Дисертації з теми "Investigation - Electronic Structure"
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1
Jones, Gareth. "Investigation of the electronic conduction of large molecules via semi-empirical electronic structure techniques." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/42005/.
Повний текст джерелаАнотація:
In this thesis a new computer code is developed to perform non-equilibrium Green’s function based calculations of electronic transmission, using a Hamiltonian computed from self consistent extended Hückle theory as input. Individual elements of this code are tested to ensure correctness. To evaluate its usefulness, the code is tested on porphyrin based systems against the more traditional density functional theory methods of generating the required Hamiltonian. It is then used on more complex porphyrin systems, and comments are made on the use of porphyrin in molecular electronics. Finally it is used on DNA based systems too large to be dealt with efficiently via density functional theory to provide predictions of the effects of DNA structure on its conductance.
2
Anderson, Phillip Alistair. "Indium Nitride: An Investigation of Growth, Electronic Structure and Doping." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1087.
Повний текст джерелаАнотація:
The growth, electronic structure and doping of the semiconductor InN has been explored and analysed. InN thin films were grown by plasma assisted molecular beam epitaxy. The significance of the relative fluxes, substrate temperature and buffer layers was explored and related to the electrical and structural properties of the films. An exploration of the effect of active nitrogen species on InN films found that excited molecular nitrogen was preferred for growth over atomic and ionic species. An optimised recipe for InN was developed incorporating all explored parameters. The bandgap of InN was explored using the techniques of optical absorption, photoluminescence and photoconductivity. All three techniques identified a feature near 0.67 eV as the only dominant and reproducible optical feature measurable from InN thin films. No evidence for any optical features above 1 eV was discovered. The effect of the Burstein-Moss effect is discussed and the debate over the relative impact of the effect is related to problems with precisely measuring electron concentrations. Photoluminescence from mixed phase InN films containing significant zincblende content is presented, with tentative evidence presented for a zincblende band gap near 0.61 eV. Native defects within InN were studied by near edge X-ray absorption fine structure spectroscopy. Nitrogen related defects were found to be unlikely candidates for the high as-grown n-type conductivity. The most likely candidate remains nitrogen vacancies. Ion implantation was shown to cause substantial damage to the InN lattice, which could not be fully repaired through annealing. The limitation on annealing temperatures may limit the use of implantation as a processing tool for InN. Mg was shown to exhibit great promise as a potential p-type dopant. Photoluminescence from Mg doped films was found to quench at high Mg concentrations, consistent with a depletion region near the surface. The potential dilute magnetic semiconductor In1-xCrxN was explored. All of the In1-xCrxN films were found to be ferromagnetic at room temperature and exhibited saturated magnetic moments of up to 0.7 emu/g. An interesting correlation between background electron concentration and remnant moment is presented and the consequences of theoretical exchange models discussed. The bandgap of chromium nitride was also investigated and found to be an indirect gap of 0.7 eV.
3
Baniasadi, Fazel. "Structure Characterization and Electronic Properties Investigation of Two-Dimensional Materials." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103904.
Повний текст джерелаАнотація:
This dissertation will have three chapters. In chapter one, a comprehensive review on defects in two dimensional materials will be presented. The aim of this review is to elaborate on different types of defects in two dimensional (2D) materials like graphene and transition metal dichalcogenides (TMDs). First, different types of point and line defects, e.g. vacancies, anti-sites, guest elements, adatoms, vacancy clusters, grain boundaries, and edges, in these materials are categorized in terms of structure. Second, interactions among defects are discussed in terms of their rearrangement for low-energy configurations. Before studying the electronic and magnetic properties of defective 2D materials, some of the structures are considered in order to see how defect structure evolves to a stable defect configuration. Next, the influence of defects on electronic and magnetic properties of 2D materials is discussed. Finally, the dynamic behavior of defects and 2D structures under conditions such as electron beam irradiation, heat treatment, and ambient conditions, is discussed. Later as a case study, defects in a two dimensional transition metal dichalcogenide will be presented. Among two-dimensional (2D) transition metal dichalcogenides (TMDs), platinum diselenide (PtSe2) stands at a unique place in the sense that it undergoes a phase transition from type-II Dirac semimetal to indirect-gap semiconductor as thickness decreases. Defects in 2D TMDs are ubiquitous and play crucial roles in understanding and tuning electronic, optical, and magnetic properties. Here intrinsic point defects in ultrathin 1T-PtSe2 layers grown on mica were investigated through the chemical vapor transport (CVT) method, using scanning tunneling microscopy and spectroscopy (STM/STS) and first-principles calculations. Five types of distinct defects were observed from STM topography images and the local density of states of the defects were obtained. By combining the STM results with first-principles calculations, the types and characteristics of these defects were identified, which are Pt vacancies at the topmost and next monolayers, Se vacancies in the topmost monolayer, and Se antisites at Pt sites within the topmost monolayer. Our study shows that the Se antisite defects are the most abundant with the lowest formation energy in a Se-rich growth condition, in contrast to cases of 2D molybdenum disulfide (MoS2) family. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in few-layer 1T-PtSe2 and other related 2D materials. Also, in order to investigate the layer dependency of vibrational and electronic properties of two dimensional materials, 2M-WS2 material was selected. Raman spectroscopy and DFT calculation proved that all Raman active modes have a downshift when material is thinned to few layers (less than 5 layers). It was proven that there is a strong interaction between layers such that by decreasing the number of layers, the downshift in Raman active modes is mostly for the ones which belong to out-of-plane atomic movements and the most downshift is for the Ag2 Raman active mode. Also, I investigated the effect of number of layers on the band structure and electronic properties of this material. As the number of layers decreases, band gap does not change until the materials is thinned down to only a single monolayer. For a single monolayer of 2M-WS2, there is an indirect band gap of 0.05eV; however, with applying in-plane strain to this monolayer, the material takes a metallic behavior as the strain goes beyond ±1%.Doctor of Philosophy
Graphite (consisting of graphene as building blocks) and TMDS in bulk form are layered and with exfoliation one can reach to few layers which is called two-dimension. Two dimensional materials like graphene have been used in researches vastly due to their unique properties, e.g. high carrier mobility, and tunable electronic properties. Transition metal dichalcogenides (TMDs) with a general formula of MX2, where M represents transition metal elements (groups 4-10) and X represents chalcogen elements (S, Se or Te), are another family of two-dimensional materials which have been extensively studied in the past few years. Besides exfoliation, there are also synthesis methods to produce two dimensional materials, e.g. chemical vapor deposition and chemical vapor transport. Normally, after synthesizing these materials, researchers investigate structure and electronic properties of these materials. There might be some atoms which no longer exist in the structure; hence, those are replaced by either vacancies or other elements which all of them are called defects. In chapter 1, defects in graphene and transition metal dichacolgenides were investigated, carefully. Later, dynamic behavior of defects in these materials were investigated and finally, the effect of defects on the electronic properties of the two dimensional materials were investigated. Chapter two talks about a case study which is two dimensional 1T-PtSe2. In this chapter, 5 different kinds of defects were studied using scanning tunneling microscopy and spectroscopy investigations and density functional theory was used to prove our assumptions of the origin of defects. Also, another thing which is investigated by researcher is that how atoms in two dimensional materials vibrate and how the number of layers in the two dimensional material influences vibrations of atoms. Other than this, electronic properties of these materials is dependent upon the number of layers. When these materials are synthesized, there is a stress applied to the material due the mismatch between the material and its substrate, so it is worth investigating the effect of stress (strain) on the structure, and electronic properties of the material of interest. For this purpose, 2M-WS2 was exfoliated on Si/SiO2 substrate and the layer dependency of its vibrational modes was investigated using Raman spectroscopy and density functional theory calculation. Also, in order to investigate the influence of stress (strain) on the electronic properties of two dimensional 2M-WS2, a single monolayer of this materials underwent a series of strains in density functional theory calculations and the effect of strain on the electronic properties of this material was investigated.
4
Odell, Anders. "Quantum transport in photoswitching molecules : An investigation based on ab initio calculations and Non Equilibrium Green Function theory." Licentiate thesis, KTH, Materials Science and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4790.
Повний текст джерелаАнотація:
Molecular electronics is envisioned as a possible next step in device miniaturization. It is usually taken to mean the design and manufacturing of electronic devices and applications where organic molecules work as the fundamental functioning unit. It involves the easurement and manipulation of electronic response and transport in molecules attached to conducting leads. Organic molecules have the advantages over conventional solid state electronics of inherent small sizes, endless chemical diversity and ambient temperature low cost manufacturing.
In this thesis we investigate the switching and conducting properties of photochromic dithienylethene derivatives. Such molecules change their conformation in solution when acted upon by light. Photochromic molecules are attractive candidates for use in molecular electronics because of the switching between different states with different conducting properties. The possibility of optically controlling the conductance of the molecule attached to leads may lead to new device implementations.
The switching reaction is investigated with potential energy calculations for different values of the reaction coordinate between the closed and the open isomer. The electronic and atomic structure calculations are performed with density functional theory (DFT). It is concluded that there is a large potential energy barrier separating the open and closed isomer and that switching between open and closed forms must involve excited states.
The conducting properties of the molecule inserted between gold leads is calculated within the Non Equilibrium Green Function theory. The transmission function is calculated for the two isomers with different basis sizes for the gold contacts, as well as the electrostatic potential, for finite applied bias voltages. We conclude that a Au 6s basis give qualitatively the same result as a Au spd basis close to the Fermi level. The transmission coefficient at the Fermi energy is around 10 times larger in the closed molecule compared to the open. This will result in a large difference in conductivity. It is also found that the large difference in conductivity will remain for small applied bias voltages. The results are consistent with earlier work.
