Cette thèse porte sur l’étude de couches minces ferroélectriques à base de BaTiO3 déposées par pulvérisation cathodique. Ces matériaux permettent par exemple de réaliser des condensateurs accordables ou encore des mémoires non-volatiles pour le stockage d’informations. Cependant, leurs propriétés diélectriques sont considérablement dégradées par des effets extrinsèques d’interfaces; film/substrat ou encore film/électrode. Dans ce contexte, la spectroscopie de photoémission (XPS) a été utilisée pour quantifier les états électroniques et chimiques de ces interfaces avec une approche in-situ. L’étude sur la formation du contact film/électrode a permis de mesurer la hauteur de barrière de Schottky partiellement responsable des caractéristiques capacités – tensions des couches. Des phénomènes de ségrégation ont été mis en évidence révélant une profonde instabilité de la stoechiométrie de surface. Enfin, la conséquence d’un dopage au niobium dans les couches minces de BaTiO3 est discutée du point de vue des modes de compensation, de la solubilité du dopant et des propriétés diélectriques. / The aim of this work was to better understand the surface and interface properties of sputtered ferroelectric BaTiO3 thin films. They are typically used as dielectrics in integrated capacitors, electromechanical sensors and so. This thesis studies the chemical and electronic structures of the interface of BaTiO3 in order to understand basic mechanisms of contact formation with the substrate and the electrode like the Schottky barrier height. Furthermore, the surface stoichiometry of such films has been investigated under different thermal preparation revealing significant instability through segregation phenomenon. Finally, the doping effect with niobium is studied regarding compensation mode, dopant solubility and dielectric properties. The experimental setup allows for in-situ analysis of surface and interface properties using photoelectron spectroscopy.

Abstract This thesis is dedicated to realizations and physical understanding of electronic and photocatalytic properties after decorating transition metals to the semiconducting molybdenum disulfide. Synthesized via facile wet chemical methods, the MoS₂-Au, MoS₂-Au-Ni and MoS₂-Ag-Ni composites were formed as binary or ternary compounds. The Au nanoparticles are stably joined to the MoS₂ matrix without deteriorating layered structures of the host. After introducing the Au nanoglue as a common buffer, a metallic contact is reached between Ni and MoS₂, and attributed to new electron migration channel via MoS₂ edge contact. Adapting the Ag as the buffer element can attach the Ni to the basal plane of the MoS₂ beside edge contact. The Ni-Ag-MoS₂ composite effectively splits water under visible light irradiation and produce hydrogen. The excellent photocatalytic activity is attributed to effective charge migration through dangling bonds at the MoS2-Ag-Ni alloy interface and the activation of MoS₂ basal planes. / Original papers The original publications are not included in the electronic version of the dissertation. W. Cao, V. Pankratov, M. Huttula, X. Shi, S. Saukko, Z. Huang, M. Zhang. Gold nanoparticles on MoS2 layered crystal flakes. Materials Chemistry and Physics, 158, 89−95 (2015). DOI: 10.1016/j.matchemphys.2015.03.041 X. Shi, S. Posysaev, M. Huttula, V. Pankratov, J. Hoszowska, J.-Cl. Dousse, F. Zeeshan, Y. Niu, A. Zakharov, T. Li, O. Miroshnichenko, M. Zhang, X. Wang, Z. Huang, S. Saukko, D. L. González, S. van Dijken, M. Alatalo, W. Cao. Metallic contact between MoS₂ and Ni via Au nanoglue. Small, 14, 1704526 (2018). DOI: 10.1002/smll.201704526 http://jultika.oulu.fi/Record/nbnfi-fe2018060525279 X. Shi, M. Huttula, V. Pankratov, J. Hoszowska, J.-Cl. Dousse, F. Zeeshan, Y. Niu, A. Zakharov, Z. Huang, G. Wang, S. Posysaev, O. Miroshnichenko, M. Alatalo, W. Cao. Quantification of bonded Ni atoms for Ni-MoS₂ metallic contact through X-ray photoemission electron microscopy. Microscopy and Microanalysis, 24, 458−459 (2018). DOI: 10.1017/S1431927618014526 http://jultika.oulu.fi/Record/nbnfi-fe2018082834233 X. Shi, M. Zhang, W. Cao, X. Wang, M. Huttula. Efficient photocatalytic hydrogen evolution via activated multilayer MoS₂. Manuscript. X. Shi, Z. Huang, M. Huttula, T. Li, S. Li, X. Wang, Y. Luo, M. Zhang, W. Cao. Introducing magnetism into 2D nonmagnetic inorganic layered crystals: a brief review from first-principles aspects. Crystals, 8, 24 (2018). DOI: 10.3390/cryst8010024 http://jultika.oulu.fi/Record/nbnfi-fe201802153441

