Les travaux présentés dans cette thèse s'inscrivent dans le cadre du projet MUSES (MUltiscale Electron Spectroscopy) qui consiste en une approche expérimentale et théorique combinée de l'étude des dynamiques électroniques dans les molécules sur une large fenêtre de temps. Ils se concentrent particulièrement sur les dynamiques électroniques dans les molécules carbonées aux échelles femtoseconde et attoseconde. Pour comprendre les processus à l'oeuvre dans ces systèmes complexes, il est nécessaire d'effectuer une étude approfondie de leurs propriétés électroniques en régime d'excitation à la fois linéaire et non linéaire. En effet, une grande partie des modèles de dynamiques électroniques valides dans le cas d'atomes s'effondrent lorsque l'on considère des molécules polyatomiques. Par ailleurs, l'accès à des sources de lumière ultrarapides permet maintenant de sonder expérimentalement des processus multiélectroniques ultrabrefs et de les confronter aux modèles théoriques. Les systèmes modèles C60, PAHs (Naphtalène, Anthracène et Pyrène) et les bases de l'ADN/ARN (bases pyrimidiques Cytosine, Thymine, Uracile) ont été les principaux systèmes étudiés dans cette perspective. Les expériences ont été conduites en spectroscopie de photoélectrons résolue en angle (VMIS) et spectroscopie de masse des produits d'ionisation, sous excitation XUV (10-30 eV) en champ faible (rayonnement synchrotron) ou proche Infrarouge en champ laser intense (∼1013 W/cm2) ainsi que sur une ligne laser pompe sonde XUV-IR disposant d'une résolution temporelle d'une centaine d'attosecondes. A l'aide de ces outils, nous avons mis en évidence et modélisé l'influence de la résonance plasmon de surface à 20 eV dans la dynamique de photoionisation du C60 à l'échelle attoseconde. Nous avons identifié la population d'états de Rydberg similaires lors de l'excitation des bases de l'ADN/ARN par un champ laser infrarouge intense, ce qui permet de contraindre les modèles théoriques sur la réponse non linéaire de systèmes complexes exposés à ce type de rayonnement. Enfin nous avons pu observer en temps des dynamiques non adiabatiques (couplages électrons-noyaux à l'échelle de plusieurs femtosecondes) dans les PAH consécutives à des processus d'ionisation et d'excitation multiélectroniques (mécanisme de shake-up) / The works presented in this thesis are part of project MUSES (MUltiscale Electron Spectroscopy) which consist in a combined experimental and theoretical approach on the study of electronic dynamics in molecules over a large time range. They concentrate particularly on electrons dynamics in carbonates molecules at the femtosecond and attosecond timescales. In order to understand processes occurring in those complex systems, it is necessary to study them in linear excitation regime as well as non linear one. Indeed, many electron dynamics theoretical models, valid in case of atoms or diatomic systems collapse in the case of polyatomic molecules. Moreover, the access to ultrafast light sources now allows to probe multielectronic processes and confront experimental results to theoretical calculations. Model systems C60, PAHs (Naphtalene, Anthracene and Pyrene) as well as DNA/RNA bases (pyrimidic bases Cytosine, Thymine, Uracile) have been the principal objects of study in that purpose. Experiments have been done in angularly resolved photoelectron spectroscopy and ionisation products mass spectroscopy, under XUV (10-30 eV) weak field synchrotron excitation, intense near infrared (I 1013 W/cm2) excitation as well as on a pump-probe XUV-IR laser beamline that give access to a hundred attosecond time resolution. With help of those tools, we evidenced and modeled the influence of the surface plasmon resonance of C60 at 20 eV in its photoionization dynamics at the attosecond timescale. We identified the population of Rydberg states during multiphoton ionisation of DNA/RNA bases similar for all the bases. This constraints theoretical models about non linear response of complex system under those excitation conditions. Finally we have been able to observe non adiabatic dynamics (electrons-nucleus couplings at a few tens of femtoseconds timescale) that appear consecutively of multielectronic excitation and ionization processes (shake-up mechanism)

