Dissertations / Theses: 'Electron theory of metals'

1

Yang, Xiaodong. "Effects of Electron-Phonon Interaction in Metals." Diss., Temple University Libraries, 2010. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/83903.

Full text

Abstract:

Physics
Ph.D.
Phonons and electrons are two types of excitations which are responsible for many properties of condensed matter materials. The interaction between them plays an important role in condensed matter physics. In this thesis we present some theoretical investigations of the effects due to the interactions between phonons and electrons interactions. We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high magnetic fields. The effect of the magnetic field is considered unusual, as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical frame-work which can be used to describe the effect of a magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant. The temperature-dependence of the phonon spectrum of alpha-uranium has recently been measured by Manley et al. using inelastic neutron scattering and x-ray scattering techniques. Although there is scant evidence of anharmonic interactions, the phonons were reported to show some softening of the optic modes at the zone boundary. The same group of authors later reported that an extra vibrational mode was observed to form at a temperature above 450 K. The existence of the proposed new mode is inconsistent with the usual theory of harmonic phonons, as applied to a structure composed of a monoclinic Bravais lattice with a two-atom basis. We investigate the effect that the f electron-phonon interaction has on the phonon spectrum and its role on the possible formation of a breathing mode of mixed electronic and phonon character. We examine the model by using Green’s function techniques to obtain the phonon spectral density. Some materials undergo phase transitions from a high temperature state with periodic translational invariance to a state in which the electronic charge density is modulated periodically. The wave vector of the modulation may be either commensurate or incommensurate with the reciprocal lattice vectors of the high temperature structure. In the case of an incommensurate charge density wave, the system supports phason excitation. For an incommensurate state, the new ground state has a lower symmetry than the high temperature state since the charge density does not have long-ranged periodic translational order. If the metal is ideal (with no impurities), a charge density wave should be able to slide throughout the crystal without resistance, resulting in current flow similar to that of a superconductor. The phason is an excitation of the charge density wave which is related to the collective motion of electrons. We estimate the phason density of states, and the phason contribution to the specific heat. Angle-resolved photoemission experiments have been performed on USb2, and very narrow quasiparticle peaks have been observed in a band which local spin-density approximation (LSDA) predicts to osculate the Fermi energy. The observed band is found to be depressed by 17 meV below the Fermi energy. The experimentally observed quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band which does not cross the Fermi energy is unprecedented. The kink in the quasiparticle dispersion relation is attributed to the effect of the interband self-energy involving transitions from the osculating band into a band that does cross the Fermi energy.
Temple University--Theses

APA, Harvard, Vancouver, ISO, and other styles

2

Hara, Takayuki. "A calculation of fermi energy in selected materials using doppler broadened positron annihilation spectroscopy." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/20238.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Breitkreiz, Maxim. "Transport Theory for Metals with Excitonic Instabilities." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-190697.

Full text

Abstract:

Metals with excitonic instabilities are multiband systems with significant electron-electron interaction. The electronic transport in such systems is affected by collective fluctuations of the electrons, leading to anomalous features in the measured transport coefficients. Many of these anomalies have not been well understood because the transport mechanisms in these systems tend to be rather complex. The complexity arises, on the one hand, from the multiband nature and, on the other, from the anisotropic scattering of electrons accompanied by emitting or absorbing collective fluctuations. Previous works considering scattering due to collective fluctuations have mainly focused on single-band systems, for example in the context of the normal-state transport in cuprates. The recent discovery of high-temperature superconductivity in iron pnictides has renewed the interest in multiband systems. Exploring the transport mechanisms in multiband systems, I find some interesting new aspects, which do not occur in single-band systems. In particular, anisotropic scattering in a model with electronlike and holelike Fermi surfaces can lead to a negative conductivity contribution of the minority carriers, i.e., in an electric field, the minority carriers drift in the direction opposite of what one would expect based on their charge. I show that this effect can explain a reduced magnetoresistance in connection with an enhanced Hall coefficient, which has been measured in pnictides. Of particular interest are multiband models with hot spots on the Fermi surface, in part because of their relevance for the iron pnictides. Hot spots are states with enhanced scattering and therefore reduced excitation lifetimes. In single-band systems, the hot spots are found to have a much lower contribution to the total conductivity than other parts of the Fermi surface, which leads to the so-called hot-spot structure. I show that in the multiband case, the conductivity contributions are much more isotropic around the Fermi surface so that hot spots contribute to transport with a similar strength as other parts of the Fermi surface. I discuss this effect on the basis of an approximate analytical solution of the transport problem and numerically calculate the temperature dependence of several transport coefficients. It turns out that in the nematic phase of iron pnictides, the unexpectedly strong conductivity contribution of hot spots can explain the puzzling behavior of the resistive anisotropy. I show that the experimental observations can be explained within a scenario in which the anisotropy is mainly due to the broken symmetry of the spin-fluctuation spectrum in the nematic phase. In the spin-density-wave state, strongly anisotropic scattering can arise due to the propagating magnons. Using a two-band model relevant for iron pnictides, I find that this scattering can lead to an unusual interruption of the orbital motion of electrons in the magnetic field. As a consequence, the low-field magnetoresistance is linear with an alternating sign of the slope as a function of the direction of the current. In strong magnetic fields, the interrupted orbital motion makes the system unstable, which is characterized by a drop of the resistivity to zero.

APA, Harvard, Vancouver, ISO, and other styles

4

Awad, Mohamed Khaled Hassan. "Small molecule chemisorption on metals and carbon-hydrogen and hydroxy 1 bond activation by electron hold centers: Molecular orbital theory." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054910441.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Östlin, Andreas. "Electronic structure studies and method development for complex materials." Licentiate thesis, KTH, Tillämpad materialfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118467.

Full text

Abstract:

Over the years electronic structure theory has proven to be a powerful method with which one can probe the behaviour of materials, making it possible to predict properties that are difficult to measure experimentally. The numerical tools needed for these methods are always in need of development, since the desire to calculate more complex materials pushes this field forward. This thesis contains work on both this implementational and developmental aspects. In the first part we investigate the structural properties of the 6d transition metals using the exact muffin-tin orbitals method. It is found that these elements behave similarly to their lighter counterparts, except for a few deviations. In these cases we argue that it is relativistic effects that cause this anomalous behaviour. In the second part we assess the Padé approximant, which is used in several methods where one wants to include many-body effects into the electronic structure. We point out difficulties that can occur when using this approximant, and propose and evaluate methods for their solution.

QC 20130219

APA, Harvard, Vancouver, ISO, and other styles

6

Thulasi, Sunita. "Theory of the two-dimensional airy electron gas Hartee-Fock and density-functional studies /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4111.

Full text

Abstract:

Thesis (Ph. D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 17, 2007) Vita. n following parenthesis in formula (LaTiO₃) should be subscript. Includes bibliographical references.

APA, Harvard, Vancouver, ISO, and other styles

7

Horne, Masae. "A theory of resonant x-ray scattering and electronic structure for light rare earth metals." Thesis, Keele University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401120.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Mizielinski, Matthew. "A theory of electron-hole pair excitation in the adsorption of simple atoms on metal surfaces." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436869.

