Global ETD Search

111	Transition des basses fréquences aux hautes fréquences d’une décharge à barrière diélectrique en hélium à la pression atmosphérique Boisvert, Jean-Sébastien 06 1900 (has links) No description available. Décharge à barrière diélectrique Plasma à la pression atmosphérique Hélium Basse fréquence Moyenne fréquence Haute fréquence Densité électronique Température électronique Atomes dans un état métastable Dielectric barrier discharge Atmospheric-pressure plasma Low frequency Medium frequency High frequency Electron density Electron temperature Atoms in a metastable state
112	Ab-initio Study of Semi-conductor and Metallic Systems: from Density Functional Theory to Many Body Perturbation Theory Yi, Zhijun 11 February 2010 (has links) Substitutional dopants in III-V semi-conductors, such as Si atoms in GaAs, are of great interest for the applications in transistors, Schottky diodes, and doping super-lattices which have been widely employed to control the electrical properties of semi-conductors. Although Si doped GaAs systems have been intensively investigated theoretically and experimentally in the last several decades, some properties are still debated. In order to give a further explanation of Si doped GaAs systems, we systematically studied DX center in bulk GaAs and in GaAs(110), as well as the relative stabilities of different charged systems for Si atom replacing Ga atom at the substitutional site near GaAs(110) surface from first principles ground state method. We show that DX centre is a metastable state in bulk GaAs and completely unstable in the top few layers of GaAs(110). When Si atom replaces Ga atom at the surface, Charge states have an important influence on the stability of the system, and the additional charge is mainly concentrated on the Si atom for charged system. In addition, we studied the STM images of clean GaAs(110) and charged Si:GaAs(110) by employing Tersoff-Hamann approximation. The calculated STM images are in good agreement with experimental results. We show that at the positive bias voltage the positively charged Si atom presents a bright feature while the negatively charged Si atom shows a dark feature. In a semi-conductor, all bands are either completely full or completely empty. It is well known that DFT underestimates the band gaps of semi-conductors, a simple rigid shift can be used to correct the band energies of semi-conductors. Unlike semi-conductor, the fermi energies of metals lie in some bands. Furthermore, it turned out that some noble metals such as Cu and Ag depend on the considered band and k point , therefore, the so-called scissors operator can not be used for the metallic systems. The most successful approach within theoretical method for these metals is the many body perturbation theory. On the other hand, an interesting study for metals is quasi-particle excitations, which play an important role in a rich variety of physical and chemical phenomena such as energy transfer in photochemical reaction, desorption and oxidation of molecules at surfaces, spin transport within bulk metals, across interfaces, and at surfaces. One of the crucial properties of quasi-particle excitation is their lifetimes which determine the duration of these excitations. We carried out the calculations of quasi-particle band-structures and lifetimes for noble metals Cu and Ag within the GW approximation. For Cu, both the calculated positions of the d bands and the width of the d bands is within 0.1 eV compared to the experimental results. For Ag, partial core correction should be included in the pseudo-potential to get reliable positions of the d bands. The calculated lifetime agree with the experiment in the energy region away from the Fermi level, but deviates from the experimental results near the Fermi level where short range interactions which GW approach fails to describe play an important role. For a better description of the lifetime near the Fermi level, higher terms beyond the GW approximation in the many body perturbation theory need to be considered. In addition, the image potential state lifetimes in Cu(100) have been calculated using GW approximation based on the localized Gaussian basis set, and the calculated n=1, 2 imagepotential state lifetimes are in good agreement with experimental results. Density functional theory Many body perturbation theory Semiconductor Lifetime 71.15.Qe - Excited states: methodology ddc:530
