Dissertations / Theses on the topic 'Electron'
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1
Foley, Simon Timothy. "Effects of electron-electron interactions on electronic transport in disordered systems." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273932.
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Tavener, P. "Electron spectroscopy of electrode materials." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370304.
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Keall, Paul J. "Electron transport in photon and election beam modelling /." Title page, contents and introduction only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phk24.pdf.
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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.
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Sergueev, Nikolai. "Electron-phonon interactions in molecular electronic devices." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102171.
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Over the past several decades, semiconductor electronic devices have been miniaturized following the remarkable "Moores law". If this trend is to continue, devices will reach physical size limit in the not too distance future. There is therefore an urgent need to understand the physics of electronic devices at nano-meter scale, and to predict how such nanoelectronics will work. In nanoelectronics theory, one of the most important and difficult problems concerns electron-phonon interactions under nonequilibrium transport conditions. Calculating phonon spectrum, electron-phonon interaction, and their effects to charge transport for nanoelectronic devices including all atomic microscopic details, is a very difficult and unsolved problem. It is the purpose of this thesis to develop a theoretical formalism and associated numerical tools for solving this problem.In our formalism, we calculate electronic Hamiltonian via density functional theory (DFT) within the nonequilibrium Green's functions (NEGF) which takes care of nonequilibrium transport conditions and open device boundaries for the devices. From the total energy of the device scattering region, we derive the dynamic matrix in analytical form within DFT-NEGF and it gives the vibrational spectrum of the relevant atoms. The vibrational spectrum together with the vibrational eigenvector gives the electron-phonon coupling strength at nonequilibrium for various scattering states. A self-consistent Born approximation (SCBA) allows one to determine the phonon self-energy, the electron Green's function, the electronic density matrix and the electronic Hamiltonian, all self-consistently within equal footing. The main technical development of this work is the DFT-NEGF-SCBA formalism and its associated codes.
A number of important physics issues are studied in this work. We start with a detailed analysis of transport properties of C60 molecular tunnel junction. We find that charge transport is mediated by resonances due to an alignment of the Fermi level of the electrodes and the lowest unoccupied C60 molecular orbital. We then make a first step toward the problem of analyzing phonon modes of the C60 by examining the rotational and the center-of-mass motions by calculating the total energy. We obtain the characteristic frequencies of the libration and the center-of-mass modes, the latter is quantitatively consistent with recent experimental measurements. Next, we developed a DFT-NEGF theory for the general purpose of calculating any vibrational modes in molecular tunnel junctions. We derive an analytical expression for dynamic matrix within the framework of DFT-NEGF. Diagonalizing the dynamic matrix we obtain the vibrational (phonon) spectrum of the device. Using this technique we calculate the vibrational spectrum of benzenedithiolate molecule in a tunnel junction and we investigate electron-phonon coupling under an applied bias voltage during current flow. We find that the electron-phonon coupling strength for this molecular device changes drastically as the bias voltage increases, due to dominant contributions from the center-of-mass vibrational modes of the molecule. Finally, we have investigated the reverse problem, namely the effect of molecular vibrations on the tunneling current. For this purpose we developed the DFT-NEGF-SCBA formalism, and an example is given illustrating the power of this formalism.
6
Sica, G. "Electron-electron and electron-phonon interactions in strongly correlated systems." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12194.
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In this work we investigate some aspects of the physics of strongly correlated systems by taking into account both electron-electron and electron-phonon interactions as basic mechanisms for reproducing electronic correlations in real materials. The relevance of the electron-electron interactions is discussed in the first part of this thesis in the framework of a self-consistent theoretical approach, named Composite Operator Method (COM), which accounts for the relevant quasi-particle excitations in terms of a set of composite operators that appear as a result of the modification imposed by the interactions on the canonical electronic fields. We show that the COM allows the calculation of all the relevant Green s and correlation functions in terms of a number of unknown internal parameters to be determined self-consistently. Therefore, depending on the balance between unknown parameters and self-consistent equations, exact and approximate solutions can be obtained. By way of example, we discuss the application of the COM to the extended t-U-J-h model in the atomic limit, and to the two-dimensional single-band Hubbard model. In the former case, we show that the COM provides the exact solution of the model in one dimension. We study the effects of electronic correlations as responsible for the formation of a plethora of different charge and/or spin orderings. We report the phase diagram of the model, as well as a detailed analysis of both zero and finite temperature single-particle and thermodynamic properties. As far as the single-band Hubbard model is concerned, we illustrate an approximated self-consistent scheme based on the choice of a two-field basis. We report a detailed analysis of many unconventional features that arise in single-particle properties, thermodynamics and system's response functions. We emphasize that the accuracy of the COM in describing the effects of electronic correlations strongly relies on the choice of the basis, paving the way for possible multi-pole extensions to the two-field theory. To this purpose, we also study a three-field approach to the single-band Hubbard model, showing a significant step forward in the agreements with numerical data with respect to the two-pole results. The role of the electron-phonon interaction in the physics of strongly correlated systems is discussed in the second part of this thesis. We show that in highly polarizable lattices the competition between unscreened Coulomb and Fröhlich interactions results in a short-range polaronic exchange term Jp that favours the formation of local and light pairs of bosonic nature, named bipolarons, which condense with a critical temperature well in excess of hundred kelvins. These findings, discussed in the framework of the so-called polaronic t-Jp model, are further investigated in the presence of a finite on-site potential U, coming from the competition between on-site Coulomb and Fröhlich interactions. We discuss the role of U as the driving parameter for a small-to-large bipolaron transition, providing a possible explanation of the BEC-BCS crossover in terms of the properties of the bipolaronic ground state. Finally, we show that a hard-core bipolarons gas, studied as a charged Bose-Fermi mixture, allows for the description of many non Fermi liquid behaviours, allowing also for a microscopic explanation of pseudogap features in terms of a thermal-induced recombination of polarons and bipolarons, without any assumption on preexisting order or broken symmetries.