Des nanobâtonnets de trioxyde de tungstène peuvent être élaborés sur un substrat de mica de type muscovite à l’aide d’une méthode simple de dépôt en phase vapeur. La croissance de ces objets semble obéir à un mode de croissance de type Stranski-Krastanov. Les nanobâtonnets sont majoritairement constitués d’une phase hexagonale métastable qui a été mise en évidence par MET. Cette structure se forme à partir d’un bronze de tungstène interfacial de structure hexagonale, qui croît en épitaxie sur le mica. Ce bronze contient du potassium provenant du substrat. Pour les bâtonnets les plus épais, la phase hexagonale est surmontée d’une structure monoclinique. La stabilité thermique de la structure hexagonale est importante puisqu’après un recuit à 600°C cette phase subsiste alors que la morphologie en bâtonnets est détruite. Les processus stabilisants la structure hexagonale sont apparemment à dissocier de ceux conduisant à la morphologie en bâtonnets. Le potassium joue un rôle majeur lors de la croissance des nanobâtonnets de WO3. Des élaborations de nanophases d’oxyde de tungstène suivies in situ par photoémission ainsi que par EXAFS de surface sur des substrats volontairement dopés avec du potassium mettent en évidence la forte affinité de cet élément avec le tungstène. Celle-ci peut même entraîner la décomposition partielle d’une molécule telle que du carbonyle de tungstène juste physisorbée à température cryogénique. En outre, la présence du potassium conduit à des phases plus oxydées qu’en son absence. / Tungsten trioxide nanorods can be elaborated on muscovite mica substrate through simple vapor deposition method. Growth of rods seems to follow a Stranski-Krastanov model. Their crystallography was investigated by TEM and reveals the presence of hexagonal phase. Such a metastable structure occurs from an interfacial hexagonal tungsten bronze which grows epitaxially on the substrate. This bronze phase contains potassium atoms coming from mica. Concerning the thickest rods, a monoclinic phase grows on the top of the hexagonal one. The hexagonal structure is thermally very stable: after annealing at 600°C, this phase is still detected whereas the rod morphology is destroyed. This point seems to indicate that processes which stabilize the hexagonal structure are different than those which are responsible of the rod shape. Potassium plays a major role in the formation of hexagonal WO3 phase. Additional tungsten oxide phase were elaborated on other substrates containing potassium atoms. Elaboration was then followed in situ by photoemission and SEXAFS and high affinity between potassium and tungsten was evidenced. Such an affinity can cause partial decomposition of tungsten hexacarbonyl molecule simply adsorbed at cryogenic temperature on substrate. Moreover, potassium atom presence leads to more oxidized phases than when this alkali metal is absent.

Metal-insulator transition is one of the most important properties observed in certain materials which has been studied widely using a wide range of experimental techniques as well as theoretical models. This kind of a transition, observed in several systems, can take place by tuning several parameters such as pressure, temperature or the composition itself. In this thesis we study a few selected transition metal oxide bronzes exhibiting such phenomenon, each of which has a different cause for undergoing the transition. In Chapter 1, we discuss briefly several mechanisms and models that have been used to understand metal-insulator transitions. We also briefly discuss the role of disorder, electron-electron correlations or both to understand the different ways in which such transitions can occur. In Chapter 2, we describe the different experimental as well as theoretical techniques that have been used in this thesis. In Chapter 3, we study the fermi-edge of the NaxWO3 systems, as a function of x, to understand the origin of the metal-insulator transition occurring in this series of compounds. The system undergoes a metal-insulator transition at the critical composition xc=0.25, below which it is found to be insulating. At the lowest temperature, the very low x compounds behave as disordered and correlated materials. Above the transition composition, the compounds behave as disordered and correlated metals. In the insulating regime, close to the critical composition, we find that the system behaves in a way that cannot be described by any known theories for metals or insulators. We have also done a systematic analysis of the Fermi-edge data for the insulating samples as a function of temperature and we find that they cannot be described by any of the known theories for solid-state systems. Further development is necessary in the theoretical side to understand and interpret our data. In Chapter 4, we study the angle-resolved photoemission data for the highly metallic sodium tungsten bronze Na0.8WO3. We have synthesized the single-crystals by high-temperature electrochemical synthesis and we have performed angle-resolved photoemission experiments to understand the band structure of this system. The experimental results have been supported by theoretical calculations. We find that the rigid band model is valid in describing the electronic structure in these systems. We also find the existence of electron-like pockets along certain symmetry directions. Further, photon energy dependent studies on the x=0.8 sample suggest that there is a difference in the surface with the bulk of the sample. The bulk is perfectly periodic and ordered, whereas the surface shows a distortion due to the rotation or deformation of the WO6 octahedra. In Chapter 5, we have studied the electronic structure of the low dimensional molybdenum oxide La2Mo2O7, which is expected to have a charge density wave(CDW)driven metal-insulator transition around 125K. We indeed observed the presence of CDWs in this system, which was observed in the angle-resolved photoemission spectra as back-folding of bands below the transition temperature. We have also studied the temperature evolution of the bands close to the Fermi level and we see a gradually weakening and finally disappearance of the back-folded bands close to and above the transition temperature. We have studied the angle-integrated spectra of this system from which we conclude that La2Mo2O7 is a CDW non-Fermi liquid system. We have also evaluated the total and partial density of states in this system using Vienna ab-initio simulation package. We find the results consistent with our experimental findings. In Chapter 6, we study the metal-insulator transition in another low-dimensional molybdenum oxide KMo4O6, which is expected to show a metal-insulator transition around 120K due to the formation of spin-density waves. We observed back-folding of bands with lower intensities at low temperature, suggesting the formation of spin density waves in the system. The angle-integrated spectra suggested that the system is a non-CDW non-Fermi liquid system. We have also evaluated the density of states and the results are in agreement with our experimental findings. In conclusion we have investigated the electronic structure of different classes of systems and we have given clue to the origin of the metal-insulator transition in these systems.