5
Sereika, Raimundas. "Investigation of Electronic Structure, Optical and Dynamical Properties of AVBVICVII type Compounds." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20130114_082030-02721.
Повний текст джерелаАнотація:
In the dissertation AVBVICVII type compounds are analyzed theoretically and experimentally. Theoretical studies were carried out using Density Functional Theory (DFT), along with the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method and the Generalized Gradient Approximation (GGA). For calculations Wien2k and PHONON comp. packages were used. Experimental studies were performed using spectroscopic ellipsometry method and measuring permittivity (electrical capacitance) as a function of temperature. The study discusses AVBVICVII type compounds’ inter-atomic chemical bonding, the electronic structure, optical properties, lattice dynamics, vibrational thermodynamic functions and dielectric properties in the paraelectric, ferroelectric and antiferroelectric phases.Disertacijoje teoriškai ir eksperimentiškai nagrinėjami AVBVICVII tipo junginiai. Teoriniai tyrimai atlikti naudojantis tankio funkcionalo teorija kartu su pilno potencialo tiesinių padidintų plokščių bangų metodu ir apibendrinto gradiento aproksimacija. Skaičiavimams naudoti Wien2k ir PHONON komp. paketai. Eksperimentiniai tyrimai buvo atliekami naudojantis spektroskopinės elipsometrijos metodais bei matuojant dielektrinės skvarbos (elektrinės talpos) priklausomybes nuo temperatūros. Darbe nagrinėjamas AVBVICVII tipo junginių tarpatominis cheminis ryšys, elektroninė struktūra, optinės savybės, gardelės dinamika, virpesių termodinaminės funkcijos ir dielektriniai pokyčiai paraelektrinėje, feroelektrinėje ir antiferoelektrinėje fazėse.
6
Reading, Martin. "An investigation into the structure and properties of polyethylene oxide nanocomposites." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/171659/.
Повний текст джерелаАнотація:
Polymer nanocomposites have attracted great interest over many years, because of the enhanced properties exhibited by such systems. However, it is only recently that the electrical characteristics of this class of material have begun to be studied in detail. Whenever fillers are added to a host polymer matrix, dispersion is of critical importance since, while a well dispersed nanophase may be beneficial, poor dispersion can have negative consequences. Hence, for the nanocomposites to be used appropriately and provide the best properties, a method for observing the dispersion within the matrix is useful. Despite this, evaluating the dispersion of nano-additives in the bulk is far from straight forward using conventional solid-state materials characterization techniques. This study set out to consider the influence of nano-additives on the physical, thermal and electrical properties of poly(ethylene oxide) systems. The initial objective is to investigate the extent to which dispersion of nanofillers and effect of host molecular weight can be inferred from rheological analysis. This investigation covers many systems based upon polyethylene oxide (PEO); PEO blends, thermally aged PEO and PEO composites with montmorillonite (MMT), micro/nano silicon dioxide (SD/nSD) and boehmite fillers (BO). The study continued from dispersion and solution characterisation onto thermal and electrical properties. The effects of additives and treatment on the crystallisation kinetics and thermal transitions are considered. Polymers are most well known for their electrically insulating properties, therefore electrical analysis into AC breakdown and dielectric spectroscopy were also performed. The research has shown that rheology is capable of producing well dispersed PEO nanocomposites. Addition of fillers during the rheology phase produced the expected monotonic increase in viscosity apart from boehmite, which formed a very viscous gel after reaching a threshold loading. Large drops in thermal transitions were observed for the composite samples. All fillers caused a large increase in breakdown strength at higher loadings, except boehmite which caused the breakdown strength to decrease,an effect discussed in detail.
7
Shpak, A. P., A. E. Pogorelov, A. E. Medvedskij, T. V. Kryshchuk, A. M. Korduban та V. A. Kandyba. "Synthesis and investigation of electronic structure features of electroexplosive Ti02 and ТO2:Аg". Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20644.
Повний текст джерелаАнотація:
Electrical explosion of wires is a promising technology which allows to obtain
nanopowders with high density of surface catalytically-active centers, that is
a sequence of nonequilibrium of synthesis process. Electroexplosive films
and titanium dioxide nanopowders are promising for using in photoelectrochemical
systems of solar energy conversion. The attention to TiO2 nanopowders
incorporated nanoparticles of noble metals is caused by the fact that
the particles of silver on the surface of metal can be centers of charge distribution
and accumulation. At that such parameter as photosensitivity greatly increases. In the work the phase contents changes of the surface of doped TiO2 nanopowders
were examined at different annealing conditions.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20644
8
Perera, Saranga D. "Investigation of exciton dynamics and electronic band structure of InP and GaAs nanowires." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352993854.
Повний текст джерела
9
Ilkiv, B. I., S. Petrovska, R. Sergiienko, and Ya V. Zaulychnyy. "X-ray Spectral Investigation of Carbon Nanoshells." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35301.
Повний текст джерелаАнотація:
Carbon nanocapsules synthesized by plasma method in hexane were investigated using the ultra-soft
X-ray emission spectroscopy method. It has been revealed that additional mixed π+σ-overlapping form in
nanocapsules in a result of folding of graphene sheets. It has been found that in nanocapsules sp-hybrid
bonds between carbon and residual iron atoms form when overlapping high-energy 3d+4s-states with spnhybrid
orbitals (2
10
Cilliers, M. E. "Investigation of an aeroelastic model for a generic wing structure." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80317.
Повний текст джерелаАнотація:
Thesis (MScEng)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Computational Aeroelasticity is a complex research field which combines structural and aerodynamic analyses to describe a vehicle in flight. This thesis investigates the feasibility of including such an analysis in the development of control systems for unmanned aerial vehicles within the Electronic Systems Laboratory at the Department of Electrical and Electronic Engineering at Stellenbosch University. This is done through the development of a structural analysis algorithm using the Finite Element Method, an aerodynamic algorithm for Prandtl’s Lifting Line Theory and experimental work. The experimental work was conducted at the Low-Speed Wind Tunnel at the Department of Mechanical and Mechatronic Engineering. The structural algorithm was applied to 20-noded hexahedral elements in a winglike structure. The wing was modelled as a cantilever beam, with a fixed and a free end. Natural frequencies and deflections were verified with the experimental model and commercial software. The aerodynamic algorithm was applied to a Clark-Y airfoil with a chord of 0:1m and a half-span of 0:5m. This profile was also used on the experimental model. Experimental data was captured using single axis accelerometers. All postprocessing of data is also discussed in this thesis. Results show good correlation between the structural algorithm and experimental data.
AFRIKAANSE OPSOMMING: Numeriese Aeroelastisiteit is ’n komplekse navorsingsveld waar ’n vlieënde voertuig deur ’n strukturele en ’n aerodinamiese analise beskryf word. Hierdie tesis ondersoek die toepaslikheid van hierdie tipe analise in die ontwerp van beheerstelsels vir onbemande voertuie binne die ESL groep van die Departement Elektriese en Elektroniese Ingenieurswese by Stellenbosch Universiteit. Die ondersoek bevat die ontwikkeling van ’n strukturele algoritme met die gebruik van die Eindige Element Methode, ’n aerodinamiese algoritme vir Prandtl se Heflynteorie en eksperimentele werk. Die eksperimentele werk is by die Department Meganiese en Megatroniese Ingensierswese toegepas in die Lae-Spoed Windtonnel. Die strukturele algoritme maak gebruik van ’n 20-nodus heksahedrale element om ’n vlerk-tipe struktuur op te bou. Die vlerk is vereenvouding na ’n kantelbalk met ’n vasgeklemde en ’n vrye ent. Natuurlike frekwensies en defleksies is met die eksperimentele werk en kommersiële sagteware geverifieer. Die aerodinamiese algoritme is op ’n Clark-Y profiel met 0:1m koord lengte en ’n halwe vlerk length van 0:5m geïmplementeer. Die profiel is ook in die eksperimentele model gebruik. Die eksperimentele data is met eendimensionele versnellingsmeters opgeneem. Al die verdere berekeninge wat op ekperimentele data gedoen is, word in die tesis beskryf. Resultate toon goeie korrelasie tussen die strukturele algoritme en die eksperimentele data.
11
Liu, Qiang. "Synthesis, characterization and investigation on the magnetic and electronic structure of strontium iron oxides." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14772/document.
Повний текст джерелаАнотація:
Les diverses perovskites de strontium-fer présentent de très fortes corrélations entre la structurecristalline et les phénomènes d’ordre de lacunes d’oxygènes, de charge, de spin et d’orbitales. Danscette thèse, nous avons réalisé une étude systématique des relations entre les ordres de charges etles ordres de spins selon les différents environnements cristallographiques rencontrés pour lescations Fe3+ et Fe4+ dans la phase Sr4Fe4O11, pour le cation Fe3+ dans les phases Sr3Fe2O6 et Sr2Fe2O10et pour le cation Fe2+ dans la phase SrFeO2. Les synthèses des phases polycristallines furent réaliséesvia des voies « solide » ou « sol-gel » en complément de la synthèse de cristaux préparés à l’aide d’unfour à image à fusion de zone verticale pour les phases Sr4Fe4O11 et Sr2Fe2O10. La qualité cristalline etchimique des oxydes fut contrôlée par diffraction de rayons X sur poudre et spectroscopieMössbauer alors que l’étude de la structure électronique de chaque phase a été réalisée à l’aide despectroscopie d’absorption de rayons X. Finalement, les structures magnétiques des phases Sr3Fe2O6et Sr4Fe4O11 sont aussi présentéesThe relationship of the crystallographic, magnetic, and electronic structure have long been of highinterest in research. Strontium iron oxides have structural, charge, spin, and orbital degrees offreedom, and thus give rich information to study for the condensed matter scientists. In this thesis,we have systematically studied the strontium iron oxides based on the freedom of the iron charge:Fe3+ and Fe4+ mixed valence compound SrFeO2,75 , Fe3+ compound Sr3Fe2O6 and SrFeO2,5 with differentcoordination around Fe3+ and Fe2+ compound SrFeO2. The synthesis of the polycrystalline compoundsare through either solid state reaction or sol-gel method. Single crystals of SrFeO2,75 and SrFeO2,5have been prepared by floating zone furnace. The purity of all the compounds is checked by lab x-raydiffraction and Mössbauer spectroscopy. Electronic structures have been studied by x-ray absorptionspectroscopy for all these compounds. Special efforts have been used to investigate the magneticstructure of SrFeO2,75 and Sr3Fe2O6
12
Bakulin, A. V., S. E. Kulkova, and O. E. Tereshchenko. "Investigation of the Ga-rich GaAs(001) Surface Reconstructions Stability and Interaction with Halogens." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35317.