La recherche d’une miniaturisation toujours plus poussée des dispositifs en micro- et opto- électronique a participé au développement des nanotechnologies. A l’échelle nanométrique, la densité des interfaces augmente énormément leur conférant un rôle crucial dans les performances des dispositifs. Dans cette thèse, l’intérêt a été porté sur les interactions aux interfaces entre matériaux hétérogènes lors des premiers stades de leur croissance par épitaxie par jets moléculaires. Chaque chapitre est dédié à l’étude d’une interface spécifique dans le cadre des recherches menées par l’équipe Hétéroépitaxie et Nanostructures de l’Institut des Nanotechnologies de Lyon. Deux approches complémentaires pour l’intégration monolithique du semiconducteur III-V GaAs sur silicium ont été étudiées: les nanofils de GaAs sur Si(111) et la recherche d’une phase Zintl pour la croissance bidimensionnelle (2D) de GaAs sur un substrat SrTiO3/Si(100). Pour ce qui concerne la croissance des nanofils de GaAs, l’étude par spectroscopie de photoémission de l’interface entre le gallium, en tant que catalyseur, et le substrat de silicium (111) recouvert de silice a montré qu’une réaction d’oxydoréduction entre les deux matériaux a lieu et est dépendante de la température pendant la croissance. Ensuite, le mécanisme d’encapsulation / désencapsulation par l’arsenic nécessaire à la protection des nanofils de GaAs lors des transferts, a été étudié structurellement en temps réel grâce à la microscopie électronique en transmission. Enfin, la croissance d'une demi-coquille métallique sur les nanofils de GaAs a été analysée in situ par diffraction et diffusion des rayons X en incidence rasante en utilisant un rayonnement synchrotron. Cette étude exploratoire a montré qu’il était possible d’obtenir une croissance partiellement épitaxiée d’or et d’aluminium sur les facettes des nanofils. Pour ce qui concerne la croissance 2D de GaAs sur un substrat SrTiO3/Si(100), la croissance de la phase SrAl2 proposée théoriquement dans la littérature a été tentée et examinée par photoémission. Une alternative, BaGe2, permettant de mieux pallier aux problèmes d’hétérogénéité chimique a finalement été proposée. / Miniaturization of micro- and opto-electronics devices has led to the development of nanotechnologies. At this scale, the density of interfaces drastically increases explaining their critical role in the device performances. In this thesis, interest has been focused on interactions at the interfaces between heterogeneous materials during their first growth stages by molecular beam epitaxy. Each chapter studies a specific interface with the objective of monolithically integrating III-V semiconductors (GaAs) on silicon substrate, which is a main goal of the INL’s Heteroepitaxy and Nanostructures team. Two complementary approaches have been considered: GaAs nanowires on Si (111) substrate and the research of a Zintl phase as a buffer layer adequate for the two-dimensional (2D) growth of GaAs on a SrTiO3 / Si (100) substrate. In the context of growing GaAs nanowires on Si(111) with gallium as catalyst, the role played by a silica overlayer has been studied by X-Ray Photoelectron Spectroscopy. It has been shown that an oxido-reduction reaction takes place at the interface, reaction which is strongly dependent on the temperature during the process. Besides, the real-time evolution of an As capping/decapping mechanism, which is needed for the protection of GaAs nanowires during transfers, has been studied thanks to electron transmission microscopy. Finally, the growth of a metal half-shell on GaAs nanowires has been investigated by in situ grazing incidence X-ray diffraction using synchrotron radiation. This exploratory study has shown that obtaining a partially epitaxial growth of gold and aluminum on nanowires facets is possible. In the context of obtaining a 2D growth of GaAs on SrTiO3/Si(100) substrate, the growth of the theoretically-suggested Zintl phase SrAl2 was tried by MBE and probed by photoemission, along with an alternative, BaGe2, which appeared more suitable for chemical reasons.