7
Sica, Gerardo. "Electron-electron and electron-phonon interactions in strongly correlated systems." Doctoral thesis, Universita degli studi di Salerno, 2013. http://hdl.handle.net/10556/1418.
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2011 - 2012In this work we investigate some aspects of the physics of strongly correlated systems by taking into account both electron-electron and electron-phonon interactions as basic mechanisms for reproducing electronic correlations in real materials. The relevance of the electron-electron interactions is discussed in the first part of this thesis in the framework of a self-consistent theoretical approach, named Composite Operator Method (COM), which accounts for the relevant quasi-particle excitations in terms of a set of composite operators that appear as a result of the modification imposed by the interactions on the canonical electronic fields. We show that the COM allows the calculation of all the relevant Green’s and correlation functions in terms of a number of unknown internal parameters to be determined self-consistently. Therefore, depending on the balance between unknown parameters and self-consistent equations, exact and approximate solutions can be obtained. By way of example, we discuss the application of the COM to the extended t-U- J-h model in the atomic limit, and to the two-dimensional single-band Hubbard model. In the former case, we show that the COM provides the exact solution of the model in one dimension. We study the effects of electronic correlations as responsible for the formation of a plethora of different charge and/or spin orderings. We report the phase diagram of the model, as well as a detailed analysis of both zero and finite temperature single-particle and thermodynamic properties. As far as the single-band Hubbard model is concerned, we illustrate an approximated selfconsistent scheme based on the choice of a two-field basis. We report a detailed analysis of many unconventional features that arise in single-particle properties, thermodynamics and system’s response functions. We emphasize that the accuracy of the COM in describing the effects of electronic correlations strongly relies on the choice of the basis, paving the way for possible multi-pole extensions to the twofield theory. To this purpose, we also study a three-field approach to the single-band Hubbard model, showing a significant step forward in the agreements with numerical data with respect to the two-pole results. The role of the electron-phonon interaction in the physics of strongly correlated systems is discussed in the second part of this thesis. We show that in highly polarizable lattices the competition between unscreened Coulomb and Fröhlich interactions results in a short-range polaronic exchange term Jp that favours the formation of local and light pairs of bosonic nature, named bipolarons, which condense with a critical temperature well in excess of hundred kelvins. These findings, discussed in the framework of the so-called polaronic t-Jp model, are further investigated in the presence of a finite on-site potential ~U , coming from the competition between on-site Coulomb and Fröhlich interactions. We discuss the role of ~U as the driving parameter for a small-to-large bipolaron transition, providing a possible explanation of the BEC-BCS crossover in terms of the properties of the bipolaronic ground state. Finally, we show that a hard-core bipolarons gas, studied as a charged Bose-Fermi mixture, allows for the description of many non Fermi liquid behaviours, allowing also for a microscopic explanation of pseudogap features in terms of a thermal-induced recombination of polarons and bipolarons, without any assumption on preexisting order or broken symmetries. [edited by author]
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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.
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Phinney, Isabelle Y. "Probing electron-electron and electron-phonon interactions in twisted bilayer graphene." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127092.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 81-86).
