomb model. Our main application is the construction of site energies from the TFW energy. The locality result implies that the response of each site energy decays exponentially with respect to a perturbation of the nuclear arrangement. Using these site energies, we then formulate the lattice relaxation problem, that was initially formulated in [23], to consider the response of a perfect crystal lattice to the introduction of a point defect. The site energies allow us to formulate a variational problem over a space of deformations of the lattice, show this problem is well-posed and finally establish the decay properties of minimisers.

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38

Engel, Michael. "Dynamics and defects of complex crystals and quasicrystals perspectives from simple model systems /." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-34692.

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39

Li, Kaile. "Defects at surface and interface of crystals : theoretical and x-ray scattering analysis /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074422.

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Nemitz, Ian R. "Liquid Crystals: Surfaces, Nanostructures, and Chirality." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480686661255562.

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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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Chirila, Madalina M. "The influence of point defects on the optical properties of cadmium tungstate." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1502.

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Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains viii, 71 p. : ill. Includes abstract. Includes bibliographical references (p. 70-71).

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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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Cameron, Daniel Stuart M. "Vortex localization in single crystals of Tlb2Bab2CuOb6+[delta] with columnar defects : an empirical model." Thesis, University of Ottawa (Canada), 1997. http://hdl.handle.net/10393/10123.

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The peaks and valleys observed by Nowak et al (Phys. Rev. B54, R12725 (1996)) in the local magnetization M(x) and local relaxation rate S(x) in a single crystal of $\rm Tl\sb2Ba\sb2CuO\sb{6+\delta}$ containing columnar defects are well reproduced by an empirical model where the critical current density $j\sb{C}$ is fractionally enhanced in the vicinity of the matching field $B\sb\phi$ and of a multiple of $B\sb\phi$ by superimposing two broad triangular peaks on a continuous dependence of $j\sb{C}$ on the magnetic flux density B. The model fits the variety of M(x) and S(x) data taking $B\sb{S1}$ and $B\sb{S2}$, the flux density at the first and second peaks in $j\sb{C}$, to have a ratio $B\sb{S2}/B\sb{S1}\approx 2.5.$ The model also makes detailed predictions regarding the structure and location of valleys for S(x) versus B(x) descending in magnitude which were not reported in the above article. We demonstrate that a "staircase" type of dependence of $j\sb{C}$ on B proposed by Radzihovsky (Phys. Rev. Letters 74, 4923 (1995)) and exploited by Beauchamp et al, (Phys. Rev. B52, 13025 (1995)) can account for the peak in $\vert M(x)\vert$ adjacent to B = 0 but cannot generate the two peaks encountered when B(x) is ascending in magnitude nor reproduce the two peaks seen at higher fields when B(x) is descending in magnitude. (Abstract shortened by UMI.)

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45

Maroudas, Dimitrios. "Dynamics of point and line defects in single semiconductor crystals grown from the melt." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12908.

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Murray, Bryce S. Murray. "Anchoring-Induced Topological Defects in Nematic Liquid Crystals: Core Relaxation Mechanisms and Electro-Optics." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1531143058239933.

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Ho, King-fung, and 何競豐. "Some positron annihilation studies on highly doped and supersaturated N-type silicon." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30287108.

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Foteinopoulou, Stavroula. "Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals." Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/822058-9BqHHS/native/.

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Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003.
Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2048" Stavroula Foteinopoulou. 12/12/2003. Report is also available in paper and microfiche from NTIS.

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GOMES, LAERCIO. "Estudo compreensivo da fotodissociacao do ion OHsub(-) nos haletos alcalinos e sua interacao com centros de cor." reponame:Repositório Institucional do IPEN, 1985. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9850.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Stevens, Kevin T. "Electron-nuclear double resonance studies of point defects in AgGaSe₂ and ZnGeP₂." Morgantown, W. Va. : [West Virginia University Libraries], 1999. http://etd.wvu.edu/templates/showETD.cfm?recnum=1130.

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Thesis (Ph. D.)--West Virginia University, 1999.
Title from document title page. Document formatted into pages; contains ix, 165 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 118-122).

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Dissertations / Theses on the topic 'Crystals – Defects'

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