Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2016-12-22T12:01:06Z No. of bitstreams: 0 / Made available in DSpace on 2016-12-22T12:01:06Z (GMT). No. of bitstreams: 0 / Os cosméticos labiais estão envolvidos em duas importantes discussões: os problemas de saúde pública e os problemas ambientais. A partir dessas informações, pretende-se analisar qual o impacto na saúde humana, verificar se há relação entre preço, duração e cor e investigar quais os prováveis impactos para o meio ambiente, supondo algumas vias de descarte. Os cosméticos analisados foram batons, divididos por marca, preço e cor. A primeira análise foi por fluorescência de raios-x (FRX). Em seguida, as matérias primas passaram por digestão com ácido nítrico e clorídrico sob aquecimento e foram diluídas com água destilada e filtradas. A seguir, foram realizadas leituras por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP-OES). A partir dos resultados da análise por FRX (foram encontrados 18 elementos metálicos) e a matriz para análise por ICP-OES foi composta por: alumínio, cálcio, cádmio, cobalto, cromo, cobre, ferro, potássio, manganês, níquel, chumbo, silício e titânio. Apesar de terem sido identificados metais tóxicos (Ni, Mn, Cd e Cr) nas amostras, os batons analisados cumprem com o requerido pela legislação nacional em relação aos limites impostos para metais pesados (Pb, Cd, Ni, Cr e Mn) em cosméticos e alimentos. Entretanto, é importante destacar que as legislações cosmética e alimentícia possuem grandes diferenças quanto aos limites impostos para metais pesados. O estudo do descarte dos batons mostrou que mesmo os batons que são mais utilizados, há um desperdício de quase 1/3 do produto por conta da embalagem interna. Essa informação pode auxiliar em um consumo consciente dos batons, tanto para a quantidade desperdiçada, quanto ao risco associado à utilização de um conjunto de maquiagens (bases, sombras, rímel, blush e batom) com outros cosméticos (cremes, perfumes, esmaltes, tintas para cabelo). Risco esse, associado a possíveis problemas à saúde. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The properties of bulk 3D materials of metals or semiconductors are manifested with various length scales(e.g., Bohr excitonic radius, magnetic correlation length, mean free path etc.) and are important in controlling their properties. When the size of the material is smaller than these characteristics length scales, the confinement effects operate reflecting changes in their physical behavior. Materials with such confinement effects can be designated as low dimensional materials. There are exceedingly large numbers of low dimensional materials and the last half a century has probably seen the maximum evolution of such materials in terms of synthesis, characterization, understanding and modification of their properties and applications. The field of” nanoscience and nanotechnology”, have become a mature field within the last three decades where, for certain application, synthesis of materials of sizes in the nanometer range can be designed and controlled. Interface plays a very important role in controlling properties of heterogeneous material of every dimensionality. For example, the interface forms in 2D thin films or interface of heterogeneous nanoparticles(0D). In recent times, a large number of remarkable phenomena have triggered understanding and controlling properties arises due to nature of certain interface. In the field of nanoparticles, it is well known that the photoluminescence property depends very strongly on the nature of interface in heterostructured nanoparticles. In the recent time a large variety of heterostructured nanoparticles starting from core-shell to quantum dot-quantum well kind has been synthesized to increase the photoluminescence efficiency up to 80%. Along with improvement of certain properties due to heterostructure formation inside the nanoparticles, the techniques to understand the nature of those interfaces have improved side by side. It has been recently shown that variable energy X-ray Photoemission Spectroscopy (XPS) can be employed to understand the nature of interfaces (internal structure) of such heterostructure nanoparticles in great detail with high accuracy. While most of the previous studies of variable energy XPS, uses photonenergies sensitive to smaller sized particle, we have extended the idea of such nondestructive approach of understanding the nature of buried interfaces to bigger sized nanoparticles by using photon energy as high as 8000eV, easily available in various 3rd generation synchrotron centers. The nature of the interface also plays an important role in multilayer thin films. Major components of various electronic devices, like read head memory devices, field effect transistors etc., rely on interface properties of certain multilayer thin film materials. In recent time wide range of unusual phenomenon such as high mobility metallic behavior between two insulating oxide, superconductivity, interface ferroelectricity, unusual magnetism, multiferroicity etc. has been observed at oxide interface making it an interesting field of study. We have shown that variable energy photoemission spectroscopy with high photon energies, can be a useful tool to realize such interfaces and controlling the properties of multilayered devices, as well as to understand the origin of unusual phenomenon exists at several multilayer interfaces. Chapter1 provides a brief description of low dimensional materials, overall perspective of interesting properties in materials with reduced dimensionality. We have emphasized on the importance of determining the internal structure of buried interface of different dimensionalities. We have given a brief overview and importance of different interfaces that we have studied in the subsequent chapters dealing with specific interfaces. Chapter 2 describes experimental and theoretical methods used for the study of interface and self-assembly reported in this thesis. These methods are divided into two categories. The first section deals with different experimental techniques, like, UV-Visible absorption and photoluminescence spectroscopy, X-Photoelectron Spectroscopy(XPS), X-Ray diffraction, Transmission Electron Microscopy(TEM) etc. This section also includes brief overview on synchrotron radiation and methods used for detail analysis of interface structure using variable energy XPS. In the second part of this chapter, we have discussed theoretical methods used in the present study. \ In Chapter 3A we have combined low energy XPS, useful to extract information of the surface of the