Two-dimensional systems, and, most recently, moire systems, have risen to the forefront of condensed matter physics with the advent of experimental techniques that allow for controlled stacking of van der Waals heterostructures [17, 54]. For example, it was recently discovered that when two pieces of atomically thin carbon (graphene) are twisted at 1.1° with respect to one another, they display a variety of effects, including superconducting behavior [10]. Experimental investigation of the behavior of small-angle twisted bilayer graphene (SA-TBG) as a function of twist angle is imperative to understanding the mechanisms that play into the many interesting, strongly-interacting phenomena that the moire system displays. In this thesis, I present three experiments which explore electron-electron and electron-phonon interactions in SA-TBG. I first consider SA-TBG as a host for a viscous electron fluid and look for the onset of fluid behavior via electron transport. Then I investigate the temperature dependence of resistivity in SA-TBG devices at a number of angles. The final experiment examines magnetophonons in three devices above the magic angle and compares the findings to theoretical results.
by Isabelle Y. Phinney.
S.B.
S.B. Massachusetts Institute of Technology, Department of Physics
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Kula, Mathias. "Understanding Electron Transport Properties of Molecular Electronic Devices." Doctoral thesis, KTH, Teoretisk kemi, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4500.
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his thesis has been devoted to the study of underlying mechanisms for electron transport in molecular electronic devices. Not only has focus been on describing the elastic and inelastic electron transport processes with a Green's function based scattering theory approach, but also on how to construct computational models that are relevant to experimental systems. The thesis is essentially divided into two parts. While the rst part covers basic assumptions and the elastic transport properties, the second part covers the inelastic transport properties and its applications. It is discussed how di erent experimental approaches may give rise to di erent junction widths and thereby di erences in coupling strength between the bridging molecules and the contacts. This di erence in coupling strength is then directly related to the magnitude of the current that passes through the molecule and may thus explain observed di erences between di erent experiments. Another focus is the role of intermolecular interactions on the current-voltage (I-V) characteristics, where water molecules interacting with functional groups in a set of conjugated molecules are considered. This is interesting from several aspects; many experiments are performed under ambient conditions, which means that water molecules will be present and may interfere with the experiment. Another point is that many measurement are done on self-assembled monolayers, which raises the question of how such a measurement relates to that of a single molecule. By looking at the perturbations caused by the water molecules, one may get an understanding of what impact a neighboring molecule may have. The theoretical predictions show that intermolecular e ects may play a crucial role and is related to the functional groups, which has to be taken into consideration when looking at experimental data. In the second part, the inelastic contribution to the total current is shown to be quite small and its real importance lies in probing the device geometry. Several molecules are studied for which experimental data is available for comparison. It is demonstrated that the IETS is very sensitive to the molecular conformation, contact geometry and junction width. It is also found that some of the spectral features that appear in experiment cannot be attributed to the molecular device, but to the background contributions, which shows how theory may be used to complement experiment. This part concludes with a study of the temperature dependence of the inelastic transport. This is very important not only from a theoretical point of view, but also for the experiments since it gives experimentalists a sense of which temperature ranges they can operate for measuring IETS.QC 20100804. Ändrat titeln från: "Understanding Electron Transport Properties in Molecular Devices" 20100804.
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Saxena, Vishal. "Hot electron luminescence from GaAs : electric field effects." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624144.
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Geer, Steven Jon. "Electronic properties of bilayer low-dimensional electron systems." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619774.
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Zolleis, Kai Rudiger. "Electronic properties of parallel low-dimensional electron systems." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624494.
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Kula, Mathias. "Understanding electron transport properties in molecular electronic devices /." Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4500.
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Harland, C. J. "Detector and electronic developments for scanning electron microscopy." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370435.
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Ren, Yan-Ru. "Orbital spin-splitting factors for conduction electrons in lead." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25961.
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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.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Ung, Kim-Chau. "Effects of electron-electron and electron-phonon interactions in narrow-band systems." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186622.
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Different ordered states, CDW, BOW, and SDW, are investigated theoretically for both interacting and noninteracting cases as well as for different band filling systems. For noninteracting case, we find that the BOW is always accompanied by the CDW and vice versa in one-dimensional system for commensurability > 2. The strong electron-molecular vibration coupling drives both CDW and BOW, and plays thus an important role in the stabilization of the CDW state for these non-half-filled materials. Within the simply extended Peierls-Hubbard model, the experimentally observed lattice distortion of MEM(TCNQ)₂ can be precisely understood with our model calculation. In addition to the on-site repulsion U, the nearest-neighbor Coulomb interaction V is shown to play a vital role in the strongly correlated system; and a critical value V(c) is found for the quarter-filled system. With the understanding of the dominant broken symmetries in quasi-one-dimensional quarter-filled band, some implications for superconducting materials are discussed. The effect of band filling on the 4k(F) BOW instability is studied by the extended Peierls-Hubbard model; it is found that a strongly systematic tendency of the 4k(F) is dependent on the band filling. By studying the pair binding energy in some small clusters, we point out that the electron (or hole) pairing is not due to the Coulomb interaction, at least in the small U region.
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Chen, T. M. "Electron-electron interactions in GaAs quantum wires." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597526.