Le besoin croissant d'intégration de nouvelles fonctions dans les futures générations de dispositifs portables contribue au surpeuplement des circuits imprimés. Dans ce contexte, la miniaturisation des composants discrets est impérative pour compenser l'augmentation de leur nombre et pour garder la taille des cartes de circuit imprimé gérable. L'un des composants les plus courants de ce type est le condensateur, qui peut être utilisé pour découpler une partie d'un réseau électrique d'un autre. Cependant, la miniaturisation des condensateurs nécessite une augmentation de leur densité de capacité, impliquant l'intégration de condensateurs haute densité. Le succès d'une telle intégration repose sur l'utilisation à la fois de matériaux à haute constante diélectrique et d'une architecture d'empilement. Dans ce contexte, les couches de titanate-zirconate de plomb (PZT) combinées aux piles multi-MIM sont de bons candidats pour la nouvelle génération de condensateurs. La technologie multi-MIM consiste à empiler deux ou plusieurs structures MIM en parallèle afin d'augmenter la densité de la capacité sans modification effective de la surface. Avec la géométrie multi-MIM, la performance de l'appareil est fortement affectée par la qualité de l'interface Métal/PZT, il est donc important d'élaborer une chimie d'interface qui ne dégrade pas les performances des multi-MIM.Cette thèse soutenue par le projet français «Programme de l'économie numérique des investissements d'Avenir » vise deux axes de développement pour l’améliorer de la qualité des interfaces Pt/Ru/PZT: la première concerne l'optimisation du contenu de Pb en excès dans la couche de PZT, tandis que le second étudie les effets du recuit de post métallisation (PMA).La première partie de la thèse est dédiée aux analyses de densité de capacité réalisées sur les condensateurs Pt/Ru/PZT/Pt en fonction de l'excès de précurseur du Pb dans les couches de PZT déposées par voie sol-gel (10, 15, 20 et 30% de Pb respectivement pour PZT10, PZT15, PZT20 et PZT30).Nous montrons qu'une augmentation de l'excès de Pb de 10 à 20% entraîne une augmentation de la constante diélectrique maximale (environ 8,8%), ainsi qu'une diminution de la tangente de perte (de 4,36 à 3,08%) et du champ de claquage (de 1,68 à 1,26MV/cm). La PMA favorise l'augmentation du maximum de constant diélectrique (jusqu'à 7,5%) et le champ de claquage augmente de 0.5 MV/cm.Ensuite, l'influence de la chimie de surface des PZT est étudiée en fonction de l'excès de précurseur de Pb. Cet excès de Pb permet de compenser l'évaporation du plomb pendant le traitement thermique successif. En utilisant la spectroscopie de photoélectrons par rayons X (XPS), nous montrons la présence d'une phase de surface ZrOx. Les faibles niveaux d'excès de Pb conduisent à la formation de nanostructures ZrOx à la surface de la couche de PZT. Un taux plus élevé en Pb favorise la disparition totale nanostructures ZrOx en surface.Enfin, nous avons sondé l'interface Pt/Ru/PZT en fonction de l'excès de Pb et de la PMA. La microscopie électronique en transmission (TEM) montre que les nanostructures de ZrOx sont présentes à l'interface du Ru/PZT10. Les nanostructures cristallines ZrOx pourraient former une couche non ferroélectrique et ainsi affecter la densité de capacité. L'analyse en mode operando (sous polarisation in situ) par XPS haute-énergie montre une réponse électronique dépendant de la polarisation appliquée, probablement grâce à l’écrantage imparfait du champ dépolarisant à l'interface Pt/Ru/PZT10. En outre, une nouvelle phase (PbOx) est observée au niveau Pt/Ru/PZT30, probablement liée à la quantité de Pb en excès dans le PZT30. Cette phase semble induire la diminution du champ de claquage et la densité de capacité observée au niveau du Pt/Ru/PZT30/Pt. Enfin, PMA sur le Pt/Ru/PZT10 montre la création d'alliage à base de ZrRuOx et PbRuOx qui pourrait être à l'origine de