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1
Benasutti, Patrick B. "Electronic and Structural Properties of Silicene and Graphene Layered Structures." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1348192958.
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McDonald, Martin Thomas. "Structural and electronic properties of fulleride superconductors." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/301/.
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In the present thesis, I discuss some of the current advances in research in the field of the solid state science of fullerenes. The reaction of C60 with alkali metals using both conventional solid state and low temperature solution-based synthesis techniques has led to the production of fulleride salts with interesting structural and superconducting properties. In superconducting A3C60 systems, it has been widely reported that Tc increases monotonically with interfulleride separation. Of particular interest is the family Na2Rb1-xCsxC60 (0 ≤ x ≤ 1) as they display a much steeper rate of change of Tc with interfulleride spacing. Here we discuss the related family of quaternary fullerides, Na2-xKxCsC60 in an attempt to explore the consequences of this trend and produce fulleride salts with elevated Tc's In addition, the monotonic increase in Tc with increasing interfulleride separation has driven attempts towards the synthesis of new superconducting fullerides with very large lattice parameters. A key material among the A3C60 systems is the end member, Cs3C60, which has remained elusive in attempts to synthesise it by traditional solid state techniques due to the thermodynamic instability of this phase caused by the accommodation of the large Cs+ ion (r = 1.67 Å) in the small tetrahedral holes (r = 1.12 Å). Here we report the synthesis of “FCC rich” and "A15 rich" samples of the series, RbxCs3-xC60 (0.0 ≤ x ≤ 0.5) via low temperature synthetic techniques utilising the solvents ammonia and methylamine, respectively. This allowed us to study the effects of both chemical (by partial substitution of Cs+ by the smaller Rb+ cation) and physical pressure upon the electronic and superconducting properties of these materials. For all samples, detailed structural studies have been performed using synchrotron X-ray powder diffraction and magnetic behaviour using SQUID magnetometry techniques.
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Samarakoom, Duminda K. "Structural and electronic properties of Hydrogenated Graphene." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2011. http://digitalcommons.auctr.edu/dissertations/202.
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Graphane is a two-dimensional system consisting of a single planar layer of fully saturated carbon atoms, which has recently been realized experimentally through hydrogenation of graphene membranes. We have studied the stability of chair, boat, and twist-boat graphane structures using first-principles density functional calculations. Our results indicate that locally stable twist-boat membranes significantly contribute to the experimentally observed lattice contraction. The band gaps of graphane nanoribbons decrease monotonically with the increase of the ribbon width and are insensitive to the edge structure. We also have studied the electronic structural characteristics in a hydrogenated bilayer graphene under a perpendicular electric bias. The bias voltage applied between the two hydrogenated graphene layers allows continuously tuning the band gap and leads a transition from semiconducting to metallic state. Desorption of hydrogen from one layer in the chair conformation yields a ferromagnetic semiconductor with tunable band gap.
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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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Millburn, Julie Elizabeth. "Structural and electronic properties of transition metal oxides." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364166.
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Hargrove, Jasmine J. "Structural and electronic properties of grapheme-based materials." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2014. http://digitalcommons.auctr.edu/dissertations/2273.
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This thesis includes work done on graphene-based materials, examining their unique electronic properties using first-principles density-functional calculations. Abinitio methods such as density functional theory (DFT) are widely accepted as computational methods in condensed matter and materials physics. We begin by studying the electronics properties of graphene intercalation compounds (GICs). In order for bilayer graphene to be used for field effect transistors, the GIC must decouple the adajent graphene layers and decrease interlayer interaction. We conducted a theoretical study in order to elucidate the electronic characteristics of methane intercepted bilayer graphene under a perpendicularly applied electric field. We show that methane intercalated graphene can make a promising material for implimentations of graphene based field effect transistors since it has a controllable band gap.
Finally, we show the evolution of band structure of graphene treated with fluorinated olefins through covalent functionalization. The bonding of fluorine to the graphene surface results in the transformation of orbital hybridization from sp2 to sp3. We find that the modification of graphene's electronic properties by such a drastic change in hybridization can lead to the elimination of the bands near the Fermi level and the opening of a band gap. We hope this work will help bring to light the promising electronic properties of graphene based materials for future device applications.
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Jones, Christopher Wynne. "Structural and electronic properties of mixed metal oxides." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235645.
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Sheikh, Ansar. "Structural and electronic properties of reduced magnesium titanates." Thesis, University of Aberdeen, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320237.
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Measurement of electrical resistivity in the magnesium titanate spinel system Mg2-xTiy+1+xO4, give rise to three types of electrical resistivity behaviour, in the composition range y=+3.25 (x=0.6) to y=+3.333 (x=0.5): (I) From room temperature to 100K a rapid non-linear increase in resistivity occurs with decreasing temperature. (II) Below 100K the resistivity decreases linearly with temperature. (III) For some samples below 50K a transition to zero resistance was observed. Type III behaviour was the most interesting, since there is, as yet, no conclusive evidence for the occurrence of superconductivity in the magnesium titanate spinel system. The zero resistance behaviour was very sensitive to composition and sample history, making reproducibility difficult. Powder x-ray diffraction patterns showed the spinel phase to contain a small amount of a second phase, with an x-ray diffraction pattern similar to MgTiO3, which has the ilmenite structure. Care in sample preparation increased phase purity but, did not lead to better reproducibility of the zero resistance behaviour. In addition, the zero resistance only lasted a few hours to a few days. The presence of low resistance, in some samples, and the apparent zero resistance is due to the overlap of the 3d energy levels of the titanium ions, which reside on the octahedral sites. Doping of the magnesium titanate spinels with M3+ cations, in an effort to increase the stability of the zero resistance behaviour, proved to be unsuccessful. Substitution of M3+ ions onto the octahedral sites appears to interfere with the overlap of the 3d energy levels of the titanium ions causing an increase in electrical resistivity. The deterioration of the zero resistance, with time, appears to be catalysed by air and moisture. Keeping the samples in dry, vacuum conditions allowed critical current behaviour to be measured in one sample. Magnetic susceptibility measurements showed no diamagnetic signal, which is necessary, along with the zero resistance and critical current measurements, to prove the existence of superconductivity.
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Rochford, Luke A. "Structural, electronic and magnetic properties of metal phthalocyanines." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/60649/.