Full text

Abstract:

Recent experiments have provided direct evidence for the excitation of electronhole pairs during the adsorption of atoms on metal surfaces. The excitation of electron-hole pairs is an inherently non-adiabatic process which is often ignored in standard theoretical treatments of surface phenomena, using tools such as density functional theory (DFT), as the Born-Oppenheimer approximation cannot be used. To obtain a theoretical model for the electronic excitation process it is therefore necessary to go beyond conventional methods. Previous theoretical descriptions have used a nearly-adiabatic approximation to describe electronic excitations. However, these methods have been found to fail in situations where an adsorbing atom undergoes a transition between a spin-polarised and unpolarised state. In this thesis we develop a fully non-adiabatic theory using a simple description of the adsorbate-metal interaction; the time-dependent, mean-field Newns- Anderson model. This model describes a simple electronic system in which a band of metal states interacts with a single atomic orbital, which can undergo a ‘spin-transition’. We derive expressions describing the time-dependent transfer of charge and energy between the adsorbate and surface, as well as the spectrum of electronic excitations generated. Each of these results describe the evolution of the electronic system in terms of a simple set of parameters. These results are demonstrated using a set of example parameter variations to explore the impact of variables such as adsorbate speed and the temperature of the system. A set of parameter variations describing the interaction of hydrogen isotopes with copper and silver surfaces are obtained from DFT calculations. These parameters are used to drive our model through a single approach of the adsorbate to the surface. We find the results of these calculations to be in good agreement with reported experimental results. Our conclusions, and some possible directions for further work, are summarised in the final chapter.

APA, Harvard, Vancouver, ISO, and other styles

9

Jenkins, Anne Ceri. "Applications of spin-polarised relativistic scattering theory to the calculation of the electronic properties of heavy metals and alloys." Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321408.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Li, Peng. "Novel quantum magnetic states in low dimensions." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36883062.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Li, Peng, and 李鵬. "Novel quantum magnetic states in low dimensions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36883062.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Baǧcı, V. M. Kemal Krokhin Arkadii. "Anderson localization in two-channel wires with correlated disorder DNA as an application /." [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-5204.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Janke, Svenja Maria. "Theoretical Description of Hydrogen Atom Scattering off Noble Metals." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-0028-87A3-4.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Burema, Shiri. "Inelastic Electron Tunneling Spectroscopy with the Scanning Tunneling Microscope : a combined theory-experiment approach." Thesis, Lyon, École normale supérieure, 2013. http://www.theses.fr/2013ENSL0821.

Full text

Abstract:

La Spectroscopie par Effet Tunnel Inélastique (IETS) avec un Microscope à Effet Tunnel (STM) est une nouvelle technique de spectroscopie vibrationnelle, qui permet de caractériser des propriétés très fines de molécules adsorbées sur des surfaces métalliques. Des règles de selection d’excitation vibrationnelle basées sur la symétrie ont été proposées, cependant, elles ne semblent pas exhaustives pour expliquer la totalité du mécanisme et des facteurs en jeu; elles ne sont pas directement transposables pour les propriétés d'un adsorbat et sont lourdes d'utilisation. Le but de cette thèse est donc d'améliorer ces règles de selection par une étude théorique. Un protocole de simulation de l'IETS a été développé, paramétré, et évalué, puis appliqué pour calculer des spectres IETS pour différentes petites molécules, qui sont systématiquement liées, sur une surface de cuivre. Des principes additifs de l'IETS ont été developpés, notamment concernant l’extension dans le vide de l’état de tunnel, l'activation/ quench sélectif de certains modes du aux propriétés électroniques de certains fragments moléculaires, et l'application de certaines règles d'addition de signaux IETS. De plus, des empreintes vibrationnelles par des signaux IETS ont été determinées pour permettre de différentier entre les orientations des adsorbats, la nature chimique des atomes et les isomères de structures. Une stratégie simple utilisant les propriétés de distribution de la densité électronique de la molécule isolée pour prédire les activités IETS sans des couts importants de calculs a aussi été développée. Cette expertise a été utilisée pour rationaliser et interpréter les mesures expérimentales des spectres IETS pour des métalloporphyrines et métallophtalocyanines adsorbées. Ces études sont les premières études IETS pour des molécules aussi larges et complexes. L'approche expérimentale a permis de déterminer les limitations actuelles des simulations IETS. Les défauts associés à l'identification ont été résolus en faisant des simulations d'images STM complémentaires
Inelastic Electron Tunneling Spectroscopy (IETS) with the Scanning Tunneling Microscope (STM) is a novel vibrational spectroscopy technique that permits to characterize very subtle properties of molecules adsorbed on metallic surfaces. Its proposed symmetry-based propensity selection rules, however, fail to fully capture its exact mechanism and influencing factors; are not directly retraceable to an adsorbate property and are cumbersome. In this thesis, a theoretical approach was taken to improve them. An IETS simulation protocol has been developed, parameterized and benchmarked, and consequently used to calculate IETS spectra for a set of systematically related small molecules on copper surfaces. Extending IETS principles were deduced that refer to the tunneling state’s vacuum extension, the selective activating/quenching of certain types of modes due to the moieties’ electronic properties, and the applicability of a sum rule of IETS signals. Also, fingerprinting IETS-signals that enable discrimination between adsorbate orientations, the chemical nature of atoms and structural isomers were determined and a strategy using straightforward electronic density distribution properties of the isolated molecule to predict IETS activity without (large) computational cost was developed. This expertise was used to rationalize and interpret experimentally measured IETS spectra for adsorbed metalloporphyrins and metallophthalocyanines, being the first IETS studies of this large size. This experimental approach permitted to determine the current limitations of IETS-simulations. The associated identification shortcomings were resolved by conducting complementary STM-image simulations

APA, Harvard, Vancouver, ISO, and other styles

15

Andersson, David. "From the Electronic Structure of Point Defects to Functional Properties of Metals and Ceramics." Doctoral thesis, Stockholm : Materialvetenskap, Materials Science and Engineering, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4309.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Delange, Pascal. "Many-electron effects in transition metal and rare earth compounds : Electronic structure, magnetic properties and point defects from first principles." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX040/document.

Full text

Abstract:

Le sujet de cette thèse est la théorie à partir des premiers principes de la structure électronique de matériaux présentant de fortes corrélations électroniques. D’importants progrès ont été faits dans ce domaine grâce aux implémentations modernes de Théorie de la Fonctionelle de Densité (DFT). Néanmoins, la méthode DFT a certaines limitations. D’une part, elle est faite pour décrire les propriétés de l’état fondamental mais pas des états excités des matériaux, bien que ces derniers soient également importants. D’autre part, les approximations de la fonctionnelle employées en pratique réduisent la validité de la DFT, conceptuellement exacte : en particulier elles décrivent mal les matériaux aux effets de corrélations les plus importants.Depuis les années 1990, différentes théoriques quantiques à N corps ont été utilisées pour améliorer ou compléter les simulations à base de DFT. Une des plus importantes est la Théorie du Champ Moyen Dynamique (DMFT), dans laquelle un modèle sur réseau est relié de manière auto-cohérente à un modèle plus simple d’impureté, ce qui donne de bons résultats à condition que les corrélations soient principalement locales. Nous présentons brièvement ces théories dans la première partie de cette thèse. Les progrès récents de la DMFT visent, entre autres, à mieux décrire les effets non-locaux, à comprendre les propriétés hors équilibre et à décrire de vrais matériaux plutôt que des modèles.Afin d’utiliser la DMFT pour décrire de vrais matériaux, il faut partir d’un calcul de structure électronique traitant tous les électrons au même niveau, puis appliquer une correction traitant les effets à N corps sur un sous-espace de basse énergie d’orbitales autour niveau de Fermi. La définition cohérente d’un tel sous-espace nécessite de tenir compte de la dynamique des électrons en-dehors de cet espace. Ces derniers, par exemple, réduisent la répulsion de Coulomb entre électrons dans le sous-espace. Néanmoins, combiner la DFT et la DMFT n’est pas aisé car les deux n’agissent pas sur la même observable. Dans la deuxième partie de cette thèse, nous étudions les modèles de basses énergies, comme la technique échange écranté + DMFT récemment proposée. Nous analysons l’importance de l’échange non-local et des interactions de Coulomb retardées, et illustrons cette théorie en l’appliquant aux états semi-cœur dans les métaux d10 Zn et Cd.Dans la dernière partie, nous utilisons ces méthodes pour étudier trois matériaux corrélés importants d’un point de vue technologique. Dans un premier temps, nous nous intéressons à la physique des mono-lacunes dans la phase paramagnétique du fer. De façon surprenante pour un défaut aussi simple, son énergie de formation n’a toujours pas été obtenue de manière cohérente par la théorie et l’expérience. Nous démontrons que cela est dû à de subtils effets de corrélations autour de la lacune dans la phase paramagnétique à haute température : cette phase est plus fortement corrélée que la phase ferromagnétique, où des calculs de DFT ont été faits.Dans un deuxième temps, nous étudions la transition métal-isolant dans la phase métastable VO2 B. Nous montrons que cette transition ressemble à celle entre la phase conventionnelle rutile et la phase M2 de VO2, mettant en jeu à la fois des liaisons covalentes dans les dimères et une transition de Mott sur les atomes V restants. Nous étudions également l’effet de lacunes d’oxygène sur la structure électronique de VO2.Enfin, nous proposons une technique au-delà de la DFT pour calculer le champ cristallin dans les oxydes et alliages de terres rares. Bien que l’amplitude de ce champ soit faible pour les orbitales localisées 4f des lanthanides, il est crucial pour leur caractère d’aimant permanent. En modifiant l’approximation Hubbard I pour résoudre les équations de DMFT, nous évitons une erreur d’auto-interaction faible en valeur absolue mais physiquement importante, démontrant l’importance de modèles de basse énergie correctement définis
The topic of this thesis is the first-principles theory of the electronic structure of materials with strong electronic correlations. Tremendous progress has been made in this field thanks to modern implementations of Density Functional Theory (DFT). However, the DFT framework has some limits. First, it is designed to predict ground state but not excited state properties of materials, even though the latter may be just as important for many applications. Second, the approximate functionals used in actual calculations have more limited validity than conceptually exact DFT: in particular, they are not able to describe those materials where many-electron effects are most important.Since the 1990's, different many-body theories have been used to improve or complement DFT calculations of materials. One of the most significant non-perturbative methods is Dynamical Mean-Field Theory (DMFT), where a lattice model is self-consistently mapped onto an impurity model, producing good results if correlations are mostly local. We briefly review these methods in the first part of this thesis. Recent developments on DMFT and its extensions were aimed at better describing non-local effects, understanding out-of-equilibrium properties or describing real materials rather than model systems, among others. Here, we focus on the latter aspect.In order to describe real materials with DMFT, one typically needs to start with an electronic structure calculation that treats all the electrons of the system on the same footing, and apply a many-body correction on a well-chosen subspace of orbitals near the Fermi level. Defining such a low-energy subspace consistently requires to integrate out the motion of the electrons outside this subspace. Taking this into account correctly is crucial: it is, for instance, the screening by electrons outside the subspace strongly reduces the Coulomb interaction between electrons within the subspace. Yet it is a complex task, not least because DFT and DMFT are working on different observables. In the second part of this thesis, we discuss low-energy models in the context of the recently proposed Screened Exchange + DMFT scheme. In particular, we study the importance of non-local exchange and dynamically-screened Coulomb interactions. We illustrate this by discussing semi-core states in the d10 metals Zn and Cd.In the third and last part, we use the methods described above to study the electronic structure of three fundamentally and technologically important correlated materials. First, we discuss the physics of point defects in the paramagnetic phase of bcc Fe, more precisely the simplest of them: the monovacancy. Surprisingly for such a simple point defect, its formation energy had not yet been reported consistently from calculations and experiments. We show that this is due to subtle but nevertheless important correlation effects around the vacancy in the high-temperature paramagnetic phase, which is significantly more strongly correlated than the ferromagnetic phase where DFT calculations had been done.Second, we study the metal-insulator phase transition in the metastable VO2 B phase. We show that this transition is similar to that between the conventional rutile and M2 VO2 phases, involving both bonding physics in the dimer and an atom-selective Mott transition on the remaining V atoms. Motivated by recent calculations on SrVO3, we study the possible effect of oxygen vacancies on the electronic structure of VO2.Finally, we propose a scheme beyond DFT for calculating the crystal field splittings in rare earth intermetallics or oxides. While the magnitude of this splitting for the localized 4f shell of lanthanides does not typically exceed a few hundred Kelvin, it is crucial for their hard-magnetic properties. Using a modified Hubbard I approximation as DMFT solver, we avoid a nominally small but important self-interaction error, stressing again the importance of carefully tailored low-energy models

APA, Harvard, Vancouver, ISO, and other styles

17

Sears, John Steven. "Minimalistic Descriptions of Nondynamical Electron Correlation: From Bond-Breaking to Transition-Metal Catalysis." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19807.

Full text

Abstract:

Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.
Committee Chair: C. David Sherrill; Committee Member: Jean-Luc Bredas; Committee Member: Mostafa El-Sayed; Committee Member: Peter J. Ludovice; Committee Member: Thomas Orlando.

APA, Harvard, Vancouver, ISO, and other styles

18

Pan, Cheng-Ta. "Electron energy loss spectroscopy of graphene and boron nitride with impurities or defects in the transmission electron microscope." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/electron-energy-loss-spectroscopy-of-graphene-and-boron-nitride-with-impurities-or-defects-in-the-transmission-electron-microscope(c5e574fb-fca6-4ccb-9ebc-60a3ba5c345b).html.

Full text

Abstract:

The two-dimensional material graphene possesses many impressive properties such asextraordinary carrier mobility, mechanical stiffness and optical transmittance. However,the properties of pristine graphene do not always complement the requirements of applications. Of particular interest, a band gap is needed for electronic logic devices. Recent research shows that using few-layer hexagonal boron nitride as a substrate for graphene-based electronic devices can open a band gap in graphene. Also, introducing impurities such as hydrogen atoms, transition metals or silicon atoms on or within graphene can control the electronic properties according to recent studies. Furthermore, ion irradiation is an alternative option to tailor the properties of graphene by introducing defects. In this thesis, pristine, impure or defective graphene and few-layer boron nitride were characterised by scanning transmission electron microscopy (STEM) and electron energy loss (EEL) spectroscopy. Through STEM and EEL spectroscopy, lattice structures and electronic properties of these two-dimensional materials could be investigated at the atomic scale. This thesis focuses on the frontier studies of theoretical and experimental EEL spectroscopy of graphene and few-layer boron nitride with impurities. In the EEL spectra of pristine graphene and boron nitride two prominent peaks were observed, which are attributed to the plasmon excitations of π- and π+σ-electrons. By introducing impurities such as hydrogen adatoms on graphene and substitutional oxygen and carbon atoms within single-layer boron nitride, our experimental and simulated EEL spectra show that their π-plasmon peaks are modified. The concentrations of these impurities were then evaluated via EEL spectra and atomic-resolution images. If other impurities, such as various transition metals and silicon atoms, are introduced on or within single-layer graphene, our simulated EEL spectra demonstrate that the geometry of these impurity clusters affects the π-plasmon peak in graphene and some impurities even enhance it. Finally, experiments on in-situ transmission electron microscopy and ex-situ STEM and Raman spectroscopy were conducted to investigate ion irradiated graphene. Many topological defects were, for the first time, observed in atomic-resolution STEM images of ion irradiated graphene. Simulated EEL spectra of defective graphene are also reported, which suggests that corrugations and dangling bonds in defects can modify out-of-plane EEL spectra and introduce intraband transitions, respectively.

APA, Harvard, Vancouver, ISO, and other styles

19

Dednam, Wynand. "Atomistic simulations of competing influences on electron transport across metal nanocontacts." Thesis, Universidad de Alicante, 2019. http://hdl.handle.net/10500/26155.