l'amélioration des réponses électriques des condensateurs PZT après PMA. / The growing need for the integration of an increasing number of functions into the new generation of portable devices contributes to overcrowding of printed circuit boards. In this context, the miniaturization of discrete components is imperative to maintain a manageable size of the printed circuit boards. Decoupling capacitors are one of the most important such discrete components. Miniaturization requires an increase of capacitance density, involving the integration of high-density capacitors. The success of such integration relies on the use of both high dielectric permittivity materials and a suitable stacking architecture. Lead zirconate titanate (PZT) in decoupling multiple metal-insulator-metal (multi-MIM) stacks is a good candidate for the new generation of integrated capacitors. The multi-MIM technology consists in stacking two or more PZT film-based MIM structures connected in parallel in order to increase the density of the capacitance without any effective surface area change. Device performance is heavily affected by the quality of the interface with the electrodes, so it is important to engineer interface chemistry which does not degrade the multi-MIM performance.This thesis, supported by the French “Programme de l’économie numérique des investissements d’Avenir” addresses two aspects of development aiming to improve the quality of the Pt/Ru/PZT interfaces: the first one concerns the optimization of Pb excess content in the PZT film, while the second one investigates the Post Metallization Annealing (PMA) done after deposition of electrode/PZT multilayer.The first part of the thesis presents the capacitance density analysis performed on Pt/Ru/PZT/Pt capacitors as a function of Pb excess in the sol-gel precursor solution (10, 15, 20 and 30% of excess Pb for PZT10, PZT15, PZT20 and PZT30, respectively). Pb excess compensates the lead evaporation during calcination.An increase of Pb excess from 10 to 20% leads to an increase of the maximum dielectric constant of 8.8%, a decrease of the loss tangent from 4.36 to 3.08% and breakdown field from 1.68 to 1.26MV/cm. PMA favors the enhancement of the maximum of dielectric constant by 7.5%, and the breakdown field increases to 0.5 MV/cm.The influence of the surface chemistry is studied as a function of Pb precursor excess. X-ray photoelectron spectroscopy (XPS) demonstrates that low level of Pb excess leads to the presence of a ZrOx surface phase in the form of nanostructures. Higher Pb precursor content allows the PZT synthesis to proceed to its end-point, fully consuming the ZrO2 precursor and eliminating the low dielectric constant ZrOx surface phase.We have then studied the Pt/Ru/PZT interface as a function of Pb excess and PMA. Transmission Electron Microscopy (TEM) cross-sectional analysis shows that the crystalline ZrOx nanostructures are still present at the electrode interface, constituting a dielectric layer which contributes to defining capacitor performance. Operando (under bias in situ) hard X-ray photoelectron spectroscopy (HAXPES) analysis using synchrotron radiation highlights an electronic response dependent on the applied polarization, most probably due to imperfect screening of the depolarizing field at the Pt/Ru/PZT10 interface. Furthermore, a new phase (PbOx) is observed at the Pt/Ru/PZT30 due to the high Pb excess. This new phase seems to induce a reduction in breakdown field and capacitance density. Finally, PMA on the Pt/Ru/PZT10 suggests the creation of interface ZrRuOx and PbRuOx which could be at the origin of the improvement of electrical responses of PZT capacitors after PMA.In conclusion, this thesis has provided valuable information and methodology on the correlation between surface and interface physical chemistry of PZT and Pt/Ru/PZT and electric characteristics of PZT based MIM capacitors.

