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1
Hoffrogge, Johannes Philipp. "A surface-electrode quadrupole guide for electrons." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-155503.
Testo completo
2
Papageorgiou, George. "Counting electrons on helium using a single electron transistor." Thesis, Royal Holloway, University of London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415196.
Testo completo
3
Schäfer-Bung, Boris, and Mathias Nest. "Correlated dynamics of electrons with reduced two-electron density matrices." Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2010/4177/.
Testo completoAbstract (sommario):
We present an approach to the correlated dynamics of many-electron systems. We show, that the twoelectron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the
computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented.
4
Krecinic, Faruk [Verfasser]. "Ultrafast electron diffraction and imaging using ionized electrons / Faruk Krecinic." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1142155447/34.
Testo completo
5
Miller, Nathan A. "Using electron-tunneling refrigerators to cool electrons, membranes, and sensors." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315773.
Testo completo
6
Hardy, Thomas M. "Superconductivity with strongly correlated electrons and an electron-phonon interaction." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/34947.
Testo completoAbstract (sommario):
The effect on the stability of the superconducting phase due the addition of an electron–phonon interaction to a repulsive Hubbard model is studied. Our Hubbard–Fröhlich Hamiltonian includes electron hoping, the on-site Coulomb repulsion, vibrating ions (phonons) and the electron–phonon interaction. A Lang–Firsov transformation is used to integrate out the phonon degrees of freedom. The transformation reduces the model to simple a Hubbard Hamiltonian with an additional long-range electron–electron attraction. A variational Monte Carlo technique, with a projected BCS trial function, is used to investigate the ground state energies of our transformed Hubbard–Fröhlich Hamiltonian. For various electron densities, with a d-wave superconducting order parameter, it is found that the inclusion of the electron-phonon interaction significantly enhances the condensation energy (the energy required to break paired electrons). We show that increasing the strength of the electron-phonon interaction increases the condensation energy. It is also found that even with an infinite on-site repulsion, where the resonating valence bond state cannot exist, the EPI does still lead to a d-wave superconducting state. In addition we examine, analytically, the coexistence of ferromagnetism and superconductivity. Allowing different masses for spin-up and spin-down electrons in a BCS-type Hamiltonian two new branches in the energy spectrum are found. Including a spatially varying order parameter a new expression for the pairing amplitude of finite momentum pairs is derived.
7
Siedlein, Rupert V. "A search for excited electrons in electron-proton collisions at HERA /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487854314871133.
Testo completo
8
Moreira, Leandro Malard. "Raman spectroscopy of graphene:: probing phonons, electrons and electron-phonon interactions." Universidade Federal de Minas Gerais, 2009. http://hdl.handle.net/1843/ESCZ-7ZFGDY.
Testo completoAbstract (sommario):
Since the identification of mono and few graphene layers in a substrate in 2004, intensive work has been devoted to characterize this new material. In particular, Raman spectroscopy played an important role in unraveling the properties of graphene systems. Moreover resonant Raman scattering (RRS) in graphene systems was shown to be an important tool to probe phonons, electrons and electronphononinteractions. In this thesis, by using different laser excitation energies, we obtain important electronic and vibrational properties of mono- and bi-layer graphene. For monolayer graphene, we determine the phonon dispersion near the Dirac point for the in-plane transverse optical (iTO) mode and the in-plane longitudinal acoustic (iLA) mode. These results are compared with recent theoretical calculations for the phonon dispersion around the K point. For bilayer graphene we obtain the Slonczewski-Weiss-McClure band parameters. These results show that bilayer graphene has a strong electron-hole asymmetry, which is larger than in graphite. In a gating experiment, we observe that the change in Fermi level of bilayer graphene gives rise to a symmetry breaking, allowing the observation of both the symmetric (S) and anti- symmetric (AS) phonon modes. The dependence of the energy and damping of these phonons modes on the Fermi level position is explained in terms of distinct couplings of the S and AS phonons with intraand inter-band electron-hole transitions. Our experimental results confirm the theoretical predictions for the electron-phonon interactions in bilayer graphene. We also study the symmetry properties of electrons and phonons in graphene systems as a function of the number of layers, by a group theory approach. We derive the selection rules for the electron-radiation and for the electron-phonon interactions at all points in the Brillouin zone. By considering these selection rules, we address the double resonance Raman scattering process. The selection rules for monolayer and bilayer graphene in the presence of an applied electric field perpendicular to the sample plane are also discussed.<br>Desde a identificação de uma ou poucas camadas de grafeno em um substrato em 2004, trabalhos intensivos tem sido feitos para se caracterizar esse novo material. Em particular, a Espectroscopia Raman Ressonante tem sido muito importante para elucidar propriedades físicas e químicas em sistemas de grafeno. A Espectroscopia Raman Ressonante também tem se mostrado como uma ferramenta importante para se estudar fônons, elétrons e interações elétron-fônon em grafeno. Nesta tese, ao usarmos diferentes energias de laser de excitação, nós obtivemos propriedades importantes sobre as estruturas eletrônicas e vibracionais para uma e duas camadas de grafeno. Para uma monocamada de grafeno, nós determinamos a dispersão de fônons perto do ponto de Dirac para o modo óptico transversal no plano (iTO) e para o modo acústico longitudinal no plano (iLA). Comparamos nossos resultados experimentais como cálculos teóricos recentes para a dispersao de fônons nas proximidades do ponto K. Para a bicamada de grafeno, nós obtivemos os parâmetros de estrutura eletrônica do modelo de Slonczewski-Weiss-McClure. Nossos resultados mostram que a bicamada de grafeno possue uma forte assimetria elétron-buraco, que por sua vez é mais forte que no grafite. Em experimentos aplicando uma tensão de porta, variamos o nível de Fermi em uma bicamada de grafeno, o que levou uma quebra de simetria, deixando assim ambos os modos de vibração simétricos (S) e anti-simétricos (AS) ativos em Raman. A dependência da energia e do amortecimento desses modos de fônons com a energia de Fermi é explicada através do acoplamento elétron-buraco intra- ou inter- banca. Nossos resultados experimentais deram suporte às previsões teóricas para interações elétron-fónon em uma bicamada de grafeno.
9
Ren, Yan-Ru. "Orbital spin-splitting factors for conduction electrons in lead." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25961.
Testo completoAbstract (sommario):
A detailed experimental study has been made of the spin-splitting factors ℊc for magnetic Landau levels associated with conduction electrons in extremal orbits on the Fermi surface of lead. This information has been derived from the waveform of the de Haas-van Alphen (dHvA) quantum oscillations in the magnetization of single-crystal lead spheres at temperatures of about 1.2 K and with applied magnetic fields in the range 50-75 kG. A commercial spectrum analyzer has been used to provide on-line values of the harmonic amplitudes in the dHvA waveform, and the values of ℊc have been extracted from the relative strengths of the harmonics.
Serious systematic errors in ℊc can arise on account of waveform distortions caused by the small and subtle difference between the externally applied field H and the magnetizing field B acting on the conduction electrons. In 1981 Gold and Van Schyndel demonstrated that these 'magnetic-interaction' distortions could be suppressed to a large extent by using negative magnetic feedback to make the induction B within the sample be the same as H (or very nearly so). This thesis describes the first in-depth application of the magnetic-feedback technique to the systematic study of any metal. Particular attention has been paid to the effect of sample inhomogeneity, and Shoenberg's treatment of the magnetic interaction in a non-uniform sample has been generalized to include magnetic feedback. This theory accounts well for many features in the experimental data, especially those which remained a puzzle in the earlier work of Gold and Van Schyndel.