Повний текст джерелаАнотація:
Atomic and electronic structures for a number of GaAs(001) surface geometries were studied within the density functional theory in order to re-examine the energy stability of surface reconstructions in the Ga-rich limit. It was shown that among geometries with (42) symmetry so-called ζ-model is most stable but the energetically favored Ga-rich (24) reconstructions are stabilized by dimerized Ga and As atoms. Our calculations predict the coexistence of (24) and (44) reconstructions on GaAs(001) in the Ga-rich limit. Comparative study of the halogens (F, Cl, I) adsorption on the -GaAs(001)-(42) surface were performed. The energetically preferable positions for all considered halogens are found on-top sites above dimerized and nondimerized Ga atoms. The electronic properties of the semiconductor surface and its change upon halogen adsorption are discussed. It was shown that the interaction of halogen with the Ga dimerized at-oms leads to the weakening of the chemical bonds between surface atoms that determines the initial stage of surface etching.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35317
13
Mehmood, Faisal. "Ab initio electronic structure investigation of adsorption, coadsorption and reactions on selected transition metal surfaces /." Search for this dissertation online, 2006. http://wwwlib.umi.com/cr/ksu/main.
Повний текст джерела
14
Rees, N. V. "The electronic structure of bulk transition metal silicides : an investigation of the silicide silicon interface." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232913.
Повний текст джерела
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Kaltsoyannis, Nikolas. "Investigation of the electronic structure of transition metal compounds by photoelectron spectroscopy with variable photon energy." Thesis, University of Oxford, 1992. https://ora.ox.ac.uk/objects/uuid:5887001c-df99-4427-8e80-d3b0f52fd9b2.
Повний текст джерелаАнотація:
Relative partial photoionisation cross section (RPPICS) data have been obtained for a variety of transition metal compounds using synchrotron radiation in the incident photon energy range 17-115 eV. Cross section features such as pâd giant resonances, delayed maxima, Cooper minima and molecular shape resonances have been identified and interpreted in terms of the localisation properties of the ionising electrons. The RPPICS behaviour of the photoelectron (PE) band corresponding to ionisation of the 1a1g highest occupied molecular orbital (HOMO) of [Moη-C6H5Me)2] indicates that it is essentially metal-localised. The pâd giant resonant absorption enhancement of the cross section is found to be almost coincident in photon energy with a molecular shape resonance. Similar features in the 1e2g-1 and 1e1g-1 bands provide strong evidence for metal-ligand covalency in the associated MOs. In contrast, the monotonic fall off with increasing photon energy of the RPPICS of the 1e1u-1 band is typical of ligand-localised MOs. Studies of the closely related [Mη-C7H7)(η-C5H4R)] (M=Ti, Nb, Mo; R=H: M=Ta; R=Me) reveal a significant degree of both metal and ligand character to the 1e2 MOs, suggesting that neither the +1 nor the -3 formalism for the charge on the cycloheptatrienyl ring in its complexes is a good one, as they imply a metal- and ligand-localised 1e2 level respectively. Analysis of the occurrence and magnitude of shape resonances in all of these sandwich molecules suggests that they are governed chiefly by the amount of metal d orbital character in an MO. The 5e MOs of PF3, traditionally regarded as fluorine 2p lone pair MOs, have been shown to possess significant phosphorus 3p atomic orbital (AO) character. Comparison of the data obtained on PF3 with those on [Ni(PF3)4] indicates that the Ï back donation from the nickel 3d orbitals to the 7e lowest unoccupied MO of PF3 also affects the composition of the 5e derived orbitals. A combined experimental and theoretical study has resulted in an assignment of the PE spectrum of OsO4 in which an osmium np AO (n=5 and/or 6) derived spin-orbit splitting of the lower ionisation energy (IE) 2T2 primary ion state is found. RPPICS results obtained on TiCl4, TiBr4 and ZrBr4 indicate that their PE spectra may be interpreted within a framework in which the primary ion state ordering is preserved on moving from chloride to bromide and from first to second row transition metal. Bromine-centred spin-orbit coupling produces the more complicated spectra of TiBr4 and ZrBr4. In all cases, the highest IE band shows RPPICS behaviour which indicates that it arises from the 2a1 MO, resolving the debate as to the assignment of the PE spectrum of TiCl4. The He I and He II spectra of [(CH3)ReO3] have been measured and Extended Hückel MO calculations performed upon both this molecule and ReO3Cl. A consistent assignment of their spectra has been achieved, based upon that of OsO4, and it is found that the methyl group represents a much greater perturbation to tetrahedral symmetry than does a chlorine atom. The bonding between the metal and dithiolene fragments in [Fe2(CO)6S2C2(CF3)2] has been shown to be primarily due to an interaction between the b1 symmetry Fe2(CO)6 HOMO and the n. MO of the dithiolene, which is doubly reduced. In [Ni(S,sub>2C2(CF3)2)2], however, the closer energy match of metal and ligand valence orbitals results in monoanionic dithiolene groups and a more complex PE spectrum.
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Kumar, Ajay. "An Investigation of Functionalization, Electronic structure of Multilayer Graphene Nanoflake Films (MGNFs)and their electrochemical properties." Thesis, University of Ulster, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516459.
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Hope, B. T. "The electronic structure and spintronic potential of carbon nanotubes and transition metal nanowires : a theoretical investigation." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604218.
Повний текст джерелаАнотація:
The new technology of spintronics seeks to employ the quantum mechanical spin of electrons to encode and process information. For the construction of spintronic devices, a wide range of possible materials is available. Two highly promising candidates are carbon nanotubes (CNTs) and transition metals (TMs). The former are famous for their long coherence-lengths and novel electronic properties; the latter bring strong exchange forces and ferromagnetism. In this thesis I investigate, theoretically, a number of CNT and TM-nanowire systems to characterize their potential for use in spintronics. First the idea of using applied magnetic fields to influence spin in CNTs is studied to see if they could act either as polarizers or to rotate the polarization angel. Then the spin-dependent electronic structure of free-standing and CNT-encapsulated Co nanowires is examined for signs of spin-polarization under the density of states (DOS), ballistic and diffusive definitions. A variety of methods are used in the investigation. Tight-binding, elementary energy-scale analysis and free-electron rectangular-barrier models are applied to study CNTs in magnetic fields. To compute magnetic moments, energy bands and DOS of the Co nanowires, density-functional theory is used, implemented by the Vienna ab initio Simulation Package (VASP). It is shown that magnetic fields of feasible strength, applied to CNTs, do have potential in certain specialized schemes, most relevant to the quantum computation (QC) regime, but in general are too weak to have an impact on the spin ensembles relevant to classical computation (CC) applications. Unless acting upon isolated resonances, the system is inefficient both as a polarizer and as a spin processor. In contrast, very significant spin-polarization, with CC potential, is found to arise spontaneously in CO nanowires, albeit in a highly definition-dependent manner. For all but the monatomic wire, there is stark disagreement between the DOS, ballistic and diffusive degree of spin-polarization (DSPs). This is shown to result from the intrinsic nature of d and sp bands together with hybridization effects. Magnetism is also a central theme in nanoscience, in particular for high-density information storage. Magnetic moments tend to increase at reduced dimensionality but long-range order is more sensitive to temperature effects which can result in superparamagnetism unless it is supported by magnetic anisotropy. With relevance to this, the analysis of Co nanowires encompasses the mechanisms of ferromagnetism and the degree of magnetic apisotropy. An inverse correlation between magnetic moment and coordination number is found and discussed with reference to the Stoner model, the second moment theorem, and sp-d hybridization. The magnetocrystalline anisotropy is found to be much larger than in bulk Co and the easy axis depends sensitivity on wire diameter. Encapsulating Co wires inside CNTs provides a way of protecting the Co against oxidation. It also has the potential to unify the desirable properties of the component systems in a novel approach to inducing spin-polarization in CNTs. By repeating the VASP simulations on these hybrid nanostructures, I show that a high DSP can be associated with a CNT in this way, but it is argued that the transport length-scales of pure CNTs are no longer applicable.
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Fugate, Elizabeth Anne. "Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462868623.
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Bajorek, Tom Werstiuk Nick H. "The UV photoelectron spectroscopy of transients : An experimental and computational investigation of electronic structure and reaction mechanisms /." *McMaster only, 2003.
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Wong, Shun Ha Sylvia. "An investigation into the use of argument structure and lexical mapping theory for machine translation." Thesis, University of Birmingham, 2000. http://etheses.bham.ac.uk//id/eprint/4656/.