The present thesis concerns aspects of the interaction ofmatter in gas, liquid and solid phases, with electromagneticradiation, ranging from the optical to the X-ray region. Overthe last decade the availability of ultrashort strong laserpulses as well as of high power synchrotron sources of tunableX-ray radiation has stimulated a rapid development of newexperimental techniques which makes it possible to analysedifferent physical, chemical and biological processes inunprecedented detail. All of this urges a concomitantdevelopment of adequate theoretical language and methodscombined with simulation techniques. The first part of the thesis addresses nonlinear propagationof strong optical pulses. This study is motivated by thebreakthrough in synthesis of novel organic materials possessingprespecified nonlinear optical properties and which has led toa multitude of potential applications such as, for example, 3Dimaging and data storage, optical limiting and photodynamiccancer therapy. In order to clarify the underlying physics, astrict solution has been derived of the density matrixequations of a material aiming at an explicit treatment of itsnonlinear polarization without addressing a conventional Taylorexpansion over field amplitudes. Such a formalism is developedfor many-level molecules, allowing to solve the coupledMaxwell's and density matrix equations for the propagation of afew interacting laser pulses through a nonlinear molecularmedium. The theory presented is capable to account formulti-photon processes of an arbitrary order and for differentsaturation effects. The theory is applied to simulations oftwo- and three-photon absorption as well as to upconvertedstimulated emission of organic molecules in solvents. The second part of the thesis is devoted to resonant X-rayRaman scattering from free molecules, solutions and polymerfilms. The temporal analysis of the spectral profiles isperformed using the technique of scattering duration whichallows to select physical processes with different time scales.The slowing-down/speeding-up of the scattering by frequencydetuning provides insight in the formation of the differentparts of the scattering profile like atomic and molecularbands, resonant and vertical scattering channels, anomalousenhancement of the Stokes doubling effect. The lifetimevibrational interference (LVI), playing a crucial role inresonant scattering, is found to strongly influence thedispersion of the Auger resonances of polymers in agreementwith experiment. An almost complete quenching of the scatteringcross section by LVI is observed for the N2molecule. It is found that the interferenceelimination of the scattering amplitude gives valuableinformation on molecular geometry. The electron Doppler effectis minutely studied making use of a wave packet technique. Thesimulations show an "interference burning" of a narrow hole onthe top of the Doppler broadened profile of the Auger spectraof molecular oxygen. For the SF6molecule the Auger Doppler effect is found to besensitive to the detuning due to the scattering anisotropy. Inall of these studies the temporal language was foundconstructive and enormously helpful for understanding theunderlying physical processes. Most theoretical predictionsmade have been verified by experiments.

Capacitance-voltage-frequency measurements on n+-GaN/AlxGa1−xN UV/IR dual-band detectors are reported. The presence of shallow Si-donor, deep Si-donor, and C-donor/N-vacancy defect states were found to significantly alter the electrical characteristics of the detectors. The barrier Al fraction was found to change the position of the interface defect states relative to the Fermi level. The sample with Al fraction of 0.1 shows a distinct capacitance-step and hysteresis, which is attributed to C-donor/N-vacancy electron trap states located above the Fermi level (200 meV) at the heterointerface; whereas, the sample with Al fraction of 0.026 shows negative capacitance and dispersion, indicating C-donor/N-vacancy and deep Si-donor defect states located below the Fermi level (88 meV). When an i-GaN buffer layer was added to the structure, an anomalous high-frequency capacitance peak was observed and attributed to resonance scattering due to hybridization of localized Si-donor states in the band gap with conduction band states at the i-GaN/n+-GaN interface.