Full text

Abstract:

In our pursuit of ever smaller transistors, with greater computational throughput, many questions arise about how material properties change with size, and how these properties may be modelled more accurately. Metallic nanocontacts, especially those for which magnetic properties are important, are of great interest due to their potential spintronic applications. Yet, serious challenges remain from the standpoint of theoretical and computational modelling, particularly with respect to the coupling of the spin and lattice degrees of freedom in ferromagnetic nanocontacts in emerging spintronic technologies. In this thesis, an extended method is developed, and applied for the first time, to model the interplay between magnetism and atomic structure in transition metal nanocontacts. The dynamic evolution of the model contacts emulates the experimental approaches used in scanning tunnelling microscopy and mechanically controllable break junctions, and is realised in this work by classical molecular dynamics and, for the first time, spin-lattice dynamics. The electronic structure of the model contacts is calculated via plane-wave and local-atomic orbital density functional theory, at the scalar- and vector-relativistic level of sophistication. The effects of scalar-relativistic and/or spin-orbit coupling on a number of emergent properties exhibited by transition metal nanocontacts, in experimental measurements of conductance, are elucidated by non-equilibrium Green’s Function quantum transport calculations. The impact of relativistic effects during contact formation in non-magnetic gold is quantified, and it is found that scalar-relativistic effects enhance the force of attraction between gold atoms much more than between between atoms which do not have significant relativistic effects, such as silver atoms. The role of non-collinear magnetism in the electronic transport of iron and nickel nanocontacts is clarified, and it is found that the most-likely conductance values reported for these metals, at first- and lastcontact, are determined by geometrical factors, such as the degree of covalent bonding in iron, and the preference of a certain crystallographic orientation in nickel.
Physics
Ph. D. (Physics)

APA, Harvard, Vancouver, ISO, and other styles

20

D'Acchioli, Jason S. "On the nature of the electronics structure of metal-metal quadruply bonded complexes." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1126621699.

Full text

Abstract:

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xii, 286 p.; also includes graphics (some col.). Includes bibliographical references (p. 273-286). Available online via OhioLINK's ETD Center

APA, Harvard, Vancouver, ISO, and other styles

21

Giesbrecht, Garth Ronald. "Amidophosphine complexes of electron-poor metals." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27147.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Brett, Constance M. "Investigation of the structure and bonding of metal complexes through the use of density functional theory." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1118688725.

Full text

Abstract:

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xxxi, 309 p.; also includes graphics Includes bibliographical references. Available online via OhioLINK's ETD Center

APA, Harvard, Vancouver, ISO, and other styles

23

Souza, de Almeida Jailton. "Designing and Tuning the Properties of Materials by Quantum Mechanical Calculations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6923.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Kokott, Sebastian. "First-principles Investigation of Small Polarons in Metal Oxides." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19535.

Full text

Abstract:

Ein limitierender Faktor der Leitfähigkeit ist die Wechselwirkung der Ladungsträger mit polaren Phononenmoden; das resultierende Quasiteilchen wird als Polaron bezeichnet. Die Stärke der Elektron-Phonon (el-ph)-Wechselwirkung bestimmt die Stärke der Lokalisierung des Polarons, die z.B. die Charakteristik der Temperaturabhängigkeit der Mobliltät definiert. Wir fokussieren uns auf Metalloxide mit starker (el-ph)-Kopplung, bei der sich kleine Polaronen bilden. Die Dichtefunktionaltheorie wird häufig für zur Simulation von Polaronen verwendet. Jedoch treten hierbei zwei Schwierigkeiten auf: Die Sensitivität der berechneten Eigenschaften in Abhängigkeit der Fehler im Austausch-Korrelations (XC)-Funktional und der Effekt der endlichen Superzellgröße. Beide Probleme werden in dieser Arbeit untersucht. Die Polaroneneigenschaften werden auf einer modifizierten Potentialoberfläche (PES) berechnet. Durch Variierung des Anteils der exakten Austauschenergie im hybriden HSE-Funktional zeigen wir, dass das modifizierte PES-Modell deutlich die Abhängigkeit der Polaroneneigenschaften vom XC-Funktional reduziert. Basierend auf dem Potential der el-ph-Kopplung von Pekar leiten wir das korrekte elastische langreichweitige Verhalten des Polarons und darauf aufbauend eine Korrektur für den Fehler durch die endliche Superzellgröße her. Diese Erkenntnisse werden durch ausgiebige Tests an MgO und Rutil TiO2 überprüft. Die oben beschriebene Methode wird zur Untersuchung des Einflusses der Kristallstruktur auf die Bildung von Polaronen in Rutil und Anatas TiO2 und in der β- und κ-Phase von Ga2O3 angewendet. Während in Rutil nur kleine Elektronpolaronen stabil sind, finden wir in Anatas nur stabile Lochpolaronen. Hingegen existieren in beiden Phasen von Ga2O3 nur stabile Lochpolaronen, jedoch mit deutlich unterschiedlichen Bindungsenergien. Dadurch kann durch Verwendung unterschiedlicher Kristallstrukturen Eigenschaften wie Leitfähigkeit und Mobilität der Ladungsträger beeinflusst werden.
An important factor limiting the conductivity is the interaction of the charge carrier with polar phonon modes. Such a phonon-dressed charge carrier is called polaron. The strength of the electron-phonon (el-ph) interaction determines the localization of the polaron, which in turn e.g. defines its characteristic temperature dependence for the charge-carrier mobility. We focus on metal oxides with strong el-ph coupling, where small polarons are formed. Density-functional theory is often used for calculating properties of polarons. However, there are two challenges: sensitivity of the calculated properties to the errors in exchange-correlation (XC) treatment and finite-size effects in supercell calculations. In this work, we develop an approach that addresses both challenges. The polaron properties are obtained using a modified neutral potential-energy surface (PES). By changing the fraction of exact exchange in the hybrid HSE functional we show that the modified PES model significantly reduces the dependence of the polaron properties on the XC functional. Based on Pekar's potential for the long-range el-ph coupling, we derive the proper elastic long-range behavior of the polaron and a finite-size correction for the polaron properties. These findings are proofed by an extensively test for rock salt MgO and rutile TiO2. Finally, the approach is used to investigate the influence of the crystal structure on the polaron properties for rutile and anatase TiO2, as well as for the monoclinic β- and orthorhombic κ-phase of Ga2O3. While in rutile TiO2 only small electron polarons are stable, only small hole polarons are found in anatase. Further, small hole polarons exist in both Ga2O3 polymorphs but have significantly different binding energies. Thus, we conclude that growing crystals of the same material but with different structure can be used to manipulate conductivity and charge-carrier mobility.

APA, Harvard, Vancouver, ISO, and other styles

25

Sinha, Roy Rajarshi. "Ab initio simulation of optical properties of noble-metal clusters." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0017/document.

