Dissertations / Theses on the topic 'Structural properties of condensed matter'
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Lee, Dok Won. "Structural and magnetic properties of copperiron multilayers." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20264.
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The structural and magnetic properties of Diamagnetic/Ferromagnetic: Cu/Fe multilayers, prepared by DC-magnetron sputtering, were studied as a function of Fe layer thickness tFe. Structural characterization reveals the successful growth of high-quality layered structures along the film growth direction. However, the increasing contribution of the interface roughness was visible with decreasing tFe . X-ray diffraction data indicate the dissolution of Fe atoms in fcc Cu medium due to interfacial mixing.The magnetic transition from ferromagnetism to paramagnetism with decreasing tFe was confirmed by conversion-electron Mossbauer spectroscopy (CEMS), vibrating sample magnetometry, and magnetotransport measurements. The monotonic decrease in the average hyperfine field with t Fe indicates that the transition is a gradual process as t Fe decreases from 34 A down to 7 A. The isomer shift of the singlets in the CEM spectra suggests the presence of fcc Fe, while the observed doublet is assigned to the Cu-Fe alloy phase at the interfaces.
The variation of magnetoresistance (MR) with t Cu indicates that for a nominal t Fe of 20 A the multilayer has a well-defined superlattice structure, whereas multilayers with nominal tFe, of 5 A have a granular-alloy-like structure. AC susceptometry provided direct evidence for island formation for nominal tFe = 5 A by exhibiting the blocking characteristics of superparamagnets. The temperature-dependence of the magnetization suggests that for nominal tFe = 5 A, 75% of the Fe atoms are in the superparamagnetic bcc phase, leaving the remaining 25% in the Cu-Fe alloy and fcc Fe phases.
The observed magnetic transition is likely due to superparamagnetic relaxation rather than a structural transition from bcc Fe to fcc Fe as t Fe decreases below a critical thickness tC at which a multilayer structure becomes an island structure.
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Church, Christopher J. "The structural, thermal, and magnetic properties of manganese silicon sulfide." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6806.
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$\rm Mn\sb2SiS\sb4$ is a synthetic Olivine in which we have discovered an exceptional temperature dependent magnetic behavior that may lead to interesting applications. A state of spontaneous magnetization was found to exist in this material, but only between 83 and 86.5 K. In order to explain this unusual magnetic phenomena, polycrystalline samples of $\rm Mn\sb2SiS\sb4$ were first prepared from the elements and studied by SQUID magnetometry in low fields, by X-ray and neutron diffraction, by electron spin resonance (ESR) and by specific heat calorimetry. This research, in which the author was a member of a team, is described. His specific contributions include among others; the debugging and extension of some of the computer programs used to analyze the neutron diffraction results, the interfacing of the Bruker ESR spectrometer to a IBM compatible computer and the development of the computer progams to acquire the resonance curves and analyze the line spectra, the analysis of the ESR results, the assembly of parts of an apparatus and the development of a procedure to measure the specific heat of small samples in the 77 to 150 K range as well as some preliminary measurements on a sample of $\rm Mn\sb2SiS\sb4.$ These contributions are emphasized in this thesis. (Abstract shortened by UMI.)
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Kim, Jeha. "Structural and elastic properties of silver-palladium and copper-palladium superlattices." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186275.
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I prepared Ag/Pd and Cu/Pd superlattices using both sputtering and molecular beam epitaxy. For the Ag/Pd (t(Ag):t(Pd) = 1:1) superlattices, I observed two distinctive behaviors in the structural coherence length ξ as a function of modulation wavelength Λ. Using Brillouin light scattering (BLS) I observed a 50% enhancement of the shear elastic constant c₅₅ and a 16% increase of c₁₁ with decreasing Λ. Annealing study showed that a high structural order of the films in the growth direction was strongly correlated to the increase of c₅₅. For the 3:1 and 1:3 Ag/Pd samples, I also observed a monotonic increase of the Rayleigh velocity υ(R) (or c₅₅) with decreasing Λ and similar behavior in the structural coherence length to the 1:1 samples. In conclusion, the recrystallization of the alloy and the formation of extended interfaces by intermixing at the Ag-Pd interfaces are responsible for a large enhancement of c₅₅. Using BLS for the Cu/Pd superlattices, I observed a 24% decrease of c₅₅ as Λ was decreased to ∼30-40 Å, followed by a rapid increase for smaller Λ. The observed homogeneous strain in the growth direction showed a strong relationship with c₅₅. The strain was localized at the interface and the Cu/Pd films were in compressive stress for Λ < 38 Å. In conclusion, a localized strain at the interfaces in Cu/Pd is related to the softening in c₅₅. The measurements of in-plane lattice spacing d[220] indicated a structural transformation of the films at Λ = 14 Å from an incoherent to a coherent structure. However, the in-plane strain did not show any relationship with the softening of c₅₅. For single crystalline Cu/Pd superlattices, well-defined RHEED streaks showed incommensurate growth of Cu(111) on Pd(111) layer. The measured shear elastic constant c₅₅ showed a 26% decrease with respect to the largest Λ film with a peak at Λ ≃ 40 Å. Unlike the sputtered films, while c₅₅ decreases by 26% with decreasing Λ, the Cu/Pd films show no change in d(avg)[111] for Λ > 40 Å. I observed no in-plane anisotropies in υ(R) as predicted from theory for single crystal films.
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Freitag, James M. (James Mac). "Structural and magnetotransport properties of nickelcobalt multilayers." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24003.
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Ferromagnetic/ferromagnetic Ni/Co multilayers with component layer thicknesses ranging from 40 A down to 5 A were prepared by DC-magnetron sputtering. Due to the fact that Ni and Co alloys share a common d band, it is expected that the total resistance of the multilayers, including the elemental resistance of the layers and the resistance of the interdiffused alloyed region at the interfaces, will be lower than for other 3d transition metal combinations. Consequently, the magnetoresistance ratio $ Delta rho/ rho$ is expected to be enhanced.Structural characterization by grazing-angle X-ray reflectivity reveals high-quality layered structures with a well-defined composition modulation along the film growth direction. Wide-angle X-ray diffraction scans display the polycrystalline nature of the Ni/Co multilayers which grow in an FCC phase with a preferred (111) orientation and a fraction of (200) structural domains.
Measurements of the magnetotransport properties of these multilayers indicate that the magnetoresistance (MR) effect, $ Delta rho sim0.35 mu Omega cdot$cm, is roughly constant over the entire compositional range. The MR ratio $ Delta rho/ rho,$ which is as high as 3.0% in a Si/(Ni40A/Co5A) $ times$ 6 multilayer, is therefore more strongly dependent on the zero-field resistivity $ rho.$ By fitting a semi-classical model to the resistivity compositional variation, we determined the interface contribution to the resistivity. The MR measurements as well as the magnetic anisotropy of the films, studied by vibrating sample magnetometry (VSM) and magneto-optical Kerr effect (MOKE) magnetometry, are consistent with the origin of the observed MR effect being anisotropic magnetoresistance (AMR). The highest magnetic sensitivity measured at zero-field and constant in the range from ${ sim}{-}10$ Oe to +10 Oe was 0.1%/Oe. This value compares well with other alloys being developed as magnetic sensors. (Abstract shortened by UMI.)