nanoparticles, with high energy XPS, important to extract bulk information and have characterized the internal structure of nanoparticle system of different heterogeneity. We have chosen two important heterostructure systems namely, inverted core-shell(CdScore-CdSeshell) type nanoparticles and homogeneous alloy(CdSeS)type nanoparticles. Such internal structure study revealed that the actual internal structure of certain nanomaterial can be widely different from the aim of the synthesis and knowledge of internal structure is a prerequisite in understanding their property. We were able to extend the idea of variable energy XPS to higher energy limit. Many speculations have been made about the probable role of interface in controlling properties, like blinking behavior of bigger sized core-shell nanoparticles, but no conclusive support has yet been given about the nature of such interface. After successfully extending the technique to determine the internal structure of heterostructured nanoparticles to very high photon energy region, we took the opportunity to determine the internal structure of nanoparticles of sizes as large as 12nm with high energy photoemission spectroscopy for the first time. In Chapter 3B we emphasize on the importance of interface structure in controlling the behavior of bigger sized nanoparticles systems, the unsettled issues regarding their internal structure, and described the usefulness of high energy XPS in elucidating the internal structure of such big particles with grate accuracy to solve such controversies. The existence of high density storage media relies on the existence of highly sensitive magnetic sensors with large magnetoresistance. Today almost all sensor technologies used in modern hard disk drives rely on tunnel magnetoresistance (TMR) CoFeB-MgO-CoFeB structures. Though device fabrication is refined to meet satisfactory quality assurance demands, fundamental understanding of the refinement in terms of its effect on the nature of the interfaces and the MgO tunnel barrier leading to improved TMR is still missing. Where, the annealing condition required to improve the TMR ratio is itself not confirmatory its effect on the interface structure is highly debatable. In particular, it has been anticipated that under the proposed exotic conditions highly mobile B will move into the MgO barrier and will form boron oxide. In Chapter 4 we are able to shed definite insights to heart of this problem. We have used high energy photoemission to investigate a series of TMR structures and able to provide a systematic understanding of the driving mechanisms of B diffusion in CoFeBTMR structures. We have solved the mix-up of annealing temperature required and have shown that boron diffusion is limited merely to a sub-nanometer thick layer at the interface and does not progress beyond this point under typical conditions required for device fabrication. We have given a brief overview on the evolution of magnetic storage device and have described various concepts relevant for the study of such systems. The interface between two nonmagnetic insulators LaAlO3 and SrTiO3 has shown a variety of interface phenomena in the recent times. In spite of a large number of high profile studies on the interface LaAlO3 and SrTiO3 there is still a raging debate on the nature, origin and the distribution of the two dimensional electron gas that is supposed to be responsible for its exotic physical properties, ranging from unusual transport properties to its diverse ground states, such as metallic, magnetic and superconducting ones, depending on the specific synthesis. The polar discontinuity present across the SrTiO3-LaAlO3 interface is expected to result in half an electron transfer from the top of the LaAlO 3 layer to each TiofSrTiO3 at the interface, but, the extent of localization that can make it behave like delocalized with very high mobility as well as localized with magnetic moments is not yet clear. In Chapter 5 we have given a description of this highly interesting system as well as presented the outcome of our depth resolved XPS investigation on several such samples synthesized under different oxygen pressure. We were able to describe successfully the distribution of charge carriers. While synthesizing and understanding properties of nanoparticles is one issue, using them for device fabrication is another. For example, to make a certain device often requires specific arrangements of nanoparticles in a suitable substrate. Self-assembly formation can be a potential tool in these regards. Just like atom or ions, both nano and colloidal particles also assemble by themselves in ordered or disordered structure under certain conditions, e.g., the drying of a drop of suspension containing the colloid particles over a TEM grid. This phenomenon is known as self-assembly. Though, the process of assembly formation can be a very easy and cost-effective technique to manipulate the properties in the nano region, than the existing ones like lithography but, the lack of systematic study and poor understanding of these phenomena at microscopic level has led to a situation that, there is no precise information available in literature to say about the nature of such assembly. In Chapter 6 we have described experiments that eliminate the dependence of the self-assembly process on many complicating factors like substrate-particle interaction, substrate-solvent interaction etc., making the process of ordering governed by minimum numbers of experimental parameter that can be easily controlled. Under simplified conditions, our experiments unveil an interesting competition between ordering and jamming in drying colloid systems similar to glass transition phenomenon Resulting in the typical phase behavior of the particles. We establish a re-entrant behavior in the order-disorder phase diagram as a function of particle density such that there is an optimal range of particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory. In summary, we were able to extend the idea of variable energy XPS to higher energy limit advantageous for investigating internal structure of nonmaterial of various dimensionalities and sizes. We were able to comprehend nature of buried interface indicating properties of heterostructures quantum dots and thin films. Our study revealed that depth resolved XPS combined with accessibility of high and variable energies at synchrotron centers can be a very general and effective tool for understanding buried interface. Finally, we have given insight to the mechanism of spontaneous ordering of nanoparticles over a suitable substrate.