Повний текст джерелаАнотація:
In recent work on the Lexical-Functional Grammar (LFG) formalism, argument structure (a-structure) and lexical mapping theory have been used to explain many linguistic behaviours across languages. It has been suggested that the combination of c-structure, f-structure and a-structure might form a suitable architecture for Universal Grammar. If this suggestion is valid, the LFG formalism would be a suitable linguistic model for Machine Translation (MT). This thesis reports on the investigations carried out on using a-structure and lexical mapping theory for aiding various sub-tasks in MT. The two investigations described in this thesis are the abilities of a-structure and lexical mapping theory to: (1) aid different kinds of lexical and structural disambiguations involving verbs and prepositions, and (2) act as a suitable medium for carrying out source-to-target language transfer. Based on the results of these investigations, this thesis also gives an evaluation of how well a-structure and lexical mapping theory can improve the existing models of linguistic-based MT.
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Huang, Jianqiu. "First-Principles Study of Band Alignment and Electronic Structure at Metal/Oxide Interfaces: An Investigation of Dielectric Breakdown." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/95967.
Повний текст джерелаАнотація:
Oxide dielectric breakdown is an old problem that has been studied over decades. It causes power dissipations and irreversible damage to the electronic devices. The aggressive downscaling of the device size exponentially increases the leakage current density, which also raises the risk of dielectric breakdown. It has been proposed that point defects, current leakages, impurity diffusions, etc. all contribute to the change of oxide chemical composition and ultimately lead to the dielectric breakdown. However, the conclusive cause and a clear understanding of the entire process of dielectric breakdown are still under debate. In this research, the electronic structure at metal/oxide interfaces is studied using first-principle calculations within the framework of Density Functional Theory (DFT) to investigate any possible key signature that would trigger the dielectric breakdown.
A classical band alignment method, the Van de Walle method, is applied to the case study of the Al/crystal-SiO2 (Al/c-SiO2) interface. Point defects, such as oxygen vacancy (VO) and hydrogen impurity (IH), are introduced into the Al/c-SiO2 interface to study the effects on band offset and electronic structure caused by point defects at metal/oxide interfaces. It is shown that the bonding chemistry at metal/oxide interfaces, which is mainly ionic bond, polarizes the interface. It results in many interface effects such as the interface dipole, built-in voltage, band bending, etc. Charge density analysis also indicates that the interface can localize charge due to such ionic bonding. It is also found that VO at the interface traps metal electrons which closes the open -sp3 orbital. The analysis on local potential shows that the metal potential penetrates through a few layers of oxide starting from the interface, which metalizes the interfacial region and induces unoccupied states in the oxide band gap. In addition, it is shown that higher oxygen content at metal/oxide interfaces minimizes such metal potential invasion. In addition, an oxygen vacancy is created at multiple sites through the Al/c-SiO2 and Al/a-SiO2 interface systems, separately. The oxygen local pressure is also calculated before its removal using Quantum Stress Density theory. Correlations among electronic structure, stress density, and vacancy formation energy are found, which provide informative insights into the defect generation controlling and dielectric breakdown analysis.
A new band alignment approach based on the projection of plane-waves (PWs) into the space-dependent atomic orbital (LCAO) basis is presented and tested against classical band offset methods -- the Van de Walle method. It is found that the new band alignment approach can provide a quantitative and reliable band alignment and can be applied to the heterojunctions consisting of amorphous materials. The new band alignment approach reveals the real-space dependency of the electronic structure at interfaces. In addition, it includes all interface effects, such as the interface dipole, built-in voltage, virtual oxide thinning, and band deformation, which cannot be derived using classical band offset methods. This new band alignment approach is applied to the case study of both the Al/amorphous-SiO2 (Al/a-SiO2) interface and the Al/c-SiO2. We have found that at extremely low dimensions, the reduction of the insulator character due to the virtual oxide thinning is a pure quantum effect. I highlight that the quantum tunneling current leakage is more critical than the decrease of the potential barrier height on the failure of the devices.PHD
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Zhang, Chaofan. "Multicomponent Clusters/Nanoparticles : An Investigation of Electronic and Geometric Properties by Photoelectron Spectroscopy." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205651.
Повний текст джерелаАнотація:
Clusters/nanoparticles are aggregates of a “small” number of building blocks, atoms or molecules, ranging from two up to millions of atoms. Two main groups of clusters have been studied using photoelectron spectroscopy based on synchrotron radiation. They are dry/wet alkali-halide clusters, including pure water clusters, and metal-based nanoparticles. For the dry alkali halide clusters, analysis of the data and theoretical modeling has allowed us insights into the local electronic properties at nanoscale: a change of polarizability of ions in the alkali-halide clusters due to the varying environment has been suggested. The study of the wet salt clusters shows that the alkali-halides are already solvated at the nanoscale reached by water clusters doped with salt vapor. The photoelectron angular distribution of water cluster shows lower anisotropy parameters as compared to the separate monomers. A model based on intracluster scattering has been built to partly explain the reduction. In the last part of the thesis, metal-based multi-component nanoparticles have been produced by self-assembly processes using reactive magnetron sputtering. Depending on the specific metal element, oxidation processes have been applied before or after the aggregation. Clearly radial distributions such as core-shell and “sandwich-like” structures have unambiguously determined by photoelectron spectroscopy.
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Ehret, Fabian [Verfasser], and Wolfgang [Akademischer Betreuer] Kaim. "Synthesis and electronic structure investigation of ruthenium complexes containing novel redox-active ligands / Fabian Ehret. Betreuer: Wolfgang Kaim." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1053327730/34.
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Golnak, Ronny [Verfasser]. "Investigation of the Electronic Structure of Transition Metal-Ions in Solution from Aqua-Complexes to Porphyrins / Ronny Golnak." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1132547318/34.
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BEZERRA, IURY STEINER DE OLIVEIRA. "INVESTIGATION OF AN AB INITIO MODEL TO ELECTRONIC STRUCTURE OF ATOMS BASED ON EVOLUTIVE ALGORITMS, WAVELETS AND LAGUERRE POLYNOMIALS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34924@1.
Повний текст джерелаАнотація:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE EXCELENCIA ACADEMICA
A simulação da estrutura eletrônica de átomos e moléculas, desde do início da década de 90, tem se mostrado uma ferramenta imprescindível para o desenvolvimento de áreas estratégicas, ainda emergentes, mas fundamentais, como por exemplo, a área de Nanotecnologia. No entanto, esse tipo de simulação, ainda hoje é de grande complexidade e exige alto poder computacional. Dessa forma, torna-se fundamental a criação de métodos de simulação mais precisos e computacionalmente menos custosos. Este trabalho utiliza Algoritmos Evolutivos e métodos de Inteligência Computacional junto de algumas ferramentas desenvolvidas e estudadas tradicionalmente pela Matemática Aplicada em cálculos de estrutura eletrônica. Em particular, são construídas novas formas de aproximação de soluções para equação de Schrodinger, que contemplem os requisitos físicos necessários. Essas soluções serão nomeadas de funções de ondas evolucionárias, que neste trabalho serão tratadas como pontos em um espaço de Hilbert formado pelo fecho em L (2) da interseção das funções definidas na semi-reta, contínuas e de derivadas contínuas, simétricas ou antissimétricas com relação à permutação de suas coordenadas. São demonstrados alguns resultados, requisitos para utilização de Algoritmos Evolucionários e Séries de Fourier Generalizadas, baseadas em polinômios de Laguerre modificados e Wavelets. Esta pesquisa é desenvolvida inicialmente para sistemas de dois elétrons, e mais tarde é estendida para sistemas mais complexos, a fim de criar uma abordagem alternativa as tradicionais.
The simulation of the electronic structure of atoms and molecules has been shown to be, from the beginning of 90 s, an indispensable tool for the development of strategic areas, that are still emergent, but fundamental, like nanotechnology. However, this type of simulation is still of great complexity today and demands high computational power. Thus, the creation of more precise and less costly methods becomes fundamental. With the elaboration of this research, the intention is to create alternatives basis that can be used into the traditional methods of simulation of electronic structure, such as the Hartree-Fock method, GVB, among others. This essay intends to investigate part of the mathematical tools used in the calculations of electronic structure, in order to create disruptive approaches, related to the precision or velocity of the obtainment of relevant results. The new methods are based in Computational Intelligence and concepts of Functional Analysis like Wavelets.
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Choi, Hyun-jin. "Investigation of resonant Raman scattering in type II GaAs/A1As superlattices." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365725.
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Fu, Guopeng. "INVESTIGATION ON THE STRUCTURE-PROPERTY RELATIONSHIPS IN HIGHLY ION-CONDUCTIVE POLYMER ELECTROLYTE MEMBRANES FOR ALL-SOLID-STATE LITHIUM ION BATTERIES." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1508508844968127.
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Choulis, Stylianos Athanasiou. "Investigation of GaInNAs/GaAs quantum wells and vertical-cavity surface-emitting laser structures using modulated reflectance spectroscopy." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/843776/.