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Metal phthalocyanines (MPcs) prepared as single crystals, polycrystalline powders and thin films have been analysed using a combination of surface science techniques, diffraction based structural characterisation and magnetic characterisation. Vanadium oxide phthalocyanine (VOPc) prepared as thin films on the (111) surface of gold, silver and copper is analysed by (STM) low energy electron diffraction (LEED) and ultraviolet photoemission spectroscopy (UPS). Similar surface and electronic structure is observed on gold and silver, but profoundly different assembly and electronic properties were observed on copper. The effect of increasing the substrate temperature during growth on the structure and morphology of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc) is investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). An evaporated copper iodide (CuI) structural template layer is also used to alter the arrangement of FePc molecules in thin films. The single crystal structure of fluorinated copper phthalocyanine (F16CuPc) is re-determined using synchrotron X-ray diffraction. Thin films of F16CuPc grown on graphene oxide supports are analysed using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). This allows assignment of both crystal structure and texture in polycrystalline thin films of a variety of thicknesses. F16CuPc is also analysed using superconducting quantum interference (SQUID) magnetometry in both powder and thin film morphologies. 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) structural template layers are used to alter the orientation of crystallites and the effect of this on the magnetic properties are analysed.
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Zadik, Ruth Helen. "Structural, electronic and magnetic properties of fulleride materials." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/11187/.
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This thesis outlines new research findings into the solid-state properties of selected alkali- and alkaline-earth-intercalated fullerides, focusing on their structural, electronic and magnetic properties at ambient and non-ambient temperatures and pressures, primarily employing synchrotron X-ray powder diffraction and SQUID magnetometry. Understanding the relationship between superconducting, neighbouring insulating and normal metallic states above Tc in unconventional superconductors is fundamentally important. Highly expanded fcc Cs3C60 behaves very differently to underexpanded A3C60 alkali fullerides such as K3C60 and Rb3C60. Whilst superconductivity in the latter seems well described by conventional Bardeen-Cooper-Schrieffer (BCS) theory, Cs3C60, a Mott-Jahn-Teller insulator under ambient pressure, exhibits distinctly non-BCS type superconductivity upon pressurisation. The intermediate regime adjacent to the Mott boundary, where strong electronic correlations are prominent, was hitherto only studied through physical pressurisation of Cs3C60 to tune the intermolecular spacing. This thesis reports the solid-state synthesis of fcc-rich RbxCs3−xC60 (0.25 ≤ x ≤ 2) bulk superconducting materials, with excellent stoichiometry control, and the effects on the electronic properties in situ of tuning intermolecular separation by varying temperature, physical and chemical pressurisation via adjusting the cation dopant ratio. It is shown that the Mott boundary can be traversed at ambient pressure upon cooling, and the metal-insulator crossover temperature tuned by chemical and physical pressurisation. A15 Cs3C60 orders antiferromagnetically below 46 K. Previous studies found no evidence of symmetry lowering or discontinuous structural changes upon magnetic ordering, despite theoretical predictions to the contrary. This issue is addressed with the first systematic ultrahigh-resolution investigation of its structural evolution with temperature, evidencing a transition to a rhombohedral phase below TN. The structural properties of A15 Cs3C60 and Ba3C60 in situ upon pressurisation are described, extending previous work on A15 Cs3C60. This first study of the effects of compression on the latter system reveals a pressure-induced structural transition to a hitherto unreported monoclinic phase.
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Skellern, Matthew G. "Structural and electronic properties of barium lanthanum vanadates." Thesis, University of Aberdeen, 2003. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU167989.
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A study of the subsolidus region of the BaO-La2O3-V 2O5 phase diagram has been carried out. Four ternary phases can be prepared, one of which has not been previously identified. The four ternary phases are a palmierite solid solution Ba3-3xLa2x V2O8, Ba2LaV3O11, BaLa10V4O26 (new phase) and Ba3La 40V12O93. Addition of BaLa10V 4O26 and the previously omitted phase La1.42V 0.58)3.58 to the ternary system has resulted n a re-determination of the complete phase diagram. A comprehensive study of the Ba3-3xLa 2xV2O8 solid solution has been carried out, employing a number of techniques including x-ray diffraction, infra-red spectroscopy, thermogravemetric analysis, impedance spectroscopy, electron paramagenetic resonance spectroscopy, inductively coupled plasma mass spectroscopy and x-ray absorption near edge structure spectroscopy. Conductivity measurements show the end-member Ba3V2O8 to be an oxide ion conductor, with the conduction mechanism being facilitated by the ease of transformation of the BaO3 layers to BaO2 and vice versa. The La-doped members show an increase in conductivity, with electrons becoming the dominant conducting species. The crystal structure of Ba2LaV 3O11 was confirmed to be isostructural with Ba2BiV 3O11. A full refinement of the structural parameters has been performed. The unit cell is primitive monoclinic, a = 12.44510(3)A, b = 7.78854(12)A, c = 11.26245(21)A and beta = 103.134(4)°, space group P21/c. Preliminary structural studies have begun on the new phase BaLa10V4O26. The x-ray powder pattern has been fully indexed and a possible monoclinic unit cell of a = 20.2939A, b = 5.886A, c = 12.6234A and beta = 118.05° is proposed. The serendipitous synthesis of a barium-deficient celsian phase, Ba0.8A11.6 Si2.4O8, is reported; the structure was solved using Patterson methods. The phase has a monoclinic unit cell with, a = 8.6090(8)A, b = 13.0858(12)A, c = 7.2047(7)A and beta = 115.418(2)°, space group C2/m.
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Silva, Francisco Wellery Nunes. "Structural, electronic and transport properties of nanoscaled systems." reponame:Repositório Institucional da UFC, 2016. http://www.repositorio.ufc.br/handle/riufc/22496.