Experimental ℊc values are given for the first time for most of the extremal orbits on the lead Fermi surface and for high-symmetry directions of the magnetic field. Indeed these are the most detailed data reported for any polyvalent metal. The ℊc factors for the different orbits and field directions are found to span the range from 0.56 to 1.147. These large net deviations from the free-electron value ℊ₀ = 2.0023 are consequences of the strong spin-orbit and electron-phonon interactions, and an attempt has been made to separate these two contributions to the ℊ-shifts.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate
10
Dogbe, John Kofi. "Comparing cluster and slab model geometries from density functional theory calculations of si(100)-2x1 surfaces using low-energy electron diffraction." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258835.
Testo completo
11
Guinea, William Edward. "Polarisation and Alignment Studies in Electron Scattering From Rubidium." Thesis, Griffith University, 2009. http://hdl.handle.net/10072/367197.
Testo completoAbstract (sommario):
Measurements have been made of the A2 spin asymmetry in the scattering of polarised
electrons from rubidium atoms. Results have been taken at an incident energy of 15,
20, 30, 50 and 80eV for elastic scattering, and at 15, 20, 30 and 50eV for 5S to 5P
excitation where the fine structure has not been resolved. The measurements covered
the angular range 30° to 110°. Results were taken using a crossed beam type
experiment, with a hemispherical electrostatic detector. Polarised electrons were
provided by a conventional gallium arsenide spin-polarised electron source. The Rmatrix
and relativistic distorted wave calculations available demonstrate good
agreement with the experimental results, though there are some clear discrepancies
between the magnitudes and positions of the extrema as predicted by theory. These A2
results follow on from those taken by Went (2003).
A study of the autoionisation resonances of rubidium has also been undertaken. This
consisted of first measuring the angular variation of the autoionisation resonances in
the angular range 30° to 130°, at an incident energy of 1keV. A crossed beam method
was also used for these results, though electrons were provided by a conventional
electron gun. Significant relative angular variation between sets of autoionisation
resonances was observed. The results taken represent the first experimentally
determined values of the alignment parameter, A20 and R0, the isotropic distribution
ratio for the leading autoionisation doublet of rubidium. The experimentally
determined values of A20 and R0 were not inconsistent with the theoretical values
available for comparison.
Finally an attempt was made to measure a circular dichroism in the angular
distribution of autoionised electrons due to stepwise laser/electron impact excitation
(CPDAD). The experimental detection of such a circular dichroism would be the very
first of its kind. Such a measurement would also help validate the theoretical approach
that predicted its existence. Preliminary investigation requires identification of an
autoionisation resonance that is enhanced with the stepwise excitation procedure. A
crossed beam experiment identical to the procedure immediately above was
undertaken using a conventional electron gun. Laser light resonant with the D2 line of rubidium was provided by a titanium-sapphire laser, while a diode laser was used to
repump the dark state. Measurements were taken at incident energies of 250, 450, 700
and 1000eV at ejected electron angles of 75°, 75°, 90° and 90° respectively. No
enhancement was visible with the stepwise process for any of the observed
autoionisation resonances, so it was not possible to study CPDAD.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>School of Biomolecular and Physical sciences<br>Science, Environment, Engineering and Technology<br>Full Text
12
PEROSA, GIOVANNI. "Impact of the Electrons Dynamics on the Free-electron Lasers Radiation Coherence." Doctoral thesis, Università degli Studi di Trieste, 2023. https://hdl.handle.net/11368/3041022.
Testo completoAbstract (sommario):
Modern science advancements rely on the possibility of producing short laser-like coherent pulses in the XUV and in the X-rays wavelength ranges to probe electronic structure in atoms, molecules and solid-state matter. For this reason, light-sources including synchrotrons, inverse Compton scattering, high harmonic generation in gas (HHG) and free electron lasers (FELs) are invaluable tools for research in these fields.
In particular, they all have in common the exploitation of the radiating process resulting from electrons’ acceleration under the influence of an electromagnetic field.
The aim of this thesis is to explore the impact of electrons’ dynamics on the coherence of FELs seeded by an external laser. In this thesis I demonstrate that electrons’ dynamics plays a major role in the conversion and transformation of light’s features, such as coherence, which can be transmitted to electrons and "inherited" from the re-emitted light. To fulfill this purpose, both the theoretical and the experimental approaches have been used. Most of the models presented, derived or extended in this work are, in fact, supported by experimental evidence.
The interplay between electrons and light’s properties is investigated using both classical and quantum dynamics. While the former is routinely adopted to describe the FEL dynamics and collective phenomena in an electron bunch, the latter becomes mandatory to fully achieve a faithful description of the varieties of phenomena that involve the emission of photons.
From the classical point of view, a comprehensive analytical model for electron beam longitudinal dynamics is derived by including a new phenomenon, known as intrabeam scattering, and by investigating its effect on the electrons’ distribution. The predictions of this model can be directly compared with both beam and FEL measurements, showing a good agreement with both.
From the quantum-dynamical point of view, we start to explore the possibility to answer the following question: "is it possible to introduce quantum features, such as coherence, in any process of harmonic generation from a coherent light pulse?" In order to do so, we focus our attention on the characterization of quantum coherence via photon number distribution and the quantum electrodynamics of an electron in a laser field.
The practical aspect of my investigation is threefold: the prediction and characterization of electron beam quality; the optimization of seeded and unseeded FELs performances, that is possible through the mitigation of instabilities originated in the electron bunch; the investigation of unexplored FELs features and configurations that could be exploited for novel experiments.
Finally, although the results and discussions are directly applied to the FEL case, some of the theoretical results regarding the coherence can be applied, without loss of generality, to any process of electrons-light interaction.<br>Modern science advancements rely on the possibility of producing short laser-like coherent pulses in the XUV and in the X-rays wavelength ranges to probe electronic structure in atoms, molecules and solid-state matter. For this reason, light-sources including synchrotrons, inverse Compton scattering, high harmonic generation in gas (HHG) and free electron lasers (FELs) are invaluable tools for research in these fields.
In particular, they all have in common the exploitation of the radiating process resulting from electrons’ acceleration under the influence of an electromagnetic field.
The aim of this thesis is to explore the impact of electrons’ dynamics on the coherence of FELs seeded by an external laser. In this thesis I demonstrate that electrons’ dynamics plays a major role in the conversion and transformation of light’s features, such as coherence, which can be transmitted to electrons and "inherited" from the re-emitted light. To fulfill this purpose, both the theoretical and the experimental approaches have been used. Most of the models presented, derived or extended in this work are, in fact, supported by experimental evidence.
The interplay between electrons and light’s properties is investigated using both classical and quantum dynamics. While the former is routinely adopted to describe the FEL dynamics and collective phenomena in an electron bunch, the latter becomes mandatory to fully achieve a faithful description of the varieties of phenomena that involve the emission of photons.
From the classical point of view, a comprehensive analytical model for electron beam longitudinal dynamics is derived by including a new phenomenon, known as intrabeam scattering, and by investigating its effect on the electrons’ distribution. The predictions of this model can be directly compared with both beam and FEL measurements, showing a good agreement with both.
From the quantum-dynamical point of view, we start to explore the possibility to answer the following question: "is it possible to introduce quantum features, such as coherence, in any process of harmonic generation from a coherent light pulse?" In order to do so, we focus our attention on the characterization of quantum coherence via photon number distribution and the quantum electrodynamics of an electron in a laser field.
The practical aspect of my investigation is threefold: the prediction and characterization of electron beam quality; the optimization of seeded and unseeded FELs performances, that is possible through the mitigation of instabilities originated in the electron bunch; the investigation of unexplored FELs features and configurations that could be exploited for novel experiments.