Повний текст джерелаАнотація:
We investigate the electronic band structure of device relevant GaInNAs/GaAs multiple quantum wells (MQWs) and veitical-cavity surface-emitting laser (VCSEL) structures. We report photo-modulated reflectance (PR) studies under applied pressure and variable temperature that probe the influence of N-related states on the electronic structure of dilute nitrogen (N) III-V MQWs. The pressure and temperature dependence of the intersubband transitions within the MQWs is reduced by addition of N. By matching our experimental results with a theoretical model important predictions for the ground-state electron effective mass and conduction band offset as a function of N and pressure are made. We present results of angle- and temperature-dependent electro-reflectance (ER) measurements on a dilute-N GaInNAs VCSEL and show that these explain how the corresponding VCSEL device can operate over a such a wide range of temperatures. We argue that intrinsic properties of dilute-N QWs provide novel ways to design laser devices, especially in the crucial telecommunication range of wavelengths. We show how non-destructive ER and PR measurements can be used, in order to estimate the QW transition energy when it is coupled with the cavity mode (CM). The energy of the main exciton is determined by monitoring the amplitude and the phase of the PR spectra. The ER measurements are presented on the GaInNAs VCSEL described in the previous paragraph. Furthermore we present a growth characterisation study on a representative InGaAs/GaAs/AlAs/AlGaAs as-grown VCSEL structure, using PR spectroscopy as a function of position on a non-uniform wafer. We also show how temperature dependent PR and the appropriate lineshape model can be used to obtain a full picture of the relative movements between the gain and the CM over the full range of temperature. This information allows calculating the material gain in the temperature range of interest, independent from the effect of the CM and also provides an alternative method for characterising the growth, which can be applied to uniform wafers. PR and non-destructive ER can be used to identify regions suitable for fabrication into devices. For this reason modulation spectroscopy can be very useful for industry to reject wafers where good alignment between the CM and the QW does not occur and can thus save on the time consuming and expensive fabrication procedures.
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Wiengarten, Alissa Charlotte [Verfasser], Johannes [Akademischer Betreuer] Barth, and Joost [Akademischer Betreuer] Wintterlin. "Scanning tunneling microscopy investigation of structure and electronic properties of surface-confined tetrapyrrolic species / Alissa Charlotte Wiengarten. Gutachter: Johannes Barth ; Joost Wintterlin. Betreuer: Johannes Barth." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1075858275/34.
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Taylor, Jonathan W. "An experimental investigation of the lattice-magnetism interactions in rare earth and transition metal compounds." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/13758.
Повний текст джерелаАнотація:
The interaction between magnetism and the nuclear lattice is investigated experimentally, using thermal expansion, magnetostriction, specific heat, magnetisation and neutron scattering measurements. Both localised moment systems, as represented by the rare earth compounds Tb2Agln, Pd2Gdln and Cu2Gdln, as well as transition metal compounds, Ni2MnGa and V20 3 have been characterised at low temperatures. Measurements of the lattice properties are important due to the intrinsic coupling of magnetic degrees of freedom to them. The response of the lattice to magnetic order, and also to applied magnetic fields have been probed by the use of the aforementioned techniques. Such techniques allow the direct determination of the coefficient of linear thermal expansion, over a wide temperature range and the forced magnetostriclion in applied fields of 0 to 7T. Indirect determination of the spontaneous magnetostriction and the total magnetic entropy contribution via measurements of isostructural compounds further enhance the range of experimental data available. The dynamic properties are characterised by spin polarised neutron scattering measurements. The experimental results are presented and discussed. Various methods of coupling lattice and electronic degrees of freedom have been investigated. It is argued that in order to fully understand and appreciate the low temperature properties of the materials investigated such a coupling must be taken into account.
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CALZIA, VASCO. "Atomistic investigation of morphology and optoelectronic properties of bismuth sulfide nonostructures." Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266789.
Повний текст джерелаАнотація:
Nanostructured metal sulfides (MS) have attracted great interest in
recent years because of the possibility to synthesize nanoparticles from
solution and tuning their optoelectronic properties through quantum
confinement phenomena. A large number of applications have been
reported in the field of solar cells, light-emitting diodes, lithium-ion
batteries, thermoelectric devices, sensors, fuel cells and nonvolatile
memory devices. Among the large family of semiconductor sulfides,
the present Thesis is focussed on bismuthinite. The choice was motivated
by a combination of factors. Its non-toxicity, low cost synthesis
and high absorption properties make Bi2S3 a promising material for
several application, such as solid-state semiconductor-sensitized solar
cells. The intrisic anisotropy in the crystal structure of this material
facilitates the formation of elongated nanostructures, in particular
nanorods, nanoribbons, and nanowires. These structures find important
applications in many nanodevices, for example field emitters,
solar cells, and lithium-ion batteries.
On the other hand, researchers are still far from a complete understanding
of Bi2S3 properties. The colloidal synthesis of bismuthinite
nanostructures, although cheap and environmentally friendly, does
not allow a perfect control on stoichiometry and surface passivation.
The large majority of the experimental studies does not report photoluminescence
of the nanocrystals, which indicates the presence of
trap states and a low defect tolerance of the material. These facts
cause a lower efficiency of the devices based on Bi2S3 nanoparticles
with respect to anologous system based on other nanomaterials (e.g
Sb2S3 in solid-state sensitized solar cells). The absence of linear optical
data makes more difficult to investigate the electronic structure of
the material by means of spectroscopic techniques. Ab initio atomistic
simulations represent a valid alternative to get an insight on the
optoelectronic properties of bismuth sulfide. Despite some computational
work on bulk Bi2S3 is already present in literature, there are
currently no ab initio studies concerning nanostructures of this material.
Such lack of information motivates the work of the present
thesis that focuses on the investigation of morphology and electronic
properties of Bi2S3 nanocrystals.
The thesis is organized as follows. In the first chapter the main differences
and advantages of nanostructured materials over the bulk counterpart
are presented. I put the accent on metal sulfide nanocrystals,
in particular those of the Bi2S3 family (pnictogen chalcogenide) and
their application in several fields of physics, environmental science,
and engineering. A section is reserved to report the development
of elongated semiconductor nanostructures and their peculiarity with
respect to nanocrystals with lower aspect ratio.
The second chapter describes the computational and experimental
methods used in this study. The basic concepts of density functional
theory and its implementation in quantum-chemistry codes are reported.
A description of the synthesis and spectroscopic methods
used to check the validity of the theoretical predictions is also given.
For the detailed list of the basis sets, pseudopotentials, and exchangecorrelation
functionals used in each calculation I refer to the end of
Chapter 3 and 4.
Chapter 3 deals with the bulk properties of Bi2S3. Atomic and crystal
cell relaxation are performed. Also I investigated electronic properties
from the calculation of the band structure, density of states, and
efficient mass. These simulations are an important preliminary to
the study of Bi2S3 nanostructures. By comparing my results with
the previous studies present in literature it is possible to validate
the method (functionals, pseudopotentials, etc) and proceed with the
study of unexplored systems.
Chapter 4 investigates the properties of Bi2S3 nanostructures. First,
I focus on elongated nanoribbons (that are the building blocks of the
crystal structure) and study saturated and unsaturated nanocrystals
of finite size in comparison with one-dimensional infinite ones. By
means of (time-dependent) density functional theory calculations it
is demonstrated that the optical gap can be tuned through quantum
confinement with sizable effects for nanoribbons smaller than three
nanometers. A comparison with Sb2S3, shown that Bi2S3 nanostructures
have similar tunability of the band gap and a better tendency of
passivating defects at the (010) surfaces through local reconstruction.
Then, the focus shifts over ultrathin nanowires formed by the aggregation
of a small number of nanoribbons, with lateral sizes as small as
3 nm as in fact observed by transmission electron microscopy. Their
electronic properties are investigated finding that surfaces induce peculiar
1D-like electronic states on the nanowire edges that are lo- cated
300 meV above the valence band. Sulfur vacancies are also responsible
for localized states a few hundreds meV below the conduction
band. The possibility to remove the surface-induced intragap states
is further investigated by passivating the surfaces of the nanowires
with carboxylic and amine groups that are commonly employed in
colloidal synthesis. The small methylamine and acetic acid molecules
are expected to fully passivate the surfaces of the nanowires removing
the edge states and restoring a clean band gap.
Conclusions are finally reported in Chapter 5. The results of the
present Thesis provide a characterization of the energetics and optoelectronic
properties of bismuth sulfide nanostructures showing the
relevance of surface defects and suggesting a possible route for improving
optoelectronic properties of Bi2S3 nanostructures by tuning
the size of the ligand molecules.
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Bose, Peter [Verfasser], Ingrid [Akademischer Betreuer] Mertig, Wolfram [Akademischer Betreuer] Hergert, and Peter [Akademischer Betreuer] Dederichs. "Influence of the interface structure on the electronic transport in planar tunnel junctions : a first-principles investigation / Peter Bose. Betreuer: Ingrid Mertig ; Wolfram Hergert ; Peter Dederichs." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2010. http://d-nb.info/1024976270/34.
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Smykalla, Lars. "Investigation of the supramolecular self-assembly, electronic properties, and on-surface reactions of porphyrin and phthalocyanine molecules." Doctoral thesis, Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-216602.
Повний текст джерелаАнотація:
Das grundlegende Verständnis der Adsorption, der Eigenschaften, und der Wechselwirkungen von komplexen organischen Molekülen auf Festkörperoberflächen ist für die Entwicklung neuer Anwendungen in der Nanotechnologie von entscheidender Bedeutung. Die in dieser Arbeit untersuchten funktionellen Bausteine gehören zu den Porphyrinen und Phthalocyaninen. Deren Adsorption, elektronische Struktur, und Reaktionen der Moleküle auf Edelmetalloberflächen wurden mit mehreren Methoden charakterisiert, insbesondere der Rastertunnelmikroskopie, Rastertunnelspektroskopie, Röntgen-Nahkanten-Absorptions-Spektroskopie und Photoelektronenspektroskopie, welche zudem durch theoretische Simulationen unter Verwendung der Dichtefunktionaltheorie ergänzt wurden.
