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21	Untersuchung der elektronischen Struktur quasi-zweidimensionaler Einlagerungsverbindungen Danzenbächer, Steffen 13 November 2001 (has links) (PDF) Thema der vorliegenden Arbeit ist die Untersuchung ausgewählter niederdimensionaler Schichtgittersysteme, wobei das Hauptinteresse in der Erforschung der elektronischen Struktur im Zusammenhang mit Interkalationsexperimenten liegt. Einkristalline Graphit-, TiSe2- und TaSe2-Proben wurden vor und nach der Interkalation mit winkelaufgelöster Photoemission, Fermi- und Isoenergieflächenmessungen und Elektronenbeugung (LEED) analysiert. Als Interkalationsmaterialien wurden U, Eu, Gd und Cs verwendet. Die experimentellen Daten wurden mit Ergebnissen von LDA-LCAO-Bandstrukturrechnungen und Simulationen im Rahmen eines Single-Impurity-Anderson-Modells verglichen. Neben dem Einfluß unterschiedlicher Valenzelektronen der interkalierten Atome auf den Einlagerungsprozeß werden Fragen zum Lokalisierungsverhalten von 4f- und 5f-Zuständen und zu den Veränderungen in der Dimensionalität der Verbindungen durch die Einlagerung diskutiert. Ein weiterer Schwerpunkt dieser Arbeit befaßt sich mit Untersuchungen zur temperaturabhängigen Ausbildung von Ladungsdichtewellen in 1T-TaSe2. / Subject of the present thesis are investigations of selected low-dimensional layered lattice systems, with the principal goal to study the electronic structure in relation to intercalation experiments. Single-crystalline graphite-, TiSe2 - and TaSe2- samples were analyzed by angle-resolved photoemission, Fermi- and isoenergy-surface measurements, and low energy electron diffraction experiments before and after intercalation. U, Eu, Gd, and Cs were used as materials for the intercalation process. The experimental results were compared with theoretical LDA-LCAO band-structure calculations and with simulations in the framework of a single-impurity Anderson model. In addition to the influence of different numbers of valence electrons from intercalated atoms, questions concerning the localization of 4f and 5f states and changes in the dimensionality of the compounds due to the intercalation process are discussed. Investigations of the temperature dependent formation of charge density waves in 1T-TaSe2 complete this work. Graphit TiSe2 TaSe2 Interkalationsexperimente LDA-LCAO-Bandstrukturrechnungen Ladungsdichtewellen U Eu Gd Cs elektronische Struktur niederdimensionale Systeme winkelaufgelöste Photoemission LDA-LCAO band-structure calculations U Eu Gd Cs angle-resolved photoemission charge density waves electronic structure graphite TiSe2 TaSe2 intercalation experiments low-dimensional systems ddc:29 rvk:UP 3150 Bandstrukturberechnung Elektronenstruktur Graphiteinlagerungsverbindungen Interkalation Schichtgitter niederdimensionaler Halbleiter
22	Étude par ARPES et STS des propriétés éléctroniques de réseaux métalliques et organiques nanostructurés / Electronic properties of nanostructured metallic and organic interfaces studied by ARPES and STS Vasseur, Guillaume 13 November 2014 (has links) Dans ce travail nous démontrons, au travers de deux études, l'intérêt fondamental du couplage des techniques de photoémission résolue en angle (ARPES) et de spectroscopie tunnel (STS) dans l'analyse des propriétés électroniques d'interfaces nanostructurées. Dans la première partie, nous présentons une méthodologie permettant de déduire le potentiel de surface induit par la reconstruction triangulaire d'une monocouche d'Ag/Cu(111). Cette méthode est basée sur la mesure des gaps caractérisant la structure de bande de l'état de Shockley du système aux points de haute symétrie de la zone de Brillouin. L'évaporation d'adatomes de potassium permet d'augmenter le nombre de gaps accessibles en photoémission en décalant les bandes vers les états occupés. Dans un modèle d'électrons presque libres, leur amplitude nous donne accès aux premières composantes de Fourier du potentiel. La reconstruction de ce dernier dans l'espace direct nous permet ensuite de calculer la densité d'états locale que nous comparons aux mesures de conductance STS. La seconde partie est consacrée à l'étude de la croissance et des propriétés électroniques des molécules de 1,4-dibromobenzène (DBB) et 1,4-diiodobenzène (DIB) évaporées