Finally, although the results and discussions are directly applied to the FEL case, some of the theoretical results regarding the coherence can be applied, without loss of generality, to any process of electrons-light interaction.
13
Le, Duc-Anh. "Electrons in 5f Systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-61720.
Testo completoAbstract (sommario):
The localized/delocalized duality of 5f electrons plays an important role in understanding the complex physics of actinides. Band-structure calculations based on the ad hoc assumption that 5f electrons are simultaneously localized and delocalized explained the observed dHvA experiments very well. This ad hoc assumption also gives the correct equilibrium volume for delta-Pu. Experimentally, the duality of 5f electrons is observed by inelastic neutron scattering experiments, or by soft X-ray angle-resolved photoelectron spectroscopy. It is worth recalling that the origin of partial localization in the 3d and 5f systems is quite different. In compounds with 3d electrons, the large crystalline electric field set up by the surrounding environment of transition metal ions plays a major role. On the other hand, in 5f systems, the Hund's rule correlations play the key role whilst the crystalline electric field is less important.
In this thesis we have studied the effect of intra-atomic correlations on anisotropies in hopping matrix elements of different 5f orbitals. For that purpose, we used the effective model that includes on-site interactions that are responsible for Hund's rules and effective hopping terms that result from the hybridization of different 5f orbitals with the environment. Two different approximations, namely, rotationally invariant slave-boson mean-field (RISBMF) and infinite time-evolving block decimation (iTEBD), have been used to investigate the ground-state properties of the Hamiltonian. We have demonstrated that Hund's rule correlations enhance strongly anisotropies in hopping matrix elements. For a certain range of 5f bandwidth parameters this effect may result in a complete suppression of hopping processes for some of 5f orbitals, i.e., the system is in a partially localized phase. Within the RISBMF method, we calculated the ground-state properties and the phase diagram of the system. The suppression of hopping processes in some of 5f orbitals due to Hund's rule correlations can be seen through orbital-dependent quasiparticle weights. In a mean-field theory, a quasiparticle weight of zero for an orbital means a complete suppression of hopping processes in this orbital. Thus, quasiparticle weights and occupation numbers were used to classify partially localized phases. In the calculated phase diagram we obtain four partially localized phases that can be separated into two different sets. In the first set electrons in two orbitals are localized. In the second, electrons in one orbital are localized. The difference between the two sets is not simply the number of localized orbitals but the mechanism for the partial localization. For the first set, the Hund's rule mechanism applies: only those 5f electrons that enable the remaining ones to form a Hund's rule state will delocalize. This mechanism requires to have at least two localized orbitals, therefore it is definitely not applicable to those phases with only one localized orbital. For the second set, a situation similar to a single-band Mott-Hubbard transition applies. The direct on-site Coulomb interaction between jz and -jz electrons plays the key role for understanding the partial localization transition. In order to assess the validity of the RISBMF results we have used the iTEBD method to calculate the ground-state properties of a 1D system. Qualitatively, the two approaches agree with each other. However, we found an area where the RISBMF yields an artificial ground-state. Note that the mean-field method is worst for a 1D system. Therefore one shoud not judge from it the quality of the RISBMF method for the more general case.
14
Hodgson, Matthew J. P. "Electrons in model nanostructures." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/15657/.
Testo completoAbstract (sommario):
For calculating the properties of solids and molecules, density functional theory (DFT) has become extremely popular because of its inherent computational efficiency. However, despite being in principle exact, an approximation must be introduced into DFT in practice. The accuracy of DFT has been key to its popularity; however, even for some of the simplest systems, using common approximations to the exchange-correlation (xc) functional may give inaccurate results. Therefore, we aim to contribute to the development of improved approximate xc functionals. It is logical to begin by studying the most elementary of systems where the common approximate xc functionals require improvement, as one can model these systems exactly by solving the many-electron Schrödinger equation. By allowing us to study DFT and time-dependent DFT (TDDFT) in the absence of approximations for prototype systems, this approach provides insight into the fundamental principles of the theory, informing the development of new approximations. We show that steps arise in the level of the exact xc potential: steps are known to be important for giving accurate electron and current densities, yet little about their origin is understood. We show that steps form due to a change in the 'local effective ionisation energy' of the electrons: this concept is well defined for strongly localised electrons. We find that the tendency of an electron to exclude others from its vicinity (electron localisation) is surprisingly high in our finite systems; hence, we develop an approximate functional that uses a measure of localisation as an ingredient, with the analytical form of the Kohn-Sham potential in the limit of complete localisation. Our functional, termed the mixed localisation potential, gives accurate electron and current densities for our test systems where local approximations are less valid. The approximation’s success stems in part from its ability to reproduce steps in the xc potential.
15
BARUE, CHRISTOPHE. "Etude des electrons chauds dans une source d'ions a resonance cyclotron des electrons." Paris 6, 1992. http://www.theses.fr/1992PA066405.
Testo completoAbstract (sommario):
La comprehension du comportement d'une source d'ions a resonance cyclotron des electrons (source d'ions ecr) est liee a la population des electrons chauds. Pour obtenir des informations sur la population des electrons chauds, on a utilise trois diagnostics: bremsstrahlung, emission cyclotron et diamagnetisme. On a realise deux types d'experiences: 1) experiences en regime transitoire (emission cyclotron et diamagnetisme) consistant a pulser la puissance hf a un niveau donne mais variable d'une serie de pulses a l'autre. Le diamagnetisme donne une densite d'electrons chauds de l'ordre de dix puissance onze par centimetre cube pour deux cents watt de puissance hf injectee. Le temps de vie est de l'ordre de dix ms pour la meme puissance hf, et decroit avec la puissance hf; 2) experiences en regime continu (emission cyclotron et bremsstrahlung) consistant a maintenir constants les parametres de fonctionnement de la source. L'energie moyenne des electrons chauds est de l'ordre de quatre-vingt-dix kev pour deux cents watt de puissance hf injectee, et ne varie pratiquement pas au-dessus de deux cents watt. L'energie moyenne decroit avec la pression. En conclusion, le principal effet de l'augmentation de puissance hf est d'augmenter la densite. L'amelioration des performances d'une source d'ions ecr avec la puissance hf est probablement due a l'augmentation de la densite electronique
16
Anbumony, Kasi Lakshman Karthi Lee Soo-Young. "Analysis and correction of three-dimensional proximity effect in binary E-beam nanolithography." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2006%20Fall/Theses/ANBUMONY_KASI_19.pdf.
Testo completo
17
Fernández, Varea José María. "Interactions of electrons with matter." Doctoral thesis, Universitat de Barcelona, 1992. http://hdl.handle.net/10803/667581.
Testo completoAbstract (sommario):
The interaction of electrons with matter has been a subject of intense work since the beginning of the century. Although we know that the interaction is purely electromagnetic, its theoretical description is complicated by two different reasons. On the one hand, the number of particles that participate in the interaction may be very large. Even when the target is a single hydrogen atom, the collision is a three body problem for which only approximate solutions of the wave equation are known. Therefore, the interaction can only be treated by using approximate many-body methods. In particular, scattering of fast electrons by single atoms can be reasonably well understood on the basis of independent particle models. On the other hand, when the medium where the projectile moves extends over a. large volume, the projectile may interact repeatedly with the medium. The proper tools to deal with problems involving electron penetration in matter are multiple scattering theories and/or Monte Carlo simulation.