Le contexte général de ce travail est le développement et l'intégration de nouveaux matériaux magnétiques ayant des propriétés originales et d'intérêt potentiel pour la spintronique. En tant que matériau ferromagnétique d’aimantation nulle, le composé Sm1-xGdxAl2 (SGA) suscite un intérêt particulier, puisqu’il est capable, dans son état magnétique compensé, de polariser en spin un courant d’électrons. Dans un premier temps, des expériences de photoémission résolues en angle et en spin sur synchrotron ont permis d’effectuer une analyse précise de la structure électronique selon diverses directions de la zone de Brillouin et d’estimer de manière directe la polarisation de spin au niveau de Fermi du composé SGA. Dans un second temps, une attention particulière a été portée aux multicouches [Co/Pt] et aux JTMs à base de [Co/Pt]. Les multicouches [Co/Pt] constituent la seconde électrode des JTMs à base de SGA. Leurs propriétés magnétiques (en particulier l'anisotropie perpendiculaire et l'aimantation à saturation) ont été soigneusement étudiées en fonction de l'épaisseur de Pt et de la nature de la couche tampon (Pt, MgO ou Al2O3), et en liaison avec leurs caractéristiques structurales. Leur intégration dans des JTMs à base de [Co/Pt] a permis ensuite de remonter d’une part à la polarisation tunnel effective des multicouches [Co/Pt] et d’autre part aux configurations magnétiques des différentes électrodes, configurations parfaitement expliquées et reproduites par des simulations micro-magnétiques. Dans un troisième temps, les résultats de magnéto-transport au sein des JTMs SGA/MgO/[Co/Pt] sont présentés et discutés / The general context of this work is the development and integration of new magnetic materials with original properties of potential interest for spintronic applications. In this field, the Sm1-xGdxAl2 (SGA) compound drives a particular attention, as a zero-magnetization ferromagnet that can exhibit a spin polarization in its magnetic compensated state. In a first step, synchrotron-based angle and spin resolved photoemission spectroscopy experiments have permitted to perform an accurate analysis of the electronic structure along various directions of the Brillouin Zone and to get a direct estimation of the spin polarization at the Fermi level. In a second step, a special attention has been the paid to [Co/Pt] multilayers and to [Co/Pt]-based MTJs. The [Co/Pt] multilayers would constitute the second electrode in SGA-based MTJs. Their magnetic properties (especially the perpendicular anisotropy and the saturation magnetization) have been carefully investigated as a function of Pt thickness and nature of the buffer layer (Pt, MgO or Al2O3), and in close connection with structural characteristics. Their integration in [Co/Pt]-based MTJs has permitted to determine the [Co/Pt] effective tunnel polarization and to unravel the magnetic configurations of both electrodes which are perfectly explained and reproduced by micromagnetic simulations. In a third step, the results concerning the magneto-transport experiments in SGA/MgO/[Co/Pt] MTJs are presented and discussed

La qualité des interfaces dans les multicouches périodiques est essentielle au développement de miroirs réfléchissant efficacement dans les domaines des rayons X et extrême ultraviolet (X-EUV). De manière générale, la structure des interfaces dépend des possibles interdiffusion et processus chimiques aux interfaces entre couches. L'idée principale de cette thèse est d'appliquer la technique des ondes stationnaires dans le domaine X à la caractérisation de matériaux, principalement mais non exclusivement aux multicouches périodiques. Cette méthode est basée sur l'interférence de deux faisceaux de rayons X cohérents. L'interférence constructive sur un plan anti-nodal amplifie le champ électrique tandis que l'interférence destructive minimise ce dernier sur un plan nodal. Cette technique des ondes stationnaires dans le domaine X permet l'excitation (photoémission, fluorescence, ...) d'endroits spécifiques dans un empilement périodique de matériaux. De cette manière, les spectres expérimentaux ainsi obtenus sont principalement les spectres caractéristiques des atomes situés sur un plan anti-nodal. Combinée avec d'autres techniques expérimentales telles que la spectroscopie d'émission X (XES) ou la spectroscopie de photoélectrons dans le domaine X (XPS), une information sélective en profondeur, avec une sensibilité sub-nanométrique, peut être obtenue. / The interfacial information of periodic multilayers can be crucial for the development of reflecting mirrors which operate in the X-ray and extreme ultraviolet (X-EUV) ranges. Such information may contain the interdiffusion and chemical process at the interfaces of the layers. The idea of this thesis is to apply the X-ray standing wave technique to the characterization of materials, mainly but not limited to the periodic multilayers. X-ray standing wave technique enables to enhance the excitation (photoemission, fluorescence etc.) of specific locations within a periodic stack. The nature of such advantage is the interference of two coherent X-ray beams. One may compare the X-ray standing waves with the mechanical standing waves. The constructive interference at the anti-nodal plane amplifies the electric field; while the destructive interference at the nodal plane minimizes the electric field. In this way, the experimental spectra obtained under standing wave field will be mostly the material located on the anti-nodal plane. Combined with other techniques such as X-ray emission spectroscopy and X-ray photoelectron spectroscopy, a depth-selective information with a sub-nanoscale sensitivity can be obtained.