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SILVA, F. W. N. Structural, eletronic and transport properties of nanoscaled systems. 2016. 93 f. Tese (Doutorado em Física) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2016.Submitted by Giordana Silva (giordana.nascimento@gmail.com) on 2017-04-10T22:30:18Z No. of bitstreams: 1 2016_tese_fwnsilva.pdf: 1674224 bytes, checksum: ed456e87a0f175e5aa88644ad830b785 (MD5)
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Band structure methods are applied in this work in order to study electronic and transport properties in nano-scaled systems. Density Functional Theory (DFT) has been employed in order to study the electronic properties of a hexagonal island of boron nitrite (hBN) embedded into graphene nanoribbons (GNRs) in both edge chiralities, zigzag and armchair. Furthermore, in our electronic calculation the spin contribution has been taken into account. The results regarding the non-doped systems revealed that a natural spin splitting is associated to the zigzag edged systems, while the armchair one is found to have a spin degenerated ground state. We also investigate the effects due carbon doping in the innermost ring of the h-BN cluster, where the C atom take the place either the Boron or Nitrogen atom. The doping lead to an even more polarized band structure, for energies nearby the Fermi level. The electronic transport properties have been studied applying the Landauer-B¨uttiker formalism, for all proposed systems, and the quantum conductance also exhibit a spin dependence. An application of the systems, as spin dependent molecular sensors is also considered. We have adsorbed different molecules onto electron rich/deficient devices and observed that the electronic conductance may be modulated by those adsorbed systems. Also, in order to verify the thermodynamic stability of the adsorbed systems we have performed Molecular Dynamics calculations under the Nos´e thermostat algorithm. In this thesis, we also have studied the electronic properties of the transition metal dichalcogenides (TMDCs) by means the Slater-Koster tight-binding method for the electronic structure. The electronic transport properties of molybdenum disulfide (MoS2) nanoribbons (MoS2-NR) is considered, and our results show that the edges of the ribbons play an important role in the conductance framework. Our results show that even a small defect due the lack of a MoS2 triplet in the edge is sufficient to lead to a strong suppression of the conductance over the system. Furthermore, interference effects due to defects suggest that MoS2-NR may be applied as nano-diodes.
Métodos para cálculos de estrutura de banda são aplicados neste trabalho, a fim de estudar as propriedades eletrônicas e de transporte de sistemas em nanoescala. A teoria do funcional da densidade (DFT) foi empregada para estudar as propriedades eletrônicas de uma ilha hexagonal de nitreto de boro (h-BN) embutida em nanofitas de grafeno (GNRs), considerando ambas as quiralidades de bordas, zigzag e armchair. Além disso, a contribuição do spin foi levada em conta no nosso cálculo eletrônico. Os resultados referentes aos sistemas não dopados mostraram a existência de uma polarização de spin natural associado a sistemas de borda zigzag, enquanto os sistemas de borda armchair são encontrados com spin degenerados no estado fundamental. Nós também investigamos os efeitos devido a dopagem com carbono no anel mais interno de um cluster de h-BN, onde o átomo C toma o lugar de um átomo de Boro ou de um átomo de Nitrogênio. A dopagem conduz a uma estrutura de bandas ainda mais polarizada, para energias próximas ao nível de Fermi. As propriedades de transporte eletrônico foram estudadas aplicando o formalismo de Landauer-Büttiker, para todos os sistemas propostos, e a condutância quântica também apresenta uma dependência de spin. Uma aplicação dos sistemas, como sensores moleculares dependentes de spin também é considerada. Nós adsorvemos diferentes moléculas em dispositivos ricos/deficientes de elétrons e observamos que a condutância eletrônica pode ser modulada por esses sistemas moleculares. Além disso, a fim de verificar a estabilidade termodinâmica dos sistemas adsorvidos realizamos cálculos de dinâmica molecular sob o algoritmo de termostato proposto por Nosé. Nessa tese, nós também estudamos as propriedades eletrônicas dos metais de transição dicalgogenados (TMDCs) por meio do método tight-binding como proposto por Slater-Koster, aplicado a estrutura eletrônica. As propriedades de transporte eletrônico das nanofitas de dissulfeto de molibdênio (MoS2NRs) são consideradas, e os nossos resultados mostram que as bordas das fitas desempenham um papel importante no quadro da condutância. Os nossos resultados mostram que mesmo um pequeno defeito devido a falta de um trío de MoS2 na borda é suficiente para levar a uma forte supressão da condutância ao longo do sistema. Além disso, efeitos de interferência devido aos defeitos, sugerem que MoS2NRs podem ser aplicadas como nanodiodos.
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Zhou, Ruiping. "Structural And Electronic Properties of Two-Dimensional Silicene, Graphene, and Related Structures." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1341867892.
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Johansson, Malin. "Nanocrystalline Tungsten Trioxide Thin Films : Structural, Optical and Electronic Characterization." Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-211855.
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This thesis concerns experimental studies of nanocrystalline tungsten trioxide thin films. Functional properties of WO3 have interesting applications in research areas connected to energy efficiency and green nanotechnology. The studies in this thesis are focused on characterization of fundamental electronic and optical properties in the semiconducting transition metal oxide WO3. The thesis includes also applied studies of photocatalytic and photoelectrochemical properties of the material. All nanocrystalline WO3 thin films were prepared using DC magnetron sputtering. It was found that structures like hexagonal and triclinic phase with different properties can be produced with sputtering technique. Thin film deposition has been performed using different process parameters with emphasis on sputter pressure and films that mainly consist of monoclinic γ-phase, with small contributions of ε-phase. Changes in the pressure are shown to affect the number of oxygen vacancies in the WO3 thin film, with close to stoichiometric WO3 formed at high pressures (30 mTorr), and slightly sub-stochiometric WO3-x, x = 0.005 at lower pressures (10 mTorr). Both stoichiometric and sub-stoichiometric thin films have been characterized by several structural, optical and electronic techniques. The electronic structure and especially band gap states have been explored and optical properties of WO3 and WO3-x have been studied in detail. The band gap has been determined to be in the range 2.7-2.9 eV. Absorption due to polaron absorption (W5+ -W6+), oxygen vacancy sites (Vo -W6+), and due to differently charged oxygen vacancy states in the band gap have been determined by spectrophotometry and photoluminescence spectroscopy, in good agreement with resonant inelastic x-ray spectroscopy and theoretical calculations. The density of electronic states in the band gap was determined from cyclic voltammetry measurements, which correlate with O vacancy concentration as compared with near infrared absorption. By combining different experimental methods a thorough characterization of the band gap states have been possible and this opens up the opportunity to tailor the WO3 functionalities. WO3 has been shown to be visible active photocatalyst, and a promising electrode material as inferred from photo-oxidation and water splitting measurements, respectively. Links between device performance in photoelectrochemical experiments, charge transport and the electronic structure have been elucidated.
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Frenzel, Johannes. "Structural, electronic and optical properties of cadmium sulfide nanoparticles." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1170678349152-44850.
