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Licsandru, Erol-Dan. "Dynamic systems for the translocation of water, ions or electrons." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS213/document.
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L'objectif de ce travail concerne le transport à travers des membranes lipidiques de l'eau et d' ions par des canaux artificiels auto-assembles, et le design des nano-contacts organiques auto-assembles pour des applications macro échelle : biocathodes. La première partie est concentre sur le transport de l'eau et d'ions à travers des membranes bicouches. L'objectif est la réplication de la fonction des protéines naturelles, utilisant des composées ureido-heterocycle. L'influence de la composition des espèces est évaluée par rapport à leur structure supramoléculaire et la liaison entre elle et son activité. Le premier chapitre traite le transport des ions travers les bicouches lipidiques générées en grandes vésicules unilamellaires (LUVs), en termes d'activité et sélectivité dépendants de la structure de composées. Le deuxième chapitre présente le transport de l'eau à travers des systèmes LUV. Une approche combinée a été utilisée pour évaluer l'activité des canaux, par les placer a l'extérieur des liposomes comme même directement dans le couche lipidique. Finalement le transport de protons a été évalué pour ces structures, relevant des canaux de protons très efficients. Le troisième chapitre aborde une approche interdisciplinaire. Certaines triarylamines (TAAs) ont la propriété à former des nano fibrilles sur l'irradiation par la formation des radicaux-cations. Ceci représente une voie de conduction directionnelle pour électrons avec une conductivité similaire aux métaux. Les fibrilles, quelles déchire en absence de lumière, offrent des possibilités intéressants au rapport de nano-échelle contacts électriques. Une matrice de silice mésoporeuse a été utilisée pour confiner les TAAs . La nouveauté de cette approche c'est que le système présent des conductivités à travers les nano fils de TAA, alors que la matrice de silice est isolante. Ce dispositif a été caractérisé et utilisé comme un bio cathode contenant l'enzyme laccase et ont été testes pour prouver le role des nano contacts TAAs comme les seuls fournisseurs d'électrons pour l'enzymeThe objective of this work is the study of the transport through lipid membranes of water and ions using self-assembled artificial channel structures and the design of nano sized self-assembled organic contacts for macroscale applications: biocathodes.The first part focuses on the transport through membrane bilayers. The objective is to replicate the function of naturally occurring proteins using ureido-hetreocycle compounds. The influence of species composition is assessed versus the supramolecular structure it generates and the link between it and activity. The first chapter treats the transport of ions through the lipid bilayers of large unilamellar vesicles (LUVs), in terms of total activity and selectivity vs. the structure of compounds. The second chapter refers to the transport of water on LUV systems. Here, a combined approach was used in evaluating the channels' activity, by placing them both on the outside of the liposomes but also directly in the lipid layer. Finally the protons transport of these structures was assessed reveling very efficient proton channels. The third chapter has an interdisciplinary approach combining several topics. The triaryl amines (TAAs) have to propriety of forming self-assembled nano sized fibrils when irradiated by the generation of cation-radicals. These present a directional electronic conduction pathway and are reported to display metal-like conductivity. These fibrils, which unravel in the absence of light, provide interesting possibilities as organic nano scale electrical contacts. A matrix of mesoporous silica was created via electrodeposition in order to enclose the TAAs in a confined medium. The novelty of the approach is that the system only has electron conductivity trough the TAAs nano wires while the silica mass is insulating. The resulting device's proprieties were characterized and further it was used as a bio cathode. The biocathodes containing the enzyme Laccase were then tested to prove the functioning of the matrix of nano contacts as the only providers of electrons to the enzyme
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Iyer, Venkatraman 1967. "Discretized path integral molecular dynamic simulations with quantum exchange of two electrons in molten potassium chloride." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278142.
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This study presents the use of Feynman's Quantum Path Integral (QPI) approach in the Molecular Dynamic Simulation of two electrons in molten KCl. In this research, we have successfully implemented an original technique to tackle the questions of spin dependent quantum exchange phenomenon between two electrons. It was found that two electrons with antiparallel spins form a stable bipolaronic complex and those with parallel spins repel each other and form two dissociated or singlet states. Calculations of the average energies compare well with previous computational findings by Selloni et al. who used a direct integration of the time dependent Schrodinger equation. The radial distribution function illustrated clearly that the triplet state nests itself among the cations, namely K+. The electron-electron separation distance was found to be ∼3.5 A for the triplet state and the singlet case showed the electrons being repelled as far as possible; namely half the size of the simulation cell ∼7 A.
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CORNIER-QUIQUANDON, MARIANNNE. "Theorie dynamique de la diffraction des electrons rapides par les cristaux et quasicristaux." Paris 6, 1988. http://www.theses.fr/1988PA066167.
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Description de la diffraction des electrons par les solides ordonnes a longue distance. Le formalisme necessite d'exprimer l'hamiltonien de diffraction sur une base discrete d'ondes planes. Le spectre des etats propres de l'hamiltonien de diffraction est dense non uniforme. Les calculs dynamiques peuvent donc etre effectues en echantillonant le spectre par valeurs discretes. Application de la methode a la simulation des images de microscopie electronique en haute resolution sur une phase icosaedrique en utilisant la description 6d de la structure. Interpretation des resultats experimentaux par la representation 6d
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Lanier, Steven t. "Dynamic Screening via Intense Laser Radiation and Its Effects on Bulk and Surface Plasma Dispersion Relations." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1011758/.
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Recent experimentation with excitation of surface plasmons on a gold film in the Kretschmann configuration have shown what appears to be a superconductive effect. Researchers claimed to see the existence of electron pairing during scattering as well as magnetic field repulsion while twisting the polarization of the laser. In an attempt to explain this, they pointed to a combination of electron-electron scattering in external fields as well as dynamic screening via intense laser radiation. This paper expands upon the latter, taking a look at the properties of a dynamic polarization function, its effects on bulk and surface plasmon dispersion relations, and its various consequences.
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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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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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Blidberg, Andreas. "Iron Based Materials for Positive Electrodes in Li-ion Batteries : Electrode Dynamics, Electronic Changes, Structural Transformations." Doctoral thesis, Uppsala universitet, Strukturkemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-317014.
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Li-ion battery technology is currently the most efficient form of electrochemical energy storage. The commercialization of Li-ion batteries in the early 1990’s revolutionized the portable electronics market, but further improvements are necessary for applications in electric vehicles and load levelling of the electric grid. In this thesis, three new iron based electrode materials for positive electrodes in Li-ion batteries were investigated. Utilizing the redox activity of iron is beneficial over other transition metals due to its abundance in the Earth’s crust. The condensed phosphate Li2FeP2O7 together with two different LiFeSO4F crystal structures that were studied herein each have their own advantageous, challenges, and scientific questions, and the combined insights gained from the different materials expand the current understanding of Li-ion battery electrodes. The surface reaction kinetics of all three compounds was evaluated by coating them with a conductive polymer layer consisting of poly(3,4-ethylenedioxythiophene), PEDOT. Both LiFeSO4F polymorphs showed reduced polarization and increased charge storage capacity upon PEDOT coating, showing the importance of controlling the surface kinetics for this class of compounds. In contrast, the electrochemical performance of PEDOT coated Li2FeP2O7 was at best unchanged. The differences highlight that different rate limiting steps prevail for different Li-ion insertion materials. In addition to the electrochemical properties of the new iron based energy storage materials, also their underlying material properties were investigated. For tavorite LiFeSO4F, different reaction pathways were identified by in operando XRD evaluation during charge and discharge. Furthermore, ligand involvement in the redox process was evaluated, and although most of the charge compensation was centered on the iron sites, the sulfate group also played a role in the oxidation of tavorite LiFeSO4F. In triplite LiFeSO4F and Li2FeP2O7, a redistribution of lithium and iron atoms was observed in the crystal structure during electrochemical cycling. For Li2FeP2O7, and increased randomization of metal ions occurred, which is similar to what has been reported for other iron phosphates and silicates. In contrast, triplite LiFeSO4F showed an increased ordering of lithium and iron atoms. An electrochemically induced ordering has previously not been reported upon electrochemical cycling for iron based Li-ion insertion materials, and was beneficial for the charge storage capacity of the material.