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The first experiment presents a novel method for continuously tracking the energies of the 1D subbands as a function of carrier density. I show a peculiar dc conductance feature in the region where the so-called 0.85(2e2/h) plateau in differential conductance is observed, directly demonstrating the pinning effect of the energy level of the minority spin-up electrons. A model concerning providing for non-linear population of the 1D subband with dc bias is proposed to explain the unusual differential conductance value of the 0.85(2e2/h) plateau. The second experiment shows that a fully spin-polarised current, consisting of a single spin-type only, can be created without external magnetic fields. When a source-drain bias lifts the momentum degeneracy, the dc measurements show that it is possible to achieve a unidirectional transport with a ferromagnetic order and this ordered spin array is destroyed once transport in both directions commences. The degree of spin polarisation of currents, between full spin polarisation, partial spin polarisation, and spin degeneracy, is thus simply controlled by source-drain bias and split-gate voltage, something of considerable value for spintronics. I then present four odd-even spin phenomena in the third experiment, showing clear evidence that a quasi-one-dimensional system tends to spontaneous spin polarisation with the energy band of minority spin-up electrons being reluctant to populate, thus widening the energy gap between two spin types. Variation of g-factor within a single subband is measured using a dc conductance technique, showing the g-factor oscillates as the 1D subbands are filled one by one with increasing carrier density. The last experiment introduces new experimental data of the zero-bias anomaly (ZBA), showing clear evidence that the ZBA observed in quantum wires in fact has a different origin from the Kondo effect seen in quantum dots. I propose a phenomenological model wherein the zero-bias anomaly in 1D quantum wires is in fact attributed to a upward shift of the 1D subband energy with source-drain bias.
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Pierre, Frédéric. "Interactions electron-electron dans les fils mesoscopiques." Paris 6, 2000. http://www.theses.fr/2000PA066375.
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Les interactions electron-electron limitent la coherence quantique des electrons dans les metaux et leur permettent d'atteindre l'equilibre thermique a basse temperature. Ces interactions sont faibles car les electrons dans les metaux sont etroitement ecrantes par la polarisation qu'ils induisent dans le milieu forme par les autres electrons. Dans le regime mesoscopique, on s'attend a ce que les chocs elastiques sur les defauts du reseau, les bords du metal et les impuretes diminuent l'efficacite de l'ecrantage et donc augmentent les interactions. L'objet de cette these est precisement de determiner experimentalement la nature des interactions inelastiques subies par les electrons a basse temperature dans les fils mesoscopiques. Dans la premiere partie, nous presentons la mesure du taux avec lequel les electrons echangent de l'energie dans des fils d'argent, de cuivre et d'or. Pour cela, nous mesurons la fonction de distribution en energie des electrons dans un regime stationnaire hors-equilibre. Dans la deuxieme partie, nous presentons la mesure du temps de coherence de phase des electrons en fonction de la temperature, egalement dans des fils de cuivre d'or et d'argent. La coherence quantique des electrons est limitee par toutes les collisions inelastiques independamment de l'energie echangee. Nous avons deduit le temps de coherence de phase de la mesure des corrections de localisation faible a la conductance des fils. Dans la troisieme partie, nous presentons des mesures de l'anomalie de conductance aux petites tensions d'une longue jonction tunnel entre un fil d'aluminium et un plan de masse. Cette depression de la conductance tunnel est un autre effet de l'interaction coulombienne. Pour comparer mesures et predictions theoriques, nous avons reformule les predictions du calcul microscopique des interactions entre electrons en terme d'impedance electromagnetique, dans un langage similaire a celui utilise par la theorie phenomenologique du blocage de coulomb.
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Jin, Liang. "Direct electron detection in transmission electron microscopy." Diss., [La Jolla, Calif.] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3344737.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed April 3, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 148-151).
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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/.
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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.
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Krecinic, Faruk [Verfasser]. "Ultrafast electron diffraction and imaging using ionized electrons / Faruk Krecinic." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1142155447/34.
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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.
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Hardy, Thomas M. "Superconductivity with strongly correlated electrons and an electron-phonon interaction." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/34947.
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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.
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Cao, Hui. "Dynamic Effects on Electron Transport in Molecular Electronic Devices." Doctoral thesis, KTH, Teoretisk kemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12676.