The aim of this thesis is to provide a consistent basis for the development of Monte Carlo simulation algorithms which are more accurate than the ones presently available. In fact, a high-energy simulation code based on relevant parts of this thesis is already operable; and a program to simulate electron transport at intermediate and low energies (below about 100 keV) is currently being developed from the theory presented in this work. The reliability of the simulation results obtained with these codes will offer the ultimate demonstration of the correctness and effectiveness of the approaches described here.
The thesis is structured in four chapters. Chapter 1 is devoted to the evaluation of reliable single elastic scattering cross sections for high energies. Multiple elastic scattering is considered in detail in chapter 2. Chapter 3 is devoted o the inelastic scattering of low-energy electrons in solids. In chapter4 we consider the energy loss of high-energy electrons and positrons in matter.
18
McDonough, Johnathan. "F electrons in CePbâ†3." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338253.
Testo completo
19
Green, D. G. "Positron annihilation on core electrons." Thesis, Queen's University Belfast, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557607.
Testo completoAbstract (sommario):
Diagrammatic many-body theory (MBT) is used to calculate the -y-spectra and an- nihilation rates for positrons annihilating on the core electrons of many-electron atoms. Long-range positron-atom and short-range positron-electron correlations are accounted for through the evaluation of the positron Dyson orbital and the true many-body annihilation vertex, which includes the exact electron-positron ladder series. The numerical implementation of the theory proceeds through the employment of a B-spline basis. It is tested through a comprehensive study of positron annihilation in the hydrogen-like ions He ", Li2+, BH and F8+, the ionization energies of which span those typical of the core electrons of many-electron atoms. The scattering phase shifts and normalized annihilation rate parameters Zeff are found to be in excellent agreement with existing sophisticated variational calculations, and -y-spectra are also predicted. , The annihilation ')'-spectra and partial annihilation rates are then calculated for ther- malized positrons annihilating on the core and valence electrons of the noble gas atoms Ar, Kr and Xe. Although stronger for the valence shells, the short-range correlations are found to significantly enhance the -y-spectra of the core subshells. For Ar, Kr and Xe, the core contributions to Zeff are found to be 0,55%, 1.5% and 2.2% respectively, their small values reflecting the difficulty for the positron to probe distances close to the nucleus. However, the core subshells have a broad momentum distribution and they markedly contribute to, and even dominate, the -y-spectra at Doppler energy shifts .2::. 3 ke V. It is found that proper inclusion of the core spectra is crucial in bringing the theoretical spectra into agreement with the experiment across the full range of Doppler energy shifts. State-dependent vertex enhancement factors 1nl, which quantify the effects of the short- range correlations, are estimated analytically and calculated using the MBT. They are found to follow a simple and physically motivated scaling with the subshell ionization energy Inz: 1nl = 1 + AI.;r;:z + sr], where A, Band (3 are positive constants. These factors can be incorporated in simple independent-particle-model calculations to reconstruct the true annihilation -y-spectra for annihilation on core electrons of atoms across the periodic table, and on the localized atomic-like core electrons of condensed matter systems. In the last part of the work, the atomic MBT is used to address the important problem of calculating the annihilation -y-spectra of molecues, with focus on the role of the positron- nuclear repulsion and correlation effects.
20
Chi, Xinyu. "Electrons in the cosmic radiation." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6570/.
Testo completoAbstract (sommario):
The nature of cosmic ray electrons and their radiation in the Universe has been studied. A convection associated diffusion model is proposed to describe the main characteristics of the large-scale distribution of cosmic ray electrons in the Galaxy: (1) a small Galacto-centric radial gradient; (2) spectral flattening with Galactic latitude; and (3) an extensive halo above the Disk. A new derivation of the interstellar radiation field indicates the existence of an inverse Compton γ -ray halo. This γ -ray halo can contribute up to 60% of the observed diffuse Galactic γ-ray flux at intermediate latitudes and also accounts for the spectral flattening with latitude. This result leads to a new estimate of the extragalactic γ -ray background flux. An energy equipaxtition theory is proposed for the global correlation between radio power and far-infrared luminosity for spiral galaxies, in which the dynamical role of cosmic rays in galactic evolution is implied. The model successfully explains the non-unity slope of the correlation and predicts the escape of cosmic ray electrons from our Galaxy. The interstellar flux of MeV cosmic ray electrons is derived from γ -ray data. The flux is found to be surprisingly high and a new type of source is required. The lower hybrid plasma instability initiated by stellar winds is suggested to be the acceleration mechanism. This high flux of electrons is sufficient to account for the interstellar ionization and heating in HI regions. Features of the local Galactic magnetic field are revealed by analysing pulsar rotation measure data. The large scale regular field is found to be in a bisymmetric configuration and to be stronger in the interarm region (3 µG) than in the arm region (1 µG). The derived small-scale irregular field is shown to have a dominant strength of 6 µG.
21
Kaube, Benjamin. "Plasmonics : from electrons to devices." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/58997.
Testo completoAbstract (sommario):
From molecular sensors to perfect lenses, plasmonic devices promise a wealth of breakthrough applications by coupling light to oscillations of the electron plasma. In order to harness the full technological potential of plasmonics, coherent plasma excitations must be sustained over many cycles. On the scale of practical devices, optical properties of media are characterised by the mascroscopic dielectric function. This quantity can be determined from first principles in terms of transitions between electronic states. Understanding of losses within plasmonic systems must thus be built up from electrons to devices -- the approach taken in this thesis. Optical losses are explored with application to prototypical plasmonic systems, noble metals copper, silver and gold. Density functional theory with quasiparticle self-consistent GW (QSGW) corrections are employed in order to build up an accurate description of the electronic states. Interband dielectric functions are consequently obtained within the linear response formalism, finding good agreement with experimental literature. Electron interactions with lattice vibrations are found to be an essential feature in describing optical losses at low energies (also known as Drude losses). Electron-phonon interactions are included by two approaches: many body perturbation theory via the phonon contribution to the self energy and the semi-classical Williams Lax averages over nuclear displacements. The latter approach was used to determine the temperature dependence of silver optical spectra and constants from first principles, achieving agreement with experiment. Lastly, first principles calculations of silver nanodots are presented.
22
Thorn, Penny Anne, and penny thorn@flinders edu au. "Electronic State Excitations in the Water Molecule by Collisions with Low Energy Electrons." Flinders University. Chemistry, Physics and Earth Sciences, 2008. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20080714.112505.
Testo completoAbstract (sommario):
The present study was largely concerned with measuring accurate absolute values for the electronic state excitation cross sections in H2O, in the incident electron energy range 15eV to 50eV. It is hoped that these data will eventually help to improve the current state of electron - molecule scattering theory, as well as being useful in various fields of modelling. As an illustration of this latter point, the cross sections determined here were used to calculate quantities of importance in atmospheric modelling, namely, electron energy transfer rates and rates for the excitation of water molecules by auroral secondary electrons.
23
Hoffrogge, Johannes Philipp [Verfasser], and Peter [Akademischer Betreuer] Hommelhoff. "A surface-electrode quadrupole guide for electrons / Johannes Philipp Hoffrogge. Betreuer: Peter Hommelhoff." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1033270865/34.