113	Trajectory and channeling effects in the scattering of ions off a metal surface - Probing the electronic density corrugation at a surface by grazing axial ion channeling Robin, Abel 25 November 2003 (has links) The presented work investigates planar and axial channeling effects in ion-surface collisions. Therefore, energy loss and charge state distributions depending on the crystalline surface direction are recorded and analyzed. Several additional scattering parameters, like the primary energy, the outgoing charge state, the scattering angle, and the angle of incidence are varied. Multi-peak structures in the energy spectra are observed under axial channeling conditions and attributed to different trajectory classes. Using combined trajectory and inelastic energy loss calculations we are able to unambiguously assign the different peaks in the energy spectra to the different types of trajectories found in the calculations. By this, we investigate the electronic density corrugation at different metal surfaces. Die vorliegende Arbeit untersucht den Einfluß von axialem und planarem Channeling auf den Energieverlust von oberflächengestreuten Ionen. Es werden Energieverlustspektren und Ladungsverteilungen in Abhängigkeit der Parameter Primärenergie, gestreuter Ladungszustand, Streuwinkel, Einfallswinkel und der azimuthalen Ausrichtung der Oberfläche gemessen. Im Fall von axialem Channeling beobachten wir in den Energiespektren eine Multi-Peak Struktur. Diese läßt sich auf unterschiedliche Teilchentrajektorien zurückführen. Zusammen mit theoretischen Berechnungen des inelastischen Energieverlustes kann eine eindeutige Zuordnung zwischen dem gemessenen Energieverlust und der dazugehörigen Trajektorienart gemacht werden. Diese Technik erlaubt es uns, die elektronische Dichtekorrugation an Oberflächen zu studieren. Ion surface scattering Surface channeling Energy loss Stopping Platinum Palladium Trajectory calculations Electron density corrugation 29 - Physik, Astronomie 61.85. plus p ddc:530
114	Etude radiative d’un plasma d’argon à la pression atmosphérique produit par des micro-ondes en régime pulsé Maris, Raphaël 08 1900 (has links) Le présent mémoire de maîtrise a pour but de jeter les bases sur la physique des plasmas micro-ondes en régime pulsé dans l’argon à la pression atmosphérique. Pour cela, nous avons utilisé une photodiode nous permettant d’acquérir l’émission globale du plasma pour différentes positions du tube où celui-ci détient trois types d’évolutions. La partie croissante, où nous avons observé un retard d’allumage du plasma qui augmente en s’éloignant de l’excitateur. Nous l’avons estimé en dérivant l’émission du plasma afin d’en obtenir ensuite une vitesse de front d’ionisation. Cette méthode de dérivée nous a permis également de constater que l’émission plasma détient un comportement exponentiel en croissance d’émission où nous avons pu en extraire des coefficients homogènes à des fréquences pour chacune des positions. Nous en avons ensuite interprété sous l’appui d’une mise en équation de l’émission plasma que la partie croissante est fortement sensible en début d’ignition, au chauffage des électrons Te(t) et à la multiplication électronique ne(t) puis tardivement au chauffage du gaz Tg(t). Ensuite, la partie stationnaire, pour laquelle nous avons remarqué que la densité électronique ne(z) est fortement dépendante de l’émission intégrée le long du tube. En parallèle, nous avons eu recours à la spectroscopie d’émission optique afin d’en déterminer Tg(z) où nous avons constaté que celui-ci est sensible au rapport cyclique. Enfin, la partie décroissante, où nous avons constaté un pic d’émission plasma au moment de l’extinction du plasma où nous avons supposé qu’il fût associé à la recombinaison radiative des dimères de l’argon Ar2+ avec les électrons. De même que pour la phase d’allumage, la dérivée et la mise en équation de l’émission plasma, nous a permis d’interpréter qu’après l’extinction du plasma, nous avons en première partie Te(t) et ne(t) qui contribuent fortement pour ensuite se terminer sur une décroissance exponentielle lente que nous avons associée à Tg(t). / The present master thesis aims to develop the foundations for the physics of pulsed microwave