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HTML clipboardIn this thesis, dynamic effects on electron transport in molecular electronic devices are presented. Special attention is paid to the dynamics of atomic motions of bridged molecules, thermal motions of surrounding solvents, and many-body electron correlations in molecular junctions. In the framework of single-body Green’s function, the effect of nuclear motions on electron transport in molecular junctions is introduced on the basis of Born-Oppenheimer approximation. Contributions to electron transport from electron-vibration coupling are investigated from the second derivative of current-voltage characteristics, in which each peak is corresponding to a normal mode of the vibration. The inelastic-tunneling spectrum is thus a useful tool in probing the molecular conformations in molecular junctions. By taking account of the many-body interaction between electrons in the scattering region, both time-independent and time-dependent many-body Green’s function formula based on timedependent density functional theory have been developed, in which the concept of state of the system is used to provide insight into the correlation effect on electron transport in molecular devices. An effective approach that combines molecular dynamics simulations and first principles calculations has also been developed to study the statistical behavior of electron transport in electro-chemically gated molecular junctions. The effect of thermal motions of polar water molecules on electron transport at different temperatures has been found to be closely related to the temperature-dependent dynamical hydrogen bond network.QC20100630
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Sze, Kong Hung. "Electronic excitation of polyatomic molecules by fast electron impact." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29302.
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High resolution electron energy loss spectroscopy has been used to examine the inner-shell and valence-shell electronic excitation of a number of polyatomic molecules, including SF₆, SeF₆, TeF₆, ClF₃, C₂H₃F, C₂H₃Cl, C₂H₃Br, C₂H₃I, Ni(CO)₄, (CH₃)₂SO and SO₂. The inner-shell and valence-shell electron energy loss spectra (ISEELS and VSEELS) were measured under low momentum transfer conditions with impact energy in the range of 1-3.7 keV and 0° scattering angle. Under these conditions the spectra are dominated by electric dipole-allowed transitions. The ISEELS spectra include all accessible core excitations of these molecules below 1000 eV equivalent photon energy. A number of specific investigations have been performed in order to extend present understanding of the physical nature of electronic excitation phenomena, in particular those involving inner-shell electrons. In addition the present work illustrates new applications of ISEELS to the study of chemical phenomena.
In the investigation of (Coulombic) potential barrier effects in the "cage" molecules SF₆, SeF₆, TeF₆ and ClF₃, f-type continuum shape resonances are observed for the first time in the spectra of TeF₆ and they show very different spectral behavior from the d-type continuum shape resonances observed in the spectra of SF₆ and SeF₆. Consideration of both the ISEELS and VSEELS spectra indicates that there is a weakening of the potential barrier in going through the series from SF₆ to SeF₆ to TeF₆. The Coulombic potential barrier model provides an extremely satisfactory understanding of (a) the co-existence of intense continuum shape resonances and intense Rydberg transitions plus direct ionization continuum; and (b) the number and symmetry of continuum shape resonances observed in the ISEELS spectra of ClF₃. The physical significance of Coulombic potential barrier effects is further convincingly demonstrated by a comparison of the "central atom" inner-shell spectra of SF₆, ClF₃ and HCl.
In contrast to earlier work, the present comparative study of the He(I) and He(II) photoelectron spectra and the VSEELS excitation spectra of the monohaloethylenes (i.e. C₂H₃X; X = F, Cl, Br and I) suggests that the HOMO orbital in C₂H₃I is predominantly of iodine 5p[sub ⊥](out-of-plane) character rather than of π character whereas the reverse situation applies to the HOMO orbitals of C₂H₃F, C₂H₃Cl and C₂H₃Br. Based on a term value correlation analysis, substitutional effects are found to be most prominent in the σ* -type orbitals, while the π* and Rydberg orbitals are less influenced. Linear correlations between the C-X bond strength and the term values for both inner-shell and valence-shell transitions to the σ* (CX) orbital are also observed.
The ISEELS and VSEELS spectra of Ni(CO)₄ are compared with the
corresponding spectra in free CO. The C and O Is spectra of these two molecules show
some notable similarities despite the very different manifold of final states available. In
particular the inner-shell spectra of both molecules exhibit intense ls → π* and ls → σ* transitions. High resolution ISEELS has been used to obtain vibrational resolved C Is spectra of Ni(CO)₄ and free CO. The implications and possibilities of studying dπ →pπ back-bonding in transition metal carbonyl complexes by high resolution ISEELS spectroscopy are discussed.
The inner-shell (S 2s, 2p, C Is) excitations of (CH₃)₂SO (DMSO) measured by ISEELS are compared with synchrotron radiation studies of the S Is photoabsorption spectrum. The pre-edge regions of these spectra are interpreted as excitations to common manifolds of virtual valence and Rydberg orbitals. A linear correlation between the S-C bond lengths and the term values of S 2p[sub 3/2] → σ* (S-C) transitions is demonstrated for DMSO and a number of other sulfur compounds.