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Grumbling, Emily Rose. "Electronic Structure, Intermolecular Interactions and Electron Emission Dynamics via Anion Photoelectron Imaging." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195933.
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This dissertation explores the use of anion photoelectron imaging to interrogate electronic dynamics in small chemical systems with an emphasis on photoelectron angular distributions. Experimental ion generation, mass selection, laser photodetachment and photoelectron imaging were performed in a negative-ion photoelectron imaging spectrometer described in detail. Results for photodetachment from the simplest anion, H⁻, are used to illustrate fundamental principles of quantum mechanics and provide basic insight into the physics behind photoelectron imaging from a pedagogical perspective. This perspective is expanded by introducing imaging results for additional, representative atomic and small molecular anions (O⁻, NH₂⁻ and N₃⁻) obtained at multiple photon energies to address the energy-dependence of photoelectron angular distributions both conceptually and semi-quantitatively in terms of interfering partial photoelectron waves. The effect of solvation on several of these species (H⁻, O⁻, and NH₂⁻) is addressed in photoelectron imaging of several series of cluster anions. The 532 and 355 nm energy spectra for H⁻(NH₃)n and NH₂⁻(NH₃)n (n = 0-5) reveal that these species are accurately described as the core anion solute stabilized electrostatically by n loosely coordinated NH3 molecules. The photoelectron angular distributions for solvated H⁻ deviate strongly from those predicted for unsolvated H⁻ as the electron kinetic energy approaches zero, indicating a shift in the partial-wave balance consistent with both solvation-induced perturbation (and symmetry-breaking) of the H⁻ parent orbital and photoelectron-solvent scattering. The photoelectron energy spectra obtained for the cluster series [O(N₂O)n]⁻ and [NO(N₂O)n]⁻ indicate the presence of multiple structural isomers of the anion cores, the former displaying sharp core-switching at n = 4, the latter isomer coexistence over the entire range studied. The photoelectron angular distributions for detachment from the O⁻(N₂O)n and NO⁻(N₂O)n isomers deviate strongly from those expected for bare O⁻ and NO⁻, respectively, in the region of an anionic shape resonance of N₂O, suggesting resonant photoelectron-solvent scattering. Partial-wave models for two-centered photoelectron interference in photodetachment from dissociating I₂⁻ is presented and discussed in the context of previous results. New time-resolved photoelectron imaging results for I₂⁻, for both parallel and perpendicular pump and probe beam polarizations, are presented and briefly discussed. Finally, new ideas and directions are proposed.
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Okhrimenko, Albert N. "ULTRAFAST EXCITED STATE RELAXATION DYNAMICS OF ELECTRON DEFICIENT PORPHYRINS: CONFORMATIONAL AND ELECTRONIC FACTORS." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=bgsu1126888140.
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Biswas, Somnath. "Watching Electrons Move in Metal Oxide Catalysts : Probing Ultrafast Electron Dynamics by Femtosecond Extreme Ultraviolet Reflection-Absorption Spectroscopy." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586375150350782.
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Jabbour, Ghassan Elie. "First principles molecular dynamics simulation: An electron in non-local pseudopotential; electrons in molten alkali-alkali halide solutions." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186995.
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This study presents an ab-initio method based on the Discretized Path Integral Molecular Dynamics (DPIMD) to simulate the electronic behavior in the following systems: (a) an electron in the field of sodium ion, and (b) multi-electron solvation in molten KCl at 1300 K. For the first system, a non-local pseudopotential was incorporated in the path integral derivation of the quantum amplitude. The resulting formalism was then implemented in a molecular dynamics simulation of an electron in the field of sodium ion. The obtained amplitude for the electronic states considered, namely 3s and 3p, came to an excellent agreement with previous computational findings based on Coreless Hartree-Fock method carried by Melius and Goddard III (53). For the second system, the solvation of four, six, and eight electrons in molten KCl, at 1300 K, was studied. In this case a successful incorporation of exchange in DPIMD was made. Bipolarons were formed in each case. However, their electronic charge distribution ranged from two bipolarons with some common charge region, to an elongated structure that stretched over the entire allowed range of interaction. In each case, the size of the bipolaron was found to be ∼4 Å. In this aspect of the study, the results came to an excellent agreement with those of Parrinello and Rahman (9), Fois et al (71), and Selloni et al (72). Apparent in the results of this study is the independence of the local ionic structure on the electron concentration. This observation is in accord with (71), (72), and experimental studies done by Jal (92), and Steininger (93).
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Siraj-Dine, Sami. "Dynamics of electrons in 2D materials." Thesis, Paris Est, 2020. http://www.theses.fr/2020PESC1039.
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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 graphèneDuring 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
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Eklund, John C. "Electrode reaction dynamics." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297021.
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Bushong, Neil G. "Electron dynamics in nanoscale systems." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3283964.
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Thesis (Ph. D.)--University of California, San Diego, 2007.Title from first page of PDF file (viewed March 14, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 88-96).
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Smith, Robert Alan Lundie. "Electron dynamics in Rydberg molecules." Thesis, King's College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404481.
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Yanik, Mehmet Faith 1977. "Electron spin dynamics in semiconductors." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/86562.
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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (p. 65-67).
by Mehmet Faith Yanik.
M.Eng.
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Little, D. A. "Electron-N₂⁺ scattering and dynamics." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1464074/.
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Molecular nitrogen, N₂, is the most abundant molecule in the terrestrial atmosphere. Its cation N₂⁺ is therefore prevalent in the earth's ionosphere as well as in nitrogen plasmas produced for reasons varying from lightning strikes to combustion. Any model which seeks to describe plasmas in air must contain a description of nitrogen ion chemistry. Despite this, there is a distinct paucity of data describing electron-N₂⁺ interactions and the resultant bound and quasi-bound electronic structure of N₂. The characterisation of these states is essential for describing dissociative recombination which is the main destroyer of molecular ions in a plasma. This thesis aims to alleviate this problem by performing extensive ab initio R-matrix calculations to create a comprehensive map of the highly-excited electronic structure of N₂ which can the be used to perform a dissociative recombination cross-section calculation. Potential energy curves were found by performing resonant and bound state calculations for all singlet and triplet molecular symmetries of N₂ up to l ≤ 4. The use of a dense grid meant that highly-excited electronic states could be found with an unprecedented level of detail. Many of the states were previously unknown. A new fitting method was developed for the characterisation of resonant states using the time-delay method. It was shown that whilst the R-matrix method is not competitive with conventional quantum chemistry techniques for low lying valence states, it is particularly appropriate for highly-excited states, such as Rydberg states. The data gained from these calculations was then used as an input for a multichannel quantum defect theory calculation of a dissociative recombination cross-section. A description is given of how to prepare the data from the R-matrix calculation for input into a multichannel quantum defect theory dissociative recombination cross-section calculation. Cross-sections were found for v=0-3 including three ionic cores. Whilst previous studies of dissociative recombination using R-matrix data required some empirical intervention, the cross-section found in this thesis is completely ab initio and is in good agreement with experiment.