sur Cu(110). Leur dépôt à température ambiante sur la surface entraîne la déshalogénation des molécules et la formation de phases organométalliques. A 200°C, le système polymérise pour former des chaînes unidimensionnelles de poly(p-phénylène) parfaitement alignées. Les mesures ARPES révèlent l'existence d'une bande pi unidimensionnelle d'états HOMOs dispersant sous le niveau de Fermi. En STS, nous observons également, pour des petites chaînes, le confinement des états LUMOs dans la partie inoccupée du spectre. Le déconfinement de ces états pour les grandes chaînes conduit à la formation d'une bande continue croisant le niveau de Fermi, conférant au polymère un caractère métallique 1D. Le gap HOMO-LUMO est alors mesuré à 1.15 eV / In this work, through two different studies, we demonstrate the fundamental interest in the coupling of angle resolved photoemission (ARPES) and scanning tunneling spectroscopy (STS) to investigate the electronic properties of nanostructured interfaces. In the first part we present a methodology to determine the surface potential of the triangular reconstructed one monolayer of Ag/Cu(111) interface from ARPES. This method is based on the measurement of the Shockley state band structure’s gaps at the high symmetry points of the Brillouin zone. Deposition of potassium adatoms allows us to shift the surface state towards higher binding energies in order to increase the number of accessible gaps in photoemission. From the magnitude of these gaps we deduce the two first Fourier components of the potential felt by electrons using the nearly free electron model. Then we reconstruct it and calculate the local density of states in order to compare it with the conductance maps probed by STS. In the second part we report the study of the growth and the electronic properties of the two molecules 1,4-dibromobenzene (DBB) and 1,4-diiodobenzene (DIB) evaporated on Cu(110). For room temperature deposition, we first observe their deshalogenation and the formation of an intermediate organometallic phase. Then, above 200°C, the system polymerizes into a long-range ordered array of one dimensional poly(p-phenylene) polymer. ARPES intensity maps allowed us to identify a one dimensional graphene-like strongly dispersive pi-band below the Fermi energy. By STS we also observed LUMOs confined states for small chains over the Fermi level. The loss of confinement for long chains induces the formation of a continuous dispersive band which crosses the Fermi energy, conferring a 1D metallic character to the polymer. The HOMO-LUMO gap is found to be 1.15 eV Photoémission résolue en angle Diffraction d’électrons lents Surface nanostructurée Structure électronique État de Shockley K/Ag/Cu(111) Potentiel de surface Dibromobenzène Diiodobenzène Couplage d’Ullmann Polymérisation Poly(p-phénylène) Low energy electron diffraction Nanostructured surface Electronic properties Shockley state K/Ag/Cu(111) Surface potential Dibrobenzene Diiodobenzène Ullmann coupling Polymerization Poly(p-phenylene) 530.412 620.192
23	Untersuchung der elektronischen Struktur quasi-zweidimensionaler Einlagerungsverbindungen Danzenbächer, Steffen 29 November 2001 (has links) Thema der vorliegenden Arbeit ist die Untersuchung ausgewählter niederdimensionaler Schichtgittersysteme, wobei das Hauptinteresse in der Erforschung der elektronischen Struktur im Zusammenhang mit Interkalationsexperimenten liegt. Einkristalline Graphit-, TiSe2- und TaSe2-Proben wurden vor und nach der Interkalation mit winkelaufgelöster Photoemission, Fermi- und Isoenergieflächenmessungen und Elektronenbeugung (LEED) analysiert. Als Interkalationsmaterialien wurden U, Eu, Gd und Cs verwendet. Die experimentellen Daten wurden mit Ergebnissen von LDA-LCAO-Bandstrukturrechnungen und Simulationen im Rahmen eines Single-Impurity-Anderson-Modells verglichen. Neben dem Einfluß unterschiedlicher Valenzelektronen der interkalierten Atome auf den Einlagerungsprozeß werden Fragen zum Lokalisierungsverhalten von 4f- und 5f-Zuständen und zu den Veränderungen in der Dimensionalität der Verbindungen durch die Einlagerung diskutiert. Ein weiterer Schwerpunkt dieser Arbeit befaßt sich mit Untersuchungen zur temperaturabhängigen Ausbildung von Ladungsdichtewellen in 1T-TaSe2. / Subject of the present thesis are