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In this work, the structural, electronic, and optical properties of CdS nanoparticles with sizes up to 4nm have been calculated using density-functional theory (DFT). Inaccuracies in the description of the unoccupied states of the applied density-functional based tight-binding method (DFTB) are overcome by a new SCF-DFTB method. Density-functional-based calculations employing linear-response theory have been performed on cadmium sulfide nanoparticles considering different stoichiometries, underlying crystal structures (zincblende, wurtzite, rocksalt), particle shapes (spherical, cuboctahedral, tetrahedral), and saturations (unsaturated, partly saturated, completely saturated). For saturated particles, the calculated onset excitations are strong excitonic. The quantum-confinement effect in the lowest excitation is visible as the excitation energy decreases towards the bulk band gap with increasing particle size. Dangling bonds at unsaturated surface atoms introduce trapped surface states which lie below the lowest excitations of the completely saturated particles. The molecular orbitals (MOs), that are participating in the excitonic excitations, show the shape of the angular momenta of a hydrogen atom (s, p). Zincblende- and wurtzite-derived particles show very similar spectra, whereas the spectra of rocksalt-derived particles are rather featureless. Particle shapes that confine the orbital wavefunctions strongly (tetrahedron) give rise to less pronounced spectra with lower oscillator strengths. Finally, a very good agreement of the calculated data to experimentally available spectra and excitation energies is found.
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Ramzan, Muhammad. "Structural, Electronic and Mechanical Properties of Advanced Functional Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205243.
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The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage. Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials. Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies. MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method. Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature. In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.
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Samarakoon, Duminda K. "Structural, electronic, and magnetic properties of graphene-based nanomaterials." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2013. http://digitalcommons.auctr.edu/dissertations/708.
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The binding of radical groups such as hydrogen, hydroxyl, epoxide, or fluorine to the graphene surface, forms covalent bonds and transforms the trigonal sp2 orbital to the tetragonal sp3 orbital. Such a transformation drastically modifies electronic properties, which leads to the opening of a bandgap through the removal of the bands near the Fermi level of the pristine graphene. We have investigated the structural, electronic, magnetic, and vibrational properties of functionalized graphene based on first-principles densityfunctional calculations. A twist-boat conformation is identified as the energetically most favorable nonmetallic configuration for fully oxidized graphene. The calculated Raman G-band blue shift is in very good agreement with experimental observations. A detailed analysis of fluorographene membranes indicates that there exist prominent chair and stirrup conformations, which correlate with the experimentally observed in-plane lattice expansion contrary to a contraction in graphane. The optical response of fluorographene is investigated using the GW-Bethe-Salpeter equation approach. The results are in good conformity with the experimentally observed optical gap and reveal predominant chargetransfer excitations arising from strong electron-hole interactions. The appearance of bounded excitons in the ultraviolet region can result in an excitonic Bose-Einstein condensate in fluorographene. Hydrogenated epitaxial graphene has distinctive electronic properties compared to the two-sided hydrogenated graphene. The stability of a given hydrogenation pattern is strongly influenced by the amount of sp2-hybridized bonding in the structure. A trigonal planar networked hydrogenation pattern is identified as an intrinsic ferromagnetic semiconductor, which is in good conformity with experimental observations. The electronic structure of graphite and rotational-stacked multilayer epitaxial graphene as a function of the applied electric bias is investigated using dispersion-corrected density-functional theory. The tailoring of electronic band structure correlates with the interlayer coupling tuned by the applied bias. The implications of controllable electronic structure of rotationally fault-stacked epitaxial graphene grown on the C-face of SiC for future device applications are discussed. We have also investigated the electronic properties of fully hydrogenated boron-nitride (BN) layer and zigzag-edged nanoribbons using dispersion-corrected density-functional calculations. Among various low-energy hydrogenated membranes referred to as chair, boat, twist-boat, and stirrup, the stirrup conformation is the most energetically favorable one. The zigzag-edged BN nanoribbon, prominently fabricated in experiments, possesses intrinsic half-metallicity with full hydrogenation. The half-metallicity can be tuned by applying a transverse electric bias, thereby providing a promising route for spintronics device applications.
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Potenza, Alessandro. "Structural, electronic and magnetic properties of superconductor/ferromagnet multilayers." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426850.
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Evans, Martin Peter. "Surface structural and electronic properties of Sc and Dy." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318253.
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Lague, Stephen Brian. "The structural and electronic properties of some liquid semiconductors." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336931.
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Warren, Rachel Frances. "Optical, electronic and structural properties of metal halide intercalates." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333365.
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Frenzel, Johannes. "Structural, electronic and optical properties of cadmium sulfide nanoparticles." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A23935.
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In this work, the structural, electronic, and optical properties of CdS nanoparticles with sizes up to 4nm have been calculated using density-functional theory (DFT). Inaccuracies in the description of the unoccupied states of the applied density-functional based tight-binding method (DFTB) are overcome by a new SCF-DFTB method. Density-functional-based calculations employing linear-response theory have been performed on cadmium sulfide nanoparticles considering different stoichiometries, underlying crystal structures (zincblende, wurtzite, rocksalt), particle shapes (spherical, cuboctahedral, tetrahedral), and saturations (unsaturated, partly saturated, completely saturated). For saturated particles, the calculated onset excitations are strong excitonic. The quantum-confinement effect in the lowest excitation is visible as the excitation energy decreases towards the bulk band gap with increasing particle size. Dangling bonds at unsaturated surface atoms introduce trapped surface states which lie below the lowest excitations of the completely saturated particles. The molecular orbitals (MOs), that are participating in the excitonic excitations, show the shape of the angular momenta of a hydrogen atom (s, p). Zincblende- and wurtzite-derived particles show very similar spectra, whereas the spectra of rocksalt-derived particles are rather featureless. Particle shapes that confine the orbital wavefunctions strongly (tetrahedron) give rise to less pronounced spectra with lower oscillator strengths. Finally, a very good agreement of the calculated data to experimentally available spectra and excitation energies is found.
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Lew, Albert Yuet-Sang. "Atomic-scale structural and electronic properties of semiconductor heterostructures /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9732711.
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Smith, Kurt Vernon. "Structural and electronic properties of III-V nitride heterostructures /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9984803.
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Irrera, Simona. "Structural and electronic properties of chiral molecules on surfaces." Doctoral thesis, La Sapienza, 2006. http://hdl.handle.net/11573/917346.
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Carroll, Richard Lloyd. "Studies of the Structural and Electronic Properties of Self-Assembled Monolayers ? Towards Molecular Electronics." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010709-120336.
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The field of Molecular Electronics (ME) is growing at a rapid pace. The study of materials that have utility at the level of several, or single, molecules is exciting becausethe development of these sorts of systems offers a pathway to potentially avoid the perils of continually shrinking Silicon-based fabrication. This work examines the state of the art in fabrication techniques for semiconductor systems, then examines current examples of ME to be found in the academic literature. This review is designed to plumb the depths of a few important demonstrations, as opposed to a broad overview of the entire body of work. Further, scanning probe lithography techniques are demonstrated that allow for the study of small ensembles of interesting molecules in isolation. By utilizing these techniques, the structural and electronic properties of molecules can be studied, with a focus towards determining the likely utility of a particular species in a ME framework. Experimental study of redox-active self-assembled monolayer (SAM) films shows that under specific conditions, some films display a negative differential resistance (NDR) response that has possible utility in the development of ME devices. Ferrocene- and galvinol-terminated SAMs both show NDR at room temperature. A possible mechanism for the NDR behavior is believed to be resonant tunneling through low-lying, accessible redox-states in the molecule.