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Dong, Jingwei. "Electron dynamics in layered materials." Thesis, Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAX019.
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Actuellement,les matériaux lamellaires suscitent un grand intérêt en raison de leurs propriétés électriques et optiques.On peut dire que le domaine de recherche des matériaux à basse dimensionnalité a été initié par la découverte du graphène et c’est rapidement élargi à d'autres matériaux comme les dichalcogénures de métaux de transition,le phosphore noir et le séléniure d'indium.Nos travaux portent sur la dynamique des états excités dans ces composés,ainsi que sur l'évolution de la structure des bandes lors d’un fort dopage de surface.Le manuscrit est organisé comme suit :Lechapitre1 est une introduction générale sur les matériaux lamellaires.En particulier,nous discutons des propriétés structurelles et électroniques des composés plus connus.Lechapitre2 décrit les principes de fonctionnement de la spectroscopique ultra-rapides et montre nombreuses applications sur des matériaux lamellaires.Nous attirons principalement l’attention sur la dynamique des électrons dans les cristaux semi-conducteurs ou avec onde de densité de charge.Lechapitre3 illustre la technique expérimentale que nous avons employée et l’enceinte dans lequel nous avons effectuées les mesures.La dynamique des électrons des matériaux lamellaires a été étudiée au moyen de la spectroscopie photoélectronique résolue en temps et en angle,qui est un outil puissant pour cartographier la structure des bandes électronique et pour suivre la dynamique des électrons photo-injectés via une source laser ultra-rapide. La discussion des données originales de notre travail débute dans lechapitre4.Les mesures TrARPES sur le phosphore noir suivent la distribution électronique dans la bande de conduction en fonction du délai temporale par rapport à l’instant de la photoexcitation.Nos données montrent qu'après thermalisation,les électrons photo-injectés ne produisent pas une diminution de bande d’énergie interdite,ni génèrent-ils une multiplication appréciable du nombre des porteurs.D'autre part,un élargissement Stark de la bande de valence est due à l’écrantage inhomogène d'un potentiel local autour de défauts chargés.Lechapitre5 présente les données ARPES résolues en temps sur une surface de phosphore noir dopée in situ par évaporation des métaux alcalins.Nous mesurons l'effondrement de la bande interdite dans la couche d'accumulation électronique avec une précision inédite et nous observons des états enterrés qui sont détectable à cause de la faible énergie de photons dans notre sonde.Ces états acquièrent une vitesse de bande étonnamment élevée quand la concentration de dopants augmente.Lechapitre6 montre la modification de la dynamique des porteurs chauds lors de la variation du dopage de surface de BP.Dans ce cas, l'analyse proposé est encore préliminaire et doit être complémenté par des calculs ab-initio.Lechapitre7 contient notre travail sur le composé ɛ-InSe.Comme dans le cas de phosphore noir, nous générons une couche d'accumulation de densité électronique variable à la surface du semi-conducteur.En variant le niveau de dopage à partir du limite semi-conducteur jusqu’au limite métallique,nous observons que l’écrantage quantique des phonons optiques longitudinaux n'est pas aussi efficace qu'il le serait dans un système strictement bidimensionnel.Ce résultat indique la présence d’un couplage à distance entre les états confinés à la surface et les phonons polaires du volume.Dans lechapitre8,nous étudions le 1T-TaS2.Ce matériau appartient aux systèmes d'ondes de CDW et a été largement étudié par plusieurs équipes de chercheurs.Dans le 1T-TaS2,la combinaison d'une distorsion structurelle avec des fortes corrélations électroniques conduit à un diagramme de phase complexe et fascinant.Nous reproduisons des données controversées qui ont été récemment publiées dans la littérature et qui identifient une nouvelle instabilité en proximité de la transition métal-isolant.Enfin,lechapitre9 résume les conclusions de nos résultats et aborde brièvement les orientations de recherche à venirCurrently,layered materials attract great interest due to their electrical and optical properties. Such crystals display an electronic band structure that strongly depends on the sample thickness.The large tunability of the electronic screening and gap size can be very attracting for the creation of heterostructures whose properties can be designed on demand. We can say that the research field of low dimensional materials has been boosted by the discovery of graphene and quickly has been enlarged to other materials as transition metal dichalcogenides,black phosphorous and Indium selenide.Our work will focus on the excited state dynamics in these compounds,as well as on the evolution of the band structure upon surface doping.The manuscript is organized as follow:Chapter1 provides a general introduction of layered materials.In particular,we discuss the structural and electronic properties of some relevant compounds.Chapter2 describes the principles of ultrafast spectroscopic methods and shows many applications to the case of the layered materials.We mainly focus our attention on the electron dynamics in semiconducting crystals and charge density waves systems. The electron dynamics of layered materials have been investigated by means of time-and angle-resolved photoelectron spectroscopy (TrARPES),which is a powerful tool to directly map the electronic band structure and to follow the dynamics of the electrons photoinjected via an ultrafast laser source.Chapter3 discusses the experimental technique of choice and the setup where we have been performed in the reported measurements.we begin the discussion of our original data in Chapter4.The TrARPES measurements of layered black phosphorus(BP) monitor the electronic distribution in the conduction and valence band as a function of delay time from photoexcitation.The data show that,after thermalization,the photo-injected electrons do not lead to sizable band gap renormalization,neither do they generate an appreciable amount of carrier multiplication.On the other hand,a Stark broadening of the valence band is ascribed to the inhomogeneous screening of a local potential around charge defects.Chapter5 shows time resolved ARPES data on a BP surface that is doped in-situ by means of alkali metals evaporation. We monitor the collapse of the band-gap in the accumulation layer with unmatched accuracy and we observe that the buried states detected by the low energy photons of our probing pulse acquire a surprisingly high band velocity at large dopants concentration.Chapter6 deals with the modification of hot carrier dynamics upon increasing the surface doping of BP.In this case the reported analysis is still preliminary and needs to be backed by ab-initio calculations.Chapter7 contains our work on layered ɛ-InSe.As in the case of BP,we generate an accumulation layer of varying electronic density on the surface of such semiconductor.By spanning the doping level from the semiconducting to the metallic limit,we observe that quantum screening of Longitudinal Optical phonons is not as efficient as it would be in a strictly bidimensional system,indicating a remote coupling of confined states to polar phonons of the bulk.Furthermore,we show that a 3D Fröhlich interaction with Thomas-Fermi screening can be used to mimic the effects of such a remote coupling at the ɛ-InSe surface.In Chapter8,we study the layered 1T-TaS2.This material belongs to the Charge density waves (CDW) systems and has been extensively investigated by several research groups.In 1T-TaS2,the combination of structural distortion with high electronic correlations leads to a complex and fascinating phase diagram.We could reproduce controversial data that have been recently published in the literature and that identify a new instability in proximity of the metal to-insulator transition.Finally,chapter9 summarizes the conclusions of our work and briefly discusses the perspectives of some future directions of research
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Rettig, Laurenz [Verfasser]. "Ultrafast dynamics of correlated electrons / Laurenz Rettig." Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1028497407/34.
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Parker, William P. (William Peter). "Output devices for dynamic electronic holography." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/12714.
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Searle, Graham Ellis. "Dynamic modelling of electronic nose systems." Thesis, University of Warwick, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251118.