In this thesis I present studies of some transport and spectroscopic properties for two di erent materials exhibiting large magnetoresistance. Both of these materials are oxides of transition metals, showing exotic magnetic and transport properties. Despite these similarities, they are very different in many other aspects. One of them is an oxide of Manganese, along with a rare-earth metal, and exhibits large magnetoresistance under certain conditions, when doped by an alkaline earth metal. They are known as doped rare-earth manganites. The other material, Sr2FeMoO6, exhibits large magnetoresistance in the parent compound, without any doping, but only in the polycrystalline state. The manganites, on the other hand, show magnetoresistance under appropriate conditions in both single crystal and in polycrystalline state. Moreover, manganites exhibit several Metal-Insulator Transitions (MIT) as a function of doping, temperature and magnetic field. Sr2FeMoO6, on the other hand, is usually always metallic. In the first chapter, a brief introduction is provided regarding different types of magnetoresistance (MR) phenomena observed in different materials, namely Anisotropic MR (AMR), Giant MR (GMR), Collosal MR (CMR), Tunneling MR (TMR), Powder MR (PMR) etc. Out of these, CMR and PMR are found in doped manganites, while Sr2FeMoO6 exhibits PMR only. Next, a brief overview of the structure, properties and theories for both of these materials is provided. For the case of doped manganites, a short introduction is given for a novel two-fluid hamiltonian (called l - b model) which was proposed recently by Ramakrishnan et. al.. This model reproduces several exotic transport and magnetic properties of manganites which were inexplicible by earlier theories. The model was solved within the Dynamical Mean Field Theory (DMFT) framework by Hassan et. al.. A brief description of this DMFT solution is given. Many of the DMFT results for this model have been used in the subsequent chapters. In the second chapter, the hysteresis behaviour of the magnetoresistance and the magnetization (M ) of powdered Sr2FeMoO6 is considered in detail. In a recent experi- ment by Sarma et. al., it was found that this material, when powdered exhibits an exotic variety of PMR. In ordinary PMR, the hysteresis behaviour of the MR is supposed to follow that of M, in the sense that the coercive fields should be identical in both cases. Also, the MR is supposed to be roughly proportional to the square of the magnetization. However, in the experiments by Sarma et. al. on cold-pressed Sr2FeMoO6 powder, it was observed that the M R did not appear to be determined purely by the magnetization. Rather, the coercive fields for the hysteresis of the MR was almost 6 times that of M . Moreover, the quantity M R/M2, instead of remaining constant with changing magnetic field, itself has a hysteresis loop. Apart from establishing the exotic nature of the PMR, the experiment also tries to determine whether the MR originates from intra-grain or inter-grain tunneling. In the second chapter we present a simple toy model to reproduce the experimental results, and provide theoretical explanations. A combination of Monte Carlo and transfer matrix methods are used to simulate the hysteresis behaviour of the M R as well as of M . We show that the observed data can be understood if it is as- sumed firstly that the MR arises predominantly from inter-grain rather than intra-grain tunneling, and that the inter-grain boundaries are themselves magnetic with a coercive field higher than that of the grains. In order to motivate the use of Monte Carlo method for studying hysteresis, a brief survey of main results obtained for some simple models using this technique is also provided. In the third chapter, we study the doping and temperature dependence of core-level photoemission spectra in doped rare-earth manganites. In some recent experiments on Strontium doped (LSMO) and Barium doped (LBMO) samples, it has been observed that the M n2p3/2 core-level spectra shows an intriguing spectral weight transfer over a range of several eV , as a function of doping (x) and temperature (T ), in the ferromagnetic metallic phase. Specifically, there appears a shoulder adjacent to the main peak on the side of lower binding energy, which increases in weight and intensity as the doping increases or the temperature decreases. In LSMO samples, another shoulder was noticed on the higher binding energy side also. Moreover, in data obtained from LBMO samples, the