investigations of selected low-dimensional layered lattice systems, with the principal goal to study the electronic structure in relation to intercalation experiments. Single-crystalline graphite-, TiSe2 - and TaSe2- samples were analyzed by angle-resolved photoemission, Fermi- and isoenergy-surface measurements, and low energy electron diffraction experiments before and after intercalation. U, Eu, Gd, and Cs were used as materials for the intercalation process. The experimental results were compared with theoretical LDA-LCAO band-structure calculations and with simulations in the framework of a single-impurity Anderson model. In addition to the influence of different numbers of valence electrons from intercalated atoms, questions concerning the localization of 4f and 5f states and changes in the dimensionality of the compounds due to the intercalation process are discussed. Investigations of the temperature dependent formation of charge density waves in 1T-TaSe2 complete this work. info:eu-repo/classification/ddc/29 ddc:29
24	Constructing and Commissioning HELIOS – A High Harmonic Generation Source for Pump-Probe Measurements with sub 50 fs Temporal Resolution : The Development of Experimental Equipment for Extreme Ultraviolet Spectroscopy Terschlüsen, Joachim A. January 2016 (has links) This thesis presents HELIOS, an in-house laboratory for time-resolved pump-probe spectroscopy with extreme-ultraviolet (XUV) probe radiation. A wide span of pump wavelengths can be generated using commercial laser equipment while XUV probe radiation is generated via a high harmonic generation process in a noble gas delivering probe photons with energies between 20 eV and 72 eV. The XUV beam path features a time-preserving monochromator and was constructed and built in-house. HELIOS features an overall time resolution of about 50 fs when using 800 nm pump and 41 eV probe photons. An energy resolution of 110 meV at 41 eV photon energy can be achieved. HELIOS features two beamlines. One µ-focus beamline with an XUV focal size of about 20 µm can be used with experiments that require such a small XUV focal size as well as with different end stations. The other beamline features a semi-permanently mounted end station for angle-resolved photoelectron spectroscopy under ultra-high vacuum conditions. Experiments demonstrating the usability of HELIOS and the two beamlines are presented. A pump-probe measurement on graphene demonstrates the capability of determining a large part of the k-space in only one measurement due to the use of an ARTOF angle-resolved time-of-flight electron spectrometer. A non-angle-resolved pump-probe measurement on the conducting polymer PCPDTBT demonstrates the high signal-to-noise ratio achievable at this beamline in non-angle-resolved photoelectron-spectroscopy pump-probe measurements. The usability of the µ-focus beamline is demonstrated with time-resolved measurements on magnetic samples employing an in-house-designed spectrometer. These experiments allow the retrieval of element-specific information on the magnetization within a sample employing the transversal magneto-optical Kerr effect (T-MOKE). Additionally, a Fourier transform spectrometer for the XUV is presented, the concept was tested at a synchrotron and it was used to determine the longitudinal coherence of the XUV radiation at HELIOS. Angle-resolved time-of-flight Angle resolved time of flight ARTOF ARPES tr-ARPES fs fs resolution Fourier transform spectrometer Fourier-transform spectrometer Fourier transform spectroscopy Fourier-transform spectroscopy FTS gas cell high harmonic generation laser liquid jet monochromator HELIOS HHG off-plane mount off plane mount OPA optical parametric amplifier PCPDTBT pulse shaping pump probe pump-probe measurements pump-probe measurements pump-probe spectroscopy pump-probe spectroscopy Rowland spectrometer time-of-flight spectrometer time of flight spectrometer TOF time-resolved spectroscopy time resolved spectroscopy time-resolved experiments time resolved experiments T-MOKE tr-PES PES photoelectron spectroscopy transverse magneto optical Kerr effect transverse magneto-optical Kerr effect ultrafast ultra-high vacuum ultra high vacuum UHV XUV VUV X-rays Permalloy magnetization dynamic

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