The S 2p, 2s and O Is ISEELS spectra of SO₂ as well as the S ls photoabsorption spectrum are compared with and assigned according to the results of multichannel quantum defect theory calculations. The calculated energies and oscillator strengths of spectral features in these spectral regions are generally in good quantitative agreement with the measurements.Science, Faculty of
Chemistry, Department of
Graduate
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Li, Yuesong. "Electronic structure and spectra of few-electron quantum dots." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-05172007-110916/.
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Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008.Minqiang Li, Committee Member ; Constantine Yannouleas, Committee Member ; Michael Pustilnik, Committee Member ; Mei-Yin Chou, Committee Member ; Uzi Landman, Committee Member.
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Zhou, Wen. "Electronic structure and single electron reactivity in organochromium complexes." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44188.
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Condylis, Paul Constantine. "Measuring the electron electric dipole moment using supersonic YbF." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429391.
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Taylor, M. E. "Substrate and electrode effects in inelastic electron tunnelling spectroscopy." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235265.
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Inelastic Electron Tunnelling Spectroscopy is a powerful and versatile technique for obtaining vibrational densities of states of amorphous materials and adsorbed molecules. The experimental device, or tunnel junction, consists of two metal electrodes separated by a thin (2nm) layer of the material under study. This thesis looks at features in the tunnelling spectrum due to electrode phonons, and also at the effects of substrate roughness on the spectrum. Two coupled linear chains are used to model the vibrational behaviour of joined lattices in order to consider the penetration of phonons of one material into the other; penetration does not occur unless the two chains have very similar properties. Work with Al-I-Al-Pb tunnel junctions confirms the model results, as no sign is seen of lead phonon peaks in the tunnelling spectrum. However, other workers have seen lead peaks in Al-I-Ag-Pb junctions, and invoked phonon penetration in explanation. Microscopic examination of similarly prepared silver films reveals that they are pinholed; and this, it is argued, gives rise to the lead peaks. Results are presented on the magnitudes of electrode phonon structure in tunnelling spectra, and models for the occurrence of these features are reviewed. It is argued, from comparison of the experimental data with bulk self energies from superconducting tunnelling, that the electron-phonon coupling responsible is characteristic of the bulk metal; interaction does not take place in the barrier. This is consistent with the linear chain model. The effects of roughening tunnel junctions with calcium fluoride substrates are studied. Little change is noted with undoped junctions, but investigation of formate-doped junctions confirms the loss in dopant peak intensity seen by other workers and some variation is noticed in the rate of loss of intensity between C-H and CO2 modes. The mechanism which best explains these observations is that roughening encourages penetration of the organic layer by atoms of the top electrode metal.
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Galda, Alexey. "Electronic properties of Luttinger Liquid with electron-phonon interaction." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4293/.
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This thesis addresses a theoretical study of the problem of a single impurity embedded in a one-dimensional system of interacting electrons in presence of electron-phonon coupling. First we consider a system with a featureless point-like potential impurity, followed by the case of a resonant level hybridised with a Luttinger Liquid. The stress is made on a more fundamental problem of a featureless scatterer, for which two opposite limits in the impurity strength are considered: a weak scatterer and a weak link. We have found that, regardless of the transmission properties of phonons through the impurity, the scaling dimensions of the conductance in these limits obey the duality condition, \( \triangle_{WS}\) \( \triangle_{WL}\) = 1, known for the Luttinger Liquid in the absence of phonons. However, in the case when the strength of phonon scattering is correlated with electron scattering by the impurity, we find a nontrivial phase diagram with up to three fixed points and a possibility of a metal-insulator transition. We also consider the case of a weakly interacting electron-phonon system in the presence of a single impurity of an arbitrary scattering potential. In the problem of a resonant level attached to the Luttinger Liquid we show that the electron-phonon coupling significantly modifies the effective energy-dependent width of the resonant level in two different geometries, corresponding to the resonant and anti-resonant transmission in the Fermi gas.
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Wu, Dennis M. (Dennis Meng-Jiao). "Quantum-coupled single-electron thermal to electric conversion scheme." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42421.
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Includes bibliographical references (p. 236-242).Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2008.
A new thermal to electric conversion scheme based on an excitation transfer and tunneling mechanism is studied theoretically. Coulomb coupling dominates when the hot side and the cold side are very close. Two important concepts went into the device scheme: (1) Coulomb coupling, to try to increase throughput power (which is not subject to blackbody limit), and (2) a quantum dot implementation, to restrict number of states, to try to increase efficiency. Modeling efforts from Bloch equations, brute force numerical simulations, and the secular equations partitioning method are discussed. A hot-side quantum dot design of the device is considered. Alternative implementation where the hot-side is a plain sheet of metal or aluminum oxide is analyzed. We found that the model power/area is higher than the blackbody limit, and the predicted conversion efficiency is very high.
by Dennis M. Wu.
Ph.D.