plasmas in argon at atmospheric pressure. For this, we used a photodiode allowing us to acquire the global plasma emission for different positions of the tube where it has three types of evolution. The increasing part, where we observed a plasma ignition delay which increases away from the exciter. We estimated it by deriving the emission from the plasma in order to then obtain an ionization front velocity. This derivative method also allowed us to see that the plasma emission has an exponential behavior in emission growth where we were able to extract homogeneous coefficients at frequencies for each of the positions. We then interpreted, with the support of an equation of the plasma emission, that the increasing part is highly sensitive at the start of ignition, to the heating of the electrons Te(t) and to the electronic multiplication ne(t) then later on heating the gas Tg(t). Then, the stationary part, for which we noticed that the electron density ne(z) is strongly dependent on the emission integrated along the tube. In parallel, we used optical emission spectroscopy to determine Tg(z) where we found that it is sensitive to the duty cycle. Finally, the decreasing part, where we observed a peak of plasma emission at the time of the extinction of the plasma where we supposed it to be associated to the radiative recombination of the dimers of argon Ar2+ with electrons. As for the ignition phase, the derivative and the equation of the plasma emission allowed us to interpret that after the extinction of the plasma, we have in the first part Te(t) and ne(t) which contribute strongly, and then end in a slow exponential decay that we have associated with Tg(t). Plasma micro-onde d’argon pulsé émission globale dérivée coefficient fréquence mise en équation température du gaz température électronique densité électronique spectroscopie optique d'émission pulsed argon microwave plasma global emission derivative coefficient frequency equation setting optical emission spectroscopy gas temperature electron temperature electron density
115	Elucidation of Unconventional Bonding in Lithium Organic Compounds / Untersuchung unkonventioneller Bindungssituationen in lithiumorganischen Verbindungen Ott, Holger 28 April 2009 (has links) No description available. 540 Chemie Mathematics and Computer Science Röntgenbeugung Quantentheorie der Atome in Molekülen Lithiumorganische Verbindungen Picolyllithium Benzyllithium Trimethylsilylmethyllithium X-ray Diffraction Quantum Theory of Atoms in Molecules Lithium Organic Compounds Picolyllithium Benzyllithium Trimethylsilylmethyllithium 35.11 35.25 35.44 35.59 35.60 35.90 SP 000: Strukturchemie STJ 250: Lithium {Anorganische Chemie} STJ 300: Natrium {Anorganische Chemie} STL100
116	Design of Phosphorus Centered Janus Head Ligands / Design phosphorzentrierter Januskopf-Liganden Objartel, Ina 31 October 2011 (has links) No description available. 540 Chemie Chemistry Januskopf-Liganden Di-2-picolylphenylphosphan Röntgenbeugung Lithium Natrium Zinn Superbasen Phosphorane Janus Head Ligands Di-2-picolylphenylphosphane X-ray Diffraction Experimental Electron Density Studies Lithium Sodium Tin Superbases Phosphoranes 35.11 35.25 35.42 35.43 35.44 35.45 35.47 35.59 35.60 STJ 250: Lithium {Anorganische Chemie} STJ 300: Natrium {Anorganische Chemie} STM 350: Zinn {Anorganische Chemie} STN 250: Phosphor {Anorganische Chemie}
117	Syntheses and Electron Density Determination of Novel Polyimido Sulfur Ylides / Synthesen und Elektronendichtebestimmung an neuen Polyimido-Schwefelyliden Deuerlein, Stephan 31 October 2007 (has links) No description available. 540 Chemie Mathematics and Computer Science Schwefelylide Organolithiumchemie Ladungsdichte Bindung QTAIM ylidisch ylenisch Metallcomplexe Zinn Magnesium Arsen Schwefel Stickstoff Kohlenstoff Lithium Imide Januskopf-Ligand homobimetallische Komplexe Komplexchemie Polymorphie sulfur ylides organolithium chemistry charge density bonding QTAIM ylidic ylenic metal complexes tin magnesium arsenic sulfur nitrogen carbon lithium imides janus-head ligand homobimetallic complexes complex chemistry polymorphism 35.11 35.44 35.60 35.90 SP 000: Strukturchemie SOC 250: Metallkomplexe Chelate {Chemie: Verbindungstypen} STJ 250: Lithium {Anorganische Chemie} STO 270: Schwefeloxyde

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