Full text

Abstract:

L'intérêt de la recherche fondamentale pour les morceaux nanométriques de métaux nobles est principalement dû à la résonance localisée des plasmons de surface (LSPR) dans l'absorption optique. Différents aspects, liés à la compréhension théorique de la LSPR dans le cas de clusters de métaux nobles de taille dite intermédiaire, sont étudiés dans ce manuscrit. Afin d'avoir une vision plus large nous utilisons deux approches : l'approche électromagnétique classique et le formalisme ab initio en temps réel de la théorie de la fonctionnelle de la densité dépendant du temps (RT-TDDFT). Une comparaison systématique et détaillée de ces deux approches souligne et quantifie les limitations de l'approche électromagnétique lorsqu'elle est appliquée à des systèmes de taille quantique. Les différences entre les excitations plasmoniques collectives et celles impliquant les électrons d, ainsi que leurs interactions, sont étudiées grâce au comportement spatial des densités correspondantes. Ces densités sont obtenues en appliquant une transformée de Fourier dans l'espace à la densité obtenue par les simulations DFT utilisant une perturbation delta-kick. Dans ce manuscrit, des clusters de métaux nobles nus et protégés par des ligands sont étudiés. En particulier, motivé par de récents travaux sur les phénomènes d'émergence de plasmon, l'étude par TD-DFT de nano-alliages Au-Cu de taille tout juste inférieure à 2nm à fourni de subtiles connaissances sur les effets d'alliages sur la réponse optique de tels systèmes
The fundamental research interest in nanometric pieces of noble metals is mainly due to the localized surface-plasmon resonance (LSPR) in the optical absorption. Different aspects related to the theoretical understanding of LSPRs in `intermediate-size' noble-metal clusters are studied in this thesis. To gain a broader perspective both the real-time \ai formalism of \td density-functional theory (RT-TDDFT) and the classical electromagnetics approach are employed. A systematic and detailed comparison of these two approaches highlights and quantifies the limitations of the electromagnetics approach when applied to quantum-sized systems. The differences between collective plasmonic excitations and the excitations involving $d$-electrons, as well as the interplay between them are explored in the spatial behaviour of the corresponding induced densities by performing the spatially resolved Fourier transform of the time-dependent induced density obtained from a RT-TDDFT simulation using a $\delta$-kick perturbation. In this thesis, both bare and ligand-protected noble-metal clusters were studied. In particular, motivated by recent experiments on plasmon emergence phenomena, the TDDFT study of Au-Cu nanoalloys in the size range just below 2~nm produced subtle insights into the general effects of alloying on the optical response of these systems

APA, Harvard, Vancouver, ISO, and other styles

26

Taillefer, L. "Spin fluctuations in itinerant electron ferromagnets." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372917.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Zheng, Pengyuan. "Electron Scattering at Surfaces and Interfaces of Transition Metals." Thesis, Rensselaer Polytechnic Institute, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10010793.

Full text

Abstract:

The effect of surfaces on the electron transport at reduced scales is attracting continuous interest due to its broad impact on both the understanding of materials properties and their application for nanoelectronics. The size dependence of for conductor?s electrical resistivity ? due to electron surface scattering is most commonly described within the framework of Fuchs and Sondheimer (FS) and their various extensions, which uses a phenomenological scattering parameter p to define the probability of electrons being elastically (i.e. specularly) scattered by the surface without causing an increase of ? at reduced size. However, a basic understanding of what surface chemistry and structure parameters determine the specularity p is still lacking. In addition, the assumption of a spherical Fermi surface in the FS model is too simple for transition metals to give accurate account of the actual surface scattering effect. The goal of this study is to develop an understanding of the physics governing electron surface/interface scattering in transition metals and to study the significance of their Fermi surface shape on surface scattering. The advancement of the scientific knowledge in electron surface and interface scattering of transition metals can provide insights into how to design high-conductivity nanowires that will facilitate the viable development of advanced integrated circuits, thermoelectric power generation and spintronics. Sequential in situ and ex situ transport measurements as a function of surface chemistry demonstrate that electron surface/interface scattering can be engineered by surface doping, causing a decrease in the ?. For instance, the ? of 9.3-nm-thick epitaxial and polycrystalline Cu is reduced by 11-13% when coated with 0.75 nm Ni. This is due to electron surface scattering which exhibits a specularity p = 0.7 for the Cu-vacuum interface that transitions to completely diffuse (p = 0) when exposed to air. In contrast, Ni-coated surfaces exhibit partial specularity with p = 0.3 in vacuum and p = 0.15 in air, as Cu2O formation is suppressed, leading to a smaller surface potential perturbation and a lower density of localized surface states, yielding less diffuse electron scattering. The localized surface density of states (LDOS) at the Fermi level N(Ef) as a primary parameter determining the surface scattering specularity is further confirmed by a different surface dopant. In particular, the measured sheet resistance of 9-25-nm-thick epitaxial Cu(001) layers increases when coated with dTi = 0.1-4.0 monolayers (ML) of Ti, but decreases again during exposure to 37 Pa of O2. The corresponding changes in ? are a function of dCu and dTi and are due to a transition from partially specular electron scattering at the Cu surface to completely diffuse scattering at the Cu-Ti interface, and the recovery of surface specularity as the Ti is oxidized. X-ray reflectivity and photoelectron spectroscopy indicate the formation of a 0.47?0.03 nm thick Cu2O surface layer on top of the TiO2-Cu2O during air exposure, while density functional calculations of TiOx cap layers as a function of x = 0-2 and dTi = 0.25-1.0 ML show a reduction of N(Ef) by up to a factor of four. This reduction is proposed to be the key cause for the recovery of surface specularity and results in electron confinement and channeling in the Cu layer upon Ti oxidation. Transport measurements at 293 and 77 K confirm the electron channeling and demonstrate the potential for high-conductivity metal nanowires by quantifying the surface specularity parameter p = 0.67?0.05, 0.00?0.05, and 0.35?0.05 at the Cu-vacuum, Cu-Ti, and Cu-TiO2 interfaces. In order to determine the effect of the Fermi surface shape on the size effect, experimental and simulation results are combined to study how the resistivity changes with film thickness dw on monocrystalline W layers with different surface orientation, W(001) and W(110). As the first step of the experiments, the growth of epitaxial W(001) layers on MgO(001) substrates by ultra-high vacuum magnetron sputtering is studied, in order to obtain an alternative W layer orientation in addition to the well-known growth of epitaxial W(011) on Al2O3 substrates. X-ray diffraction ?-2? scans, ?-rocking curves, and pole figures show that 5-400 nm thick W(001) layers grown at Ts = 900 ?C are monocrystalline with a relaxed lattice constant of 3.167?0.001 nm, as determined from high resolution reciprocal space mapping. The magnitude of the residual in-plane compressive strain decreases from -1.2?0.1% to 0.1?0.1% with increasing dw. This is attributed to the glide of threading dislocations which increases the average misfit dislocation length, causing relaxation of the stress associated with differential thermal contraction. X-ray reflectivity measurements indicate smooth surfaces with a root-mean-square surface roughness ?1.0 nm and a roughness exponent of 0.38 for dw below 20 nm. Secondly, the effect of surface roughness on surface scattering is investigated to ensure its contribution to the resistivity size effect is properly included when comparing W films grown on different substrates. In fact it is found the ? of in situ annealed 4-20 nm thick epitaxial W(001) layers grown on MgO(001) samples show weaker dw dependence than that of unannealed samples in vacuum and air at both 295 and 77 K although completely diffuse surface scattering are present on both sets of films. No significant change in the structural quality of the samples after annealing is observed for d ? 20 nm. While a combination of X-ray reflectivity and Atomic Force Microscope study on surface morphology shows flatter surface mounds after annealing. Consequently, in situ annealing treatment is carried out on both epitaxial W(110) and W(001) from dw =4-320 nm to obtain surface with comparable rms roughness and lateral correlation length. Thus the ? increase due to the surface roughness is estimated in similar degree for the two types of films. Finally, a transport model for thin films with anisotropic Fermi surfaces is presented, which includes the effect of electron surface scattering. Simulations done using the calculated W Fermi surface show the resistivity ? to be 1.15-2.23 and 1.21-3.14 times larger than that of bulk W for (011) and (001) oriented thin films, respectively at a layer thickness d = 37.5- 3.75 nm, indicating an orientation dependent surface scattering effect on ?. The resistivity of epitaxial W(110) increases from 5.77?0.03 to 13.24?0.24 ??-cm as d decreases from 320 to 5.7 nm, but increases stronger for epitaxial W(001) from ? = 5.77?0.03 to 24.42?0.58 ??-cm for d = 320 and 4.5 nm. This orientation dependence is quantified with a different effective mean free path lambda(110) = 18.5?0.3 nm vs lambda(001) = 33?0.4 nm at 295 K by fitting using ? vs t with the Fuchs-Sondheimer (FS) model for spherical Fermi surfaces since their surface scattering is found completely diffuse by sequential in situ and ex situ electron transport measurements. Similarly, the ? from simulation can be fitted to obtain another set of lambda(110) and lambda(001) . The ratio lambda(110)/lambda(001) = 0.57?0.01 from simulations, in good agreement with 0.56?0.01 from experiment. The orientation dependent size effect is the result of (1) the projected Fermi surface area along the surface normal and (2) the rate of electrons approaching the surfaces due to the anisotropic electron Fermi velocity distribution along different directions.