This thesis analyzes charge properties of (undoped) cuprate compounds from a theoretical point of view. The central question considered here is: How does the dimensionality of the CU-O sub-structure influence its charge degrees of freedom? The model used to describe the Cu-O sub-structure is the three- (or multi-) band Hubbard model. Analytical approaches are employed (ground-state formalism for strongly correlated systems, Mori-Zwanzig projection technique) as well as numerical simulations (Projector Quantum Monte Carlo, exact diagonalization). Several results are compared to experimental data. The following materials have been chosen as candidates to represent different Cu-O sub-structures: Bi2CuO4 (isolated CuO4 plaquettes), Li2CuO2 (chains of edge-sharing plaquettes), Sr2CuO3 (chains of corner-sharing plaquettes), and Sr2CuO2Cl2 (planes of plaquettes). Several results presented in this thesis are valid for other cuprates as well. Two different aspects of charge properties are analyzed: 1) Charge properties of the ground state 2) Charge excitations. (gekürzte Fassung)

L’étude des symétries d’un système peut en révéler de nombreuses propriétés physiques. La brisure, spontanée ou non, d’une de ces symétries implique alors d’importantes conséquences sur le comportement du système. On le voit dans la description actuelle de la physique des particules, avec notamment la création de la masse, ou dans la physique des solides, domaine de cette thèse, avec l’apparition de phases aux propriétés diverses, comme le magnétisme ou la supraconductivité. Le présent travail étudie par spectroscopie de photoémission résolue en angle (ARPES) les effets d’une brisure de symétrie dans deux systèmes différents : le système de fermions lourds URu2Si2 et l’oxyde de métal de transition (TMO) KTaO3. Le cristal d’URu2Si2 passe d’une phase paramagnétique pour T>THO, sujette à la cohérence de Kondo, vers la phase dite d’ordre caché pour T<THO, avec THO ≈ 17.5 K, brisant potentiellement plusieurs symétries. Bien qu’il y a presque trente ans que cettetransition de phase fut mesurée expérimentalement, aucun modèle théorique n’a encore réussi à faire consensus dans la communauté. Malgré une caractérisation expérimentale désormais très poussé de ce système, des informations résolues en angle manquent cruellement pour la compréhension de cette mystérieuse phase. Ce travail de thèse utilise donc des installations ARPES pour mettre en évidence, entre autre, le gap d’ordre caché, d’une amplitude inférieure à 10 meV. Nous montrons que ces mesures s’accordent avec plusieurs travaux expérimentaux précédents. Finalement, nous trouvons de fortes similarités entre les dispersions mesurées et celles calculées par LSDA, soulignant toutefois la nécessité d’introduire une renormalisation importante des masses effectives. Ce résultat contraint fortement les futures modélisations du comportement électronique de l’URu2Si2, tranchant sur l’approche à adopter.Contrairement au dernier système, où nous étudions une transition de phase, dans le tantalate de potassium KTaO3, notre attention se porte sur la brisure de symétrie de translation provoquée par la surface (111). Faisant suite à des mesures de transport qui revélèrent l’existence d’un gaz d’électron bidimensionnel (2DEG) à l’interface d’une hétérostructure de deux TMOs isolants de bandes, notre groupe mesura, plus tard, des 2DEGs aux surfaces (001) nues de SrTiO3 et de KTaO3, par ARPES. C’est dans la continuité de ces résultats que se place le présent travail, avec le désir d’élargir les caractéristiques de ces 2DEGs. Ainsi, poussé par la prédiction théorique d’état au caractère topologique non-trivial, nous apportons l’évidence d’un 2DEG à la surface (111) de KTaO3. Nous modélisons ensuite avec succès sa dispersion particulière grâce à des calculs de liaisons fortes. Ce travail constitue une étape dans la possible mise en évidence d’états au caractère topologique non-trivial dans les TMOs. / Several physical properties of a system can be understood by looking at the symmetries involved. Breaking of a symmetry affects the behavior of the system, regardless ifit happens spontaneously or not. This is observed with the emergence of the mass inparticle physics models, or with the diverse phases arising in condensed matter systems,as magnetism or superconductivity. Using angle-resolved photoemission spectroscopy (ARPES), this work studies theeffects of a symmetry breaking for two different systems : the heavy fermion systemURu2Si2 and the transition metal oxide (TMO) KTaO3. In URu2Si2, a transition occurs from a paramagnetic phase at T>THO to the hiddenorder phase at T<THO, with THO ≈ 17.5 K. This new order potentially breaks several symmetries. Although this transition was measured almost thirty years back, usingelectrical transport, no theoretical model could yet bring a consensus in the community. Since then, various characterizations of this system have been realized, howevermomentum-resolved informations are still missing to help unravel this mystery. Thus,during this thesis, we used state-of-the-art ARPES setups to measure several gaps located at different points in the Brillouin zone, and with amplitudes below 10 meV. Someof them are related to the Kondo coherence, and one is the hidden