Tetra(p-hydroxyphenyl)porphyrin Moleküle ordnen sich durch Selbstorganisation zu verschiedenen, durch Wasserstoffbrückenbindungen stabilisierten Nanostrukturen an, welche in Abhängigkeit von dem Substratoberflächengitter untersucht wurden um das komplizierte Zusammenspiel von Molekül−Molekül und Molekül−Substrat-Wechselwirkungen bei der Selbstorganisation zu verstehen. Erhitzen der Adsorbatschichten dieses Moleküls führt zu einer schrittweisen Deprotonierung, und außerdem konnte auch ein Schalten der Leitfähigkeit einzelner Porphyrin-Moleküle durch lokale Deprotonierung mittels Spannungspulsen demonstriert werden. Eine Polymerisationsreaktion, welche auf der Ullmann-Reaktion basiert, aber direkt auf einer Oberfläche stattfindet, wurde für Kupfer-octabromotetraphenylporphyrin Moleküle, die auf Au(111) adsorbiert sind, gefunden. Nach einer thermischen Abspaltung der Bromatome von den Molekülen reagieren dabei die Radikalmoleküle bei hohen Temperaturen miteinander und bilden geordnete, kovalent gebundene Netzwerke aus. Die Bromabspaltung und die nachfolgenden Reaktionen und Veränderungen der elektronischen Struktur der Moleküle wurden ausführlich für die Substratoberflächen Au(111) sowie Ag(110) untersucht. Weiterhin, wird die Adsorption und Selbstorganisation von metall-freien Phthalocyanin-Molekülen auf einer Ag(110)-Oberfläche, und deren Selbstmetallierungsreaktion mit Silberatomen des Substrats umfassend und verständlich beschrieben. Zuletzt wurden organische Hybrid-Grenzflächen zwischen verschiedenen Metall-Phthalocyaninen untersucht, wobei ein Ladungstransfer zwischen Kobalt- und Platin-Phthalocyanin-Molekülen gefunden wurde. Dotierung gemischter Metall-Phthalocyanin-Filme durch Einlagerung von Kaliumatomen und deren selektive Adsorption im Molekülgitter führt zu einer deutlichen Veränderung der elektronischen Eigenschaften, aufgrund einer Ladungsübertragung an die Kobalt-Phthalocyanin Moleküle.
34
Vanacore, Giovanni Maria. "INVESTIGATION OF Ge SURFACE DIFFUSION AND SiGe NANOSTRUCTURES BY SPECTRO-MICROSCOPY TECHNIQUES." Phd thesis, Ecole Polytechnique X, 2011. http://tel.archives-ouvertes.fr/tel-00725427.
Повний текст джерелаАнотація:
SiGe nanostructures on crystalline Si substrates with (001) orientation are among the most studied system in condensed matter physics and nanoscience. This interest has been mainly driven by the important potential applications in opto and nano-electronic devices thanks to the improvement of the optical and electronic properties compared to bulk systems. These features come essentially from the possibility of engineering the strain field within the nanostructures using the lattice mismatch of ~ 4 % between Ge and Si and from the spatial confinement, capable of modifying the electronic band structure leading to an increase of the charge carrier mobility. It is obvious that these applications largely depend on the control of surface processes during the growth of the nanostructures, and their performance are strongly dependent on strain relaxation and dislocation injection. Besides the technological interest, the SiGe/Si(001) system has received much attention since it is also a model for understanding the fundamental processes occurring during 3D island formation and self-organization phenomena. In fact, the lattice mismatch between Ge and Si introduces a stress field which has dramatic effects on the growth process and is responsible for a number of structural and electronic phenomena. In particular, the stored elastic energy can be partially relieved by spontaneous formation of 3D objects of nanometric size on top of a pseudomorphic SiGe wetting layer. This growth mode, called Stranski-Krastanov (SK), is a way of easily forming self-assembled nanostructures, which can be used to obtain quantum confinement of charge carriers in nanoelectronics device applications. In recent years, considerable efforts have been devoted to the growth of hetero-epitaxial SiGe nanostructures with well controlled size, shape and positioning, and with defined stoichiometry and strain state. However, some aspects still need to be addressed for a complete understanding of this system, including: (i) the competition between kinetic and thermodynamic factors for island formation, (ii) the mechanisms governing the relative growth of individual nanostructures, (iii) the interplay between SiGe intermixing and strain relaxation mechanisms. In the present work, we carry out an experimental investigation of the relationship between morphology, elemental composition, strain state and electronic structure of self-assembled and lithographically defined SiGe nanostructures by means of several spectro-microscopy techniques. The Si and Ge diffusion dynamics and the self-organization phenomena during the growth of SiGe islands have been studied by Scanning Auger Microscopy (SAM) and Atomic Force Microscopy (AFM). Micro-Raman, SAM and Scanning Transmission Electron Microscopy coupled with Electron Energy Loss Spectroscopy (STEM-EELS) techniques have been used for the investigation of the interplay between strain relaxation mechanisms and SiGe intermixing in self-assembled islands. The effects of strain and composition on the electronic band structure in lithographically defined SiGe nanostructures, in layout very close to those used in prototype devices, have been characterized with nanoscale spatial resolution joining information from Tip Enhanced Raman Spectroscopy (TERS), nanofocused X-Ray Diffraction (XRD) and Energy-Filtered PhotoElectron Emission Microscopy (PEEM). The thesis is conceptually divided in two main parts: the first, to which belong Chapters 1, 2 and 3, deals with the experimental investigation of the Ge surface diffusion and of the self-organization phenomena of SiGe islands grown in a bottom-up approach; the second, including Chapters 4 and 5, is based on the experimental characterization of the strain state and of the strain-induced effects on the electronic band structure of lithographically defined SiGe nanostructures obtained in a top-down approach Chapter 1 presents an overview on the basic processes occurring during hetero-epitaxial growth of thin solid films. In the Chapter 2 the surface diffusion of Ge on a clean and C covered Si(001) surface promoted by annealing at high temperatures in UHV of pure Ge stripes is experimentally investigated by means of in-situ Scanning Auger Microscopy. The influence of a controlled carbon coverage on the Ge surface diffusion is quantitatively studied, showing that the diffusion coefficient presents a strong dependence on carbon coverage (see Fig. 1(a)). Chapter 3 deals with the experimental investigation of the growth process of self-assembled SiGe islands on Si(001) (see Fig. 1(b)). From the size and density evolution exhibited by the nucleated islands, we propose a scenario where the island growth is essentially driven by kinetic factors within a diffusion limited regime. Finally, we investigated the interplay among SiGe intermixing and plastic relaxation, showing that the surface thermal diffusion growth method leads to the formation of coherent islands (dislocation-free), as shown in Fig. 1(c), larger than those attainable by MBE and CVD. Chapter 4 presents the mapping with nanoscale resolution of strain, composition, local work function and valence band structure of lithographically defined SiGe embedded nano-stripes using TERS and Energy-Filtered PEEM (see Fig. 1(d) showing the Ge concentration mapping of the nano-stripes as obtained by PEEM analysis). In Chapter 5 are presented the first results of a direct characterization of the strain state of lithographically defined SiGe nano-ridges using the recently developed nanofocused XRD technique. The work presented in this thesis is the outcome of an experimental PhD research project developed at the Politecnico di Milano (Milano, Italy) in co-tutorship with the École Polytechnique (Paris, France) and the French Atomic Energy Commission (CEA-Saclay, France). SAM and AFM have been performed at Department of Physics of the Politecnico di Milano. Micro-Raman Spectroscopy has been carried out at the Materials Science Department of the Università Milano-Bicocca. PEEM measurements have been realized at CEA and during two standard experimental runs at the TEMPO beamline of SOLEIL Synchrotron (France). TERS and preliminary TEM analysis have been performed at the École Polytechnique, while more extensive TEM and STEM-EELS measurements have been developed at IMM-CNR in Catania. The nano-XRD experiment has been carried out during a standard experimental run at ID13 beamline of the European Synchrotron Radiation Facility (ESRF). The close collaboration with the laboratory L-NESS in Como made available the set of the lithographically-defined investigated samples. The experimental results have been exploited in close collaboration with a theory group at the Materials Science Department of the Università Milano-Bicocca for a deeper insight into the atomic level mechanisms during island growth process.
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Jacobi, Carolin Claudia Verfasser], Matthias [Akademischer Betreuer] Wuttig, and Joachim [Akademischer Betreuer] [Mayer. "The organic-metal interface : design of an inverse photoemission spectrometer for the investigation of the energy level alignment and the electronic structure / Carolin Claudia Jacobi ; Matthias Wuttig, Joachim Mayer." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1162629649/34.
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Jacobi, Carolin Claudia [Verfasser], Matthias Akademischer Betreuer] Wuttig, and Joachim [Akademischer Betreuer] [Mayer. "The organic-metal interface : design of an inverse photoemission spectrometer for the investigation of the energy level alignment and the electronic structure / Carolin Claudia Jacobi ; Matthias Wuttig, Joachim Mayer." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1162629649/34.
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Monir, Md M. "A COMPUTATIONAL INVESTIGATION OF SECTORAL ZONING OF RARE EARTH ELEMENTS (REE) IN FLUORITE." Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1438881165.
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Brumboiu, Iulia Emilia. "The Electronic Structure of Organic Molecular Materials : Theoretical and Spectroscopic Investigations." Licentiate thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-218225.