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Ospanov, Asset. "DELAY DIFFERENTIAL EQUATIONS AND THEIR APPLICATION TO MICRO ELECTRO MECHANICAL SYSTEMS." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5674.
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Delay differential equations have a wide range of applications in engineering. This work is devoted to the analysis of delay Duffing equation, which plays a crucial role in modeling performance on demand Micro Electro Mechanical Systems (MEMS). We start with the stability analysis of a linear delay model. We also show that in certain cases the delay model can be efficiently approximated with a much simpler model without delay. We proceed with the analysis of a non-linear Duffing equation. This model is a significantly more complex mathematical model. For instance, the existence of a periodic solution for this equation is a highly nontrivial question, which was established by Struwe. The main result of this work is to establish the existence of a periodic solution to delay Duffing equation. The paper claimed to establish the existence of such solutions, however their argument is wrong. In this work we establish the existence of a periodic solution under the assumption that the delay is sufficiently small.
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Porath, Ron. "Dynamics of hot electrons in ultra-thin metallic films and small structures theory and experiments: electron lifetime, plasmons, quantum well states." Saarbrücken VDM Verlag Dr. Müller, 2002. http://d-nb.info/991274733/04.
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Knoop, Steven. "Electron dynamics in ion-atom interactions." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2006. http://irs.ub.rug.nl/ppn/292151632.
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McDonald, Christopher. "Electron Dynamics in Finite Quantum Systems." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26105.
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The multiconfiguration time-dependent Hartree-Fock (MCTDHF) and multiconfiguration time-dependent Hartree (MCTDH) methods are employed to investigate nonperturbative multielectron dynamics in finite quantum systems. MCTDHF is a powerful tool that allows for the investigation of multielectron dynamics in strongly perturbed quantum systems. We have developed an MCTDHF code that is capable of treating problems involving three dimensional (3D) atoms and molecules exposed to strong laser fields. This code will allow for the theoretical treatment of multielectron phenomena in attosecond science that were previously inaccessible. These problems include complex ionization processes in pump-probe experiments on noble gas atoms, the nonlinear effects that have been observed in Ne atoms in the presence of an x-ray free-electron laser (XFEL) and the molecular rearrangement of cations after ionization. An implementation of MCTDH that is optimized for two electrons, each moving in two dimensions (2D), is also presented. This implementation of MCTDH allows for the efficient treatment of 2D spin-free systems involving two electrons; however, it does not scale well to 3D or to systems containing more that two electrons.
Both MCTDHF and MCTDH were used to treat 2D problems in nanophysics and attosecond science. MCTDHF is used to investigate plasmon dynamics and the quantum breathing mode for several electrons in finite lateral quantum dots. MCTDHF is also used to study the effects of manipulating the potential of a double lateral quantum dot containing two electrons; applications to quantum computing are discussed. MCTDH is used to examine a diatomic model molecular system exposed to a strong laser field; nonsequential double ionization and high harmonic generation are studied and new processes identified and explained. An implementation of MCTDHF is developed for nonuniform tensor product grids; this will allow for the full 3D implementation of MCTDHF and will provide a means to investigate a wide variety of problems that cannot be currently treated by any other method. Finally, the time it takes for an electron to tunnel from a bound state is investigated; a definition of the tunnel time is established and the Keldysh time is connected to the wavefunction dynamics.
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Lantz, Gabriel. "Ultrafast electron dynamics in Mott materials." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112014/document.
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Les isolants de Mott sont un exemple parfait de l’impact des corrélations électroniques locales sur les propriétés macroscopiques des matériaux. En variant légèrement le dopage ou la pression, un métal peut se transformer en un isolant. Ces propriétés peuvent être modifiées de manière très rapide en plaçant ces matériaux loin de l'équilibre. Nous avons étudié un prototype de Mott-Hubbard, V2O3 dopé en Cr, en utilisant l'état de l’art des techniques pompe-sonde, à savoir la photoémission résolue en angle, la réflectivité optique, la spectroscopie THz, et la diffraction des rayons X. La réponse électronique du système, après une excitation laser femtoseconde, qui a été maintenue pour chaque expérience à une longueur d'onde de 800 nm, a pu être déconvoluée de la réponse du réseau. Une étude comparative de ces réponses transitoires démontre un fort couplage électron-phonon dans ce prototype de matériau fortement corrélé. Avant thermalisation, le poids spectral est transféré de la bande de Hubbard inférieure vers le gap de Mott. Sur une échelle de temps plus long un état métastable est stabilisé par un changement structural. Pour mieux comprendre la réponse transitoire des isolants de Mott, nous avons également étudié un autre composé de Mott, BaCo1-xNixS2. Les tendances générales des isolants de Mott après photoexcitation ont été analysées en utilisant un modèle à deux orbitales. Nous interprétons que le remplissage du gap comme un changement spécifique des occupations orbitalesMott insulators are a perfect example of how local electronic correlations can change macroscopic properties of materials. Varying slightly the doping or the pressure can transform a metal to an insulator. These properties can be modified extremely rapidly by driving these materials far from equilibrium. We have investigated the model Mott-Hubbard material Cr-doped V2O3 using state of the art pump-probe techniques, namely angle resolved photoelectron spectroscopy, optical reflectivity, THz time-domain spectroscopy, and X-ray diffraction. We were able to unequivocally disentangle the electronic and the lattice response of the system to a femtosecond laser excitation, which was kept in all cases at a wavelength of 800 nm. We present a comparative study of these transient responses, which demonstrates the strong electron-phonon coupling of this strongly correlated model material. We show that before thermalization, spectral weight is transferred from the lower Hubbard band towards the Mott gap. On a longer time scale a metastable state is stabilized by the lattice structure. To further understand the transient response of Mott insulators, we have also studied another Mott compound, BaCo1-xNixS2. The general trends of photoexcitation in Mott insulators are analyzed using a two orbital model. We argue that the filling of the gap can be due to a change of the specific orbital fillings
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ROSSETTI, CONTI MARCELLO. "BEAM DYNAMICS FOR EXTREME ELECTRON BEAMS." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/622706.
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The extreme electron beams are characterized by parameters that are comparable or superior to the state of the art. The beams parameters proposed in the more advanced machines under development or in operation demonstrate that extreme beam qualities are necessary to conceive experiments meeting the demands of cutting-edge research.
The optimization of parameters such as brightness, beam current or energy spread plays a major role in the design choices of new and competitive machines.
A large amount of simulations of beam dynamics is required, accompanied later by a specific R&D of machine components and demonstration experiments.
In the field of beam dynamics, the development and improvement of tracking simulators and optimization tools is a main topic. For this reason, in the beam physics group of INFN & University of Milan the code GIOTTO, based on a genetic algorithm, is being developed for years specifically for this purpose.
During the work of PhD, I developed new features in the GIOTTO code that allowed me to apply it to new type of problems: simulation of a beam based method for the increase of the brightness of linac beams, design from scratch of matching lines for plasma driven FELs (Free Electron Lasers), the study of new linear acceleration and compression techniques and a preliminary study on how to produce an ultra-cold beam for a quantum-FEL.
All these works are united by being applied to linear machines dedicated to the production of high-brightness electron beams for various purposes.
During the last year of PhD, I had the opportunity to participate in the design of an FEL source, named MariX. MariX is based on a compact acceleration scheme where the electron beam propagates twice through a superconducting standing wave linac thanks to an arc compressor that reverses the direction of the beam and compresses it.