order gap. We showthat these measurements are consistent with previous experimental works. Finally, weobserved that our measurements differ from LSDA calculations solely by a renormalization of the effective masses by, at least, a factor 10 close to the Fermi level. Taking intoaccount some interactions, such as electronic ones, could lead to a more accurate model.Our measurements provide the constraints for this possible modeling. Unlike the transition we just described, the symmetry breaking in potassium tantalate KTaO3 is not spontaneous. In this system, we look at the (111) surface, wherethe translation symmetry is broken. A metallic two-dimensional electron gas (2DEG)has been measured in 2004 by Ohtomo at the interface between two insulating TMOs :strontium titanate SrTiO3 and lanthanum aluminate LaAlO3. The possible electronicapplications of exotic properties in TMOs, resulting from the d orbitals, has brought anew wave of activity to this topic. Later, our group measured 2DEGs at the (001) baresurfaces of SrTiO3 and KTaO3. Following these results, we wished to tailor the characteristic of such 2DEGS. Led by the theoretical prediction of states with non-trivialtopological character, we are presenting the evidence of a 2DEG at the (111) surface ofKTaO3. We also discuss its dispersion and introduce a tight binding calculation modelsuccessfully. This work is a step towards the realization of non-trivial topological statesin transition metal oxides.

Dans ce travail de thèse, nous illustrons la pertinence de la technique de photoémission pour l'étude des propriétés électroniques des matériaux. Dans la première partie, nous détaillons le développement et la phase de tests d'un nouveau bâti expérimental composé d'une chambre d'épitaxie par jets moléculaires (MBE) ainsi que d'une chambre de photoémission résolue en angle et en spin (SR-ARPES), connecté au tube Daum à l'Institut Jean Lamour. Les hautes performances de ce nouveau dispositif sont d'une part évaluées par une série de mesures expérimentales sur un système connu de la littérature (état de Shockley à la surface de l'Au(111)), et d'autre part illustrées par l'analyse de matériaux originaux (isolants topologiques, effet Kondo moléculaire …). Les valeurs de résolution en énergie sont inférieures à 2 meV et 300 meV pour la photoémission utilisant les rayonnements UV (UPS) et X (XPS) respectivement. La résolution angulaire est quant à elle meilleure que 0,2° et la température minimale atteignable est de 8,7 K. Finalement, des premières mesures de SR-ARPES ont démontré la capacité de ce nouveau bâti à mesurer les détails les plus fins de la structure de bandes polarisée en spin, se rapprochant ainsi de l'état de l'art dans le domaine. Ce nouveau dispositif est donc pleinement opérationnel. La seconde partie est consacrée à l'étude d'un oxyde de silicium ultra-mince bidimensionnel (2D) à la surface d'un substrat monocristallin de Ru(0001). Nous étudions tous les stades de croissance en partant du substrat nu de Ru(0001) jusqu'à une bicouche cristalline de cet oxyde, par XPS haute résolution (rayonnement synchrotron) et photoémission résolue en angle (ARPES). Nous confirmons la structure atomique établie dans la littérature pour ce système à la monocouche, avec en particulier l'existence de deux types de liaisons inéquivalentes Si-O-Ru révélées par des mesures inédites d’XPS haute résolution au niveau de la raie de cœur de l'O1s. En outre, nos mesures ARPES mettent en évidence l'existence d'états dispersifs bidimensionnels propres à ce matériau 2D. Alors que la monocouche est fortement connectée au substrat de ruthénium (liaisons covalentes), la bicouche en est déconnectée (liaisons de van der Waals). Notre étude confirme l'existence d’une telle transition avec des signatures claires à la fois en XPS et en ARPES, démontrant notamment la disparition des liaisons Si-O-Ru. Nous démontrons également la robustesse de ce système, qui une fois cristallisé peut être remis à l'air sans modifications majeures de ses propriétés électroniques, lui donnant ainsi un fort potentiel de fonctionnalisation (par exemple au sein d'hétérostructures 2D complexes comme couche isolante). Finalement, dans une troisième partie nous nous intéressons aux aspects théoriques de la photoémission résolue en angle. Alors que la structure de bandes est périodique dans l'espace réciproque, ce n'est pas le cas de l'intensité de photoémission, qui peut présenter des variations complexes dépendant de nombreux paramètres. Ces aspects sont généralement mal compris par les expérimentateurs. Nous présentons ici un modèle simple récemment proposé qui s'inscrit dans une description en trois étapes du processus de photoémission, et qui permet d'évaluer les éléments de matrice à un électron. Ces éléments de matrice représentent l'ingrédient essentiel permettant de comprendre la répartition du poids spectral en photoémission. Nous démontrons que dans ce modèle ils sont proportionnels à la transformée de Fourier de l'état de Wannier du système considéré, ainsi qu'à un terme de polarisation contenant les effets géométriques inhérents à toute expérience de photoémission. Nous appliquons alors cette approche à des systèmes physiques comme le graphène, ou encore au cas de mesures de dichroïsme