APA, Harvard, Vancouver, ISO, and other styles

28

Thetford, Roger. "Theory of defect interactions in metals." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:f6a8f36e-4d17-4834-a4b5-5ce2de9aab11.

Full text

Abstract:

The static relaxation program DEVIL has been updated to use N-body Finnis-Sinclair potentials. Initial calculations of self-interstitial and monovacancy formation energies confirm that the modified program is working correctly. An extra repulsive pair potential (constructed to leave the original fitting unaltered) overcomes some deficiencies in the published Finnis-Sinclair potentials. The modified potentials are used to calculate interstitial energies and relaxations in the b.c.c. transition metals vanadium, niobium, tantalum, molybdenum and tungsten. Further adaptation enables DEVIL to model dislocations running parallel to any lattice vector. Periodic boundary conditions are applied in the direction of the dislocation line, giving an infinite straight dislocation. The energies per unit length of two different dislocations are compared with experiment. A study of migration of point defects in the perfect lattice provides information on the mobility of interstitials and vacancies. The possible reorientation of split dumbbell interstitials in a migration step comes under scrutiny. The total energy needed to form and migrate an interstitial is compared with that required for a vacancy. The interaction between point defects and dislocations is studied in detail. Binding energies for both sclf-intcrstitials and monovacancies at edge dislocations are calculated for the five metals mentioned above. Formation energies of the point defects in the neighbourhood of the edge dislocation are calculated for niobium, and the extent of the regions from which the defects are spontaneously absorbed are found. For split dumbbell interstilials, the size and shape of the absorption region depends on the orientation of the dumbbell. Migration of both interstitials and vacancies into the absorption zone is studied; the presence of the dislocation has a particularly dramatic effect on vacancy migration. The results on absorption zones are related to the dislocation sink strengths vital in radiation damage theory.

APA, Harvard, Vancouver, ISO, and other styles

29

Shaikh, Yasin Shadi. "Electron spin resonance in low-dimensional spin chains and metals." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-38273.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Sugimoto, Koudai. "Theoretical Study of Electron Dynamics in Multi-Orbital Antiferromagnetic Metals." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199089.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Olson, Ryan Michael. "Electron correlation theory and practice /." [Ames, Iowa : Iowa State University], 2007.

Find full text

APA, Harvard, Vancouver, ISO, and other styles

32

McNeil, Brian W. J. "Theory of free-electron lasers." Thesis, Heriot-Watt University, 1987. http://hdl.handle.net/10399/1057.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Deshpande, Amit Anand. "Improved understanding of metal cutting based on slip-line field theory." Diss., Wichita State University, 2012. http://hdl.handle.net/10057/5576.

Full text

Abstract:

This dissertation consists of three papers, which describe a new capability for deriving slip-line fields (SLFs) from results of finite element analyses, and its application to the problem of metal cutting. The first paper describes the new SLF generation capability, that uses the stress components obtained from FE analysis (which already satisfy the equations of equilibrium) to obtain the first and second directions of maximum shear stress, the streamlines of which are the slip-lines. This new capability for slip-line field generation has been validated using the problem of compression of a plate between rough platens and there is an exact match between the slip-lines generated from FEA results and the analytical slip-line solution.. This study also shows the importance of alignment of the mesh with the velocity discontinuities in order to capture them accurately, as pointed out by various researchers. In the next chapter, the reason the hydrostatic pressure around the cutting edge in machining is much lower than that under an indenter, has been investigated by comparing the machining process with flat punch indentation. Using finite element simulations of flat punch indentation, it is shown that for confinement ratios above the critical value, the field is that given by Prandtl for flat punch indentation. But for confinement ratios less than the critical value, the indentation field changes to a ‘S’ shaped shear plane field which is similar to that in machining. The analogy with machining is made clear using finite element simulation of the initial contact between the workpiece and a tool with a rake angle of 0.05°. It is found that the slip line field is initially an indentation field. As the contact length increases, the field switches over to the ‘S’ shaped shear plane field at the exact confinement ratio (8.59) given by Chakrabarty (1987), to within the resolution of the mesh. This makes it clear that the ratio of the depth of cut to the contact length between the tool and the chip is the confinement ratio in machining. As the length vii of contact increases further, the contact pressure is observed to decrease. In metal cutting, the contact length is typically larger than the uncut chip thickness, making the confinement ratio less than one. Since the confinement ratio is very small compared to that in indentation, the hydrostatic pressure observed at the cutting tool tip is much smaller compared to that under the indenter. The new slip-line field generation capability is then applied to metal cutting. A new slip-line field model is developed for machining with tools having a finite cutting edge radius. The slip-line field model is based on the results of finite element simulations carried out under different conditions of friction, rake angle, and the ratio of the uncut chip thickness to the cutting edge radius ratio. It is shown that there exists a Dead Metal Zone (DMZ) for all non-zero values of sticking friction coefficient (m>0). For m<1, it is clearly shown that the plastic deformation originating from the lower boundary of the DMZ reaches the free surface of the chip forming a Primary Shear Zone (PSZ). At point A on the free surface, the width of the PSZ is zero making it a pressure singularity.
Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Industrial Engineering

APA, Harvard, Vancouver, ISO, and other styles

34

Nunes, A. C. "The theory of uranium impurities in metals." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375291.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Xia, Tingkang. "Topics in the theory of granular metals /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487686243822318.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Hannah, P. H. "The band structures of simple metals, transition metals, noble metals and their alloys, probed by X-ray excited Auger- and photo-electron spectroscopy." Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356279.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Dalgarno, B. G. "The determination of metals in water by electron spin resonance spectroscopy." Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372989.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Mäkinen, A. (Ari). "Experimental spectroscopic studies of metals with electron, ion, and optical techniques." Doctoral thesis, University of Oulu, 2014. http://urn.fi/urn:isbn:9789526203140.

Full text

Abstract:

Abstract In this thesis, different spectroscopic methods are used for studying metals. Electron spectroscopy is applied for the study of binding energy shifts between atomic vapor and solid metals. Photoionization and Auger decay of high temperature aluminum vapors are investigated. Ionization of atomic chromium metal vapor by light absorption is studied with synchrotron radiation and time-of-flight ion mass spectroscopy. Optical spectroscopy is used for studying light emission from electric arc furnace plasma in experimental apparatuses developed during this work. Experimental techniques and sample preparation methods are presented
Original papers The original publications are not included in the electronic version of the dissertation. Huttula, M., Jänkälä, K., Mäkinen, A., Aksela, H., & Aksela, S. (2008). Core shell electron spectroscopy on high temperature vapors: 2s photoionization and Auger decay of atomic aluminium. New Journal of Physics, 10(1), 13009. https://doi.org/10.1088/1367-2630/10/1/013009 Huttula, M., Partanen, L., Mäkinen, A., Kantia, T., Aksela, H., & Aksela, S. (2009). KLL Auger decay in free aluminum atoms. Physical Review A, 79(2). https://doi.org/10.1103/physreva.79.023412 Aksela, S., Kantia, T., Patanen, M., Mäkinen, A., Urpelainen, S., & Aksela, H. (2012). Accurate free atom–solid binding energy shifts for Au and Ag. Journal of Electron Spectroscopy and Related Phenomena, 185(8–9), 273–277. https://doi.org/10.1016/j.elspec.2012.05.007 Mäkinen, A., Patanen, M., Aksela, S., & Aksela, H. (2012). Atom-solid 3p level binding energy shift of transition metals Cr, Mn, Fe, Co, and Ni. Journal of Electron Spectroscopy and Related Phenomena, 185(12), 573–577. https://doi.org/10.1016/j.elspec.2012.12.006 Mäkinen, A., Niskanen, J., & Aksela, H. (2012). Relative photoionization cross section of Cr atoms in the valence region. Physical Review A, 85(5). https://doi.org/10.1103/physreva.85.053411 Mäkinen, A., Niskanen, J., Tikkala, H., & Aksela, H. (2013). Optical emission from a small scale model electric arc furnace in 250–600 nm region. Review of Scientific Instruments, 84(4), 43111. https://doi.org/10.1063/1.4802833