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Niles, Julian C. "The structural, electronic, vibrational and optical properties of C₇₈ isomers." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/30513.
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Allen, Christopher Stephen. "Structural characterisation, fabrication and electronic properties of carbon nanotube devices." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521441.
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Yildirim, Handan. "STRUCTURAL, ELECTRONIC, VIBRATIONAL AND THERMODYNAMICAL PROPERTIES OF SURFACES AND NANOPARTICLES." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3533.
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The main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the  bottom-up approach for which the knowledge gathered at the scale of atoms and NPs serves as a base to build, at the macroscopic scale, materials with desired physical and chemical properties. We use a variety of theoretical and computational tools with different degrees of accuracy to study problems in different time and length scales. Interactions between the atoms are derived using both Density Functional Theory (DFT) and Embedded Atom Method (EAM), depending on the scale of the problem at hand. For some cases, both methods are used for the purpose of comparison. For revealing the local contributions to the vibrational dynamics and thermodynamics for the systems possessing site-specific environments, a local approach in real-space is used, namely Real Space Green s Function method (RSGF). For simulating diffusion of atoms/clusters and growth on metal surfaces, Molecular Statics (MS) and Molecular Dynamics (MD) methods are employed.Ph.D.
Department of Physics
Sciences
Physics PhD
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Branford, William Richard. "Relationship of structural and electronic properties in transition metal oxides." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407974.
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Nicklin, Christopher L. "Electronic and structural properties of ultra-thin rare earth overlayers." Thesis, University of Leicester, 1993. http://hdl.handle.net/2381/35750.
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Photoelectron spectroscopy, low energy electron diffraction (LEED), Auger electron spectroscopy (AES), secondary electron emission crystal current (SEECC) and work function change measurements have been used to correlate the electronic and geometric structures of well characterised overlayers of Tm and Gd on Mo(110) and Ag(001). Tm deposited on Mo(110) is shown to form two ordered structures with (10x2) and c(8x4) symmetry before a hexagonal monolayer is formed. Mixed valence, caused by low co-ordinated adatoms, has been observed for sub-monolayer coverages of this system at room temperature. Tm alloys with Ag(001) at room temperature and above, and is found to be trivalent. At 130K the diffusion is inhibited and low co-ordinated atoms are again found to be the cause of mixed valence. Resonant photoemission measurements of thick, mixed valent Tm layers at the 4d-4f absorption threshold indicate that the 4d hole, caused by three strong absorption processes, decays in all cases by direct recombination. Strong enhancement of the trivalent 5s and 5p photoemission are noted for the lowest energy absorption peak and the second two peaks result in enhanced trivalent 4f features. There is also evidence of divalent 4f level enhancement. Gd grows on Mo(110) in a layer by layer mode, and forms six different sub-monolayer structures. The symmetry of the overlayers is similar to Gd/W(110) but with an extra (4x2) phase occurring. The initial growth is characterised by a constant ordering in the [001] direction and gradual contraction in the [110] direction, before isotropic growth of hexagonally based structures. The 3d-4f absorption process for thick Gd layers, reveals two strong peaks due to absorption from the 3d3/2 and 3d5/2 electron energy levels. The 3d hole decays by direct recombination leading to enhanced photoemission features, although a significant Auger intensity is observed on the high energy sides of the absorption peaks.
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Jewell, Catherine Mary. "Structural & electronic properties of some early transition metal oxides." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446632/.
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Low-dimensional spin systems with S = 1/2 and a singlet ground state attract intensive research efforts because of the quantum nature of their ground state. Since the discovery of the singlet plaquette CaV4O9 compound more attention has been paid to chemical analogues with S = 1/2, V4+ (d1) ions. For example, the V2O5 network exhibits the characteristics of layered and crystallographic shear structures and there is a large vanadium oxide bronze family, MxV2O5 (M = alkali, alkaline earth metals), which shows several original [V2O5] networks. For this reason, the atomic architectures of V2O5 and its derivatives provide a stage where various lower-dimensional quantum critical phenomena can be realised. Compounds in the series LixV2O5 were synthesised via soft chemistry methods and characterised structurally and magnetically via high-resolution x-ray and neutron diffraction and magnetization measurements using a SQUID magnetometer. Additional weaker peaks observed in certain of the diffraction patterns suggested the occurrence of charge ordering of vanadium ions in an incommensurately modulated superstructure for some of the E-LixV2O5 and E'-LixV2O5 phases. Having discovered a possible magnetic transition (Tf ~ 25 K) in one of these dilute-spin phases, Li0.50V2O5, believed to be associated with the low-dimensional, chain-like arrangement of the V4+ (S = 1/2, d1) cations over the non-magnetic V5+(S = 0, d0) network, a local probe, SR, was applied to investigate its ground state and the ground states of other members of the series LixV2O5 with x = 0.55, 0.64 and 0.72 which also exhibit interesting magnetic behaviour. Lack of oscillation in the SR data revealed the absence of any long-range magnetic order for Li0.50V2O5, Li0.55V2O5, Li0.64V2O5, and Li0.72V2O5, supportive of a true one-dimensional ground state, suggesting the formation of domains of one-dimensional antiferromagnetic chains, consistent with the Bonner-Fisher model for low-dimensional magnetic behaviour which provided a good fit to the SQUID data collected.
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Lord, Alexander M. "Electronic and structural properties of Au contacts on ZnO nanowires." Thesis, Swansea University, 2013. https://cronfa.swan.ac.uk/Record/cronfa42804.