spectra at different temperatures was subtracted from the spectra at/above Tc, and then this difference spectrum was integrated. The integrated weight, when normalized by the weight at the lowest temperature, appears to follow the square of the measured magnetization almost exactly. In order to understand the experimental data, we extended the aforementioned l - b model to include a core-level, and the attractive interaction due to a core-hole on the local valence levels. The impurity problem arising in DMFT, consisting of a single impurity site coupled to a bath, was tailored for the photoemission problem, by including this extra core-level at the impurity site. The hybridization parameters for the bath were determined self-consistently from the DMFT, and then the single particle spectral function for the core-hole was determined. This spectral function is proportional to the photo emission intensity. We found that our calculations reproduced the observed spectral weight transfer as a function of x and T both in trends and in magnitude. The integrated difference spectra weight was found to follow the square of the DMFT magnetization, just as in the experiment. Linear discretization of the conduction bath was used for all the above-mentioned cases. In one particular case, a logarithmic discretization was also undertaken for comparison, and also to obtain the exponents of the edge singularities in the theoretical spectra. In the fourth chapter, the possibility of Anderson Localization in manganites is in- vestigated, using the l - b model. According to this model, a large fraction of the valence electrons are polaronically self-trapped even in the ferromagnetic metallic phase. Due to strong on-site Coulomb interaction, these polarons provide a strongly scattering background, which can localize the mobile-electron band states close to the band edges. Since the fraction of valence electrons which are truly mobile is small, hence the Fermi energy lies close to the lower band edge. Hence, there is a possibility of an Anderson Insulator phase where all charge carriers are localized. To investigate this, we studied the behaviour of the mobility edges as a function of doping. DMFT alone does not include the physics of localization. Hence, in order to obtain the mobility edges, we combined the DMFT results with the Self-consistent Theory of Localization (STL), using a simplified prescription called Potential Well Analogy (PWA) due to Economou et. al.. We found that there is indeed an Anderson Insulator phase in a certain region of doping, which would otherwise have been supposed to be metallic based on purely DMFT results. Finally, we have compared this result, obtained using effective field theories, with an actual real space simulation of the l - b model at T=0. In this case, the mobility edge trajectories were obtained by studying the Inverse Participation Ratio (IPR), as a function of band energy and doping. In the concluding chapter, the principal results presented in this thesis are summa- rized. The limitations of the approach or approximations used are discussed, and future possibilities for overcoming these limitations outlined.

While in conventional superconductors coupling between electrons and phonons is known to be responsible for the electron pairing, for the high temperature superconductors the pairing media remains under debates. Since the interactions of electrons with other degrees of freedom (phonons, magnetic excitations, etc) manifest themselves by an additional renormalization in the electronic dispersion, they can be investigated by means of Angle Resolved Photoelectron Spectroscopy. In the work renormalization in two families of high Tc cuprates have been studied. Along the diagonal of the two-dimensional BZ, the renormalization effects are represented by an unusual band dispersion that develops a so-called ‘‘kink’’. In the vicinity of the (pi, 0) point of the BZ, where the order parameter reaches its maximum, the renormalization is noticeably stronger and makes itself evident even in the shape of a single spectral line measured for a fixed momentum. It was shown that for the Bi-2212 samples substitution of Cu atoms in Cu-O plane changes renormalization features in ARPES spectra both in nodal and antinodal parts of the Brillouin zone. The smearing of the dip in the in the spectral line shape measured at (pi; 0) point can be well explained by coupling of electrons to the magnetic resonance mode. The effect of Zn and Ni substitution on the antinodal ARPES