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Zhao, Xu S. M. Massachusetts Institute of Technology. "Electric field engineering in GaN high electron mobility transistors." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/43062.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2008.Includes bibliographical references (leaves 66-70).
In the last few years, AlGaN/GaN high electron mobility transistors (HEMTs) have become the top choice for power amplification at frequencies up to 20 GHz. Great interest currently exists in industry and academia to increase the frequency to mm-wave frequencies. The goal of this thesis has been to identify new solutions to some of the main challenges to increase this frequency performance even further. Electron velocity is a critical parameter affecting the transistor performance. In standard GaN transistors, the extremely high electric fields present in the channel of the device reduce the average electron velocity well below the peak electron velocity, resulting in low cutoff frequencies. In this thesis, we introduced a partial recess in the drain access region of the transistor to engineer the electric field along the channel of the device without introducing parasitic capacitances. By reducing the peak electric field, the average electron velocity is increased by 50%. This new technology has the potential to improve not only the cutoff frequencies, but also the breakdown voltage of GaN transistors. To successfully engineer the electric field in GaN devices, an accurate, reliable and low damage etching technology is needed. However none of the traditional GaN dry etching technologies meets these requirements. This lack of suitable technology has motivated us to develop a new atomic layer etching technique of AlGaN/GaN structures. This technology has been shown to be a self limited process with very high reliability and low damage, which will be very useful both in electric field engineering and gate recess. Finally, another factor hindering GaN HEMTs from competing with InGaAs devices at high frequencies are their high parasitic capacitances and resistances. In this thesis, ohmic drain contacts are replaced with Schottky drain contacts to reduce the drain access resistance.
(cont) ADS simulations predict a very significant increase in the cutoff frequencies by virtue of the lowered parasitic resistances. In conclusion, the theoretical and experimental work developed during this project has demonstrated the great potential of three new technologies to overcome the main challenges of mm-wave GaN HEMTs. The application of these technologies to actual devices is under way and it will represent an important element of the ultra-high GaN transistors of the future.
by Xu Zhao.
S.M.
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Restivo, Rick A. "Free electron laser weapons and electron beam transport." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA333358.
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Price, Adam Scott. "Coulomb drag, mesoscopic physics, and electron-electron interaction." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/55093.
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The first part of this thesis deals with the study of mesoscopic fluctuations of the Coulomb drag resistance in double-layer GaAs/AlGaAs heterostructures, both in weak magnetic fields and strong magnetic fields. In the second part, measurements are made in a monolayer graphene structure, specifically of the quantum lifetime, and the mesoscopic resistance fluctuations at quantising magnetic fields.
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Bassett, L. C. "Probing electron-electron interactions with a quantum antidot." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596454.
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In the integer quantum Hall (IQH) regime, an antidot provides a finite, controllable ‘edge’ of quantum Hall fluid which is an ideal laboratory for investigating the collective dynamics of large numbers of interacting electrons. Transport measurements of single antidotes probe the orbital energy spectra of the antidot edge, and gate-defined antidot devices offer the flexibility to vary both the dimensions of the antidot and the couplings to the extended IQH edge modes which serve as leads. We can also use the spin-selectivity of the IQH edge modes to perform spin-resolved transport measurements, from which we can infer the antidot spin-structure. This thesis describes a combination of such experimental measurements and related computational models designed to investigate the effects of electron-electron interactions in quantum antidotes, with general implications for the physics of spin and charge in IQH systems. Our work provides a powerful example of the practical applications of IQH edge modes for selective transport in mesoscopic quantum electronics, which we have used to perform the first spin-resolved measurements of VAD = 2 transmission resonances. Our discovery of spin-charge separation in the low-field antidot excitation spectrum paints a picture of the antidot as a finite droplet of interacting IQH fluid in the LLL, with all of the rich physics of exchange, collective modes, spin textures, etc., which this entails. Our results are therefore relevant not only for the physics of antidots, but more broadly for the understanding of interacting electronic systems of many particles in the IQH regime.
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Bawa, Ramadan Ali. "Electron-rich and electron-deficient anthracene chiral auxiliaries." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420777.
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Lea-Wilson, M. A. "Electron spin resonance studies of electron irradiated diamond." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381911.
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Nagy, O. Z. I. "Analysis of electron-atom and electron-molecule collisions." Thesis, University of Stirling, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370537.
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Hoffmann, Ryan Carl. "Electron-Induced Electron Yields of Uncharged Insulating Materials." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/749.