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Pavlenyi, Marc. "Effects of short range order on structural and transport properties of Cu-Ni-Zr amorphous alloys." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59379.
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The effects of short range order on the structural and transport properties of the $ rm Cu sb{1-x}Ni sb{x}Zr sb2$ amorphous metallic alloy system are studied. Depending on composition, these amorphous alloys crystallize into different structures. CuZr$ sb2$ has the I4/mmm (C11) structure and NiZr$ sb2$ has the I4/mcm (C16) structure. It is believed that the short range order in the amorphous phase is related to the final crystalline phase. A careful study (using differential scanning calorimetry, X-ray diffraction on as made and crystallized states, room temperature magnetic susceptibility and resistivity, and a determination of the superconducting transition temperature of as-made and annealed states) has been done to see what transport properties are affected.It is observed that there is a linear increase in the values of the susceptibility, resistivity, and superconducting transition temperature of the system from CuZr$ sb2$ to NiZr$ sb2.$ This is attributed to an increase of the electronic density of states as the concentration of Ni increases. There is little or no influence on transport properties due to topological short range order.
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Van, Leeuwen Robert Alan. "Structural and magnetic properties of cobalt/palladium superlattices, ultra-thin cobalt films and manganese antimony alloys." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186431.
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Structural, magnetic, and magneto-optical properties of Co/Pd and Co/Pd/Cu superlattices, ultra-thin Co films and MnSb alloys have been studied. The superlattices and Co films were grown by molecular beam epitaxy (MBE) while the MnSb alloy films were made by sputtering techniques. Several x-ray diffraction techniques were used to analyze the physical structure of the superlattices and alloys. Magnetometry techniques were used to determine some of the room temperature and temperature dependent magnetic properties of the films. In situ and ex situ measurements of the magneto-optical properties of the ultra-thin Co films and alloys also were made.
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NGUYEN, TUAN ANH. "INVESTIGATIONS OF ELECTRONIC STRUCTURE AND OPTICAL PROPERTIES OF II-VI SELF-ASSEMBLED QUANTUM DOTS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1143155352.
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Hugger, Peter George 1980. "Structural and electronic properties of hydrogenated nanocrystalline silicon employed in thin film photovoltaics." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11255.
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xxi, 134 p. : ill. (some col.)Hydrogenated nanocrystalline silicon (nc-Si:H) is a semiconducting material that is very useful as a thin film photovoltaic. A mixture of amorphous and crystalline silicon components, nc-Si:H shows good carrier mobilities, enhanced infrared response, and high resilience to light-induced degradation of its electronic properties, a thermally reversible degenerative phenomenon known as the Staebler-Wronski Effect (SWE). However, production of nc-Si:H is difficult in part because the structural and electronic properties of this material are not well understood. For example, its electronic properties have even been observed by some authors to improve upon prolonged light exposure, in direct opposition to the SWE observed in purely amorphous thin film silicon. We used several junction capacitance based measurements together with characterization methods such as Raman spectroscopy and secondary ion mass spectroscopy to better understand the structure/function relationships present in nc-Si:H. Drive level capacitance profiling (DLCP) was used to determine densities, spatial distributions, and energies of deep-gap defects. Transient photocapacitance (TPC) and transient photocurrent (TPI) were used to characterize optical transitions and the degree of minority carrier collection. Materials had crystallite volume fractions between 20% and 80% and were deposited using RF and modified VHF glow discharge (PECVD) processes at United Solar Ovonic, LLC. Measurements were made as a function of metastable state: annealed states were produced by exposing the material to temperatures above 370K for 0.5h and the lightsoaked state was produced by exposure to 200mW/cm 2 610nm long-pass filtered light from an ELH halogen source for 100h. We identified two deep defects in nc-Si:H. A primary defect appearing throughout the material at an electronic transition energy of roughly 0.7eV below the conduction band, and a second defect 0.4eV below the conduction band which was localized near the p/i junction interface. Results suggested that the deeper defect is related to the presence of oxygen and is located in grain boundary regions. The energy depth of this defect appears also to be somewhat dependent on metastable state. This phenomenon, and the universal decrease in minority carrier collection upon lightsoaking are accounted for in a model of electronic behavior we have developed over the course of this study.
Committee in charge: Dr. Miriam Deutsch, Chairperson; Dr. J. David Cohen, Advisor; Dr. Roger Haydock, Member; Dr. Heiner Linke, Member Dr. Mark Lonergan Outside Member
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Baumgartl, Jörg. "Colloids as model systems for condensed matter investigation of structural and dynamical properties of colloidal systems using digital video microscopy and optical tweezers /." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-31322.
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Chen, Hsiung. "Preparation, properties, and structure of hydrogenated amorphous carbon films." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054566593.
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Russell, David D. "Design, synthesis, crystal structure and magnetic properties of novel osmium-based B-site ordered double perovskites." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10011271.
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Transition metal oxides (TMOs) with face centered cubic arrangement of magnetic ions are composed of triangular sub-lattices. When antiferromagnetic (AFM) interactions of the same strengths between all three pathways in triangular settings are in place, spin constraints cannot be fulfilled simultaneously and the system undergoes geometric magnetic frustration (GMF). The purpose of the work presented in this thesis is to better understand the criteria for a system to undergo GMF. To achieve this, the novel B-site ordered double perovskites Ca2ScOsO6 and Ca2.2Mg0.8OsO6 were synthesized in polycrystalline form utilizing the conventional solid-state method. The crystal structure of these compounds were characterized through X-ray diffraction, and magnetic properties were explored through magnetic susceptibility measurements. Employing the spin-dimer analysis method, relative magnetic exchange interactions were calculated and modeled. These novel osmium-based B-site ordered double perovskites were then compared to isostructural compounds to study the effects of the osmium oxidation state on crystal structure and the exhibited properties.
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Thompson, Justin K. "STRUCTURAL, TRANSPORT, AND TOPOLOGICAL PROPERTIES INDUCED AT COMPLEX-OXIDE HETERO-INTERFACES." UKnowledge, 2018. https://uknowledge.uky.edu/physastron_etds/52.
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Complex-oxides have seen an enormous amount of attention in the realm of Condensed Matter Physics and Materials Science/Engineering over the last several decades. Their ability to host a wide variety of novel physical properties has even caused them to be exploited commercially as dielectric, metallic and magnetic materials. Indeed, since the discovery of high temperature superconductivity in the “Cuprates” in the late 1980’s there has been an explosion of activity involving complex-oxides. Further, as the experimental techniques and equipment for fabricating thin films and heterostructures of these materials has improved over the last several decades, the search for new and more exotic properties has intensified. These properties stem from the interfaces formed by depositing these materials onto one another. Whether it be interfacial strain induced by the mismatch between the crystal structures, modified exchange interactions, or some combination of these and other interactions, thin films and heterostuctures provide an invaluable tool the modern condensed matter community.