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Hemingway, Bryan J. "Magnetoconductance and Dynamic Phenomena in Single-Electron Transistors." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352397253.
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Hardikar, Rahul Padmakar. "Dynamic electron-phonon interactions in one-dimensional models." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-11092007-143010.
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Døssland, Line Teigen. "Electro-oxidation of ethanol at Pt electrodes with the use of a Dynamic Electrochemical Impedance Spectroscopy (DEIS) technique." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18864.
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Electro-oxidation of ethanol on smooth platinum surfaces was studied in thetemperature range 21C to 140C for 0.2 M ethanol in 0.5 M sulphuric acid.This was done by use of cyclic voltammetry and electrochemical impedancespectroscopy. In addition cyclic voltammetry with different ethanol concentrationsfrom 0.1 M to 1 M, in 0.5 M sulphuric acid was done at room temperature.Cyclic voltammetry with different ethanol concentrations showed a shift to morepositive potentials for the first oxidation peak in positive going scan as the ethanolconcentration increased. A shift to more positive potentials was also observed forthe oxidation peak in the negative scan as the concentration increased from 0.1M to 1 M. This indicates that the optimum surface condition is reached at higherpotentials for higher ethanol concentrations. This can be because ethanol andadsorbed ethanol derivatives take up more active sites at the surface, thus leavingless active sites available for adsorbed water derivatives which is necessary for theoxidation of ethanol to acetic acid and CO2.Cyclic voltammetry was done for increasing temperatures from 21C up to 140Cfor 0.2 M ethanol in 0.5 M sulphuric acid. These results showed an increasein oxidation current for all oxidation peaks as the temperature increased. Adecrease in peak potential for the first oxidation peak was observed for increasingtemperatures. This indicates that the optimum surface condition for ethanoloxidation is reached at lower potentials at higher temperatures. There was alsoseen an decrease in the apparent onset potential of the first oxidation peak as thetemperature increases. These effects can come from increased thermal activity forwater adsorption at higher temperatures. The peak potential for the oxidationpeak in negative going scan increased with increasing temperatures. This cancome from an easier reduction of platinum oxide at higher temperatures.Dynamic electrochemical impedance spectroscopy measurements was done atdifferent temperatures from 21C up to 140C for 0.2 M ethanol in 0.5 Msulphuric acid solution. The results from the measurements at 60C was fittedto electrochemical equivalent circuits. This gave indications of one kineticallysignificant surface adsorbed species in most potential regions with a notableoxidation current. This in combination with literature suggesting that acetic acidand acetaldehyde is the major products from ethanol electro-oxidation suggestthat the adsorbed intermediate is something other than CO(ads). Results fromthis work together with existing literature on ethanol oxidation was used to givea suggested simplified reaction mechanism for ethanol electro-oxidation.
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Turkson, Abraham K. "Electro-ultrafiltration with rotating dynamic membranes." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72036.
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In axial electrofiltration, a DC electric field is imposed between a rotating inner cylinder and a stationary outer cylinder giving rise to four mechanisms which act to minimize solute accumulation at the filter surface: turbulence, centrifugal force, electrophoresis and shear stress which removes solute aggregates.Four dynamic membranes, Zr(IV) oxide, calcium oleate, poly-2-vinylpyridine and cadmium sulfide, were used to filter bovine serum albumin (BSA) in a disodium phosphate solution at pH = 8 and Prussian blue in distilled water. Prussian blue is a particle of 0.01(mu)m diameter with a zeta potential of -41mV while BSA is a macromolecule of 69,000 molecular weight, a Stokes-Einstein radius of 0.0038(mu)m and a zeta potential of -23.3mV at pH = 8. For BSA, the flux declined with time while the rejection increased. Filtrate fluxes increased with rotation rate and electric field and declined with concentration for both feeds. The flux declined beyond N = 2000rpm and was constant above C(,0) = 5.0wt%. For Prussian blue, the rejection was greater than 90% at all levels of E, N and C(,0). For BSA, the rejection increased with rotation rate and declined with concentration. The BSA rejection declined above N = 2000rpm and was constant beyond C(,0) = 0.5wt%.
A mathematical model was derived to predict the time variation of filtrate flux and a rejection model was used to predict the effect of surface concentration on BSA rejection.
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Melgar, Freire María Dolores. "Keplerates: from Electronic Structure to Dynamic Properties." Doctoral thesis, Universitat Rovira i Virgili, 2015. http://hdl.handle.net/10803/349212.
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Aquesta tesi està centrada en l'estudi dels Keplerats, una família de polioxometalats amb simetria icosaèdrica. Els polioxometalats són clústers inorgànics aniònics formats per uniats MOn, on M és un metall de transició normalment en el seu estat d'oxidació més elevat. (Mo(VI), W(VI), V(V)...). Per una banda, l'estructura electrònica dels Keplerats s'ha estudiat des d'un punt de vista de la Teoría del Funcional de la Densitat (DFT). A més, s'ha analitzat la interacció entre la càpsula Mo132 i els seus corresponents lligands interns. Per altra banda, amb col·laboració amb altres grups, tant experimentals com teòrics, es proposa un mecanisme de formació de la càpsula Mo132 a partir de dades obtingudes mitjançant espectroscòpia Raman. Part d'aquesta informació obtinguda mitjançant DFT s'ha utilitzat per obtenir els paràmetres necessaris per portar a terme una sèrie de simulacions de Dinàmica Molecular amb la finalitat d'estudiar el comportament del macro-ió Mo132 en solució aquosa en presència de diferents cations (centrant-se en la importància de la hidrofobicitat del catió), així com els efectes de la temperatura en aquest comportament.Esta Tesis está centrada en el estudio de Kepleratos, una familia de polioxometalatos con simetría icosaédrica. Los polioxometalatos son clusters inorgánicos anionicos compuestos por unidades MOn, donde M es un metal de transición normalmente en su estado de oxidación más alto (Mo(VI), W(VI), V(V)...). Por un lado, la estructura electrónica de los Kepleratos se ha estudiado desde un punto de vista de la Teoría del Funcional Densidad (DFT). Además, se ha analizado la interacción entre la cápsula Mo132 y sus correspondientes ligandos internos. Por otro lado, en colaboración con otros grupos, tanto experimental como teórico, se propone un mecanismo de formación de la cápsula Mo132 a partir de los datos obtenidos mediante espectroscopía Raman. Parte de la información obtenida mediante DFT se ha utilizado para obtener los parámetros necesarios para realizar una serie de simulaciones de Dinámica Molecular con el fin de estudiar el comportamiento del macro-ión Mo132 en solución acuosa en presencia de diferentes cationes (centrándose en la importancia de la hidrofobicidad del catión), así como los efectos de la temperatura en dicho comportamiento.
This Thesis is aimed at the study of a family of icosahedral symmetry polyoxometalates: the so-called Keplerates. Polyoxometalates are inorganic anionic clustters composed of MOn units, where M represents a transition metal atom usually at its highest state of oxidation Mo(VI), W(VI), V(V)...). On one hand, the electronic structure of Keplerates is studied from a Density Functional Theorey (DFT) point of view. Furthermore, the interaction between the Mo132 capsule and its inner ligands has been analyzed. On the other hand, in collaboration with both experimental and theoretical groups, a formation mechanism for the Mo132 capsule is proposed, based on Raman espectroscopy data. Part of the information achieved by DFT has been used to obtain the parameters required in order to perform Molcular Dynamics simulations regarding the behaviour of the Mo132 macro-ion in aqueous solution in the presence of different cations (focusing on the relevance of the hydrophobic character of teh cation), as well as the effects that temperature has on the system.