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Segall, Darren Eric 1970. "Coarse-graining electronic behavior in condensed matter systems : from electrons to continuum elasticity." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29307.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002.<br>Includes bibliographical references (leaves 131-137).<br>In this thesis properties of various condensed matter systems are studied, whose dependency on electronic behavior is incorporated through coarse-grained interactions. Three specific systems are considered. In the first system of study, high momentum, plane wave states of the electronic wave function are coarse-grained, while the low momentum states are fully resolved. Moreover, the coarse-graining procedure incorporates the response of the high momentum states to environmental changes and its couplings to changes in the low momentum states. Within density functional theory this allows the representation of the electronic wave function, when using a plane wave basis, to be computationally feasible without having to make the pseudopotential approximation. This coarse-graining procedure is beneficial for the study of high pressure systems, where the response of the core region is important. With this method we study a number of solid phases of boron and reveal a number of important structural and electronic properties on its high pressure and superconducting phase. The second system of study focuses on a slightly coarser scale, where a theory for the elasticity of nanometer sized objects is developed. This theory provides a powerful way of understanding nanoscale elasticity in terms of local group contributions and acts as a bridge between the atomic and the continuum regimes. This theory properly describes elastic fluctuations on length scales on the order of the decay length of the force constant matrix; allowing for straightforward development of new relations between the bending and stretching properties of nanomechanical resonators, which prove to be much more accurate than the continuum-based relations currently employed in experimental analysis.<br>(cont.) This theory is then used to link features of the underlining electronic structure to the local elastic response in silicon nanoresonators, emphasizing the importance of electronic structure on the local and overall elastic response. Our final system of study focuses on the longest length scales, the continuum. It is shown that the inclusion of electronic structure is crucial in the study of the role of dislocations on the macroscopic property of slip. This thesis explores the discrepancy between experimental data and theoretical calculations of the lattice resistance in bcc metals. This thesis presents results for the temperature dependence of the Peierls stress and the first ab initio calculation of the zero-temperature Peierls stress which employ periodic boundary conditions. The ab initio value for the Peierls stress is over five times larger than current extrapolations of experimental lattice resistance to zero-temperature. Although it is found that the common techniques for such extrapolation indeed tend to underestimate the zero-temperature limit, in this work it is shown that other mechanisms other than the simple Peierls mechanism are important in controlling the process of low temperature slip.<br>by Darren Eric Segall.<br>Ph.D.
25
Sheka, E. F. "Computational Strategy for Graphene: Insight from Odd Electrons Correlation." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35023.
Testo completoAbstract (sommario):
The correlation of odd electrons in graphene turns out to be significant so that the species should be
attributed to correlated ones. This finding profoundly influences the computational strategy addressing it
to configuration-interaction computational schemes. Owing to serious problems related to the schemes
realization, a compromise can be suggested by using single-determinant approaches based on either
Hartree-Fock or Density-Functional Theory in the form of unrestricted open-shell presentation. Both
computational schemes enable to fix the electron correlation, while only the Hartree-Fock theory suggests
a set of quantities to be calculated that can quantitatively characterize the electron correlation and can be
used for a quantitative description of such graphene properties as magnetism, chemical reactivity, and
mechanical response. The paper presents concepts and algorithms of the unrestricted Hartree-Fock theory
applied for the consideration of magnetic properties of nanographenes, their chemical modification by the
example of stepwise hydrogenation, as well as a possible governing the electron correlation by the carbon
skeleton deformation.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35023
26
Bao, Yunjuan. "Theoretical study of spin transport in low-dimensional systems." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40687570.
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Nova, Araujo Miguel Antonio da. "2D Bloch electrons in magnetic fields." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387617.
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Masood, Waqas. "Electrons and waves in space plasmas." Thesis, Queen Mary, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436333.
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Greer, Ruth A. "Scattering of electrons by polyatomic molecules." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239017.
Testo completo
30
Macarie, Liliana Sandina. "Correlated electrons and high-temperature superconductivity." Thesis, University of Warwick, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307992.
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Al-Arab, A. M. H. "Cyclotron resonance lineshape of free electrons." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381924.
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Wallington, Jonathan Peter. "Effective field theories for correlated electrons." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297769.
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Dzurak, Andrew Steven. "Ballistic hot-electrons in mesoscopic transistors." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308185.
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34
Slevin, Keith Martin. "Electrons in disorded one dimensional systems." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47666.
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Smith, Scott Graeme. "Electrons as probes of chiral materials." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8580/.
Testo completoAbstract (sommario):
In this work we present electron beam techniques for probing the chiral structure of materials. The motivation for the work lies in two distinct aspects of chiral materials science. In the first case, chiral plasmonic excitations have recently been proposed for use in a variety of sensing technologies but require structural optimisation, in which modern electron microscopy techniques excel. In the second case, the recent development of intrinsically chiral electron ‘vortex beams’ suggests the prospect of being able to discriminate chiral crystal structures directly within the electron microscope. We were keen to explore this prospect because it could overcome a long-standing and fundamental limitation in TEM techniques. The introduction section of this thesis provides an overview of the essential background and theory underpinning the research, specifically considering the theory of surface plasmons, the properties of electron beams and a description of crystal chirality, all of which will be used in our work. We give a description of diffraction of electrons in a crystal and show the wavefunctions of electron vortex beams. Results show electron channeling in a simple cubic crystal, highlighting the impact of the position of the beam on the unit cell. When the beam is focused onto an atomic column the electrons are forward scattered along the column, whereas they are scattered outwards when the beam is centered between columns. In Chapter 2 we discuss the details of data acquisition and post processing techniques, namely Richardson-Lucy deconvolution and non-negative matrix factorisation, which together extract plasmonic modes from EELS data sets. We give a detailed analysis of the plasmonic excitations which exist on the surfaces of both a nanopatterned gold chiral nanoparticle and a hole in a continuous metallic film that also supports localised surface plasmon resonances. We show, using EELS in a scanning transmission electron microscope that we can map the resonance modes of the structure with high spatial resolution. We confirm the link between the modes supported by a plasmonic nanoparticle and a hole of similar shape, though we find that 3D roughness has an effect on the energy of the modes, shifting modes by around 0.3eV in some cases. The modes found are chiral leading to chiral fields, which have applications as sensors of biological molecules. In Chapter 3 we demonstrate the ability to simulate EELS, with accuracy, of realistic plasmonic nanoparticles with 3D shapes which extends beyond the usual two-dimensional or idealised simulations of the literature. We study the effects of inevitable manufacturing and other structural imperfections on the plasmonic response of real patterned structures and show that they lead to shifts in energy and spatial intensity of the modes due to these defects. We find that structural defects are enough to make so called dark modes (ie. those that do not have dipole character and are therefore not usually excited by incident photons) become bright, and shift the energy of modes between similar structures. We also illustrate the ability to predict the intensity distribution of plasmonic modes on structures using only symmetry arguments. This type of calculation gives a simple derivation of the modes which would exist on a plasmonic nanoparticle without requiring a more complicated eigenmode analysis. Using symmetry terms and irreducible representations the modes which appear on a nanoparticle can be grouped by symmetry terms, allowing the breaking of symmetry, via defects, to be better be visualised. In the latter part of this work we turn to a completely different experiment to consider the exploitation of newly-discovered vortex electron beams in assigning chirality to crystals within a simple electron microscopy experiment. With these beams, which posses a orbital angular momentum, will show that is possible (in favourable cases) to detect the handedness of the crystal via a difference in diffraction pattern intensity distribution for beams of opposite OAM, when scattering in opposite handed crystals. Our work demonstrates the ease of assigning chirality using convergent electron vortex diffraction for a crystals with a threefold, fourfold and sixfold screw axis. We present this work using modified multislice simulations of the diffraction of vortex electron beams from chiral potential layers. We demonstrate that the azimuthal phase component of electron vortex beams opens up new opportunities for rapid chiral discrimination and structural studies in electron diffraction. We show that the symmetry of the resulting convergent beam patterns matches the point symmetry of the crystal only when the handedness of both the impinging vortex probe and chirality of the crystal are congruent. This methodology was tested on the real crystal structures of α-quartz and the magnetic crystal Cr1/3NbS2. It was found that effects (due to the matching of the beam and crystal chirality) are most obvious in the overlap of diffraction disks, where interference effects allow the novel phase profile of vortex beams to produce intensity variations. The thickness of the crystal, the convergence angle and the energy of the beam were all parameters which need to be tuned in order to achieve chiral specific scattering. In thinner crystals the effects were less obvious, requiring a deduction in the beam energy in order to see a difference between CBED patterns of enantiomers. In cases where the convergence angle did not lead to overlapping disks in the CBED pattern the effects of chiral specific scattering were not obvious. Future work should include an experimental check of the feasibility of observing such weak diffraction effects in an electron microscope. Should this prove possible, this method could be of use to to discriminate chiral crystal structures directly within the electron microscope using only one set of diffraction patterns.