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Zinc Oxide has emerged from an unspectacular past in the field of electronics to become one of the most widely researched materials for future devices. Here we investigate the growth and electrical properties of semiconducting ZnO nanowires for future application in the field of Nano-Devices and present a solution to control the behaviour of the electrical contacts. ZnO nanowires (NWs) from initial growth experimentation and optimisation have been thoroughly characterised both structurally and electrically. Structural characterisation revealed the high quality of nanowires from vapour phase and hydrothermal growth that translated to similar measurements of nanowire resistivity. We have confirmed the results of atomic resolution dark field imaging with simulations that no Au catalyst contaminates ZnO nanowires, which makes the material more desirable than Silicon or GaAs. Within the limits of the dark field imaging the interface of the catalyst particle and the nanowire is abrupt, clean and intimate, with no Au diffusion, interfacial layers or roughness. Electron microscopy reveals the Au has an epitaxial relationship with the ZnO and is solid during growth. Using fabrication and contamination free nanoprobe measurements (four-probe scanning tunnelling microscope) in vacuum a transition from rectifying to Ohmic is dependent on contact size and not the materials or structural variations. We have shown this with the application of the nanoprobe on free standing as-grown catalysed ZnO nanowires. Using the most common nanowire growth methods the structure has been thoroughly characterised to allow the interpretation of electrical measurements of resistivity and Au end contacts. A regime of size dependent contacts to ZnO nanowires provides the necessary knowledge and requirements to fabricate ZnO nanowire devices with controlled properties and function. This is a major hurdle for nanodevices overcome without complicated or difficult processing steps. A nanodevice can be fabricated from a substrate, with contacts, in one- step and with tailored interface properties by controlling the catalyst particle size.
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Gunasinghe, Rosi Najeela. "Structural and electronic properties of boron nano structures: A dispersion-corrected density functional study." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2012. http://digitalcommons.auctr.edu/dissertations/341.
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We have revisited the general constructing schemes for a large family of stable hollowboron fullerenes with 80 + 8n (n = 0,2,3,...) atoms. In contrast to the hollow pentagon boron fullerenes with 12 hollow pentagons, the stable boron fullerenes constitute 12 filled pentagons and 12 additional hollow hexagons, which are more stable than the empty pentagon boron fullerenes including the “magic” B80 buckyball. Based on results from first-principles density-functional calculations, an empirical rule for filled pentagons is proposed along with a revised electron counting scheme to account for the improved stability and the associated electronic bonding feature. We have also studied the relative stability of various boron fullerene structures and structural and electronic properties of B80 bucky ball and boron nanotubes via dispersion-corrected density-functional calculations. Our results reveal that the energy order of fullerenes strongly depends on the exchange-correlation functional employed in the calculation and the vibrational stability for the icosahedral B80 with the inclusion of dispersion corrections, in contrast to the instability to a tetrahedral B80 with puckered capping atoms from preceding density functional theory calculations. Similarly, the dispersion-corrected density-functional calculations yield non-puckered boron nanotube conformations and an associated metallic state for zigzag tubes. A systematic study elucidates the importance of incorporating dispersion forces to account for the intricate interplay of two and three centered bonding in boron nanostructures.
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Moslemzadeh, Nasser. "Geometric and electronic structure of dysprosium thin films on tungsten surfaces." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250404.
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Bröker, Benjamin. "Electronic and structural properties of interfaces between electron donor & acceptor molecules and conductive electrodes." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16257.
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Die vorliegende Arbeit behandelt Fragestellungen aus der Organischen Elektronik, in der die Ladungsträgerinjektion in alle Arten von Bauteilen kritisch von der elektronischen und morphologischen Struktur der Grenzflächen zwischen Elektrode und den konjugierten organischen Molekülen (KOM) abhängt. Näher betrachtet wurden: die Energieniveauanpassung mit starken (i) Elektronendonatoren und (ii) -akzeptoren und (iii) die dichteabhängige Umorientierung einer molekularen Monolage. Zur Analyse wurden Photoelektronen- und Reflektionsabsorptionsinfrarotspektroskopie angewandt. Weitere Informationen konnten durch Modellierung mit Dichtefunktionaltheory gewonnen werden, die über Kollaborationen zur Verfügung standen. (i) Das Konzept der optimierten Energieniveauanpassung mit starken Elektronenakzeptoren konnte auf Donatoren erweitert und damit erfolgreich von der Anode zur Kathode transferiert werden. Auch hier führte der Ladungstransfer zu einem Dipol über die Grenzfläche, womit die Austrittsarbeit um bis zu 2.2 eV reduziert wurde. Als Resultat konnte die Elektroneninjektionsbarriere in nachfolgende Materialien entscheidend verringert werden (bis zu 0.8 eV). (ii) Ein bis dato unerforschter starker Elektronenaktzeptor [hexaaza-triphenylene-hexacarbonitrile (HATCN)] wurde vollständig verschiedenen Elektroden charakterisiert. HATCN zeigte dabei eine bessere Performance verglichen mit derzeit üblichen Materialien (starke Austrittsarbeitsanhebung und Verringerung der Lochinjektionsbarriere um bis zu 1.0 eV). (iii) Zusätzlich konnte mit HATCN gezeigt werden, dass eine liegende molekulare Monolage durch Erhöhung der Moleküldichte in eine stehende Monolage umgewandelt werden kann. Dies führte zu einer Änderung der chemischen Bindung zum Metall und damit zu einer starken Modifikation der elektronischen Struktur der Grenzfläche. Die vorliegende Arbeit liefert damit wertvolle Informationen für das Verständnis der Grenzfläche zwischen Elektrode und KOM in der Organischen Elektronik.The present work is embedded in the field of organic electronics, where charge injection into devices is critically determined by the electronic and structural properties of the interfaces between the electrodes and the conjugated organic materials (COMs). Three main topics are addressed: energy level tuning with new and strong electron (i) donor and (ii) acceptor materials and (iii) the density dependent re-orientation of a molecular monolayer and its impact on the energy level alignment. To study these topics photoelectron and reflection absorption infrared spectroscopy were used. Moreover, additional information was obtained from density functional theory modelling, which was available through collaboration. (i) A concept of optimizing the energy level alignment at interfaces with strong molecular acceptors was extended to donor materials and thus successfully transferred from the anode to the cathode side of the device. Also in this case, charge transfer leads to a chemisorbed molecular monolayer. Due to the dipole across the interface, the work function of the electrode is reduced by up to 2.2 eV. Consequently, a reduced electron injection barrier into subsequently deposited materials is achieved (up to 0.8 eV). (ii) A yet unexplored strong electron acceptor material [i.e. hexaazatriphenylene- hexacarbonitrile (HATCN)] is thoroughly investigated on various surfaces. HATCN shows superior performance as electron acceptor material compared to presently used materials (e.g. work function modification and hole injection barrier reduction by up to 1 eV). (iii) Also with HATCN, the orientation of a molecular monolayer is observed to change from a face-on to an edge-on depending on layer density. This is accompanied by a re-hybridization of molecular and metal electronic states, which significantly modifies the interface electronic properties. All findings presented are valuable for the understanding of electrode-COM interfaces in organic electronics.