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In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively. The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure is the first step in elucidating the photodegradation process. The electronic excitations from core levels to unoccupied molecular orbitals reveal not only the empty level structure of the molecule, but provide additional information related to the chemical bonds involving a specific atom type. In this way, they represent a means of determining the chemical changes that the molecule might withstand. The electronic transitions from carbon 1s core levels to unoccupied states are explained for the unmodified PCBM by a joint theoretical (DFT) and experimental study using the near edge x-ray absorption fine structure (NEXAFS) spectroscopy. The second investigated system is the transition metal phthalocyanine with a manganese atom as the metal center. Manganese phthalocyanine (MnPc) is a single molecular magnet in which the spin switch process can be triggered by various methods. It has been shown, for instance, that the adsorption of hydrogen to the Mn center changes the spin state of the molecule from 3/2 to 1. More interestingly, the process is reversible and can be controlled, opening up the possibility of using MnPc as a quantum bit in magnetic memory devices. Up to this date, the d orbital occupation in MnPc has been under a long debate, both theoretical and experimental studies revealing different configurations. In this thesis the electronic structure of the phthalocyanine is thoroughly analysed by means of DFT and the calculated results are compared to photoelectron spectroscopy measurements. The combination of theoretical and experimental tools reveals that in gas phase at high temepratures the molecule exhibits a mixed electronic configuration. In this light, the possible control of the specific electronic state of the central metal represents an interesting prospect for molecular spintronics.
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Penny, George B. S. "High-pressure synthesis of electronic materials." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4161.
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High-pressure techniques have become increasingly important in the synthesis of ceramic and metallic solids allowing the discovery of new materials with interesting properties. In this research dense solid oxides have been synthesised at high pressures, and structural investigations have been conducted using x-ray and neutron diffraction. The perovskite LaPdO3 has been synthesised at pressures of 6{10GPa. Neutron diffraction studies have been carried out from 7{260K to investigate any structural distortions, particularly related to the possibility of charge order at low temperatures. No reduction in symmetry associated with charge ordering has been observed; the material appears to remain metallic with only one unique Pd site down to 7K. LaPdO3 adopts the GdFeO3-type Pbnm structure. The PdO6 octahedra exhibit a tetragonal distortion throughout the temperature range with a shortening of the apical Pd{O bonds of 2:5% relative to the equatorial bonds. Attempts to prepare analogues of the perovskite containing smaller rare earths have resulted in multi-phase samples, and further RPdO3 perovskites remain inaccessible although there is evidence for a small amount of the perovskite phase in the products of synthesis attempts with neodymium. Three new oxypnictide superconductors, RFeAsO1 xFx (R = Tb, Dy and Ho) have been synthesised at 7{12GPa. The materials are isostructural with other recently discovered iron arsenide superconductors and have Tc's of 52:8 K, 48:5K and 36:2K respectively, demonstrating a downturn in Tc in the series for smaller R. Systematic studies on TbFeAsO0.9F0.1 and HoFeAsO0.9F0.1 show negative values of dTc=dV in contrast to those reported for early R containing materials. Low-temperature neutron diffraction measurements on both materials, and synchrotron studies on HoFeAsO0.9F0.1 reveal no tetragonal to orthorhombic transitions as observed in early R-containing materials with lower doping levels. Magnetic reflections are evident but they are shown to be from R2O3 and RAs impurities with TN's of 5:5K for Tb2O3, 6:5K for HoAs and 1:7K < TN < 4K for Ho2O3. The implications of these results for superconductivity in the iron arsenides are discussed.
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Jonasson, L. "Computational investigations of the electronic structure of molecular actinide compounds." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/15798/.
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In this PhD thesis the electronic structure of a range of actinide compounds has been investigated using density functional theory. The reason for using DFT instead of other methods is mainly due to the size of the compounds which makes multireference calculations prohibitively expensive, but also to make comparisons with previously calculated DFT results. The first chapter presents the basic concepts of electronic structure theory and the chemical properties of the actinides and lanthanides. The theoretical foundation of DFT and the consequences of relativity are also introduced. In the second chapter the bonding in mixed MUCl6, MUCl8 2-, NpReCl8 2- and PuOsC NpReCl8 2- (M = Mo, W) systems is investigated and compared with previous work on the M2Cl6, M2C NpReCl8 2- U2Cl6 and U2C NpReCl8 2- systems. The study shows that the total bonding energy in the mixed compounds is the average of the two “pure” compounds. The third chapter deals with systems of plenary or lacunary Keggin phosphomolybdate coordination to actinide (Th), lanthanide (Ce, La, Lu) and transition metal (Hf, Zr) cations: [PMo12O40]3-, [PMo11O39]2 14-, [PMo12O40]2 6- and [PMo11O39][PMo12O40]10-. These large, highly anionic systems proved to be very challenging computationally. The main result of the study confirms that the bonding is ionic and that there are few differences in the behaviour of the transition metals. In the fourth chapter the electronic spectrum of NpO2 2+, NpO2Cl4 2- and NpO2(OH)4 2- is calculated using time dependent DFT. TDDFT has proved adequate for the uranium analogues of these systems and this extends previous work on f0 systems to f1 systems. The results show that TDDFT is in poor agreement with both experimental results and multireference calculations for these compounds. In chapter five, group 15 and 16 uranyl analogues have been investigated. For the UE2 (E = O, S, Se, Te) analogues the geometry bends for all chalcogens heavier than O. The UE2 2+ analogues remain linear all the way down group 16. In U(NCH3)2 2+ the formation of a {pi} “back bone” along the axis of the molecule was noted. The {sigma}-bonding valence MOs stabilize while the {pi} MOs are destabilized down group 15 and 16. Chapter six is a summary of the results in this thesis and an outlook on potential future work.
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Ko, Hyunjin. "Structural and electronic investigations of complex intermetallic compounds." [Ames, Iowa : Iowa State University], 2008.
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Guo, Meiyuan. "Electronic structures of transition metal complexes-core level spectroscopic investigation." Licentiate thesis, Uppsala universitet, Teoretisk kemi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-275074.
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Guo, Meiyuan. "Electronic structure investigations of transition metal complexes through X-ray spectroscopy." Doctoral thesis, Uppsala universitet, Teoretisk kemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-328072.
Повний текст джерелаАнотація:
Catalysts based on the first-row (3d) transition metals are commonly seen in chemical and biological reactions. To understand the role of the transition metal in the catalyst, the element specific technique core level spectroscopy is used to probe the electronic structure and geometric properties centered around the metal site. Different types of X-ray spectra can be applied to probe the metal 3d character orbitals involved in reactions, which make it possible to identify and characterize the reactive sites of samples in different forms. A detailed interpretation and understanding of the different X-ray spectra requires a unified method which can be used to model different types of X-ray spectra, e.g., soft and hard X-rays. In this thesis, theoretical investigations of the electronic structures of 3d transition metal complexes through X-ray spectroscopy are presented. The restricted active space method (RAS) is used to successfully reproduce different types of X-ray spectra by including all important spectral effects: multiplet structures, spin-orbit coupling, charge-transfer excitations, ligand field splitting and 3d-4p orbital hybridization. Different prototypes of molecules are adopted to test the applicability of the RAS theory. The metal L edge X-ray absorption (XAS) spectra of low spin complexes [Fe(CN)6]n and [Fe(P)(ImH)2]n in ferrous and ferric oxidation state are discussed. The RAS calculations on iron L edge spectra of these comparing complexes have been performed to fingerprint the oxidation states of metal ion, and different ligand environments. The Fe(P) system has several low-lying spin states in the ground state, which is used as a model to identify unknown species by their spectroscopic fingerprints through RAS spectra simulations. To pave the route of understanding the electronic structure of oxygen evolution complex of Mn4CaO5 cluster, the MnII(acac)2 and MnIII(acac)3 are adopted as prototypical Mn-complexes. The 3d partial fluorescence yield-XAS are employed on the Mn L-edge in solution. Combining experiments and RAS calculations, primary questions related to the oxidation state and spin state are discussed. The first application to simulate the metal K pre-edge XAS of mono-iron complexes and iron dimer using RAS method beyond the electric dipole is completed by implementing the approximate origin independent calculations for the intensities. The K pre-edge spectrum of centrosymmetric complex [FeCl6]n– ferrous state is discussed as s and a donor model systems. The intensity of the K pre-edge increases significantly if the centrosymmetric environment is broken, e:g:, when going from a six-coordinate to the four-coordinate site in [FeCl4]n. Distortions from centrosymmetry allow for 3d-4p orbital hybridization, which gives rise to electric dipole-allowed transitions in the K pre-edge region. In order to deliver ample electronic structure details with high resolution in the hard X-ray energy range, the two-photon 1s2p resonant inelastic X-ray scattering process is employed. Upon the above successful applications of one-photon iron L edge and K pre-edge spectra, the RAS method is extended to simulate and interpret the 1s2p resonant inelastic X-ray scattering spectra of [Fe(CN)6]n in ferrous and ferric oxidation states. The RAS applications on X-ray simulations are not restricted to the presented spectra in the thesis, it can be applied to the photon process of interest by including the corresponding core and valence orbitals of the sample.
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Stephan, Uwe. "Theoretical methods and results for electronic-structure investigations of amorphous carbon." [S.l. : s.n.], 1996. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10324488.
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Peschiera, Ilaria <1988>. "Structural Investigation of Antigens Using Electron Microscopy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7667/1/IlariaPeschiera_PhDtesi_structural_investigation_of_antigens_using_electron_microscopy.pdf.