36
Silva, Nelson Canzian da. "UM ESPECTROMETRO \"MINI-ORANGE\" PARA ELECTRONS." Universidade de São Paulo, 1990. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-10042015-155559/.
Testo completoAbstract (sommario):
Foi projetado e construído um espectrômetro Mini-Orange (MO) para eléctrons, utilizando imãs planos permanentes e um detector de barreira de superfície. Foram determinadas as funções de transmissão de diferentes configurações do sistema, para energias entre 200-1100 keV. Foi desenvolvido um modelo matemático do sistema, a partir de solução analítica para o campo de um imã plano e da integração numérica da equação de movimento dos eléctrons no campo de MO. As funções de transmissão assim obtidas foram comparadas aos resultados experimentais e mostraram um bom acordo para energias baixas e intermediárias.<br>A Mini-Orange spectrometer for electrons was designed and built, using plane permanent magnets and a surface barrier detector. Transmission functions were obtained for various system configurations and for energies between 200-1100 keV. A mathematical model of the system was developed, using the analytical solution for the field of a plane magnet and the numerical integration of the equation of motion of the electrons in the MO magnetic field. The calculated transmission functions were compared to the experimental data, showing a good agreement for low and intermediate energies.
37
Clark, Paul. "Quantum optics of electrons in graphene." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/416896/.
Testo completoAbstract (sommario):
The unique properties of graphene's band structure can lead to negative refraction of charge carriers incident on PN junctions. When coupled with an angular dependent transmission probability this can be utilised to form a novel split path interferometer. Many practical challenges are present and novel methods of fabrication are required to realise such a device. A large mean free path is required in order to achieve ballistic transport; a fundamental requirement of such a lensing device. Graphene on a hexagonal boron nitride (hBN) substrate is used in order to remove as many scattering sites as possible to enable the devices to be modelled using ballistic transport. Bubbles between graphene and boron nitride flakes are found and a method for their removal explained. Equipment was modified to allow the use of the latest graphene flake dry transfer methods, which enable the fabrication of hBN-graphene-hBN sandwich devices with one dimensional edge contacts. Multiple device designs are proposed which would exhibit interesting physics and give evidence for negative refraction in graphene and for the angular transmission probability of Klein tunnelling. The possibility of using He ion carving to produce a very small quantum point contact was explored and a nanoribbon with a width of 8 nm was fabricated and measured.
38
Siraj-Dine, Sami. "Dynamics of electrons in 2D materials." Thesis, Paris Est, 2020. http://www.theses.fr/2020PESC1039.
Testo completoAbstract (sommario):
Au cours de cette thèse, nous avons proposé des méthodes théoriques et numériques pour étudier le comportement des électrons dans les matériaux périodiques, avec un intérêt particulier pour les matériaux 2D, comme le graphène, et les isolants topologiques. La thèse se compose de trois parties, organisées comme suit. La première partie fournit un algorithme simple et doté d’une preuve mathématique pour construire des fonctions Wannier localisées, avec pour seule condition que le système ait des nombres de Chern triviaux. Sur la base d'une preuve explicite et constructive des homotopies pour le groupe unitaire, l'algorithme permet de construire des Wannier localisés pour des isolateurs topologiques tels que le modèle Kane-Mele. La méthode est validée par des tests numériques pour plusieurs systèmes. Dans la deuxième partie, nous proposons une méthode d'approximation des fonctions de Wannier adaptée au calcul des Hamiltoniens de tight-binding dans les hétérostructures de van der Waals non périodiques, c'est-à-dire des couches de matériaux 2D empilées les unes sur les autres, liées entre elles par des forces de van der Waals relativement faibles. Ce cadre n’est pas adapté pour les outils de calcul habituels de la physique des solides, qui reposent sur la périodicité des cristaux. Dans ce contexte, une approximation du premier ordre consiste à considérer les fonctions de Wannier calculées sur chaque couche indépendamment. Nous proposons donc un schéma d'approximation pour les fonctions de Wannier qui permet un calcul efficace des coefficients de matrice tight-binding, même dans le cas non périodique. La troisième partie est théorique et consacrée à l'étude des électrons indépendants à l’état fondamental dans un cristal périodique, mis en mouvement par un champ électrique uniforme à l’instant initial. Nous définissons rigoureusement le courant par unité de volume et étudions ses propriétés en utilisant à la fois la réponse linéaire et la théorie adiabatique. Nos résultats fournissent un cadre unifié pour divers phénomènes tels que la quantification de la conductivité de Hall des isolants topologiques, le régime balistique des électrons dans les métaux, les oscillations de Bloch dans la réponse en temps long des métaux et la conductivité statique du graphène<br>During this thesis, we have proposed theoretical and numerical methods to study the behavior of electrons in periodic materials, with a particular interest for 2D materials, like graphene, and topological insulators. The thesis consists in three parts, organized as follows.The first part provides a mathematically proven and simple algorithm to build localized Wannier functions, with the only requirement that the system has vanishing Chern numbers. Based on an explicit and constructive proof of homotopies for the unitary group, the algorithm is able to build localized Wannier for topological insulators such as the Kane-Mele model. The method is validated by numerical tests for several systems.In the second part, we propose an approximation method for Wannier functions that is adapted to the computation of tight-binding Hamiltonians in non-periodic van der Waals heterostructures, that is, layers of 2D materials stacked on top of each other, bound together by the comparatively weak van der Waals forces. This setting is challenging for the usual computational tools of solid-state physics, which rely on the periodicity of crystals. In this context, a first-order approximation is to consider the Wannier functions computed on each layer independently. We therefore propose an approximation scheme for Wannier functions that allows for an efficient computation of tight-binding matrix coefficients, even in the non-periodic case.The third part is theoretical and devoted to the study of independent electrons in a periodic crystal in their ground state, set in motion by a uniform electric field at some prescribed time. We rigorously define the current per unit volume and study its properties using both linear response and adiabatic theory. Our results provide a unified framework for various phenomena such as the quantification of Hall conductivity of insulators with broken time-reversibility, the ballistic regime of electrons in metals, Bloch oscillations in the long-time response of metals, and the static conductivity of graphene
39
Scheffler, Marc. "Broadband microwave spectroscopy on correlated electrons." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11612028.
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Rusz, Ján, Ikuo Nishida, Shunsuke Muto, and Kazuyoshi Tatsumi. "Site-specific electronic configurations of Fe 3d states by energy loss by channeled electrons." AIP publishing, 2010. http://hdl.handle.net/2237/20791.
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de, Vries Rowen. "An EGSnrc Monte Carlo investigation of backscattered electrons from internal shielding in clinical electron beams." Thesis, University of Canterbury. Physics and Astronomy, 2014. http://hdl.handle.net/10092/9595.