LnBaCo2O5+δ (Ln-112) where Ln = lanthanide element; 0 ≤ δ ≤1 and LnBaCo4O7+δ (Ln-114) are highly correlated cobalt oxides. Synchrotron photoemission spectroscopy of LnBaCo2O5+δ (Ln = Gd, Dy, Dy1-xTbx) and LnBaCo4O7 (Ln = Yb) has been undertaken at the UK Synchrotron Radiation Source (Daresbury Laboratory).During the photoemission experiments, the samples were observed to be contaminated due to residual gases inside the main vacuum chamber. The surface degradation of the samples is studied using the difference spectra generated from the valence band spectra of freshly scraped and contaminated samples and the nature of contaminated species on these samples is identified in the light of the reviewed literature. High-resolution photoemission is carried out to study the metal-insulator (MI) transition in double perovskites LnBaCo2O5+δ (Ln = Gd, Dy, Dy1-xTbx - Ln-112; 0 ≤ δ ≤ 1) as a function of temperature. The high-resolution photoemission results of single crystal samples of GdBaCo2O5.5, DyBaCo2O5.5 and Dy1-xTbxBaCo2O5+δ show that the temperature-based MI transitions in these compounds occur in the 300-400 K temperature range. A post-growth oxygen annealing treatment for as-grown single crystals of Ln-112 is necessary, achieving oxygen contents close to 5.50, to observe a marked nonmetal-to-metal transition. Resonant photoemission is used to identify the atomic parentage of the valence band states. A comparison of the electronic structure of LnBaCo2O5+δ (Ln = Gd, Dy, Dy1-xTbx - Ln-112; 0 ≤ δ ≤ 1) and LnBaCo4O7 (Ln = Yb - Ln-114) single-crystal surfaces is made using synchrotron photoemission spectroscopy. In both cases, the states close to the Fermi energy are found to be of mixed Co 3d/O 2p character, and the comparison allows identification of states due to low spin Co³⁺ in octahedral environments. The contributions from Ln elements to the valence band are found at higher binding energies.