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Tran, Trung Nam. "Surface discharge dynamics : theory, experiment and simulation." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/165509/.
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The use of solid insulators in electrical generation, transmission and distribution is widespread. However, the accumulation of charge on the insulator surface has proved to be one of the major factors contributing to system failures. This research work is aimed at studying the dynamics of surface discharge in theory, by simulation and experiment. Different surface charging theories have been reviewed and classiffied according to electric field uniformity. The focus is on basic processes involved in the formation of positive and negative surface discharges. The experimental work utilises the non-destructive quantitative Pockels technique to measure surface charge density distribution. Practical considerations of the Pockels experiment together with image processing techniques are discussed in detail. Using this technique, various factors which influence the surface discharge dynamics have been studied including the effects of the applied voltage waveform, electrode shape and local gaseous environment. Results obtained using positive/negative square wave, ramp and sinusoidal voltages are reported. The impact of using a mushroom electrode instead of a needle electrode is also analysed. In addition, various insulation gases have been experimented namely dry air, N2, CO2 and their mixtures with SF6. Surface discharge measurements have been performed in these gases at various levels of pressure. Surface discharge modelling and simulation studies have also been undertaken. The simulation principles are based on a system of coupled hydrodynamic equations consisting of continuity and Poisson's equations. By solving these equations, the movement and interaction of charged particles and transient electric eld can be simulated and used to verify the discharge theories and experimental results. Due to the asymmetric lamentary nature of positive surface streamers, the development of a positive surface discharge is separated into two phases. The rst phase involves the axial streamer development in the gas gap between the needle electrode and the dielectric surface. This phase is simulated in 2D axial symmetry space dimension by the nite element package COM-SOL. The second phase simulates the streamer propagation in 1D along the dielectric surface by using the eld results from the rst phase. This part of the model is solved by the accurate ux-corrected transport algorithm. The effects of model parameters on the simulation results are discussed and a comparison with experimental data made. Prior to the simulation of a negative surface discharge, a negative corona discharge model in 2D axial symmetry has been analysed (Trichel pulses). The model behaviour is studied with reference to experimental data as model parameters are varied. When the insulators are introduced, the accumulation of surface charge distorts the electric eld leading to the formation of only one discharge current pulse. The simulation charge density distribution is in good agreement with results obtained from the Pockels experiment.
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Li, Rong Ding 1967. "Dynamic electron arc therapy with the Clinac-21EX linac." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101603.
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Electron arc therapy is the treatment modality for superficial tumors involving large curved surfaces. At the McGill University Health Centre, the characteristic angle beta concept was developed for the dosimetry and treatment planning of electron arc therapy. In this work, this concept was verified in dynamic mode with the new generation linac of Varian(TM), the Clinac-21 EX.Radial PDDs were measured for beta angles varying from 60º--120º of electron arc beams with energies of 6 MeV, 9 MeV, and 12 MeV and 2-D isodose distributions of electron arc beams were studied as well. Dose penumbral regions exist at the beam start area and stop area, and the size of these regions is a function of the beam energy and the field width. When shielded with a tertiary collimator, the size of the penumbral regions and the dose levels in the penumbral regions were reduced significantly, and it is sufficient for the shielding to cover exactly the start field and the stop field of the arc beam in a clinical setting.
The dose rate of the electron arc beam was investigated. It was found that the dose rate at the depth of dose maximum linearly increased with the arc beam field width and was independent of the arc angle.
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Armstrong, G. S. J. "Electron dynamics of one- and two-electron atoms in intense laser fields." Thesis, Queen's University Belfast, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546004.
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Harris, John Richardson. "Longitudinal dynamics of an intense electron beam." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2906.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Hultell, (Andersson) Magnus. "Electron-Lattice Dynamics in pi-Conjugated Systems." Licentiate thesis, Linköping University, Linköping University, Department of Physics, Chemistry and Biology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7996.
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In this thesis we explore in particular the dynamics of a special type of quasi-particle in pi-conjugated materials termed polaron, the origin of which is intimately related to the strong interactions between the electronic and the vibrational degrees of freedom within these systems. In order to conduct such studies with the particular focus of each appended paper, we simultaneously solve the time-dependent Schrödinger equation and the lattice equation of motion with a three-dimensional extension of the famous Su-Schrieffer-Heeger (SSH) model Hamiltonian. In particular, we demonstrate in Paper I the applicability of the method to model transport dynamics in molecular crystals in a region were neither band theory nor perturbative treatments such as the Holstein model and extended Marcus theory apply. In Paper II we expand the model Hamiltonian to treat the revolution of phenylene rings around the sigma-bonds and demonstrate the great impact of stochastic ring torsion on the intra-chain mobility in conjugated polymers using poly[phenylene vinylene] (PPV) as a model system. Finally, in Paper III we go beyond the original purpose of the methodology and utilize its great flexibility to study radiationless relaxations of hot excitons.
Report code: LiU-TEK-LIC-2007:4.
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Khaledi, Ali Abedi [Verfasser]. "Correlated Electron-Nuclear Dynamics / Ali Abedi Khaledi." Berlin : Freie Universität Berlin, 2014. http://d-nb.info/1052222331/34.
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Hultell, (Andersson) Magnus. "Electron-lattice dynamics in π-conjugated systems." Doctoral thesis, Linköpings universitet, Beräkningsfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-12590.