circulaire réalisées au niveau des états d et de l'état de Shockley d'un monocristal de Cu(111), mettant ainsi en évidence ses succès et ses limitations / In this work, we highlight the relevance of photoemission spectroscopy for investigating the electronic properties of materials. In the first part, we tackle the development and the test phase of a new experimental setup which is composed of a molecular beam epitaxy (MBE) and a spin and angle resolved photoemission (SR-ARPES) chambers, connected to the tube at the Institut Jean Lamour. The high performances of this new setup are evaluated. On one hand by measuring well known system from the litterature (Shockley state at the Au(111) surface) and on the other hand by studying materials with novel properties (topological insulators, molecular Kondo effect …). Energy resolution is better than 2 meV for UV photoemission (UPS) and 300 meV for X-ray photoemission (XPS). We also have an angular resolution better than 0.2° and a lowest sample temperature of 8.7 K. Finally, first SR-ARPES measurements demonstrate the ability of this new installation to measure finest details of the spin polarized band structure. In short, this new setup is fully operationnal. The second part is dedicated to the study of a two dimensionnal (2D) ultra thin silicon oxide at the surface of a cristalline Ru(0001) substrate. Both growth and electronic properties are studied by high resolution XPS and ARPES. We confirm the structural model accepted for the system in the litterature for the monolayer case. In particular we confirm the existence of two inequivalent Si-O-Ru bonds with unprecedented high resolution XPS measurements on the O1s core level. In addition, our ARPES measurements highlight new dispersives states with 2D character which are unambiguously attributed to this oxide. While the monolayer is strongly connected to the ruthenium substrate (covalent bonds), the bilayer is disconnected from this latter one (van der Waals). Our work confirms the existence of such a transition with unambiguous signatures both in XPS and ARPES, in particular with the breaking of Si-O-Ru bonds. We also demonstrate the robustness of this system which, after being cristallised, can go to atmosphere without fundamental modification of his electronic properties. That gives a lot of potential applications to this 2D cristalline oxide, which could play in the futur the role of a wide band gap insulator in 2D heterostructures. In the last part, we focus on the theoretical aspects of photoemission. While band structure is periodic in the reciprocal space, it is not the case of photoemission intensity which can depend on a lot of parameters. We are motivated by the fact that these considerations are generally not well understood by experimentalists. Here, we present a simple model recently proposed in the three step approach of the photoemission process. With this model we can evaluate the one-electron matrix elements which play a key role to understand the variations of spectral weight in photoemission. In this approach, one-electron matrix elements are proportionnal to both Fourier transform of the Wannier state of the system and to a polarization term. We apply this model to « real » systems, in particular to graphene and to circular dichroism measurements on Cu(111) sample, highlighting sucess and limitations of this model

Der Einfluss der Modifikation der technologisch relevanten GaAs(100) Oberfläche durch Chalkogene, i.e. Selen, Schwefel und Tellur, wird in dieser Arbeit untersucht. Es wird ein Modell vorgestellt, das die Eigenschaften der modifizierten Oberfläche beschreibt. In einem zweiten Schritt werden die so modifizierten Oberflächen mit Metallen unterschiedlicher Reaktivität und verschiedenen Elektronegativitäten bedampft. Die Bandbreite dieser Eigenschaften wird durch die Metalle Indium und Silber, das Alkalimetall Natrium, das Erdalkalimetall Magnesium und das Halbmetall Antimon abgebildet. Die Untersuchung des Einflusses der Chalkogene auf die chemischen Eigenschaften und die Barrierenhöhe der Metall/GaAs(100) Grenzfläche bilden einen weiteren Schwerpunkt. Die Änderung der Barrierenhöhe wird dabei mit Hilfe des Modells metallinduzierter Bandlückenzustände (metal induced gap states) erklärt. Als experimentelle Techniken werden Photoemissionsspektroskopie, Raman Spektroskopie und Strom-Spannungsmessungen verwendet. / The influence of a modification of the technological relevant GaAs(100) surface by chalcogens, i.e. selenium, sulphur and tellurium, is evaluated in this work. A model is proposed, which describes the properties of the modified surface. In a second step metals of different reactivity and electronegativity have been evaporated onto these modified surfaces. Among these materials were the metals indium and silver, the alkali metal sodium, the earth alkali metal magnesium and the half metal antimony. The investigation of the influence of chalcogens on the chemical properties and the barrier height of the metal/GaAs(100) interface is another point of interest. The change in barrier height is explained by the model of metal induced gap states (MIGS). Photoemission spectroscopy, Raman spectroscopy and current-voltage-measurement have been used as experimental techniques.