Повний текст джерелаАнотація:
In this research the phenomenon of monoclonal antibodies (mAbs) cooperative bactericidal activity and the structure of the N.meningitidis antigen NadA var.3 are investigated using Transmission Electron Microscopy (TEM). The mAbs cooperativity is a mechanism that occurs when mAbs that individually show low or no bactericidal activity become bactericidal when coupled together. Revealing the structural bases of cooperative bactericidal activity is fundamental for a thorough understanding of antibody-based mechanisms of protection. Meningococcal factor H binding protein (fHbp), surface-exposed lipoprotein presents in the vaccine against serogroup B Neisseria meningitidis, Bexsero®. A comparison of the structure of the murine cooperative complex with the human cooperative one has been performed revealing a higher level of flexibility and instability of the first complex. Moreover we have been able to prove a simultaneous binding of factor H (fH) to the immune cooperative complex. The 3D structures of the cooperative complexes demonstrated that the angle formed between fHbp-antibodies is orientated only depending on the epitope location on the antigen. Non-cooperative human complexes show a structural dissimilarities compared with the cooperative couples mainly for the absence of the complex formation due to the partial epitopes overlapping, as proved by Hydrogen/Deuterium Exchange Mass Spectrometry (HDX_MS).
The NadA var. 3, the variant included in Bexsero® vaccine, structure was determined by the Cryo-Electron Microscopy (Cryo-EM) technique combined with Single Particle (SP) reconstruction method. The 3D reconstruction of NadA var.3, generated from Cryo-TEM data, shows an elongated and thin stalk decorated by a globular compact head characterized by a three-fold symmetry. Moreover the 3D EM map shows three evident points of interruption in the density of the stalk region presumably correlated with the three interruptions present in the coiled-coil periodicity of NadA var.3 the sequence. This result indicates a possible alternative mechanism of the antigen flexibility.
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Peschiera, Ilaria <1988>. "Structural Investigation of Antigens Using Electron Microscopy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7667/.
Повний текст джерелаАнотація:
In this research the phenomenon of monoclonal antibodies (mAbs) cooperative bactericidal activity and the structure of the N.meningitidis antigen NadA var.3 are investigated using Transmission Electron Microscopy (TEM). The mAbs cooperativity is a mechanism that occurs when mAbs that individually show low or no bactericidal activity become bactericidal when coupled together. Revealing the structural bases of cooperative bactericidal activity is fundamental for a thorough understanding of antibody-based mechanisms of protection. Meningococcal factor H binding protein (fHbp), surface-exposed lipoprotein presents in the vaccine against serogroup B Neisseria meningitidis, Bexsero®. A comparison of the structure of the murine cooperative complex with the human cooperative one has been performed revealing a higher level of flexibility and instability of the first complex. Moreover we have been able to prove a simultaneous binding of factor H (fH) to the immune cooperative complex. The 3D structures of the cooperative complexes demonstrated that the angle formed between fHbp-antibodies is orientated only depending on the epitope location on the antigen. Non-cooperative human complexes show a structural dissimilarities compared with the cooperative couples mainly for the absence of the complex formation due to the partial epitopes overlapping, as proved by Hydrogen/Deuterium Exchange Mass Spectrometry (HDX_MS).
The NadA var. 3, the variant included in Bexsero® vaccine, structure was determined by the Cryo-Electron Microscopy (Cryo-EM) technique combined with Single Particle (SP) reconstruction method. The 3D reconstruction of NadA var.3, generated from Cryo-TEM data, shows an elongated and thin stalk decorated by a globular compact head characterized by a three-fold symmetry. Moreover the 3D EM map shows three evident points of interruption in the density of the stalk region presumably correlated with the three interruptions present in the coiled-coil periodicity of NadA var.3 the sequence. This result indicates a possible alternative mechanism of the antigen flexibility.
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Marino, Andrea. "Ultrafast investigation of electronic and structural dynamics in photomagnetic molecular solids." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S037/document.
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La capacité de photo-commuter les propriétés physico-chimiques des matériaux fonctionnels grâce à des transitions de phase induites par la lumière, ouvre des perspectives fascinantes pour diriger un matériau vers un nouvel état hors équilibre thermique. Cependant, il est fondamental de comprendre tous les phénomènes élémentaires, habituellement cachés dans une moyenne statistique lors des transformations à l'équilibre. Les études résolues en temps représentent une approche unique pour accéder à l'évolution des différents degrés de liberté du système et connaître les processus élémentaires mis en jeu lors de la commutation macroscopique. Les matériaux à transition de spin (SCO) sont d'un intérêt particulier car ce sont des systèmes photo-réversibles. Ces matériaux sont aussi des prototypes photomagnétiques et photochromiques qui commutent entre deux états de différente multiplicité de spin, nommés bas spin (LS) et haut spin (HS). Dans ce travail de thèse, nous étudions les dynamique ultrarapides électroniques et structurales de cette classe de solides moléculaires, en soulignant l'importance d'utiliser des sondes complémentaires sensibles à différents degrés de liberté. Les commutation photo-induite entre états de spin est ultra-rapide et initialement localisée à l'échelle moléculaire, où le couplage électron-phonon active des vibrations cohérentes intramoléculaires. Un transfert d'énergie ultra-rapide de la molécule au réseau, via un couplage phonon-phonon, permet de piéger efficacement le système dans le nouvel état photo-induit. Cependant, dans les solides moléculaires, l'excès d'énergie libérée de la molécule excitée résulte dans un aspect complexe multi-échelle impliquant plusieurs degrés de liberté à des échelles de temps différentes. Dans ce travail de thèse, nous avons étudié la dynamique multi-étape hors équilibre d'un système SCO présentant une brisure de symétrie entre la phase HS et la phase intermédiaire (IP) où une mise en ordre à longue distance des états HS et LS des molécules résulte en la formation d'une onde de concentration de spin (SSCW). La diffraction des rayons X résolue en temps combinée avec des études de spectroscopie optique donnent une description complète de la dynamique hors-équilibre de la SSCW hors-équilibre en mesurant l'évolution temporelle des deux paramètres d'ordre décrivant le systèmeThe ability to photo-switch physical/chemical properties of functional materials through photo induced phase transition opens fascinating perspectives for driving the material towards new state out of thermal equilibrium. However, it is fundamental to disentangle and understand all the dynamical phenomena, otherwise hidden in statistically averaged macroscopic transformations. Arguably, time-resolved studies are unique approach to access the necessary information on the multiple degrees of freedom and elementary processes involved during the macroscopic switching. As photo-reversible molecular switches, spin crossover (SCO) materials are of particular interest. These photomagnetic and photochromic prototype materials undergo metastable photoinduced phase transition between two states of different spin multiplicity, namely low-spin (LS) and high-spin (HS). In this PhD work it will be presented the ultrafast electronic and structural dynamics of SCO molecular solids emphasizing the importance of using complementary probes sensitive to different degrees of freedom. The photoinduced spin state switching concerns initially only an ultrafast, but localized, molecular response which through strong electron-phonon coupling activates coherent intra-molecular vibrations. An ultrafast energy transfer from the molecule to the lattice, via phonon-phonon coupling, allows an efficient trapping of the system in the new photoinduced state. However in molecular solids, the excess of energy released from the absorber molecule results in a complex multi-scale aspect involving several degrees of freedom at different time scales. In this contest, we investigated the multi-step out-of equilibrium dynamics of a SCO system undergoing symmetry breaking between the HS phase and the intermediate (IP) phase where a long range ordering of HS and LS molecules results in a spin state concentration wave (SSCW), analogous to charge or spin density waves. Combined time-resolved X-ray diffraction and optical spectroscopy studies provide a complete overview of the out-of-equilibrium thermodynamics of the SSCW, investigating how the two order parameters describing the system evolve in time
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Mościcka, Katarzyna Beata. "Structural investigation of membrane proteins by Electron Microscopy." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2009. http://irs.ub.rug.nl/ppn/317.
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Afaneh, Akef. "Computational investigations of the electronic structure of molecular mercury compounds: ion-selective sensors." Springer International Publishing AG, 2012. http://hdl.handle.net/1993/30661.
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This thesis presents the basic concepts of electronic structure theory and the chemical properties of mercury. The theoretical foundation of DFT and the consequences of relativity are also introduced. The electronic structure of Hg(II) ions, [Hg(L)n(H2O)m]q (L = HO-, Cl-, HS-, S2-) has been studied. We show, in this thesis, that the charge transfer (that is calculated from the hard-soft-acid-base principle (Pearson’s principle)), the total NBO charge and the interaction energies are strongly correlated. Our studies indicate the effect of the solvent on the global electrophilicity, the charge transfer and consequently the interaction strength between Hg(II) and ligand L. The formation constants, logK, of Hg2+−complexes are calculated. The procedure that we follow in this thesis to calculate the formation constants, logK’s, are in good agreement with the extrapolated experimental values. We introduce and explain why it is important adding water molecules explicitly during the calculations of the logK. The recommended logK value of HgS is 27.2. We examined two different types of organic compounds as sensors for heavy metal ions: lumazine (Lm) and 6-thienyllumazine (TLm). We found that the simple calculation of pKa values using DFT methods and implicit solvent models failed to reproduce the experimental values. However, calculated orbital energies and gas phase acidities both indicate that the compound TLm is inherently more acidic than the parent species Lm. We demonstrate that: (1) we need to take in our consideration the population of each tautomer and conformer during the calculations of the pKa values, and (2) thienyl group has indirect effect on the acidity of the proton on N1 in the uracil ring. Last but not least, the fluorescence spectrum of the sensors (L) and their [(L)nM(H2O)m]2+ complexes (L = Lumazine (Lm) and 6-thienyllumazine (TLm) and M = Cd2+and Hg2+) are calculated using time dependent DFT (TDDFT). The results show that TDDFT is in good agreement with experimental results. This chapter provides a new concept in the design of fluorescence turn-on/off sensors that has wider applicability for other systems. Finally, we provide a summary of the works compiled in this thesis and an outlook on potential future work.October 2015
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Gross, Mason A. "An investigation of nonlinear fabry-perot structures and modulators." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/14954.
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