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The work presented in this thesis concerns the dynamics in π-conjugated hydrocarbon systems. Due to the molecular bonding structure of these systems there exists a coupling between the electronic system and the phonons of the lattice. If this interaction, which is referred to as the electron-phonon (e-ph) coupling, is sufficiently strong it may cause externally introduced charge carriers to self-localize in a polarization cloud of lattice distortions. These quasi-particles are, if singly charged, termed polarons, the localization length of which, aside from the e-ph coupling strength, also depend upon the structural and energetic disorder of the system. In disordered systems localization is strong and transport is facilitated by nonadiabatic hopping of charge carriers from one localized state to the next, whereas in well-ordered systems, where extended states are formed, adiabatic transport models apply.Despite great academic efforts a unified model for charge transport in π-conjugated systems is still lacking and further investigations are necessary to uncover the basic physics at hand in these systems. The call for such efforts has been the main guidelines for the work presented in this thesis and are related to the topics of papers I-IV. In order to capture the coupled electron-lattice dynamics, we use a methodological approach where we obtain the time-dependence of the electronic degrees of freedom from the solutions to the time-dependent Schrödinger equation and determine the ionic motion in the evolving charge density distribution by simultaneously solving the lattice equation of motion within the potential field of the ions. The Hamiltonian used to describe the system is derived from an extension of the famous Su-Schrieffer-Heeger (SSH) model extended to three-dimensional systems.In papers I-III we explore the impact of phenylene ring torsion on delocalization and transport properties in poly(para-phenylene vinylene) (PPV). The physics that we are particularly interested in relates to the reduced electron transfer integral strength across the interconnection between the phenylene rings and the vinylene groups upon ring torsion. Keeping this in mind, we demonstrate in paper I the impact of static ring torsion on intrachain mobility and provide a detailed analysis of the influence of the potential barriers (due to consecutive ring torsion) on the nature of charge carrier propagation. In paper II we extend our initial approach to include also the dynamics of ring torsion. We show that without any externally applied electric field, this type of dynamics is the dominant property controlling intrachain propagation, but that when an external electric field is applied, charge carriers may traverse the potential barriers through a process that involves nonadiabatic effects and a temporary delocalization of the polaron state. Finally, in paper III we study the impact of the lattice dynamics on the electron localization properties in PPV and show that the phenylene ring torsion modes couples strongly to the electronic wave function which gives rise to electron localization at room temperature.In papers IV and V we focus on the dynamics of molecular crystals using a stack of pentacene molecules in the single crystal configuration as a model system, but study, in paper IV, the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaron drift process over the regime 20<J<120 meV. For intermolecular interaction strengths above J≈120 meV the polaron is no longer stable and transport becomes band-like. In paper V, finally, we study the internal conversion processes in these systems, which is the dominant relaxation channel from higher lying states. This process involves the transfer of energy from the electronic system to the lattice. Our results show that this process is strongly nonadiabatic and that the relaxation time associated with large energy excitations is limited by transitions made between states of different bands.I dagens samhälle är elektroniken ett allt viktigare och större inslag i vår vardag. Vi ser på TV, talar i mobiltelefoner, och arbetar på datorer. I hjärtat av denna teknologi finner vi diskreta komponenter och integrerade kretsar utformade främst för att styra strömmen av elektroner genom halvledande material. Traditionellt sett har kisel eller olika former av legeringar använts som det aktiva materialet i dessa komponenter och kretsar, men under de senaste 20 åren har såväl transistorer som solceller och lysdioder realiserats där det aktiva materialet är organiskt, d.v.s., kolbaserat.Vi befinner oss för tillfället mitt uppe i det kommersiella genombrottet för organisk elektronik. Redan idag säljs många MP3-spelare och mobiltelefoner med små skärmar där varje pixelelementen utgörs av organiska ljusemitterande dioder (OLEDs), men teknologin håller redan på att introduceras i mer storskaliga produkter som datorskärmar och TV-apparater som därigenom skulle kunna göras energieffektivare, tunnare, flexiblare och på sikt också billigare. Andra tekniska tillämpningsområden för organisk elektronik som förutspås en lysande framtid är RFID-märkning, organiska solceller, och elektronik tryckt på papper, men även smarta textiler och bioelektronik har stor utvecklingspotential.Den kanske största utmaningen kvarstår dock, att skapa elektroniska kretsar och komponenter uppbyggda kring enskilda molekyler, s.k. molekylär elektronik. Mycket snart närmar vi oss den fysikaliska gränsen för hur små komponenter som vi kan realisera med traditionella icke-organiska material som kisel och en stor drivkraft bakom forskningen på halvledande organiska material har varit just visionen om molekylär elektronik som inte är mer än några miljondelars milimeter stora. För detta ändamål krävs en mycket nogrann kontroll av tillverkningsprocesserna liksom en detaljförståelse för hur molekylerna leder ström och hur denna förmåga kan manipuleras för att realisera såväl traditionella som nya komponenter.I denna avhandling presenteras en översikt av den fysik som möjliggör ledningsförmåga hos särskilda klasser av organiska material, s.k. π-konjugerade system, samt de forskningsresultat som utgör mitt bidrag till denna disciplin. En av utmaningarna på området är den komplexitet som de organiska materialen erbjuder: laddningsprocesserna påverkas nämligen av en rad olika faktorer såsom laddningstäthet, temperatur, pålagd spänning, samt molekylernas former och inbördes struktur. I detta arbete har jag utifrån en vidareutveckling av existerande modeller genom numeriska datasimuleringar undersökt effekten av de senare tre faktorerna på elektronstrukturen, laddnigstransporten och energidissipation i denna klass av material.
Center of Organic Electronics (COE)
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Thorn, Adam Leslie. "Electron dynamics in surface acoustic wave devices." Thesis, University of Cambridge, 2009. https://www.repository.cam.ac.uk/handle/1810/224176.
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Gallium arsenide is piezoelectric, so it is possible to generate coupled mechanical and electrical surface acoustic waves (SAWs) by applying a high-frequency voltage to a transducer on the surface of GaAs. By combining SAWs with existing low-dimensional nanostructures one can create a series of dynamic quantum dots corresponding to the minima of the travelling electric wave, and each dot carries a single electron at the SAW velocity (~ 2800 m/s). These devices may be of use in developing future quantum information processors, and also offer an ideal environment for probing the quantum mechanical behaviour of single electrons. This thesis describes a numerical and theoretical study of the dynamics ofan electron in a range of geometries. The numerical techniques for solving thetime-dependent Schrödinger equation with an arbitrary time-dependent potential will be described in Chapter 2, and then applied in Chapter 3 to calculate the transmission of an electron through an Aharonov-Bohm (AB) ring. It will be seen that an important property of the techniques used in this thesis is that they can be easily adapted to study realistic geometries, and we will see features in the AB oscillations which do not arise in simplified analytic descriptions. In Chapter 4, we will then study a device consisting of two parallel SAW channels separated by a controllable tunnelling barrier. We will use numerical simulations to investigate the effect of electric and magnetic fields upon the electron dynamics, and develop an analytic model to explain the simulation results. From the model, it will be apparent that it is possible to use this device to rotatethe state of the electron to an arbitrary superposition of the first two eigenstates. We then introduce coherent and squeezed states in Chapter 5, which are ex-cited states of the quantum harmonic oscillator. Coherent and squeezed electronicstates may be of use in quantum information processing, and could also arise dueto unwanted perturbations in a SAW device. We will discuss how these statescan be controllably generated in a SAW device, and also discuss how they couldthen be detected. In Chapter 6 we describe how to use the motion of a SAW to create a rapidly-changing potential in the frame of the electron, leading to a nonadiabatic excita-tion. The nonadiabatically-excited state oscillates from side to side within a 1Dchannel on a few-picosecond timescale, and this motion can be probed by placing a tunnelling barrier at one side of the channel. Numerical simulations will beperformed to show how this motion can be controlled, and the simulation resultswill be seen to be in good agreement with recent experimental work performed by colleagues. Finally, we will show that this device can be used to measure the initial state of an electron which is an arbitrary superposition of the first twoeigenstates.
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Harvey, Christopher. "Electron dynamics in high-intensity laser fields." Thesis, University of Plymouth, 2010. http://hdl.handle.net/10026.1/301.
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We consider electron dynamics in strong electromagnetic fields, such as those expected from the next generation of high-intensity laser facilities. Beginning with a review of constant classical fields, we demonstrate that the electron motion (as given by the Lorentz force equation) can be divided into one of four Lorentz invariant cases. Parameterising the field tensor in terms of a null tetrad, we calculate the radiative energy spectrum for an electron in crossed fields. Progressing to an infinite plane wave, we demonstrate how the electron orbit in the average rest frame changes from figure-of-eight to circular as the polarisation changes from linear to circular. To move beyond a plane wave one must resort to numerics. We therefore present a novel numerical formulation for solving the Lorentz equation. Our scheme is manifestly covariant and valid for arbitrary electromagnetic field configurations. Finally, we reconsider the case of an infinite plane wave from a strong field QED perspective. At high intensities we predict a substantial redshift of the usual kinematic Compton edge of the photon emission spectrum, caused by the large, intensity dependent effective mass of the electrons inside the laser beam. In addition, we find that the notion of a centre-of-mass frame for a given harmonic becomes intensity dependent.
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Hubbard, Penny Louise. "Molecular and electron dynamics with muon spectroscopy." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268573.
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Park, Ickjin 1968. "Dynamics of an excess electron in water." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85334.