Testo completoAbstract (sommario):
The ability to accurately predict dose from electron backscatter created by internal lead shielding utilized during various superficial electron beam treatments (EBT), such as lip carcinoma, is required to avoid the possibility of an overdose. Methods for predicting this dose include the use of empirical equations or physically measuring the electron backscatter factor (EBF) and upstream electron backscatter intensity (EBI). The EBF and upstream EBI are defined as the ratio of dose at, or upstream, from the shielding interface with and without the shielding present respectively. The accuracy of these equations for the local treatment machines was recognised as an area that required verification; in addition the ability of XiO's electron Monte Carlo (eMC) treatment planning algorithm to handle lead interfaces was examined. A Monte Carlo simulation using the EGSnrc package of a Siemens Artiste Linac was developed for 6, 9, 12, and 15 MeV electron energies and was verified against physical measurements to within an accuracy of 2 % and 2 mm. Electron backscatter dose distributions were predicated using the MC model, Gafchromic film, and XiO eMC, which when compared showed that XiO's eMC could not accurately calculate dose at the lead interface. Several MC simulations of lead interfaces at different depths, corresponding to energies of 0.2-14 MeV at the interfaces, were used to validate the accuracy of the equations, with the results concluding that the equation could not accurately predict EBF and EBI values, especially at low energies. From this data, an equation was derived to allow estimation of the EBF and upstream EBI, which agreed to within 1.3 % for the EBF values and can predict the upstream EBI to a clinically acceptable level for all energies.
42
Ryll, Henning [Verfasser]. "Direct detection of electrons with the pnCCD for applications in transmission electron microscopy / Henning Ryll." Siegen : Universitätsbibliothek der Universität Siegen, 2018. http://d-nb.info/116044370X/34.
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Bartlett, Philip Lindsay. "Complete numerical solution of electron-hydrogen collisions." Thesis, Bartlett, Philip Lindsay (2005) Complete numerical solution of electron-hydrogen collisions. PhD thesis, Murdoch University, 2005. https://researchrepository.murdoch.edu.au/id/eprint/225/.
Testo completoAbstract (sommario):
This thesis presents an extensive computational study of electron-impact scattering and ionisation of atomic hydrogen and hydrogenic ions, which are fundamental to many diverse disciplines, from astrophysics and nuclear fusion to atmospheric physics. The non-relativistic Schrodinger equation describes these collisions, though finding solutions for even hydrogen, the simplest electron-atom collision, has proven to be a monumental task. Recently, Rescigno et al [Science 286, 2474 (1999)] solved this equation in coordinate space using exterior complex scaling (ECS), and presented the first electron-hydrogen differential cross sections for ionisation that matched with experiment without requiring uncontrolled approximation. This method has significant potential for extension to larger collision systems, but its large computational demand has limited its energy range and target configurations, and its application to discrete final-state collisions has been largely unexplored.
Using radically different numerical algorithms, this thesis develops methods that improve the computational efficiency of ECS by two orders of magnitude. It extends the method to calculate discrete final-state scattering cross sections and enhances the target description to include hydrogenic ions and excited initial states. In combination, these developments allow accurate solutions over a broad range of energies and targets, for both scattering and ionisation, including the important near-threshold energy region where accurate calculations have been unavailable. The refined ECS method implemented in this work now offers complete numerical solutions of electron-hydrogen collisions, and its computational efficiency will facilitate its future application to more complex targets. The thesis culminates with the first ab initio quantum mechanical confirmation of ionisation threshold laws for electron-hydrogen collisions [Bartlett and Stelbovics, 2004, Phys. Rev. Lett. 93, 233201], which have resisted confirmation through the complete solution of the Schrodinger equation for more than half a century.
44
Bartlett, Philip Lindsay. "Complete numerical solution of electron-hydrogen collisions." Bartlett, Philip Lindsay (2005) Complete numerical solution of electron-hydrogen collisions. PhD thesis, Murdoch University, 2005. http://researchrepository.murdoch.edu.au/225/.
Testo completoAbstract (sommario):
This thesis presents an extensive computational study of electron-impact scattering and ionisation of atomic hydrogen and hydrogenic ions, which are fundamental to many diverse disciplines, from astrophysics and nuclear fusion to atmospheric physics. The non-relativistic Schrodinger equation describes these collisions, though finding solutions for even hydrogen, the simplest electron-atom collision, has proven to be a monumental task. Recently, Rescigno et al [Science 286, 2474 (1999)] solved this equation in coordinate space using exterior complex scaling (ECS), and presented the first electron-hydrogen differential cross sections for ionisation that matched with experiment without requiring uncontrolled approximation. This method has significant potential for extension to larger collision systems, but its large computational demand has limited its energy range and target configurations, and its application to discrete final-state collisions has been largely unexplored.
Using radically different numerical algorithms, this thesis develops methods that improve the computational efficiency of ECS by two orders of magnitude. It extends the method to calculate discrete final-state scattering cross sections and enhances the target description to include hydrogenic ions and excited initial states. In combination, these developments allow accurate solutions over a broad range of energies and targets, for both scattering and ionisation, including the important near-threshold energy region where accurate calculations have been unavailable. The refined ECS method implemented in this work now offers complete numerical solutions of electron-hydrogen collisions, and its computational efficiency will facilitate its future application to more complex targets. The thesis culminates with the first ab initio quantum mechanical confirmation of ionisation threshold laws for electron-hydrogen collisions [Bartlett and Stelbovics, 2004, Phys. Rev. Lett. 93, 233201], which have resisted confirmation through the complete solution of the Schrodinger equation for more than half a century.
45
Shackleton, Anthony Edward. "Investigations of the Temkin-Poet model for electron-hydrogen iso-electronic series scattering." Thesis, Shackleton, Anthony Edward (2004) Investigations of the Temkin-Poet model for electron-hydrogen iso-electronic series scattering. PhD thesis, Murdoch University, 2004. https://researchrepository.murdoch.edu.au/id/eprint/303/.
Testo completoAbstract (sommario):
An important model in the study of electron-atom collisions was development by Temkin and Poet. Although the model has been used to test many theories and approximation methods, the novel method of solution used by Poet has not been developed further to any great extent. The Temkin-Poet model of electron scattering simplifies the three-body scattering problem by suppressing all angular dependence of the wavefunction.
In this thesis we return to Poet's method and apply it to a range of calculations for the hydrogen-isoelectronic series. Firstly it is demonstrated that the method provides high-precision solutions for elastic and inelastic scattering. these solutions will then be used to investigate various aspects of electron scattering including the ionisation of hydrogen in the near-threshold region, resonant states in helium, and the scaling of elastic cross sections for a number of hydrogen-like ions.
46
Shackleton, Anthony Edward. "Investigations of the Temkin-Poet model for electron-hydrogen iso-electronic series scattering." Shackleton, Anthony Edward (2004) Investigations of the Temkin-Poet model for electron-hydrogen iso-electronic series scattering. PhD thesis, Murdoch University, 2004. http://researchrepository.murdoch.edu.au/303/.
Testo completoAbstract (sommario):
An important model in the study of electron-atom collisions was development by Temkin and Poet. Although the model has been used to test many theories and approximation methods, the novel method of solution used by Poet has not been developed further to any great extent. The Temkin-Poet model of electron scattering simplifies the three-body scattering problem by suppressing all angular dependence of the wavefunction.
In this thesis we return to Poet's method and apply it to a range of calculations for the hydrogen-isoelectronic series. Firstly it is demonstrated that the method provides high-precision solutions for elastic and inelastic scattering. these solutions will then be used to investigate various aspects of electron scattering including the ionisation of hydrogen in the near-threshold region, resonant states in helium, and the scaling of elastic cross sections for a number of hydrogen-like ions.