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Presented here are electron-induced electron yield measurements from high-resistivity, high-yield materials to support a model for the yield of uncharged insulators. These measurements are made using a low-fluence, pulsed electron beam and charge neutralization to minimize charge accumulation. They show charging induced changes in the total yield, as much as 75%, even for incident electron fluences of <3 fC/mm2, when compared to an uncharged yield. The evolution of the yield as charge accumulates in the material is described in terms of electron recapture, based on the extended Chung and Everhart model of the electron emission spectrum and the dual dynamic layer model for internal charge distribution. This model is used to explain charge-induced total yield modification measured in high-yield ceramics, and to provide a method for determining electron yield of uncharged, highly insulating, high-yield materials. A sequence of materials with progressively greater charge susceptibility is presented. This series starts with low-yield Kapton derivative called CP1, then considers a moderate-yield material, Kapton HN, and ends with a high-yield ceramic, polycrystalline aluminum oxide. Applicability of conductivity (both radiation induced conductivity (RIC) and dark current conductivity) to the yield is addressed. Relevance of these results to spacecraft charging is also discussed.
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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.
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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.
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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.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.
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Okazaki, K., S. Sugai, Y. Muraoka, and Z. Hiroi. "Role of electron-electron and electron-phonon interaction effects in the optical conductivity of VO_2." The American Physical Society, 2006. http://hdl.handle.net/2237/7137.
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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/.
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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.
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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/.
Full textAbstract:
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.
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Prance, Jonathan Robert. "Cooling an electron gas using quantum dot based electronic refrigeration." Thesis, University of Cambridge, 2009. https://www.repository.cam.ac.uk/handle/1810/244593.
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Studies of two-dimensional electron gases (2DEGs) in semiconductors form an active and productive field of condensed matter physics research. As well as having interesting inherent properties, they are used as the foundation for constructing various nano-scale electronic devices, such as quantum wires and quantum dots. Conventionally, low temperature measurements of 2DEGs are made by cooling the sample to 1.5 K with liquid Helium-4, to 300 mK with liquid Helium-3, or even down to a few mK using a dilution refrigerator. However, at lower temperatures the electron gas becomes increasingly decoupled from the lattice in which it resides. Below ~ 1 K the coupling can be weak enough for the electron gas to be significantly elevated in temperature due to parasitic heating. In this thesis we present the experimental and theoretical investigation of a refrigeration scheme that has the potential to cool 2DEGs below the temperatures currently available. Cooling to ever lower temperatures would be beneficial for studying fragile fractional quantum Hall states, non-Fermi-liquid behaviour in bilayer 2DEGs, or interactions like the Kondo effect that occur between quantum dots and 2DEGs. The scheme we investigate is called the Quantum Dot Refrigerator (or QDR) and is based upon the energy selective transport of electrons through the singleparticle states of quantum dots. By using a pair of dots, both hot electrons and hot holes can be selectively removed from an otherwise electrically isolated 2DEG. The result is a net current that continuously removes heat. This type of refrigerator is best suited to be used in conjunction with a dilution fridge or Helium-3 system to provide a final stage of cooling. The scheme was first investigated theoretically in 1993 by Edwards et al. but, to our knowledge, has never before been demonstrated experimentally. We detail the fabrication and measurement of a QDR device that is designed to cool an isolated 6 µm2 2DEG. In order to interpret the behaviour of the device, a model was developed to take account of electrostatic interactions between the components of the system (the quantum dots and the isolated 2DEG). Electrostatic interactions were found to be significant for our design, but were neglected in previous work. Our model predicts that their presence complicates, but does not invalidate, the principle of operation of a QDR. By comparing measurements of the current through the QDR with predictions of the model, we show that the observed behaviour is consistent with cooling of the isolated 2DEG by up to 100 mK at ambient temperatures around 250 mK. Although these temperatures are well within the reach of conventional refrigeration techniques, the results are a compelling proof-of-concept demonstration that the QDR principle is sound and can achieve significant refrigeration in the right conditions. Finally, we discuss future directions for improving QDR performance and characterisation, and for lowering the achievable base temperature. We also suggest how QDRs could be used to provide cold reservoirs for a nano-scale electronic device, and explore the limitations that would apply to such an experiment.
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Kara, Dhiren Manji. "Toward an electron electric diploe moment measurement using Ytterbium fluoride." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.536009.
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Gardel, Emily Jeanette. "Microbe-electrode interactions: The chemico-physical environment and electron transfer." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11185.
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This thesis presents studies that examine microbial extracellular electron transfer that an emphasis characterizing how environmental conditions influence electron flux between microbes and a solid-phase electron donor or acceptor. I used bioelectrochemical systems (BESs), fluorescence and electron microscopy, chemical measurements, 16S rRNA analysis, and qRT-PCR to study these relationships among chemical, physical and biological parameters and processes.Engineering and Applied Sciences
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Al, Sawi A. N. "Study of the electronic structure of InSb by electron spectroscopy." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3007631/.
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Williams, Robert E. "Naval electric weapons : the electromagnetic railgun and free electron laser /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FWilliams.pdf.
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