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Cáceres, Alejandro. "Electron dynamics in a black hole background." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614691.
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Robinson, David Jonathan. "Atomic electron dynamics in intense laser fields." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675426.
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Electron dynamics in laser-driven one- and two-electron atoms and ions are probed through numerical integration of the full -dimensional, time-dependent Schro"dinger Equation. Physical observables, such as ionization rates and the spectrum of harmonics generated by the system, are extracted from the wavefunction. For an atom in a one-colour, linearly polarized laser field, wavepackets ejected at certain times will recoillide with the core, generating harmonics of the driving field. The harmonic spectrum is calculated using HELIUM and used to benchmark those from the time-dependent R-matrix (TDRM) method and a single-active-electron (SAE) code. HELIUM and TDRM results agree to within 20% while SAE calculations agree in the high-frequency region of the spectrum. The two-photon double ionization (TPDI) cross section of helium is calculated for frequencies 40 eV<ω< 54 a.u. In this frequency range, sequential ionization requires the absorption of three photons while non-sequential ionization is a two-photon process so that the latter mechanism is dominant for fields with low intensity. The cross section is shown to be sensitive to pulse duration, especially near the 54 eV threshold. Calculations using the HELIUM code provide TPDI cross sections accurate to a few percent across the whole frequency range. Extension of the method to treat one-electron atoms and ions in orthogonally polarized, two-colour laser fields are described. An orthogonally polarized, two-colour field will steer ionized wavepackets in the continuum. The likelihood of recollision, and the recolliding wavepackets velocity are significantly changed. These effects can be seen in the harmonic spectrum. Such a two-colour scheme has been proposed as a way to image complex molecular orbitals. The harmonic spectrum from model atomic systems in such fields is calculated. It is observed that the harmonic spectrum is sensitive to the symmetry of the electron orbitals. Thus, for the 2p state even harmonics are significantly stronger than those in the 2s case.
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Acciai, Matteo. "Single-electron dynamics in topologically protected systems." Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0528.
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L'optique quantique électronique est un domaine de recherche visant à préparer, contrôler et manipuler de manière cohérente des états à électrons uniques dans des systèmes mésoscopiques, de la même manière que les photons sont manipulés en optique quantique. Des sources d'électrons uniques peuvent être utilisées pour générer des excitations à quelques électrons dans des conducteurs balistiques, où la propagation n'est pas affectée par la rétrodiffusion.Une question particulièrement importante est celle de comprendre les effets des intéractions électroniques sur l'évolution des excitations produites par les sources, ce qui est le sujet principal de cette thèse.Tout d'abord on considère une couple de canaux conducteurs co- ou contro-propageants en présence d'intéractions répulsives. Dans les deux cas, les intéractions produisent la "fractionalisation" des excitations initiellement introduites. Les excitations ``fractionnées'' sont étudiées soit dans le domaine temporel soit dans la représentation énergie, ce qui permet d'obtenir des informations sur leur contenu de couples particule-trou. En considérant des excitations générées par des impulsions de forme lorentzienne, connues comme Lévitons, on démontre que le bruit dû à la présence d'un centre de diffusion est minimisé, indépendemment des intéractions.Ensuite, on adresse des systèmes supraconducteurs où les corrélations électroniques sont tout à fait differentes. On étudie les propriétés de transport d'une jonction tunnel supraconductrice amenée hors de l'équilibre par des impulsions de tension périodiques de forme arbitraire et on démontre que les Lévitons minimisent le bruit à basse fréquence dans ce système aussiElectron quantum optics is a research field aiming at preparing, controlling and coherently manipulating single- to few-electrons states in mesoscopic systems, in the same way as single photons are manipulated in quantum optics. Single-electron sources are used to generate few-electron excitations in ballistic conductors, where their propagation is not affected by backscattering.Among several interesting problems related to electron quantum optics, an important question is whether and how interaction effects influence the evolution of single-electron excitations generated by coherent sources. This will be the main topic of this thesis.At first we consider a couple of co- or counter-propagating conduction channels coupled by repulsive electron-electron interactions. In both systems, interactions induce a fractionalization process causing the initially generated excitations to split into smaller ones, carrying only a fraction of the injected charge. These fractionalized excitations are studied both in the time domain as well as in energy and momentum space, which allows to access their particle-hole content. Moreover, specializing to the relevant case of excitations created by quantized Lorentzian voltage pulses, known as Levitons, we show that the noise generated when they are partitioned at a scatterer is minimal, regardless of interactions.Further on, a completely different kind of interaction is addressed, namely superconducting correlations. In particular, we investigate the transport properties of a superconducting tunnel junction under the effect of an arbitrary periodic drive, showing that Levitons do minimize the low frequency noise in this kind of device too
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Zhai, Dawei. "Studies on Electron Dynamics in Deformed Graphene." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540985604827894.
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Kirchmann, Patrick S. "Ultrafast electron dynamics in low-dimensional materials." München Verl. Dr. Hut, 2009. http://d-nb.info/993731325/04.
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Gillingham, David R. "Free electron laser single-particle dynamics theory." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA246245.
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Thesis (M.S. in Physics)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Colson, William B. Second Reader: Maruyama, Xavier K. "December 1990." Description based on title screen as viewed on March 31, 2010. DTIC Identifier(s): Free Electron Lasers, Computerized Simulations, Parmela Computer Programs, Cray Computers, Theses. Author(s) subject terms: Free Electron Lasers, Computerized Simulation. Includes bibliographical references (p. 52-53). Also available in print.
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Pilgrim, Ian. "Electron Transport Dynamics in Semiconductor Heterostructure Devices." Thesis, University of Oregon, 2014. http://hdl.handle.net/1794/18503.
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Modern semiconductor fabrication techniques allow for the fabrication of semiconductor heterostructures which host electron transport with a minimum of scattering sites. In such devices, electrons populate a two-dimensional electron gas (2DEG) in which electrons propagate in exactly two dimensions, and may be further confined by potential barriers to form electron billiards. At sub-Kelvin temperatures, electron trajectories are determined largely by reflections from the billiard walls, while net conduction through the device depends on quantum mechanical wave interference.
Measurements of magnetoconductance fluctuations (MCF) serve as a probe of dynamics within the electron billiard. Many prior studies have utilized heterostructures employing the modulation doping architecture, in which the 2DEG is spatially removed from the donor atoms to minimize electron scattering. Theoretical studies have claimed that MCF will be fractal when the confinement potential defining the billiard is soft-walled, regardless of the presence of smooth potentials within the billiard such as those introduced by remote ionized donors. The small-angle scattering sites resulting from these potentials are often disregarded as negligible; we use MCF measurements to investigate such claims.
To probe the effect of remote ionized donor scattering on the phase space in electron billiards, we compare MCF measured on billiards in a modulation-doped heterostructure to those measured on billiards in an undoped heterostructure, in which this potential landscape is believed to be absent. Fractal studies are performed on these MCF traces, and we find that MCF measured on the undoped billiards do not exhibit measurably different fractal characteristics than those measured on the modulation-doped billiards.
Having confirmed that the potential landscapes in modulation-doped heterostructures do not affect the electron phase space, we then investigate the effect of these impurities on the distribution of electron trajectories through the billiards. By employing thermal cycling experiments, we demonstrate that this distribution is highly sensitive to the precise potential landscape within the billiard, suggesting that modulation-doped heterostructures do not support fully ballistic electron transport. We compare our MCF correlation data with the dynamics of charge transfer within heterostructure systems to make qualitative conclusions regarding these dynamics.