Trotz einer Vielzahl von Forschungsarbeiten auf dem Gebiet der Phthalocyanin-basierten organischen Verbindungen fehlt nach wie vor ein umfassendes Verständnis des Zusammenspiels zwischen strukturellen und elektronischen Eigenschaften, die sich bei der Abscheidung dieser Stoffe auf anorganische kristallinen Substraten ausbilden. Vor diesem Hintergrund wurden für die vorliegende Arbeit vier metallbasierte Phthalocyanine ausgewählt und mittels organischer Molekularstrahl-Abscheidung (OMBD) im Ultrahochvakuum (UHV) auf Ag (111) Einkristalle adsorbiert. Für die anschließende eingehende Untersuchung dieser Proben wurden insbesondere Rastertunnelmikroskopie (STM) und -spektroskopie (STS) angewandt. Ergänzend kamen Ultraviolett- und Röntgen-Photoelektronenspektroskopie (UPS und XPS) zum Einsatz, wodurch komplementäre Informationen gewonnen wurden. Die aus diesen Untersuchungen resultierenden Ergebnisse liefern einen wesentlichen Beitrag zum oben genannten Forschungsgebiet. Die in dieser Arbeit untersuchten Metall-Phthalocyanine (MePc) wurden so ausgewählt, dass eine möglichst große Vielfalt an geometrischen und elektronischen Eigenschaften abgedeckt wurde. Planare cobaltbasierte Phthalocyanin-Moleküle wurden in zwei Konfigurationen untersucht: einerseits das protonierte CoPc, das sich als organischer p-Halbleiter verhält, und andererseits das vollständig fluorinierte F16CoPc, das n-Halbleitereigenschaften besitzt. Bei beiden Systemen zeigte sich an der Position des Cobaltions eine Kopplung zwischen den Molkülorbitalen des Adsorbats und den Elektronenzuständen des Substrates. Das nichtplanare Zinn-Phthalocyanin ist von besonderem Interesse aufgrund seiner beiden möglichen Adsorptionskonformationen up und down, bei denen sich das Sn-Ion oberhalb beziehungsweise unterhalb des Phthalocyaninliganden befindet. Damit stellt dieses System einen möglichen Kandidaten für Anwendungen als molekularer Schalter oder als Speichereinheit dar. In der vorliegenden Studie werden lokalisierte Schaltvorgänge einzelner Moleküle zusammen mit der Möglichkeit einer kontrollierten molekularen Nanostrukturierung gezeigt. Lutetium (III) bisphthalocyanin wurde ausgewählt als Vertreter einer neuen Gruppe von MePc, die eine Sandwichstruktur ausbilden, bei der zwei π-konjugierte Phthalocyaninliganden über ein Seltenerd-Ion miteinander verbunden sind. Die Untersuchung dieses Systems liefert wichtige neue Erkenntnisse, wie zum Beispiel ein umfassendes Verständnis der Vorgänge bei der Selbstassemblierung innerhalb der ersten und zweiten organischen Monolage. Zudem wurde bei der Charakterisierung des Tunneltransports durch einzelne Moleküle mittels STS ein negativer differentieller Widerstand (NDR) gefunden, der von der Anzahl molekularer Lagen abhängt.

In this thesis the charge dynamics of correlated electron systems, in which a metallic phase lies in close proximity to an ordered phase, are investigated by means of angle resolved photoemission spectroscopy (ARPES). The analysis of the experimental data is complemented by electronic structure calculations within the framework of density functional theory (DFT). First the charge dynamics of the colossal magnetoresistant bilayer manganites are studied. The analysis of the ARPES spectra based on DFT calculations and a Peierls type charge density wave model, suggests that charge, orbital, spin and lattice degrees of freedom conspire to form a fluctuating two dimensional local order that produces a large pseudo gap of about 450 meV in the ferromagnetic metallic phase and that reduces the expected bilayer splitting. Next, the interplay of Kondo physics and (magnetic) order in the heavy fermion superconductor URu2Si2 is investigated. The low energy electronic structure undergoes strong changes at 17.5 K, where a second order phase transition occurs whose phenomenology is well characterized, but whose order parameter could not yet be unambigeously identified. Below THO, non-dispersive quasi particles with a large scattering rate suddenly acquire dispersion and start to hybridize with the conduction band electrons. Simultaniously the scattering rate drops sinificantly and a large portion of the Fermi surface vanishes due to the opening of a gap within the band of heavy quasi particles. The observed behaviour is in stark contrast to conventional heavy fermion systems where the onset of hybridization between localized and itinerant carriers happens in a crossover type transition rather than abruptly. These experimental results suggest that Kondo screening and the hidden order parameter work together to produce the unusual thermodynamic signatures observed in this compound. Finally, the