APA, Harvard, Vancouver, ISO, and other styles

39

Chatterjee, Sayandev. "Cooperative Two-Electron Reagents of Lower Transition Metals of Group 10." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250266435.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Mäkinen, A. (Ari ). "Experimental spectroscopic studies of metals with electron, ion, and optical techniques." Doctoral thesis, University of Oulu, 2014. http://urn.fi/urn:isbn:9789526203149.

Full text

Abstract:

Abstract In this thesis, different spectroscopic methods are used for studying metals. Electron spectroscopy is applied for the study of binding energy shifts between atomic vapor and solid metals. Photoionization and Auger decay of high temperature aluminum vapors are investigated. Ionization of atomic chromium metal vapor by light absorption is studied with synchrotron radiation and time-of-flight ion mass spectroscopy. Optical spectroscopy is used for studying light emission from electric arc furnace plasma in experimental apparatuses developed during this work. Experimental techniques and sample preparation methods are presented.

APA, Harvard, Vancouver, ISO, and other styles

41

Pearson, David A. "Theory of ballistic electron emission microscopy /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952664.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Durivage, Jason Curtis. "Ligand Effects on Metal-Metal Bonding: Photoelectron Spectroscopy and Electronic Structure Calculations of Dimetal Paddlewheel Complexes." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145427.

Full text

Abstract:

Paddlewheel complexes are molecules in which two interacting metal atoms are bridged by four chelating ligands. This class of complexes has a large range of electronic variability while keeping a rigid geometric structure. This variability has led to their use as catalysts, strong reductants, anti-tumor agents, and electron transfer agents. This dissertation examines the effects of changing both the dimetal core and the surrounding ligands on the electronic structure properties of the paddlewheel complexes. Examination of Bi₂(O₂CCF₃)₄, a p-orbital dimetal paddlewheel complex, provided a way to probe the orbitals that are important in metal-ligand σ bonding. The b(1g) and b(2u) ligand orbitals of Bi₂(O₂CCF₃)₄ have no dimetal orbital counterpart, unlike the case of the more familiar d-orbital dimetal paddlewheel complexes such as Mo₂(O₂CCF₃)₄. This had the effect of destabilizing these ligand orbitals compared to d-orbital paddlewheel complexes. The ligand a1g orbital in Bi₂(O₂CCF₃)₄ was also destabilized due to nodal differences in the dimetal σ orbital. The unusual coincidence of Mo-Mo σ and π ionization bands is due to a greater amount of ligand character in the Mo-Mo σ orbital compared to its ditungsten analogue, which has separate ionization bands for the σ and π bonds. A series of p-substituted dimolybdenum tetrabenzoate complexes was synthesized and studied by photoelectron spectroscopy in order to further examine the delocalization of electron density from the metals to the ligands in these complexes. A 0.89 eV shift in the δ ionization band was observed from Mo₂(O₂CPh-p-OMe) ₄ and Mo₂(O₂CPh-p-CF₃)₄. Overlap effects are the major factor causing the shift in the δ bond ionization, as the calculated charges on the molybdenum and oxygen atoms did not vary significantly on change of substituent. Molybdenum and tungsten guanidinate paddlewheel complexes have promise as good reducing agents due to their extremely low ionization energies. The solubility of the complexes poses a problem for their widespread adoption for use as reducing agents. Alkyl substituents were added to the complexes to increase their solubility. W₂(TEhpp)₄ was observed to have the lowest ionization energy at 3.71 eV (vertical ionization) and 3.40 eV (onset ionization) of any molecule yet prepared.

APA, Harvard, Vancouver, ISO, and other styles

43

Thompson, Jeffrey M. "The electronic structure and spectra of small metal clusters /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9648.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Benthem, Klaus van. "Electron microscopic investigations of the bonding behaviour of metals on SrTiO3 substrates." Stuttgart : Max-Planck-Inst. für Metallforschung, 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965395014.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Wright, Helen Elizabeth. "Studies of the electronic structure of metals and alloys by electron spectroscopy." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329397.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Hide, A. K. "Spin resolved electron spectroscopy studies of induced ferromagnetism in 4d transition metals." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263868.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Andrew), Patterson Alex A. (Alex. "Theory and modeling of field electron emission from low-dimensional electron systems." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115640.

Full text

Abstract:

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 253-271).
While experimentalists have succeeded in fabricating nanoscale field electron emitters in a variety of geometries and materials for use as electron sources in vacuum nanoelectronic devices, theory and modeling of field electron emission have not kept pace. Treatments of field emission which address individual deviations of real emitter properties from conventional Fowler-Nordheim (FN) theory, such as emission from semiconductors, highly-curved surfaces, or low-dimensional systems, have been developed, but none have sought to treat these properties coherently within a single framework. As a result, the work in this thesis develops a multidimensional, semiclassical framework for field emission, from which models for field emitters of any dimensionality, geometry, and material can be derived. The effects of quantum confinement and emitter tip geometry on the properties of emission were investigated by utilizing the framework to derive models for: i) a highly-curved, nanoscale, metal emitter tip; ii) a bulk silicon emitter with a surface quantum well formed due to electric field penetration and a mechanism that limits the maximum conduction band emitted current density (ECD) to the bulk flux density supply; and iii) a cylindrical silicon nanowire emitter. Results from a highly-curved, nanoscale, metal emitter tip reveal that despite signicant electron supply reductions as a result of quantum confinement, the emitted current density (ECD) increases as the emitter radius decreases due to the effects of electric field enhancement. Additionally, emitters with radii smaller than 5 nm exhibit a narrow total energy distribution and highly non-linear FN plots. Consistent with experimental observations, the saturation of the conduction band ECD in silicon emitters leads to the appearance of three distinct regions in FN plots, which signify conduction-band-dominated, valence-band-dominated, and transitional regimes of emission. Confinement of electrons to a nanowire emitter geometry further reduces the electron supply available for emission and, consequently, the conduction band saturation ECD. Overall, findings show that the dimensionality, geometry, and material of field emitters all play a critical role in field emission processes at the nanoscale. Accordingly, the semiclassical framework for field emission is intended to form a solid foundation upon which more complete models of emission can be developed.
by Alex Andrew Patterson.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

48

唐素明 and So-ming Glenna Tong. "Theoretical studies of transition metal containing diatomics and DNA electron transfer." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31244828.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Zienert, Andreas. "Electronic Transport in Metallic Carbon Nanotubes with Metal Contacts." Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-108205.