Dans cette thèse, la formation de monocouches auto-assemblées de différentes molécules de chalcogénure et de molécules p-conjuguées planaire et leurs caractéristiques structurelles et électroniques ont été systématiquement étudiées principalement par spectroscopie photoélectronique à rayons X effectuée utilisant la lumière synchrotron, microscopie à effet tunnel à balayage et diffraction d'électrons à faible énergie. Une étude de la formation de structures hybrides organiques-inorganiques auto-assemblées a été réalisée par assemblage couche par couche d'un dithiol sur ZnO (0001) avec dépôt de métal intermédiaire. De plus en complément de l'étude des molécules comportant un atome de chalcogènure, les caractéristiques d'adsorption du sélénium et du soufre ont été étudiées. La spectroscopie XPS à haute résolution et la spectroscopie de structure fine d’absorption au seuil d’excitation (NEXAFS) ont permis d'étudier les caractéristiques des monocouches auto-assemblées du sélénure de benzène et du sélénophène sur Cu (100) et dihexyldiselénure sur Ni (111) et Pd (111) et ont montré en particulier l’existence de processus de rupture de liaison Se-C ainsi que l’existence de différents sites d'adsorption de molécules. Ces conclusions ont été soutenues par l'étude de l'adsorption atomique du sélénium, qui montre également l'existence de différents sites d'adsorption pour le Se atomique avec différents environnements chimiques. Ces conclusions sont principalement basées sur une étude XPS haute résolution des spectres caractéristiques Se3d, Se3p, du spectre de bande de valence et de l'imagerie LEED. La formation de monocouche de 5,5-bis (mercaptéthyl) -2,20-bipyridine (BPD) avec terminaison SH libre sur ZnO(0001) a été démontrée, permettant le greffage ultérieur d'Ag et Ni et de l’ assemblage d’une autre couche de BPD sur cette couche de métal-dithiol. Les changements dans les propriétés électroniques ont été déterminés à partir des spectres de la bande de valence. La molécule π-conjuguée, NTCDA, a été déposée sur différentes surfaces métalliques et sa morphologie structurelle et ses propriétés chimiques par rapport à la surface métallique ont été étudiées. Les molécules NTCDA affichent une structure « couchée » avec deux domaines différents sur Ag (110) et Cu (100) mais trois domaines sur la surface de Cu (111). Par rapport à celui sur la surface inerte de Au, une forte interaction entre les molécules et les substrats de Cu, Ag existe et joue un rôle important dans la détermination de l'orientation et de l'état de liaison des films organiques. / In this thesis, the formation of self-assembled monolayers of different chalcogenide molecules and planer π-conjugated molecules and their electronic and structural characteristics were systematically studied mainly by synchrotron based X-ray photoelectron spectroscopy, scanning tunneling microscopy and low energy electron diffraction. A study of formation of hybrid organic-inorganic self assembled structure was performed by layer by layer assembly of a dithiol on ZnO(0001) with intermediate metal deposition. Additionally as a complement to the study of chalcogen head group molecules the adsorption characteristics of selenium and sulfur were investigated. The high resolution XPS and near edge absorption fine structure spectroscopy allowed to investigate the characteristics of self-assembled monolayers of benzene selenide and selenophene on Cu (100), and dihexyldiselenide on Ni(111) and Pd(111) and showed in particular the existence of Se-C bond breaking processes and existence of different adsorption sites of molecules. These conclusions were supported by the study of atomic selenium adsorption, which also shows existence different adsorption sites for the atomic Se with different chemical environments. These conclusions are mainly based on high resolution XPS study of characteristic Se3d, Se3p spectra, valance band spectrum and LEED imaging. The formation of a 5,5- bis (mercaptomethyl)-2,20- bipyridine (BPD) with SH termination on ZnO(0001) was demonstrated allowing subsequent grafting of Ag and Ni and further assembly of BPD on this metal-dithiol layer. The changes in electronic properties were determined from valence band spectra. The large π-conjugated molecule, NTCDA, was deposited on different metal surfaces and its structure morphology and chemical properties with respect to the metal surface was investigated. The NTCDA molecules displays a lying down structure with two different domains on Ag (110) and Cu(100) but three domain on Cu(111) surface. Compared with the one on the inert Au surface, a strong interface interaction between the molecules and Cu, Ag substrates plays an important role in determining the orientation and bonding state of the organic films.

Title: Dust - UV interaction Author: Libor Nouzak Department: Department of Surface and Plasma Science Supervisor: RNDr. Jiri Pavlu, Ph.D. Supervisor's e-mail address: jiri.pavlu@mff.cuni.cz Abstract: Micrometer objects (dust grains) are an integral part of the universe. As other objects in the plasma, these dust grains charge to potencial close to the potencial of the plasmas (in this case, interplanetary plasma). In the universe, the photoelectric charging dust grain dominantes all other charging processes. In general, the resulting charge of dust grain is given by a balance of all processes, which haven't been mostly jet theoretically described. In our laboratory, we are simulating space conditions and measure resulting charge and his changes on a single separated dust grain. This work is partly focused to UV source application and to finishing its electronics, and partly on test measurements and model calculations, connected with newly built experiment (e.g., to estimate effects of backgound currents, surfaces, and the geometry of the dust trap electrodes). The work is finished by the first measurements of glass grain charge under electron bombardment with provisional detection optics. Obtained results are compared with previous measurements on the same type of dust grains. Key words: dust, dusty plasma,...

Catalysts based on cerium oxide are ubiquitous in industrial-scale chemical conversion. Here, a thorough study of their fundamental properties is undertaken via a model system ap- proach with the goal of furthering rational design in heterogeneous catalysis. A focus is put on understanding the behavior of oxygen vacancies in cerium oxide with respect to atomic co-ordination and electronic structure perturbations. Utilizing state-of-the-art probing tech- niques, a scalable model system framework is developed that allows for control over both the oxygen vacancy concentration and local co-ordination. High precision of the innova- tive approach facilitated observation of new phases of substoichiometric cerium oxide and lead to a first-of-a-kind investigation of the electronic structure of cerium oxide throughout isostructural transition from CeO2 to Ce2O3. The acquired results advance fundamental understanding of essential properties of cerium oxide that are relevant to its utilization in heterogeneous catalysis and open new pathways for functionalization of cerium oxide-based materials. Furthermore, the methodology developed in the thesis is transferable to other important reducible oxides. 1