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Angleby, Linda. "Structural and electronic properties of bare and organosilane-functionalized ZnO nanopaticles." Thesis, Linköping University, Linköping University, Linköping University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-58691.
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A systematic study of trends in band gap and lattice energies for bare zinc oxide nanoparticles were performed by means of quantum chemical density functional theory (DFT) calculations and density of states (DOS) calculations. The geometry of the optimized structures and the appearance of their frontier orbitals were also studied. The particles studied varied in sizes from (ZnO)6 up to (ZnO)192.The functionalization of bare and hydroxylated ZnO surfaces with MPTMS was studied with emphasis on the adsorption energies for adsorption to different surfaces and the effects on the band gap for such adsorptions.
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Xiao, Li. "Structural and electronic properties and applications of platinum and gold nanoparticles /." Available to subscribers only, 2007. http://proquest.umi.com/pqdweb?did=1342740081&sid=3&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Bridges, Craig Allan Greedan John E. "Structural and electronic properties of BaV10O15, BaV10-xTixO15, and BaVO3-x /." *McMaster only, 2002.
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Hayden, Andrew Bryan. "Electronic and structural properties of adsorbates on nickel and aluminium surfaces." Thesis, University of Warwick, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387332.
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Schweitzer, Marc O'Donnell. "Structural and electronic properties of the surfaces of InSb-based materials." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386791.
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Bouhafs, Chamseddine. "Structural and Electronic Properties of Graphene on 4H- and 3C-SiC." Doctoral thesis, Linköpings universitet, Halvledarmaterial, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-132408.
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Graphene is a one-atom-tick carbon layer arranged in a honeycomb lattice. Graphene was first experimentally demonstrated by Andre Geim and Konstantin Novoselov in 2004 using mechanical exfoliation of highly oriented pyrolytic graphite (exfoliated graphene flakes), for which they received the Nobel Prize in Physics in 2010. Exfoliated graphene flakes show outstanding electronic properties, e.g., very high free charge carrier mobility parameters and ballistic transport at room temperature. This makes graphene a suitable material for next generation radio-frequency and terahertz electronic devices. Such applications require fabrication methods of large-area graphene compatible with electronic industry. Graphene grown by sublimation on silicon carbide (SiC) offers a viable route towards production of large-area, electronic-grade material on semi-insulating substrate without the need of transfer. Despite the intense investigations in the field, uniform wafer-scale graphene with very high-quality that matches the properties of exfoliated graphene has not been achieved yet. The key point is to identify and control how the substrate affects graphene uniformity, thickness, layer stacking, structural and electronic properties. Of particular interest is to understand the effects of SiC surface polarity and polytype on graphene properties in order to achieve large-area material with tailored properties for electronic applications. The main objectives of this thesis are to address these issues by investigating the structural and electronic properties of epitaxial graphene grown on 4HSiC and 3C-SiC substrates with different surface polarities. The first part of the thesis includes a general description of the properties of graphene, bilayer graphene and graphite. Then, the properties of epitaxial graphene on SiC by sublimation are detailed. The experimental techniques used to characterize graphene are described. A summary of all papers and contribution to the field is presented at the end of Part I. Part II consists of seven papers.Research Funders not listed under Research funders and strategic development areas: Marie Curie actions under the Project No.264613-NetFISiC, the centre of Nano Science and Nano technology (CeNano).
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Maxwell, Disney O. "Structural and Electronic properties of β-Al2X3 (X = O, Se, Te)." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1317158686.
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Steiner, Florian. "Multiscale modelling of structural and electronic properties of organic thin films." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/32107.
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In this thesis, we develop aspects of a framework for the multi-scale modelling of charge transport in several organic semiconductors relevant for technological application. In the first chapter, we build a coarse-grained model for fullerene multi-adducts which clearly distinguishes between the influence of energetic and structural disorder. The model reveals that charge transport in fullerene multi-adducts is limited by energetic disorder due to different isomers. Solar cells containing single isomers of higher fullerene adducts are expected to achieve higher power conversion efficiencies. Secondly, we create a multi-scale model to investigate the effect of beta-phase conformers on hole transport in poly(9,9)dicotylfluorene. A combination of quantum-chemical calculations and charge transport simulation confirms that beta-phase conformers act as traps and, when torsional disorder of the polymer backbone is included, can explain the experimentally observed mobility reduction due to beta-phase. In the third project, grain boundaries in tri-isopropylsilylethynyl (TIPS) pentacene are characterised. On the basis of two-grain structures with varied mutual orientation generated with atomistic molecular dynamics, we compute energy landscapes and electronic coupling elements. We find that the effect of the grain boundary is relatively weak for long interfaces, but that small contact areas between grains may impede charge transport more strongly due to highly non-uniform energy barrier heights. The final chapter focuses on one-dimensional organic magnetoresistors with alternating acceptor, spacer and donor units. Combining quantum-chemical calculations and kinetic Monte-Carlo simulations allow us to define design rules for high magnetoresistance, among which minimising the offset between HOMO and LUMO energy levels is the most challenging one. Within the range of researched materials, polymers built from dicyanoqyinonediimine (DCNQI) acceptors, fluorene spacers and 3-ethylendioxythiophene (3-EDOT) donors are most promising for magentoresistance application.
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BIFFI, GIULIA. "MODELLING ELECTRONIC AND STRUCTURAL PROPERTIES OF QUANTUM CONFINED METAL-HALIDE PEROVSKITES." Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1046796.
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This thesis focusses on the exploration of various theoretical methods to address the interesting questions concerning electronic and optical properties of quantum-confined systems. Chapter 1 serves the purpose of providing a sufficient background for the reader on state-of-the-art knowledge and approaches in order to understand the motivations behind the study of each system: 2D layered halide perovskites (Chapter 2), lead-halide perovskite nanocrystals (Chapter 3) and metal-insulator-metal optical nanocavities (Chapter 4).
In Chapter 4 the fundamentals of quantum mechanics are used to interpret the resonances of optical cavities as Epsilon-near-zero modes (ENZ), allowing us to describe them using the simple formalism of the particle in a box. In the various subparagraphs we use this approach to understand the polarization and coupling behaviours of such modes, eventually designing ENZ crystals.
In Chapter 3 an analytical model is built to calculate completely ab initio the excitonic energies and the exciton binding energies of perovskite nanocrystals. This is accomplished using the state-of-the-art GW correction to the calculations of molecular orbitals energies and the Bethe-Salpeter equation for a precise evaluation of the excited states in real space. This method allows to study the effect of every physical quantity entering the description (e.g. the dielectric environment, exchange and Coulomb interactions…) on the final result, providing useful insight in the physics underlying the optical properties of these nanocrystals.