spectra was shown to be in good agreement with the influence of these impurities on magnetic resonance mode seen in inelastic neutron scattering experiments. This, in addition to the previous ARPES studies of temperature and doping dependence of peak-dip-hump structure, mass renormalization near antinodal region and a kink in the nodal part of Brillouin zone, provides further evidence that the coupling to magnetic excitations, rather than to phonons, is responsible for the observed unusual renormalization. Unlike the well studied Bi-2212 family of cuprates, photoemission on YBCO-123 turns out to be much more complicated. The observed spectra have a strong contribution from a heavily overdoped surface component with the hole doping level of about x~0.30, which is weakly dependent on the sample stochiometry. Absence of any signs of superconductivity in the spectra of the overdoped component was argued to result from the unusually high doping level. This conclusion is supported by the fact that the overdoped bands give rise to the Fermi surface and band structure consistent with the predictions of the LDA calculations, as well as, by the dependence of the photoemission matrix element on the excitation energy, which closely follows that of the superconducting bulk component. Specific experimental geometry was used to enhance the signal coming from the superconducting component. In particular, experiments with circularly polarized light bundled with simple theoretical considerations enabled better separation of the surface and the bulk components. This type of experiments also suggests that the overdoped component is mainly localized in the topmost CuO2 bilayer, while the next bilayers in the YBCO-123 structure already represent bulk properties and retain superconductivity. Using partially Ca substituted samples it was possible to obtain spectra with a suppressed overdoped component. The likely reason for the suppression is a shift of the most probable cleavage plane from the Ba–O interface to the Y layer. Spectra from the Ca substituted sample clearly reveal a sizable superconducting gap, and strong renormalization effects in the vicinity of the antinodal point. The fact that the renormalization vanishes above Tc and has strong momentum dependence, diminishing away from the (pi; 0)/(0; pi) point, strongly suggests that the reason for this renormalization in YBCO-123 is coupling of the electronic subsystem to spin resonance, similar to the case of Bi-2212.

Das Forschungsgebiet der Kuprat- oder Hochtemperatursupraleiter (HTSL) ist bis heute einer der lebendigsten Bereiche der Physik kondensierter Materie. Ein besonderer Stellenwert kommt dem normalleitenden Zustand oberhalb TC zu, dessen Verständnis wesentlich zu einer Theorie der Hochtemperatur-Supraleitung beitragen könnte. Gegenstand dieser Arbeit ist die Untersuchung der Elektronenstruktur von HTSLn der Bi2Sr2CaCu2O8+[delta](Bi2212)-Familie nahe der Fermifläche im normalleitenden Zustand. Die Experimente wurden mittels winkelaufgelöster Photoemissionsspektroskopie (ARPES) durchgeführt, wobei die hohe Auflösung in Energie und Impuls recht genaue Rückschlüsse auf die Spektralfunktion und die Übergangs-Matrixelemente erlaubt. Die wichtigsten experimentellen Ergebnisse sind: 1) Hochaufgelöste ARPES-Fermiflächenkarten von Bi2212 und (Pb,Bi)2212 zeigen folgendes Bild: Die Hauptfermifläche ist lochartig und um die Ecken der Brillouinzone zentriert. Weiterer Bestandteil der Elektronenstruktur ist die Schattenfermifläche. Bei reinem Bi2212 treten außerdem extrinsische Beugungskopien der Fermifläche auf. 2) ARPES-Messungen entlang der -M-Richtung von Bi2212 zeigen eine starke Abhängigkeit von der Anregungsenergie, die auf starken Matrixelement-Effekten beruht. Verschiedene Methoden zur Bestimmung von kF zeigen, dass die Daten konsistent mit einer lochartigen Topologie der Hauptfermifläche sind. Des Weiteren wird die Qualität verschiedener Methoden zur Bestimmung von kF bei starken Matrixelement-Effekten bewertet. 3) Die Hauptfermifläche von (Pb,Bi)2212 behält ihre lochartige Topologie über einen großen Dotierungsbereich nahe optimaler Dotierung. 4) Erste hochaufgelöste ARPES-Messungen des Zirkulardichroismus wurden an (Pb,Bi)2212 durchgeführt. In der verwendeten nicht-chiralen Messanordnung wird ein CDAD (Circular Dichroism in the Angular Distribution of Photoelectrons)-Effekt beobachtet, dessen Asymmetrie antisymmetrisch bezüglich der Zweischicht-aufgespaltenen Zustände ist.

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)