influence of charge doping and impurity scattering on the superconducting porperties of the transition metal substituted iron pnictide superconductor Ba(Fe1-xTMx)2As2 (TM = Co, Ni) is studied. Here, resonant soft X-ray ARPES is applied to see element selective the contribution of the 3d states of the TM substitute to the Fe 3d host bands. The spectroscopic signatures of the substitution are found to be well reproduced by DFT supercell and model impurity calculations. Namely, the hybridization of the dopant with the host decreases with increasing impurity potential and the electronic states of the impurtiy become increasingly localized. Simultaniously, in all simulated cases a shift of the Fermi level due to electron doping is observed. The magnitude of the shift in the chemical potential that accurs in BaFe2As2, however, is in stark contrast to the marginal doping values obtained for the impurity model, where the shift of the chemical potential is largely compensated by the influence of the increasing impurity potential. This suggests that the rigid band behaviour of TM substituded BaFe2As2 is a peculiarity of the compound, which has strong implications for the developement of superconductivity. / In dieser Arbeit wird die Ladungstraegerdynamik in korrelierten Elektronensystemen, in denen eine metallische Phase in direkter Nachbarschaft zu einer geordneten Phase liegt, mit Hilfe von winkelaufgeloester Photoelektronenspektroskopie (ARPES) untersucht. Die Analyse der experimentellen Daten wird ergaenzt durch lektronenstrukturrechnungen im Rahmen der Dichtefunktionaltheorie (DFT). Zuerst wird die Ladungstraegerdynamik in gemischtvalenten zweischichtmanganaten mit kolossalem Magnetiwiderstand studiert. Die Analyse der Photoemissionsspektren basierend auf DFT Rechnungen und einem Peierls artigem Ladungsdichtewellenmodell, legt nahe, dass die Freiheitsgrade von Ladung, Orbitalen, Spin und des Ionengitters konspirieren, um eine fluktuierende zweidimensionale lokale Ordnung zu bilden, die verantwortlich ist fuer die beobachtete Pseudobandluecke von 450 meV, und die zur Reduktion der erwarteten Zweischichtaufspaltung beitraegt. Als naechstes wird das Zusammenspiel von Kondo Physik und (magnetischer) Ordung im Schwerfermionensupraleiter URu2Si2 untersucht. Die iedrigenergetische elektronische Struktur zeigt starke Veraenderungen bei 17.5 K, wo ein Phasenuebergang zweiter Ordnungstattfindet, der phenomenologisch gut charakterisiert ist, aber dessen Ordungsparameter nocht nicht eindeutig identifiziert werden konnte. Unterhalb von THOerlangen nicht dispergierende Quasiteilchen mit gro en Streuraten abrupt Dispersion und hybridisieren mit den Leitungselektronen. Gleichzeitig sinkt die Streurate und ein gro er Teil der Fermiflaeche verschwindet durch das Oeffnen einer Bandluecke innehalb des Bandes schwerer Quasiteilchen. Das beobachtete Verhalten steht in starkem Kontrast zu dem von konventionellen Schwerfermionensystemen, in denen die Hybridisierung zwischen lokalisierten und itineranten Ladungstraegern in einem kontinuierlichen Uebergang ablaeuft, anstatt abrubt. Diese experimentellen Befunde lassen den Schluss zu, dass das zusammenspiel zwischen Kondo Abschirmung und dem unbekannten Ordnungsparameter die ungewoehnlichen thermodynamischen Signaturen in dieser Verbindung hervorruft. Abschliessend wird das Zusammenwirken von Ladungstraegerdotierung und Streuung an Stoeratomen auf die Supraleitung uebergangsmetalldotierter Eisenpniktid Supraleiter Ba(Fe1-xTMx)2As2 (TM = Co, Ni) untersucht. Mit Hilfe von resonantem Weichenroentgen ARPES gelingt es, elementselektiv den Beitrag der 3d Zustaende des TM Substituenten zu den Eisen 3d Wirtsbaendern zu beobachten. Die spektroskopischen Signaturen der Substitution sind mit Hilfe von DFT Rechnungen und Modelrechnungen mit zufaellig verteilten Stoeratomen gut zu reproduzieren. Insbesondere nimmt die Hybridisierung des dotierten Uebergangsmetalls und der Eisenbaender mit zunehmender Kernladungszahl ab und die elektronischen Zustaende der Stoeratome werden zunehmen lokalisiert. Gleichzeitig wird in allen gerechneten Faellen eine Verschiebung des Fermi Niveaus durch Elektronendotierung beobachtet. Der Betrag der Verschiebung des chemischen Potentials in BaFe2As2 steht allerdings in starkem Kontrast zu den Werten, die man im Falle der Modellrechnungen erhaelt, wo die Verschiebung des Fermi Niveaus durch den Einfluss des Potentials der Stoeratome groesstenteils kompensiert wird. Dies legt nahe, dass das beobachtete "rigid band" Verhalten von TM substituiertem BaFe2As2 eine Besonderheit dieser Verbindung ist, welches starke Auswirkungen auf die Ausbildung von Supraleitung hat.