47
Olivera, Bernat. "Electronic transport in metals at the atomic scale: capacitance emergent magnetism and f-electrons influence." Doctoral thesis, Universidad de Alicante, 2017. http://hdl.handle.net/10045/73051.
Testo completoAbstract (sommario):
Hemos desarrollado una técnica de medida a 4 puntas en corriente alterna con amplificadores “Lock-in” sincronizados para obtener la variación local de la capacidad entre los electrodos de un STM simultáneamente con su conductancia. La resolución a la que llegamos es de fF. En la evolución de la capacidad frente a la distancia entre electrodos distinguimos tres regiones: capacidad clásica (cuando los electrodos están más alejados), capacidad cuántica (en un régimen intermedio) y fuga de capacidad (cuando se entra en corriente túnel). En el régimen de emisión de campo, en los puntos en los que la energía incidente del electrón coincide con la de los niveles discretos por encima de la barrera túnel, se produce fuga de capacidad. Por otro lado, hemos encontrado evidencias de una emergencia del momento magnético en cadenas atómicas de platino que conectan dos electrodos hechos del mismo metal. El ajuste de las anomalías a voltaje de polarización cero a la función Kondo-Fano muestra un apantallamiento del momento magnético por parte de los electrones de conducción. Por último, hemos estudiado el papel que juegan los electrones f en el transporte electrónico en nanocontactos. Para ello, hemos realizado medidas de corriente eléctrica en nanocontactos hechos de gadolinio y europio, respectivamente. Hemos visto que para ambos metales la conductancia del contacto de un átomo está por debajo del cuanto de conductancia. Asimismo, los histogramas de conductancia en Gd son reproducibles lo cual contrasta con el caso de Eu en el que dichos histogramas no muestran tal reproducibilidad. Atribuimos este último hecho al desorden magnético que los electrones f causan en el metal. Con el ajuste de las anomalías a voltaje cero a la función Kondo-Fano hemos visto que los electrones f son apantallados por los de conducción. Además, en el caso de Gd vemos que presenta dos temperaturas Kondo, debidas al apantallamiento de los electrones d y f, respectivamente.
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Lin, Jun. "Radiation-induced alterations in mesoporous silicas : The effect of electronic processes involving ions and electrons." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2022. http://theses.enscm.fr/ENSCM_2022_LIN.pdf.
Testo completoAbstract (sommario):
Les matériaux utilisés dans le nucléaire (combustible, matrice de conditionnement, matériaux de structure…) sont soumis à des contraintes importantes liées à la création de défauts qui modifient leurs propriétés. Plusieurs études ont montré que les interfaces peuvent agir comme un puits pour les défauts causés par l'irradiation, ce qui suggère que les nanomatériaux pourraient avoir une plus grande résistance à l'irradiation que les matériaux présentant une structure « micrométrique ». Par ailleurs, les silices mésoporeuses ont gagné en popularité ces dernières années et sont envisagées pour le traitement des effluents radioactifs (séparation, conditionnement…). Bien que de nombreuses études aient été réalisées sur le comportement de silices non poreuses sous irradiation, très peu de travaux s’intéressent à celui de la silice mésoporeuse en particulier lorsqu’elle est irradiée en régime d‘électronique.Le but de cette thèse est de comprendre et d'expliquer les modifications induites par irradiation dans les silices mésoporeuses en régime électronique. Ce travail a permis de quantifier l’évolution de propriétés physico-chimiques (polymérisation du réseau, création de défauts…) et structurales (volume poreux, diamètre et distribution des pores…) de la silice mésoporeuse irradiée par des faisceaux d'ions de haute énergie dans une gamme de pouvoirs d'arrêt variant entre 1 keV/nm et 12 keV/nm, ainsi que par des électrons (10 - 300 keV et 0.6 - 2.4 MeV). Des méthodes de caractérisation post-irradiation (réflectivité des rayons X, adsorption de gaz, SAXS et FTIR, etc.) ont été utilisées, ainsi que le suivi in situ de la structure des pores à l'aide de microscopie électronique. Les résultats expérimentaux ont indiqué que la structure des pores était sensible à l'irradiation conduisant dans certaines conditions à son effondrement, tandis que le réseau de silice lui-même évolue peu par rapport à la silice non poreuse. Parallèlement, un modèle TS3D (modèle de pointe thermique 3D) a été utilisé avec succès pour décrire et expliquer le comportement de contraction des pores observé en réponse à l'irradiation ionique. De plus, le mécanisme de contraction des pores sous irradiation par des électrons a été délimité en fonction du domaine des énergies incidentes des électrons et de la dose. Cette recherche a montré que par rapport à une silice non poreuse, la présence de pores nanométriques réduit l’accumulation des dommages causés par les irradiations. Conjointement à cet effet bénéfique, le pore se contracte jusqu’à disparaitre sous l’impact de l’irradiation. Par conséquent, d’un point de vue applicatif cette caractéristique pourrait être mise à profit pour imaginer de nouvelles voies de traitement des effluents radioactifs, par une stratégie de type « séparation/conditionnement » ou pour l'autoguérison des couches de gel poreux formées à la surface des colis de déchets vitrifiés dont l’exutoire envisagé est le stockage géologique profond<br>Materials used in nuclear energy (fuel, packaging matrix, structural materials...) are subject to significant stresses due to the creation of defects that modify their properties. Several studies have shown that interfaces can act as a sink for defects caused by irradiation, which suggests that nanomaterials could have a higher resistance to irradiation than materials with a "micrometric" structure. Simultaneously, mesoporous silica materials have grown in popularity in recent years and are becoming more involved in the domain related to radiation conditioning, such as the prospective use of conditioning for nuclear waste. While research has begun to focus on the behavior of non-porous silica materials when exposed to radiation, no extensive investigations have been conducted on the behavior of mesoporous silica when exposed to radiation, particularly at electronic irradiation regime.This thesis aims to comprehend and explain the radiation-induced changes in mesoporous silicas under electronic regimes. This work quantified the evolution of physical (pore volume, pore diameter and distribution...) and structural (polymerization of the network, creation of defects...) properties of mesoporous silica irradiated with high-energy ion beams with stopping powers ranging from 1 keV/nm to 12 keV/nm, and with electron beams (10 - 300 keV and 0.6 - 2.4 MeV). Post-irradiation characterization methods (X-ray reflectivity, gas adsorption, SAXS, FTIR, etc.) have been used, as well as in-situ pore structure monitoring using electron microscopes. The experimental findings indicated that pore structures were susceptible to a certain degree of irradiation-induced shrinking. In contrast, evidence shows that the silica network itself does not alter much in porous silica compared to non-porous silica. Meanwhile, a 3DTS (3D thermal spike) model has been successfully applied to describe and explain the observed pore contraction behavior in response to ionic irradiation. Additionally, the mechanism of pore contraction under electron irradiation has been delineated according to the domain of incident electron energies. When compared to non-porous silica, this research has demonstrated that the existence of nanoscale pores reduces the accumulation of damage induced by irradiation. In conjunction with this effect, the pore contracts until it completely disappears under the impact of irradiation. This characteristic could, from an applicative point of view, be of interest to practitioners in the context of new methods of treating radioactive effluents, such as through the use of a "separation/conditioning" strategy, or in the context of the self-healing of porous gel layers formed on the surface of vitrified waste packages whose final destination is deep geological disposal
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Bao, Yunjuan, and 暴云娟. "Theoretical study of spin transport in low-dimensional systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687570.
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Colla, Massimiliano. "Experiments with a metastable helium atomic trap /." View thesis entry in Australian Digital Theses Program, 2006. http://thesis.anu.edu.au/public/adt-ANU20060828.104229/index.html.
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