In Chapter 2, Density Functional Theory is exploited to evaluate the effects of different ligands on the structural and the electronic properties of 2D halide perovskites. In the subparagraphs, various aspects are studied, for example the effects of different binding groups on the band structure, of different ligands on the Raman response and on the phase transition temperatures.
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Farquhar, Colin Pirie. "Interface electronic structure." Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/14824.
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Sirikumara, Henaka Rallage Hansika Iroshini. "Engineering structural/electronic properties of layered Selenides : A multi-scale modeling approach." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1840.
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Since the discovery of graphene, a new era of physics called "Two Dimensional (2D)Materials" has emerged. Group IV and Group III Selenides such as SnSe and InSe arepromising members of the 2D family. Structure of Group IV selenides is unique and highlysensitive to pressure and temperature. To further tweaking their properties by structuralchanges, thorough understanding of how the structure relates to the electronic bands is veryimportant. Based on the results from DFT calculations, I carefully analyzed electronic bandstructures of layered SnSe with various interlayer stacking. The first part of this dissertationdiscussed the possible stacking-dependent indirect-direct transition of bilayer SnSe.By further analysis, these results reveal that the directionality of interlayer interactionsdetermine the critical features of their electronic band structures. Further, it demonstratedthat such changes can be achieved by substitutional chemical doping. Using a multi-scalemodeling approach by combining the result of DFT and Boltzmann Transport Theory, Idiscussed the electron transport properties of co-doped SnSe, a class of thermodynamicallyand dynamically stable structures. The second part discussed on charge transfer across InSe/Gas interface, which showsbi-polar transport properties. This finding is in a good agreement with the recent experimentalobservations. Fundamental understanding of charge transfer in few-layer InSe /gasinterfaces at the atomic level is expected to pave the path for designing gas sensing devices.
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Spivak, Mariano Alejo. "Electronic structure calculations on extended metal atom chains. Insights on structural, magnetic and transport properties." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/399580.
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En aquest treball, es van utilitzar diferents mètodes computacionals per estudiar les propietats de cadenes esteses de metalls de transició (EMACs en anglès). Es va simular la flexibilitat estructural de cadenes de tres àtoms de crom, amb CASSCF/CASPT2 i es van identificar estructures simètriques i asimètriques en un entorn de baixa energia. Basats en aquests resultats, vam realitzar dinàmiques moleculars de primers principis (AIMD) per entendre l'efecte de l'energia tèrmica i com aquesta modifica la proporció d'estructures. També es van estudiar els enllaços metall-metall en compostos de crom, utilitzant el model d'ordre d'enllaç efectiu (EBO) amb els números d'ocupació naturals de la funció d'ona CASSCF. Es van calcular constants d'acoblament magnètic per a compostos bimetàl·lics i EMACs de níquel mitjançant dues estratègies. MC-PT2 amb espai actiu mínim utilitzant orbitals moleculars millorats a partir d'un càlcul d'estats-mitjanats, i es va utilitzar un mètode nou (MCPDFT) per al magnetisme de EMACs grans, que ha mostrat bons resultats en el compost de cinc níquels. Finalment, estudiem propietats del transport d'electrons per dos EMACs de ruteni. Proposem l'ús d'un elèctrode gate metàl·lic per modular els nivells moleculars dels compostos i obtenir espècies redox actives. També utilitzem un mètode químicament més intuïtiu, que proposa crear parells iònics dins de la cel·la.En este trabajo, se utilizaron diferentes métodos computacionales para estudiar las propiedades de cadenas extendidas de metales de transición (EMACs en inglés). Se simuló la flexibilidad estructural de cadenas de tres átomos de cromo, con CASSCF/CASPT2 y se identificaron estructuras simétricas y asimétricas en un entorno de baja energía. Basados en estos resultados, realizamos dinámicas moleculares de primeros principios (AIMD) para entender el efecto de la energía térmica y como ésta modifica la proporción de estructuras. También se estudiaron los enlaces metal-metal en compuestos de cromo, utilizando el modelo de orden de enlace efectivo (EBO) con los números de ocupación naturales de la función de onda CASSCF. Se calcularon constantes de acoplamiento magnético para compuestos bimetálicos y EMACs de níquel mediante dos estrategias. MC-PT2 con espacio activo mínimo utilizando orbitales moleculares mejorados a partir de un cálculo de estados-promediados, y se utilizó un método nuevo (MCPDFT) para el magnetismo de EMACs grandes, que ha mostrado buenos resultados en el compuesto de cinco níqueles. Finalmente, estudiamos propiedades del transporte de electrones para dos EMACs de rutenio. Proponemos el uso de un electrodo gate metálico para modular los niveles moleculares de los compuestos y obtener especies redox activas. También utilizamos un método químicamente más intuitivo, que propone crear pares iónicos dentro de la celda.
In this work we use different computational methods in the study of the properties of Extended Metal Atom Chains. The structural flexibility of trichromium chains has been simulated with CASSCF/CASPT2 and symmetric and asymmetric structures were identified in an extremely flat energy landscape. Based on these results, Ab initio molecular dynamic simulations were performed to understand how the thermal energy modifies the proportion of cited structures. In addition, the metal-metal bonding of chromium compounds was characterized using the Effective Bond Order (EBO) model with the natural occupation numbers of the CASSCF wave function. Furthermore, magnetic coupling constants were computed for nickel bimetallic and EMACs compounds, using two different approaches. Minimal active space MC-PT2 was performed with improved molecular orbitals based on state-average calculations, and a recently developed method (MCPDFT) used for the magnetism of large EMACs, showing good results in the five-nickel compound. Finally, the electron transport properties were simulated for two ruthenium EMACs. We propose the use of a metallic gate electrode to modulate the molecular levels of the compounds and achieve redox active species. In addition, another more chemically intuitive approach was tested, that consist of forming an ionic pair in-situ.
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Triggs, Paul Anthony. "Electronic and structural properties of single crystals in the system TiO₂-RuO₂ /." Basel : Birkhäuser, 1985. http://library.epfl.ch/theses/?nr=559.
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Thèse, Sciences, EPF Lausanne, No 559, 1985, Département de physique. Rapporteur: F. Lévy ; Co-rapporteur: E. Mooser ; Co-rapporteur: R. Monot ; Co-rapporteur: A. Mocellin.Tiré à part de: Helvetica Physica Acta, Vol. 58, p. 657-714.
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Song, Jiaming [Verfasser]. "Structural, electronic and magnetic properties of ultrathin epitaxial manganese films / Jiaming Song." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1077768214/34.
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