This thesis is devoted to studies of high temperature superconductors and related materials using the angle-resolved photoemission spectroscopy (ARPES). Though there is no accepted theory of superconductivity, encompassing high-$T_{\\rm c}$ materials, there is enough evidence to believe that superconductivity can always be interpreted as stemming from pairing of electrons by interaction with bosons, and $T_{\\rm c}$ is determined by effectiveness of such a pairing. ARPES, owing to the possibility of recording energy- and momentum-resolved electronic spectrum, is a powerful probe of the normal-state electronic structure, which is an important prerequisite for the superconductivity, and implications of the electron pairing, such as emergence of the superconducting gap and finer features below $T_{\\rm c}$. Based on ARPES data one can quantify the electronic interactions by analysis of kinks in the dispersion curves, spectral line widths etc. In current work new methods of ARPES data analysis were developed and applied to the spectra taken from cuprate and iron-based high-$T_{\\rm c}$. The possibility to analyze the macroscopic response of solids in the normal state as well as in the superconducting and charge-density-wave phases basing on the experimentally measured renormalized band dispersion and anisotropic superconducting and charge-density-wave gap was shown. The thesis consists of five parts. Part 1 introduces the employed notions of electrons in solids and methods of their investigation. Part 2 describes the Voigt fitting procedure, allowed for purification of the spectra from resolution effects, and, consequently, for determination of the quasiparticle scattering rate with enhanced precision. In Part 3 the calculation of the temperature-dependent Hall coefficient in the charge-density-wave-bearing 2H-TaSe$_2$ from the band dispersion, measured in ARPES, is presented, and comparison to the independent magnetotransport measurements is shown. The extraction of the band dispersion of Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ and LiFeAs from ARPES data can be found in Part 4. Agreement with Hall effect measurements on the same samples is demonstrated. Part 5 introduces the extraction of the momentum-dependent superconducting gap in iron arsenides from fitting of ARPES spectra to Dynes function. The superfluid density was calculated from the band dispersion and the superconducting gap, measured in ARPES, and compared to the ones measured by different techniques.

Graphene, a two dimensional single layer of graphite, attracts a lot of attention of researchers around the globe due to its remarkable physical properties and application potential. The origin can thereby be found in the peculiar electronic structure since graphene is a zero gap semi-conductor with a linear energy dispersion in the vicinity of the Fermi level. Consequently, the charge carriers in graphene mimic massless Dirac Fermions which brings principles of quantum electrodynamics and exotic effects like Klein tunneling into a bench-top experiment. Modifying the electronic and/or crystal structure structure by functionalization might therefore as well lead to new tantalizing physical properties, novel compound materials based on graphene like graphane (fully hydrogenated graphene) or flourographene (fluorinated graphene), and ultimately new applications. In this work, the influences on the electronic structure of graphene are investigated with photoemission spectroscopies after covalent functionalization by atomic hydrogen and ionic functionalization with potassium. Regarding hydrogenation, the formation of tunable bandgap is observed along with a full recovery of the electronic properties of graphene upon removing the hydrogen by thermal annealing. Using high resolution x-ray photoemission and molecular dynamics simulations, the formation of a C4H structure is predicted for substrate supported graphene at a saturation H-coverage of 25%, due to a preferential para- arrangement of hydrogen atoms. In fully electron doped, hydrogenated graphene the formation of dispersionless hydrogen impurity state is observed with angle-resolved photoemission spectroscopy. This flat state is extended over the whole Brillouin zone and according to calculations not localized. Potassium-doped graphene shows a similar doping level as its 3D parent component, the graphite intercalation compound KC8. Investigating the electron-phonon coupling in doped graphene, by direct derivation of the Eliashberg-function, shows an asymmetric coupling strength along the high-symmetry directions in the Brillouin Zone of graphene. In the K-M direction additional low energetic contributions could be identified which may originate from out-of-plane phonon modes. Regarding the electron-phonon-coupling strength of the high energy in-plane phonon modes a reasonable agreement with theoretical predictions is found.

The effects of methane (CH4), diborone (B2H6) and nitrogen (N2) concentrations on the structure and photoelectron emission properties of chemical vapor deposition (CVD) polycrystalline diamond films were studied. The diamond films were grown on single-crystal Si substrates using the hot-tungsten filament CVD technique. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to characterize the different forms of carbon in the films, and the fraction of sp3 carbon to sp3 plus sp2 carbon at the surface of the films, respectively. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the films. The photoelectron emission properties were determined by measuring the energy distributions of photoemitted electrons using ultraviolet photoelectron spectroscopy (UPS), and by measuring the photoelectric current as a function of incident photon energy.