Simply put, a “complex-oxide” is any compound that contains Oxygen and at least two other elements; or one atom in two different oxidation states. Transition Metal Oxides (TMO’s) are a subset of complex-oxides which are of particular interest because of their strong competition between their charge, spin and orbit degrees of freedom. As we progress down the periodic table from 3d to 4d to 5d transition metals, the crystal field, electron correlation and spin-orbit energies become more and more comparable. Therefore, TMO thin films and heterostructures are indispensable to the search for novel physical properties.
KTaO3 (KTO) is a polar 5d TMO which has been investigated for its high-k dielectric properties. It is a band insulator with a cubic perovskite crystal structure which is isomorphic to SrTiO3 (STO). This is important because non-polar STO is famous for forming a highly mobile, 2-Dimensional Electron Gas (2DEG) at the hetero-interface with polar LaAlO3 (LAO) as a result of the so-called “polar catastrophe”. Here, I use this concept of polarity to ask an important question: “What happens at hetero-interfaces where two different polar complex oxides meet?” From this question we propose that a hetero-interface between two polar complex-oxides with opposite polarity (I-V/III-III) should be impossible because of the strong Coulomb repulsion between the adjacent layers. However, we find that despite this proposed conflict we are able to synthesize KTO thin films on (110) oriented GdScO3 (GSO) substrates and the conflict is avoided through atomic reconfiguration at the hetero-interface.
SrRuO3 (SRO) is a 4d TMO, and an itinerant ferromagnet that is used extensively as an electrode material in capacitor and transistor geometries and proof-of-concept devices. However, in the thin film limit the ferromagnetic transition temperature, TC, and conductivity drop significantly and even become insulating and lose their ferromagnetic properties. Therefore, we ask “Are the transport properties of SRO thin films inherently inferior to single crystals, or is there a way to maintain and/or enhance the metallic properties in the thin film limit?” We have fabricated SRO thin films of various thickness on GSO substrates (tensile strain) and find that all of our samples have enhanced metallic properties and even match those of single crystals.
Finally, we ask “Can these enhanced metallic properties in SRO thin films allow us to observe evidence of a topological phase without the complexity of off-stoichiometry and/or additional hetero-structural layers?” Recent reports of oxygen deficient EuO films as well as hetero-structures and superlattices of SRO mixed with SrIrO3 or La0.7Sr0.3MnO3 have suggested that a magnetic skyrmion phase may exist in these systems. By measuring the Hall resistivity, we are able to observer a topological Hall effect which is likely a result of a magnetic skyrmion. We find that of the THE exists in a narrow temperature range and the proposed magnetic skyrmions range in size from 20-120 nm. Therefore, the SRO/GSO system can provide a more viable means for investigating magnetic skyrmions and their fundamental interactions.
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Jiao, Jun 1957. "Comparative study of the properties, morphologies, and structures of carbon nanoclusters prepared by different methods." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282358.
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This study was undertaken to gain a greater understanding of the growth mechanism of carbon nanoclusters. A set of carbon nanocluster samples prepared by three different methods and under different conditions was characterized with respect to morphology, structure, composition, and related properties. Electron microscopy characterization techniques were used to identify these features. The carbon nanoclusters prepared by conventional arc discharge, modified arc discharge, and catalytic CO disproportionation appear quite different on the surface, but have features in common that this study emphasizes. For the understanding of the growth mechanisms of carbon nanoclusters of different morphologies, the dependence of growth features on the major processing parameters--carbon supply and carbon activity, reaction temperature, gas type and partial pressure, composition and materials involved--was interpreted systematically in a comparative manner. For the encapsulation of foreign materials into carbon cages, the ratio of the supply of carbon and encapsulants, the dimensions and configurations of the electrodes, the flow of a buffer gas across the carbon source, the nature and surface area of materials to be encapsulated or acting as catalyst were recognized as the basic components of a process that lead to properties of as-made materials such as the size distribution of the clusters, the degree of the carbonization of the encapsulants, and the predominant presence of certain morphologies. Regarding the comparison of the structural stability of different morphologies, the results of the post deposition treatments such as elevated high temperature annealing, nitric acid erosion, and electron beam bombardment provide further insight into the properties of this novel family of materials. Operating in certain domains of the parameter space, carbon-coated ferromagnetic nanoparticles, single-walled nanotubes, cylindrical multi-walled nanotubes, and conical fish-bone filaments were produced and comparatively characterized. A tentative discussion with the aim of confirming, expanding or modifying some growth models that have emerged from the work of the past was given in this dissertation. It is expected that this broad-based comparative study will advance the understanding of the growth mechanism to a point where some of the technological promise of the carbon nanoclusters may be realized.
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Ugolini, Cristofer Russell. "Optical and structural properties of Er-doped GaN/InGaN materials and devices synthesized by metal organic chemical vapor deposition." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1021.
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Khosravi, Khorashad Larousse. "Theoretical and Computational Study of Optical Properties of Complex Plasmonic Structures." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou150834414639462.
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Mandru, Andrada Oana. "Ferromagnetic Thin and Ultra-Thin Film Alloys of Manganese and Iron with Gallium and Their Structural, Electronic, and Magnetic Properties." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1458572741.
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Khan, Neelam. "Optical, structural, and transport properties of InN, In[subscript]xGa[subscript]1-xN alloys grown by metalorganic chemical vapor deposition." Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1379.
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Regoutz, Anna. "Structural and electronic properties of metal oxides." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6f425890-b211-4b35-b438-b8de18f7ae64.
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Metal oxides are of immense technological importance. Their wide variety of structural and electronic characteristics leads to a flexibility unrivalled by other groups of materials. However, there is still much debate about the fundamental properties of some of the most widely used oxides, including TiO2 and In2O3. This work presents high quality, in-depth characterisation of these two oxides in pure and doped form, including soft and hard X-ray photoelectron spectroscopy and X-ray diffraction. Bulk samples as well as thin film samples were prepared analysed. For the preparation of thin films a high quality sol-gel dip-coating method was developed, which resulted in epitaxial films. In more detail the organisation of the thesis is as follows: Chapter 1 provides an introduction to key ideas related to metal oxides and presents the metal oxides investigated in this thesis, In2O3, Ga2O3, Tl2O3, TiO2, and SnO2. Chapter 2 presents background information and Chapter 3 gives the practical details of the experimental techniques employed. Chapters 4 presents reciprocal space maps of MBE-grown In2O3 thin films and nanorods on YSZ substrates. Chapters 5 and 6 investigate the doping of In2O3 bulk samples with gallium and thallium and introduce a range of solid state characterisation techniques. Chapter 7 describes the development of a dip-coating sol-gel method for the growth of thin films of TiO2 and shows 3D reciprocal space maps of the resulting films. Chapter 8 concerns hard x-ray photoelectron spectroscopy of undoped and Sn-doped TiO2. Chapter 9 interconnects previous chapters by presenting 2D reciprocal space maps of nano structured epitaxial samples of In2O3 grown by the newly developed sol-gel based method. Chapter 10 concludes this thesis with a summary of the results.
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Kang, Yixiu. "Deposition and Characterization of Amorphous GaN Thin Films." Ohio University / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1020266055.
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Bekele, Selemon. "Structural and Dynamical Properties of Water and Polymers at Surfaces and Interfaces: A Molecular Dynamics Investigation." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1530040420616781.
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Patra, Abhirup. "Surface properties, adsorption, and phase transitions with a dispersion-corrected density functional." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/516784.
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PhysicsPh.D.
Understanding the “incomprehensible” world of materials is the biggest challenge to the materials science community. To access the properties of the materials and to utilize them for positive changes in the world are of great interest. Often scientists use approximate theories to get legitimate answers to the problems. Density functional theory (DFT) has emerged as one of the successful and powerful predictive methods in this regard. The accuracy of DFT relies on the approximate form of the exchange-correlation (EXC) functional. The most complicated form of this functional can be as accurate as more complicated and computationally robust method like Quantum Monte Carlo (QMC), Random Phase Approximation (RPA). Two newest meta-GGAs, SCAN and SCAN+rVV10 are among those functionals. Instantaneous charge fluctuation between any two objects gives rise to the van der Waals (vdW) interactions (often termed as dispersion interactions). It is a purely correlation effect of the interacting electrons and thus non-local in nature. Despite its small magnitude it plays a very important role in many systems such as weakly bound rare-gas dimers, molecular crystals, and molecule-surface interaction. The traditional semi-local functionals can not describe the non-local of vdW interactions; only short- and intermediate-range of the vdW are accounted for in these functionals. In this thesis we investigate the effect of the weak vdW interactions in surface properties, rare-gas dimers and how it can be captured seamlessly within the semi-local density functional approximation. We have used summed-up vdW series within the spherical-shell approximation to develop a new vdW correction to the meta-GGA-MS2 functional. This method has been utilized to calculate binding energy and equilibrium binding distance of different homo- and hetero-dimers and we found that this method systematically improves the MGGA-MS2 results with a very good agreement with the experimental data. The binding energy curves are plotted using this MGGA-MS2, MGGA-MS2-vdW and two other popular vdW-corrected functionals PBE-D2, vdW-DF2. From these plots it is clear that our summed-up vdW series captures the long-range part of the binding energy curve via C6, C8, and, C10 coefficients. The clean metallic surface properties such as surface energy, work functions are important and often play a crucial role in many catalytic reactions. The weak dispersion interactions present between the surfaces has significant effect on these properties. We used LDA, PBE, PBSEsol, SCAN and SCAN+rVV10 to compute the clean metallic surface properties. The SCAN+rVV10 seamlessly captures different ranges of the vdW interactions at the surface and predicts very accurate values of surface energy ( ) , and work function (𝞥) and inter-layer relaxations (𝞭%). Our conclusion is adding non-local vdW correction to a good semi-local density functional such as SCAN is necessary in order to predict the weak attractive vdW forces at the metallic surface. The SCAN+rVV10 has also been employed to study the hydrogen evolution reaction (HER) on 1T-MoS2. We have chosen as a descriptor differential Gibbs free energy (𝚫 GH ) to understand the underlying mechanism of this catalytic reaction. Density functional theory calculations agree with the experimental findings. In the case of layered materials like 1T-MoS2, vdW interactions play an important role in hydrogen binding, that SCAN+rVV10 calculation was able to describe precisely. We have also used SCAN and SCAN+rVV10 functionals to understand bonding of CO on (111) metal surfaces, where many approximations to DFT fail to predict correct adsorption site and adsorption energy. In this case SCAN and SCAN+rVV10 do not show systematic improvements compared to LDA or PBE, rather, both SCAN and SCAN+rVV10 overbind CO more compared to PBE but less compared to the LDA. This overbinding of CO is associated with the incorrect charge transfer from metal to molecule and presumably comes from the density-driven self-interaction error of the functionals. In this thesis we assessed different semi-local functionals to investigate molecule surface systems of 𝞹-conjugated molecules (thiophene, pyridine) adsorbed on Cu(111), Cu(110), Cu(100) surfaces. We find the binding mechanism of these molecules on the metallic surface is mediated by short and intermediate range vdW interactions. Calculated values of binding energies and adsorbed geometries imply that this kind of adsorption falls in the weak chemisorption regime. Structural phase transitions due to applied pressure are very important in materials science. However, pressure induced structural phase transition in early lanthanide elements such as Ce are considered as abnormal first order phase transition. The Ce 𝝰-to-𝝲 isostructural phase transition is one of them. The volume collapse and change of magnetic properties associated with this transition are mediated by the localized f-electron. Semi-local density functionals like LDA, GGA delocalize this f-electron due to the inherent self-interaction error (SIE) of these functionals. We have tested the SCAN functional for this particular problem, and, it was found that the spin-orbit coupling calculations with SCAN not only predicts the correct magnetic ordering of the two phases, but also gives a correct minima for the high-pressure 𝝰-Ce phase and a shoulder for the low-pressure 𝝲-Ce phase.
Temple University--Theses
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Hu, Zhonghan. "Transport properties, optical response and slow dynamics of ionic liquids." Diss., University of Iowa, 2007. http://ir.uiowa.edu/etd/160.
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Alhanash, Mirna. "ELECTRONIC STRUCTURE AND THERMODYNAMIC PROPERTIES OF LI-IONINSERTION IN SULFONAMIDES COMPOUNDS AS ORGANIC HIGH-ENERGY DENSITY CATHODES." Thesis, Uppsala universitet, Materialteori, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-453411.
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The world’s ever-growing energy demand has evoked great interest in exploring renewable energy sources along with sustainable energy storage systems. While inorganic physics of rocking chair mechanism used in Li-ion battery have proven to provide high energy density and high performance, there are problems yet to be overcome in terms of sustainability and recyclability. This is why research in organic batteries has been on the rise, yet the diversity of organic battery frameworks remains limited and requires overcoming multiple obstacles that restrain the performance of an all-organic battery system. A recent advance in the design of organic electrode material by Wang et al. has shown the possibility of a new stable and tunable class of conjugated sulfonamides (CSA) with an experimental voltage range between 2.85V and 3.45V [5]. A theoretical approach to study these organic materials is taken in this thesis research where the effects of such compounds on the redox potential, physics of ion insertion, and other thermodynamical properties are examined. Density Functional Theory (DFT) is employed in this investigation along with an evolutionary algorithm to generate information about the crystal structure of mentioned systems, their density of states (DOS), and charge distribution in pristine form and after lithiation. Quinone systems with oxygen groups were investigated in a previous research project that complements this thesis which looks into a quinone system with sulfonamide compounds where a comparison between the two could offer more understanding of the electrochemistry of such systems for their application in batteries as high performing organic cathode materials on a par with other inorganic materials.
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Constantinescu, Gabriel Cristian. "Large-scale density functional theory study of van-der-Waals heterostructures." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274876.
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Research on two-dimensional (2D) materials currently occupies a sizeable fraction of the materials science community, which has led to the development of a comprehensive body of knowledge on such layered structures. However, the goal of this thesis is to deepen the understanding of the comparatively unknown heterostructures composed of different stacked layers. First, we utilise linear-scaling density functional theory (LS-DFT) to simulate intricate interfaces between the most promising layered materials, such as transition metal dichalcogenides (TMDC) or black phosphorus (BP) and hexagonal boron nitride (hBN). We show that hBN can protect BP from external influences, while also preventing the band-gap reduction in BP stacks, and enabling the use of BP heterostructures as tunnelling field effect transistors. Moreover, our simulations of the electronic structure of TMDC interfaces have reproduced photoemission spectroscopy observations, and have also provided an explanation for the coexistence of commensurate and incommensurate phases within the same crystal. Secondly, we have developed new functionality to be used in the future study of 2D heterostructures, in the form of a linear-response phonon formalism for LS-DFT. As part of its implementation, we have solved multiple implementation and theoretical issues through the use of novel algorithms.
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Dupuis, Anne-Claire. "V2O3(0001)/Au(111) and /W(110) growth, electronic structure and adsorption properties /." Phd thesis, [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=966531736.
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Peters, Brian. "Tuning the structural, magnetic and transport properties of full Heusler Co2FeAlxSi1-x compounds." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1408984221.
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Li, Yuting. "Simulations and Electronic Structure of Disordered Silicon and Carbon Materials." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1395410498.
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Allan, Milan P. "The electronic structure of the nematic materials Sr₃Ru₂O₇ and Ca(Co[subscript(x)]Fe[subscript(1-x)])₂As₂." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/2610.
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We investigated the electronic structure of the two nematic materials Sr₃Ru₂O₇ and Ca(Fe₀.₉₇Co₀.₀₃As)₂ using spectroscopic – imaging scanning tunneling microscopy (SI-STM) and angle resolved photoemission spectroscopy (ARPES). – – – Sr₃Ru₂O₇ is an itinerant metamagnet that shows a putative quantum critical endpoint at 8 Tesla, submersed by the formation of a nematic electronic phase. Using ARPES, we identified at least 5 Fermi pockets in agreement with quantum oscillation measurements. Surprisingly, we found Fermi velocities up to an order of magnitude lower than in single layer Sr₂RuO₄ and up to 35 times lower than predicted by ab initio calculations. Many bands are confined in an energy range of only ∼10 meV below the Fermi level. This, as well as distinct peak-dip-hump shapes of the spectra with a characteristic energy of around ∼5 meV indicate strong correlations and a possible nontrivial mechanism that is absent in single layer Sr₂RuO₄ and connected to the nematicity. The quasiparticle interference of one of the bands was detected by SI-STM, which was also used to measure subatomic features with the symmetries of the relevant Ru d orbitals. – – – In the second mate- rial, the iron-based high-temperature superconductor Ca(Fe[subscript(1-x)]Co[subscript(x)]As)₂, we discovered electronic nematic nano-pattern in its under-doped ‘parent’ state. We spectroscopically imaged this state in real space over large areas and across domain boundaries that change the directionality of the nano-pattern by 90°. We propose that oriented, dimer-shaped electronic nematogens are responsible for this pattern, in striking contrast to what has been expected and observed in electronic nematic materials. The dimers consist of two Gaussian conductance peaks separated by about 8 a[subscript(FeFe)]. Unidirectionality also shows in the quasiparticle interference pattern of the delocalized electrons. The dispersion is in agreement with scattering from the α₂ band discovered by ARPES but has distinct C₂ symmetry, not inconsistent with a C₄-symmetric band scattered by the proposed dimers.
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Park, Kibog. "Electronic properties of stacking-fault induced heterostructures in silicon carbide studied with ballistic electron emission microscopy." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1149089614.
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Triana, Carlos A. "Atomic short-range order, optical and electronic properties of amorphous transition metal oxides : An experimental and theoretical study of amorphous titanium aTiO2 and tungsten aWO3 solid thin-film oxides." Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-318193.
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Amorphous transition metal oxides [aTMOs], have emerged as innovative functional materials for wide-ranging electronic, optical and energy-related applications. However, no systematic and broadly applicable method exists to assess their atomic-scale correlations, and since the optical and electronic processes are local structure-dependent, still there are not well-stablished mechanisms that suitably explain the physical properties of aTMOs. This thesis presents experimental and theoretical studies of the atomic short-range order, optical and electronic properties, and state-defects induced by Li+-ion-intercalation and oxygen-vacancies in amorphous titanium aTiO2 and tungsten aWO3 thin-film oxides. Those properties play a key role for application in high energy-density Li+-ion batteries and in switchable dynamical modulation of solar-irradiation transmittance for energy efficient "smart windows", where the disorder-dependent Li+-ion-intercalation and oxygen-vacancy-induced defect-states influence charge-carrier transfer mechanisms. After introducing the scope of this thesis, the fundamental theoretical concepts describing the experimental findings on amorphous solids are reviewed. Thereafter, a comprehensive analysis on the optical absorption phenomena experimentally observed in oxygen-deficient and Li+-ion-intercalated aLixTiO2−y and aLixWO3−y thin-films and a discussion on the electrochromic properties are presented. The optical absorption is described in the framework of the small polaron absorption model. Finally, a state-of-the-art systematic procedure involving theory and experiment in a self-consistent computational framework is implemented to unveil the atomic-scale structure of aTiO2 and aWO3, and its role for the electronic properties. The procedure is based in Reverse Monte Carlo [RMC] and Finite Difference Method [FDM] simulations of X-ray-Absorption spectra to construct a disordered theoretical model having the same bonding and coordination distribution as the experimental system. Ab-initio molecular dynamics simulations and density functional theory are then used to assess defect-states induced by Li+-ion-intercalation and oxygen-vacancies in aTiO2 and aWO3 oxides. The schemes introduced in this study offer a consistent route to experimentally and theoretically assess the role of the atomic-scale structure on the optical and electronic properties of aTiO2 and aWO3 and could be extended to the study of other aTMOs. The final results provide crucial insight towards the understanding of optical and electronic mechanisms where disorder-dependent ion-intercalation and oxygen-vacancy-induced localized defect-states influence charge transfer mechanisms of crucial importance for wide ranging optical and energy-related application of aTiO2 and aWO3 oxides.
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Ratnaparkhe, Amol. "FIRST PRINCIPLES STUDY OF ELECTRONIC ANDVIBRATIONAL PROPERTIES OF WIDE BAND GAPOXIDE AND NITRIDE SEMICONDUCTORS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1619606222502271.
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Lambert, Henry A. R. "Electronic excitations in semiconductors and insulators using the Sternheimer-GW method." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:eb6210c9-e0cc-45e8-93eb-719bdcc83857.
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In this thesis we describe the extension and implementation of the Sternheimer- GW method to a first-principles pseudopotential framework based on a planewaves basis. The Sternheimer-GW method consists of calculating the GW self-energy operator without resorting to the standard expansion over unoccupied Kohn- Sham electronic states. The Green's function is calculated by solving linear systems for frequencies along the real axis. The screened Coulomb interaction is calculated for frequencies along the imaginary axis using the Sternheimer equa- tion, and analytically continued to the real axis. We exploit novel techniques for generating the frequency dependence of these operators, and discuss the imple- mentation and efficiency of the methodology. We benchmark our implementation by performing quasiparticle calculations on common insulators and semiconductors, including Si, diamond, LiCl, and SiC. Our calculated quasiparticle energies are in good agreement with the results of fully-converged calculations based on the standard sum-over-states approach and experimental data. We exploit the methodology to calculate the spectral func- tions for silicon and diamond and discuss quasiparticle lifetimes and plasmaronic features in these materials. We also exploit the methodology to perform quasiparticle calculations on the 2-dimensional transition metal dichalcogenide system molybdenum disulfide (MoS2). We compare the quasiparticle properties for bulk and monolayer MoS2 , and identify significant corrections at the GW level to the LDA bandstructure of these materials. We also discuss changes in the frequency dependence of the electronic screening in the bulk and monolayer systems and relate these changes to the quasiparticle lifetimes and spectral functions in the two limits.
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Bidermane, Ieva. "Structure and Electronic Properties of Phthalocyanine Films on Metal and Semiconductor Substrates." Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-217086.
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The current thesis presents fundamental studies of phthalocyanines (Pcs), a group of organic macro-cycle molecules. The use of phthalocyanine molecular films in devices with a variety of possible technological applications has been the reason of the many studies dedicated to such molecules during the last decades. Core and valence photoelectron spectroscopies (PES), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) techniques are used to study phthalocyanine molecules in gas phase and adsorbed on gold (111) and silicon Si(100)-2x1 substrates. Density functional theory (DFT) is used to obtain further insights in the electronic structure of the phthalocyanines. The aim of our studies is to get a deeper understanding into the molecule-molecule and molecule-substrate interactions, a fundamental requirement for improving the devices based on such molecular materials. Gas phase PES and XAS studies and single molecule DFT calculations are performed on the valence band (VB) of iron phthalocyanine (FePc), manganese phthalocyanine (MnPc) and metal-free phthalocyanine (H2Pc). The VB simulations have shown how the metal atom of the Pc influences the inner valence states of the molecules. The HOMO of the H2Pc and FePc is formed by mostly C2p states, whereas the HOMO of MnPc has mainly Mn3d character. PES studies of H2Pc on Au(111) have revealed the influence of the surface on the adsorption of the monolayer. XAS studies indicate formation of ordered monolayer with the Pc ligands parallel to the surface and the change of the molecular tilt angle with increasing thicknesses. For LuPc2 adsorbed on Au(111), STM study demonstrates a formation of bilayer instead of a monolayer. A comparison between the results of LuPc2 adsorbed on pristine or passivated Si(100)-2x1 confirmes the different reactivities of these surfaces: LuPc2 retains many molecular-like characters, when adsorbed on the innert passivated Si. Instead, on the more reactive pristine Si surface, the spectroscopic results have indicated a more significant interaction, possible hybridization and charge redistribution between the molecules and the surface. Moreover, STM images show a modification of the geometrical shape of the molecules, which are proposed to adsorb in two different geometries on the pristine Si surface.
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Лэй, Сюе, and Lei Xue. "Modeling the influence of structure modification of low-size ZnO, β-C3N4, InSe, and single-layer boron on their physical properties : dissertation for the degree of candidate of physical and mathematical sciences : 01.04.07." Thesis, б. и, 2020. http://hdl.handle.net/10995/95215.
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Worth, Nicholas Gower. "Theoretical studies of compressed xenon oxides, tin selenide thermoelectrics, and defects in graphene." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274462.
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Enormous advances in computing power in recent decades have made it possible to perform accurate numerical simulations of a wide range of systems in condensed matter physics. At the forefront of this progress has been density functional theory (DFT), a very popular approach to tackling the complexity of quantum-mechanical systems that very often strikes a good balance between accuracy and tractability in light of the finite computational resources available to researchers. This thesis describes work utilising DFT methods to tackle two distinct problems. Firstly, the theoretical prediction of stable and metastable periodic structures under specified conditions using the ab initio random structure searching (AIRSS) method, which involves a large scale exploration of the Born-Oppenheimer energy surface, and secondly the use of a vibrational self-consistent field (VSCF) approach to investigate the effects of nuclear motion and anharmonicity in crystal systems, which involves a local exploration of the Born-Oppenheimer energy surface. The AIRSS crystal structure prediction method is here applied to a study of defect structures in graphene. It is also applied to a study of the xenon-oxygen binary system under a range of geological pressures (83–200 GPa). Novel xenon oxide structures are predicted and characterised theoretically. This work was carried out in collaboration with an experimental study of the system at the lower end of the pressure range. The VSCF approach to investigating anharmonicity is here applied to the study of tin selenide (SnSe), a material that has recently been shown to demonstrate consider- able promise as a thermoelectric material. In this thesis, the effects of the anharmonic nuclear motion on the vibrational and electronic properties of SnSe are investigated quantitatively.
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Noori, Keian. "Energy-level alignment at organic and hybrid organic-inorganic photovoltaic interfaces." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:d1b2a4e9-a5d6-4843-b172-6d83dea8a6cb.
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Organic and hybrid organic-inorganic photovoltaic (PV) devices have the potential to provide low-cost, large scale renewable energy. Despite the tremendous progress that has been made in this field, device efficiencies remain low. This low efficiency can be partly attributed to the low open-circuit voltages (Voc) generated by organic and hybrid organic-inorganic PV devices. The Voc is critically determined by the energy-level alignment at the interface between the materials forming the device. In this thesis we use first-principles methods to explore the energy-level alignment at the interfaces between the conjugated polymer poly(3-hexylthiophene) (P3HT) and three electron acceptors, zinc oxide (ZnO), gallium arsenide (GaAs) and graphene. We find that Voc reported in the literature for ZnO/P3HT devices is significantly lower than the theoretical maximum and that the interfacial electrostatic dipole plays an important role in the physics underlying the charge transfer at the heterojunction. We note significant charge transfer from the polymer to the semiconductor at GaAs/P3HT interfaces, and use this result to help interpret experimental data. Our findings support the conclusion that charge transferred from P3HT to GaAs nanowires can passivate the surface defect states of the latter and, as a result, account for the observed decrease in photoluminescence lifetimes. Finally, we explore the energy-level alignment at the graphene/P3HT interface and find that Voc reported for experimental devices is in line with the theoretical maximum. The effect of functionalised graphene is also examined, leading to the suggestion that functionalisation might have important consequences for device optimisation.
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Gehrmann, Jan. "Transferable reduced TB models for elemental Si and N and binary Si-N systems." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:002b0c99-0e9d-4d8c-a0dc-ad07383f083f.
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Silicon nitride is a bulk and a coating material exhibiting excellent mechanical properties. The understanding of the complex processes at the nanometre scale gained through experimental research will be enhanced by the existence of a computationally efficient and accurate model that is able to describe the mechanical properties of silicon nitride. Such a model has yet to be proposed. In this thesis we present a transferable reduced tight-binding (TB) model for the silicon nitride system. More precisely, this model consists of a reduced TB model for elemental silicon, a reduced TB model for elemental nitrogen, and a reduced TB model for silicon nitride. These models are developed within the framework of coarse-graining the electronic structure from density functional theory (DFT) to tight binding (TB) to bond-order potentials (BOPs), and can therefore be used in the future as the stepping stone to develop BOPs for the application in large scale simulations. The bond integrals employed in the reduced TB models are obtained directly from mixed-basis DFT projections of wave functions onto a minimal basis of atom-centred orbitals. This approach reduces the number of overall parameters to be fitted and provides models which are transferable through the different coarse-graining levels. We provide an example by using the same bond integrals in the reduced TB model for silicon and the preliminary bond-based BOP for silicon. DFT binding energies of ground state and metastable crystal structures are used as the benchmark to which the TB and BOP repulsive parameters are fitted. In addition to model development, we present an improved methodology when going from TB to reduced TB. By weighting all four σ TB bond integrals equally, we provide a new parameterisation (Eqs. (2.73) and (2.74)) and show that the quality of the silicon reduced TB model can be increased by choosing one of the reduced TB parameters to be distance invariant. The ingredients, the development methodology, and the quality of each of the four models are discussed in a separate chapter. The quality of the reduced TB models and BOP is demonstrated by comparing their predictions for the binding energies, heats of formation, elastic constants, and defect energies with DFT and experimental values.
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Wang, Yan-Bin. "Structural and thermal study of nitrate glasses." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26178.
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The Ca$ sb{x}$K$ sb{1-x}$(NO$ sb3) sb{1+x}$ glass system has been studied by means of X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The structure of the glass system was studied in XRD experiments and from the Radial Distribution Function (RDF). A structural model for this glass system was suggested with the agreement between the RDF calculation and structure model geometric calculation. DSC studies ranged from glass transition and crystallization to melting. The activation energy for crystallization was obtained.The difficulty of handling the glass in open air was overcome by using vacuum tube to melt the sample and glove box with Ar gas to handle the glass. It is found that the handling of the samples, i.e. avoiding exposure to moisture is critical to maintaining sample quality.
For the structural studies, glasses of $ rm Ca sb{0.4}Na sb{0.6}(NO sb3) sb{1.4}, Ca sb{0.4}Rb sb{0.6}(NO sb3) sb{1.4}$ and $ rm Mg sb{0.4}K sb{0.6}(NO sb3) sb{1.4}$ were also prepared for comparison with the $ rm Ca sb{x}K sb{1-x}(NO sb3) sb{1+x}$ glasses. The same structural model applied to all of them with similar agreement.
For the DSC studies, only the $ rm Ca sb{x}K sb{1-x}(NO sb3) sb{1+x}$ glasses were used. The relation between increase of glass transition temperature $T sb{g}$ and that of divalent cation concentration is linear. It was observed that unlike the metallic glass system, the crystallization activation energies do not change with the glass composition. We also observed the irreversible relaxation effect in this glass system and the effect of supercooling in the DSC to form the glass.
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Ford, Michael E. "Atomistic modelling of iron with magnetic analytic Bond-Order Potentials." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c824a315-4038-4777-8487-08358cb9f569.
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The development of interatomic potentials for magnetic transition metals, and particularly for iron, is difficult, yet it is also necessary for large-scale atomistic simulations of industrially important iron and steel alloys. The magnetism of iron is especially important as it is responsible for many of the element's unique physical properties -- its bcc ground state structure, its high-temperature phase transitions, and the mobility of its self-interstitial atom (SIA) defects. Yet an accurate description of itinerant magnetism within a real-space formalism is particularly challenging and existing interatomic potentials based on the Embedded Atom Method are suited only for studies of near-equilibrium ferritic iron, due to their restricted functional forms. For this work, the magnetic analytic Bond-Order Potential (BOP) method has been implemented in full to test the convergence properties in both collinear and non-collinear magnetic iron. The known problems with negative densities of states (DOS) are addressed by assessing various possible definitions for the bandwidth and by including the damping factors adapted from the Kernel Polynomial Method. A 9-moment approximation is found to be sufficient to reproduce the major structural energy differences observed in Density Functional Theory (DFT) and Tight Binding (TB) reference calculations, as well as the volume dependence of the atomic magnetic moments. The Bain path connecting bcc and fcc structures and the formation energy of mono- and divacancies are also described well at this level of approximation. Other quantities such as the high-spin/low-spin transition in fcc iron, the bcc elastic constants and the SIA formation energies converge more slowly towards the TB reference data. The theory of non-collinear magnetism within analytic BOP is extended as required for a practical implementation. The spin-rotational behaviour of the energy is shown to converge more slowly than the collinear bulk energy differences, and there are specific problems at low angles of rotation where the magnitude of the magnetic moment depends sensitively on the detailed structure of the local DOS. Issues of charge transfer in relation to magnetic defects are discussed, as well as inadequacies in the underlying d-electron TB model.
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Caramella, Lucia. "Theoretical spectroscopy of realistic condensed matter systems." Paris 6, 2009. http://www.theses.fr/2009PA066019.
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Le sujet de cette these porte sur des calculs ab initio de proprietes d'etat fondamental et excite de systemes differents, dans le cadre de la dft et de la tddft. Du cote numerique, nous avons mis en oeuvre une methode originale pour l'evaluation de la polarisabilite dynamique a particules independantes, et generalise un code au spin dans le but d'etudier les proprietes magnetiques de systemes reels. Nous avons etudie des spectres de reflectivite anisotrope et de perte d'energie pour la surface (100) du silicium, propre ou oxydee. La comparaison entre les spectres mesures et simules, nous ont permis d'exclure la reconstruction p(2x1). En suite, nous avons mis en evidence le probleme de la description des excitations des systemes a couche ouverte presente un etude des proprietes optiques d'alliage magnetique interessants pour des applications en spintronique. Nous avons evalue les proprietes d'etat fondamental de ces alliages et la conductivite du fer ccc.
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Brüning, Ralf. "Structural relaxation and the glass transition in metallic glasses." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74345.
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This thesis presents for the first time direct structural measurements of both reversible and irreversible structural relaxation and the glass transition in the metal-metalloid glass Pd$ sb{40}$Ni$ sb{40}$P$ sb{20}$. The techniques have been x-ray diffraction and Mossbauer spectroscopy, and a new analysis method for changes of amorphous diffraction patterns was developed.It is found that irreversible relaxation proceeds by many local shear-type motions involving the metal atoms, and that it is accompanied by a small densification. Reversible relaxation at high annealing temperatures entails the same microscopic processes, but it does not change the density of the glass. The type of atomic processes changes continuously as the annealing temperature is lowered, and at sufficiently low temperatures the distribution of metal atoms remains constant, so that reversible relaxation then proceeds via rearrangement of the metalloid atoms. This rearrangement leads to more ordered, but less isotropic atomic sites.
The second part of the thesis is concerned with the motion of the atoms in a metallic glass below and above the glass transition. Mossbauer spectroscopy allows the direct measurement of vibrational and diffusional motion. The increase of the amplitude of atomic vibration has the same temperature dependence as the increase in volume that marks the glass transition, thus the two processes are governed by the same mechanism. The directly measured diffusional motion is in agreement with macroscopic measurements of diffusion.
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LaSota, Christopher A. "Structural instabilities in strontium titanate from first-principles calculations." W&M ScholarWorks, 2000. https://scholarworks.wm.edu/etd/1539623958.
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For some time now, first-principles calculation methods have proven to be an effective tool for investigating the physics of condensed matter systems. The additional use of density functional theory (DFT) and the local density approximation (LDA) has permitted even complex materials to be studied on desktop workstations with remarkable success. The incorporation of linear response theory into these methods has extended their power, allowing investigation of important dynamical properties.;Contained within the following pages are the results of a first-principles study of SrTiO3. This transition metal oxide is often grouped with ferroelectric materials, due to its similar composition and perovskite structure. Although it behaves as if it were to become ferroelectric, it fails to do so, even at the lowest temperatures.;Using the LAPW method for bulk materials, the ground-state equilibrium properties for the cubic phase were found. Additional linear response calculations produced the phonon frequencies throughout the Brillouin zone. Imaginary values for these frequencies revealed two distinct regions of reciprocal space corresponding to structural instabilities of the ferroelectric (FE) and antiferrodistortive (AFD) types. A cell-doubling AFD transition to tetragonal structure is observed experimentally, so subsequent calculations were continued in this phase. Total energy calculations were performed for both FE and AFD distortions in this new phase, and it was found that the AFD instability is enhanced with decreasing lattice parameter, while the FE instability is diminished. Furthermore, these calculations suggest that this material is marginally stable against FE distortions, even at the 105 K volume.
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Rost, A. W. "Magnetothermal properties near quantum criticality in the itinerant metamagnet Sr₃Ru₂O₇ /." St Andrews, 2009. http://hdl.handle.net/10023/837.
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Mao, Ming. "Structural relaxation and the glass transition in metal-metal glasses." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41708.
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This thesis presents the results of a systematic study on the structural relaxation and the glass transition of ternary metal-metal glasses Zr$ sb{67}$(Ni$ sb{1-x}$Cu$ sb{x}) sb{33}$. Differential scanning calorimetry provides macroscopic evidence of structural changes from the compositional and temperature dependence of enthalpy change. Results from high precision x-ray diffraction and Mossbauer spectroscopy, performed mainly on $ rm Zr sb{67}Ni sb{10}Cu sb{23}$ (x = 0.7), complete the picture of structural changes at the atomic level.Irreversible structural relaxation leads to densification and enthalpy release. Shear-like atomic motion enhances local atomic order, highlighting the atomic processes during the irreversible relaxation. Reversible structural relaxation involves two partly overlapping processes initiated at different temperatures, which are characterized by the solid and liquid atomic mobilities, respectively. Interatomic positional exchanges between Cu and Ni atoms change the local structure and are active during the reversible relaxation at low temperatures, which are also partly responsible for the irreversible relaxation. Above 500 K, shear-like atomic movements characterize the reversible relaxation, involving all three atomic species in a length scale of a few near-neighbor atomic shells. The overall density is unchanged during reversible relaxation.
The strong compositional dependence of the glass transition in the ternary glasses indicates an intimate association of the glass transition with interatomic bondings among different atomic species. The atomic motion from room temperature up to above the glass transition temperature, measured by the Mossbauer spectroscopy, is macroscopically tracked by the volume expansion and the enthalpy evolution. The glass transition occurs when the length scale of the atomic motion expands so rapidly that the interatomic potential can no longer maintain the on-site atomic vibration. The rapid development of translational atomic motion upon approaching the glass transition is reflected by the dramatic enhancement of the diffusive atomic motion.
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Raymond, Sylvain. "Zero-dimensional properties of self-assembled islands." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ28370.pdf.
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Triola, Christopher Lawrence Charles. "Electronic properties of chiral two-dimensional materials." W&M ScholarWorks, 2015. https://scholarworks.wm.edu/etd/1539624004.
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In this dissertation we study the electronic properties of certain two-dimensional chiral electron systems. We study the static and dynamic screening of gapped bilayer graphene and find important qualitative differences between the dielectric screening function obtained using a simplified 2-band model and that obtained using a more sophisticated 4-band model. We also formulate a continuum model to study the low-energy electronic properties of heterostructures formed by graphene on a strong three-dimensional topological insulator (TI) both for the case of commensurate and incommensurate stacking. We find that the proximity of the TI induces a strong enhancement of the spin-orbit coupling in graphene that can be tuned via the twist angle. Additionally, we examine the effect of a spin-active interface on the symmetry of proximity-induced superconducting pairing amplitudes in topological insulators. We compare our results to those for normal metals and ferromagnetic materials finding that the nontrivial spin chirality of the TI leads to qualitatively different behavior of the pairing amplitude. Lastly, we study the many-body instabilities of the Dirac states predicted to arise on the surfaces of topological Kondo insulators identifying regions of parameter space in which the system exhibits spin density wave, and charge density wave order.
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Finnie, Paul D. "The fabrication and optical properties of quantum wires." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq26116.pdf.
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Kou, Angela. "Microscopic Properties of the Fractional Quantum Hall Effect." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11161.
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The fractional quantum Hall effect occurs when an extremely clean 2-dimensional fermion gas is subject to a magnetic field. This simple set of circumstances creates phenomena, such as edge reconstruction and fractional statistics, that remain subjects of experimental study 30 years after the discovery of the fractional quantum Hall effect. This thesis investigates the properties of excitations of the fractional quantumPhysics
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Helbers, Andrew J. "Magneto-Optical Properties of Rare-Earth Doped Semiconductors." Thesis, Lehigh University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10623187.
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Park, Jongik. "Photoemission Study of the Rare Earth Intermetallic Compounds RNi2Ge2 (R=Eu, Gd)." 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, 2004. http://www.osti.gov/servlets/purl/835299-eRe3PQ/webviewable/.
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