Full text

Abstract:

The continuous migration to smaller feature sizes puts high demands on materials and technologies for future ultra-large-scale integrated circuits. Particularly, the copper-based interconnect system will reach fundamental limits soon. Their outstanding properties make metallic carbon nanotubes (CNTs) an ideal material to partially replace copper in future interconnect architectures. Here, a low contact resistance to existing metal lines is crucial. The present thesis contributes to the theory and numerical description of electronic transport in metallic CNTs with metal contacts. Different theoretical approaches are applied to various contact models and electrode materials (Al, Cu, Pd, Ag, Pt, Au) are compared. Ballistic transport calculations are based on the non-equilibrium Greens function formalism combined with tight-binding (TB), extended Hückel theory (EHT) and density functional theory (DFT). Simplified contact models allow a qualitative investigation of both the influence of geometry and CNT length, and the strength and extent of the contact on the transport properties. In addition, such simple contact models are used to compare the influence of different electronic structure methods on transport. It is found that the semiempirical TB and EHT are inadequate to quantitatively reproduce the DFT-based results. Based on this observation, an improved set of Hückel parameters is developed, which remedies this insufficiency. A systematic investigation of different contact materials is carried out using well defined atomistic metal-CNT-metal structures, optimized in a systematic way. Analytical models for the CNT-metal interaction are proposed. Based on that, electronic transport calculations are carried out, which can be extended to large systems by applying the computationally cheap improved EHT. The metal-CNT-metal systems can then be ranked by average conductance: Ag ≤ Au < Cu < Pt ≤ Pd < Al. This corresponds qualitatively with calculated contact distances, binding energies and work functions of CNTs and metals. To gain a deeper understanding of the transport properties, the electronic structure of the metal-CNT-metal systems and their respective parts is analyzed in detail. Here, the energy resolved local density of states is a valuable tool to investigate the CNT-metal interaction and its influences on the transport
Die kontinuierliche Verkleinerung der Strukturgrößen stellt hohe Anforderungen an Materialen und Technologien zukünftiger hochintegrierter Schaltkreise. Insbesondere die Leistungsfähigkeit kupferbasierte Leitbahnsystem wird bald an fundamentale Grenzen stoßen. Aufgrund ihrer hervorragenden Eigenschaften könnten metallische Kohlenstoffnanoröhren (engl. Carbon Nanotubes, CNTs) Kupfer in zukünftigen Leitbahnsystemen teilweise ersetzen. Dabei ist ein geringer Kontaktwiderstand mit vorhandenen Leitbahnen von entscheidender Bedeutung. Die vorliegende Arbeit liefert grundlegende Beiträge zur Theorie und zur numerischen Beschreibung elektronischer Transporteigenschaften metallischer CNTs mit Metallkontakten. Dazu werden verschiedene theoretische Ansätze auf diverse Kontaktmodelle angewandt und eine Auswahl von Elektrodenmaterialen (Al, Cu, Pd, Ag, Pt, Au) verglichen. Die Beschreibung ballistischen Elektronentransports erfolgt mittels des Formalismus der Nichtgleichgewichts-Green-Funktionen in Kombination mit Tight-Binding (TB), erweiterter Hückel-Theorie (EHT) und Dichtefunktionaltheorie (DFT). Vereinfachte Kontaktmodelle dienen der qualitativen Untersuchung des Einflusses von Geometrie und Länge der Nanoröhren, sowie von Stärke und Ausdehnung des Kontaktes. Darüber hinaus erlauben solch einfache Modelle mit geringem numerischen Aufwand den Einfluss verschiedener Elektronenstrukturmethoden zu untersuchen. Es zeigt sich, dass die semiempirischen Methoden TB und EHT nicht in der Lage sind die Ergebnisse der DFT quantitativ zu reproduzieren. Ausgehend von diesen Ergebnissen wird ein verbesserter Satz von Hückel-Parametern generiert, der diesen Mangel behebt. Die Untersuchung verschiedener Kontaktmaterialien erfolgt an wohldefinierten atomistischen Metall-CNT-Metall-Strukturen, welche systematisch optimiert werden. Analytische Modelle zur Beschreibung der CNT-Metall-Wechselwirkung werden vorgeschlagen. Darauf aufbauende Berechnungen der elektronischen Transporteigenschaften, können mit Hilfe der verbesserten EHT auf große Systeme ausgedehnt werden. Die Ergebnisse ermöglichen eine Reihung der Metall-CNT-Metall-Systeme hinsichtlich ihrer Leitfähigkeit: Ag ≤ Au < Cu < Pt ≤ Pd < Al. Dies korrespondiert qualitativ mit berechneten Kontaktabständen, Bindungsenergien und Austrittarbeiten der CNTs und Metalle. Zum tieferen Verständnis der Transporteigenschaften erfolgt eine detaillierte Analyse der elektronischen Struktur der Metall-CNT-Metall-Systeme und ihrer Teilsysteme. Dabei erweist sich die energieaufgelöste lokale Zustandsdichte als nützliches Werkzeug zur Visulisierung und zur Charakterisierung der Wechselwirkung zwischen CNT und Metall sowie deren Einfluss auf den Transport

APA, Harvard, Vancouver, ISO, and other styles

50

Krämer, Tobias. "Electronic structure of open-shell transition metal complexes." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:1f4a1330-281d-4696-b3e6-62b76fb41d65.

Full text

Abstract:

This thesis presents electronic structure calculations on problems related to the bonding in inorganic coordination compounds and clusters. A wide range of molecules with the ability to exist in different structural forms or electronic states has been selected and density functional theory is systematically applied in order to gain detailed insight into their characteristics and reactivity at the electronic level. First, we address the question of redox non-innocent behaviour of bipyridine in a series of 1st row transition metal complexes. Complexes of the type [M(2,2'-bipyridine)(mes)₂]⁰ (M = Cr, Mn, Fe, Co, Ni; mes = 2,4,6-Me₃C6H₂) and their one-electron reduced forms have been explored. The results clearly show that the anions are best described as complexes of the monoanionic bipyridine radical (S_bpy = 1/2), giving a rationale for the observed structural changes within the ligand. Likewise, we have identified dianionic bipyridine in both the complexes [Zn2(4,4'-bpy)(mes)₄]²⁻ and [Fe(2,2'-bpy)₂]²⁻. In no case have we found evidence for significant metal-to-ligand backbonding. The subject of redox-noninnocence is further revisited in a comparative study of the two complexes [M(o-Clpap)₃] (M = Cr, Mo; o-Clpap = 2-[(2-chloro-phenyl)azo]-pyridine), and their associated electron transfer series. The results indicate that all electron transfer processes are primarily ligand-based, although in the case of the Mo analogue these are coupled to substantial electron density changes at the metal. The ability of pap to form radical anions finds a contrasting case in the di- nuclear Rh complex [Rh₂(μ-p-Clpap)₂ (cod)Cl₂], where the two ligand bridges act as acceptors of strong dπ∗ backbonding from a formally Rh^–I centre. We then direct our attention to the endohedral Zintl clusters [Fe@Ge₁₀]³⁻ and [Mn@Pb₁₂]³⁻, which reveal peculiar topologies. We have probed the electronic factors that influence their geometric preferences, and propose a model based on the shift of electron density from the endo- hedral metal to the cage to account for the observed geometries. Subsequently, we reassess the electronic structure of the xenophilic clusters Mn₂(thf)₄(Fe(CO)₄)₂ and [Mn(Mn(thf)₂)₃(Mn(CO)₄)₃]^–. We conclude that these are best viewed as exchange coupled Mn^II centres bridged by closed- shell carbonylate fragments. In the closing chapter the reduction of NO₂^– to NO by the complex [Cu(tct)(NO₂)]⁺ (tct = cis,cis-1,3,5-tris(cinnamylideneamino)cyclohexane) is studied, a process that mimics the enzyme-catalysed reaction. Two viable pathways for the reaction have been traced and key inter-mediates identified. Both direct release of NO or via decomposition of a Cu-NO complex are kinetically and thermodynamically feasible.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Electron theory of metals'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles