This thesis contains two parts. The first part concerns the research work on free molecules using synchrotron-radiation-related techniques. Auger electron spectra of two free open-shell molecules, O2 and NO, were studied experimentally and theoretically. Photoionization experimental technique with tunable synchrotron radiation source was used to induce core-level electron ionization and obtain the KVV normal Auger electron spectra. A quantitative assignment of O2 normal Auger spectrum was obtained by applying ab initio CI calculations and LVI Auger line shape simulations including the bond length dependence of Auger transition rates. The photon energy dependence of normal Auger electron spectra was focused on with photon energies in the vicinities of core-ionization threshold energies. Consequently, the MAPCI (Molecular Auger Post Collision Interaction) theory was developed. Taking the near-threshold O2 normal Auger spectrum as an example, the two extreme cases of MAPCI effect, “atomic-like PCI” and “molecular PCI”, were discovered and discussed. The effect of shape resonance on near-threshold molecular normal Auger spectrum was discussed taking NO near threshold normal Auger spectra as example. The second part deals with research work on the chemisorption of small epoxy organic molecules, ethylene oxide, methyl oxirane, on Si (100) surfaces. Synchrotron radiation related techniques, UPS, XPS and NEXAFS, were applied. Based on the valence photoemission spectra, C 1s and Si 2p XPS spectra, the epoxy ring opening reactions of these molecules in chemisorption process were proved. Further tentative search for the surface-adsorbate CDAD effect was performed, and no evident circular dichroism was confirmed.

Le travail réalisé au cours de cette thèse concerne l'analyse des conséquences de l'oxydation à 950°C des alliages base Ni sur la composition de l'alliage à proximité de l'interface alliage/oxyde. Deux catégories d'alliages ont été analysées : alliages à faible teneur en chrome conduisant à l'oxydation interne et l'alliage chromino-formeur Ni-16Cr-9Fe.Une description complète des mécanismes de l'oxydation interne du chrome est obtenue à partir du développement du modèle analytique de Wagner d'oxydation interne et du développement du modèle numérique de Feulvarch. Ces modèles décrivent l'évolution de l'oxydation interne jusqu'à la transition oxydation interne / oxydation externe à 11 %poids de chrome environ.L'analyse par la spectroscopie d'électrons Auger de l'alliage modèle Ni-16Cr-9Fe à 950°C oxydé pendant 10 heures a permis d'explorer la zone à proximité immédiate de l'interface alliage/oxyde et de déterminer la concentration en chrome à l'interface à 0,5%poids (i.e. dans 20 premiers nanomètres), ce qui est en accord avec le modèle analytique de Wagner d'oxydation en couche compacte. La description des profils de déchromisation et des profils de cavités pour plusieurs temps d'exposition allant de 100h à 5000h a permis de mettre en évidence une corrélation forte entre ces deux phénomènes (même constante parabolique). Pour ces durées d'oxydation les profils de déchromisation présentent un point d'inflexion ce qui se traduit par l'augmentation de la teneur en chrome à l'interface. Les résultats sont interprétés dans le cadre d'un nouveau modèle analytique avec l'hypothèse d'injection des lacunes produites par l'effet Kirkendall au point d'inflexion.

Thesis (Ph.D.); Submitted to the University of California, Berkeley, Berkeley, California (US); 15 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56814" Westerberg, Staffan Per Gustav. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 12/15/2004. Report is also available in paper and microfiche from NTIS.

Le travail réalisé au cours de cette thèse concerne l’analyse des conséquences de l’oxydation à 950°C des alliages base Ni sur la composition de l’alliage à proximité de l’interface alliage/oxyde. Deux catégories d’alliages ont été analysées : alliages à faible teneur en chrome conduisant à l’oxydation interne et l’alliage chromino-formeur Ni-16Cr-9Fe.Une description complète des mécanismes de l’oxydation interne du chrome est obtenue à partir du développement du modèle analytique de Wagner d’oxydation interne et du développement du modèle numérique de Feulvarch. Ces modèles décrivent l’évolution de l’oxydation interne jusqu’à la transition oxydation interne / oxydation externe à 11 %poids de chrome environ.L’analyse par la spectroscopie d’électrons Auger de l’alliage modèle Ni-16Cr-9Fe à 950°C oxydé pendant 10 heures a permis d’explorer la zone à proximité immédiate de l’interface alliage/oxyde et de déterminer la concentration en chrome à l’interface à 0,5%poids (i.e. dans 20 premiers nanomètres), ce qui est en accord avec le modèle analytique de Wagner d’oxydation en couche compacte. La description des profils de déchromisation et des profils de cavités pour plusieurs temps d’exposition allant de 100h à 5000h a permis de mettre en évidence une corrélation forte entre ces deux phénomènes (même constante parabolique). Pour ces durées d’oxydation les profils de déchromisation présentent un point d’inflexion ce qui se traduit par l’augmentation de la teneur en chrome à l’interface. Les résultats sont interprétés dans le cadre d’un nouveau modèle analytique avec l’hypothèse d’injection des lacunes produites par l’effet Kirkendall au point d’inflexion. / The present work is focused on the consequences of oxidation at 950°C on the nature of a chromium-depleted area in Ni-based alloys. Two classes of alloys were analysed : low chromium Ni-Cr alloys and a typical chromia-former Ni-16Cr-9Fe.A complete description of the mechanisms of nodular oxidation is obtained from the development of both the Wagner’s analytical model of internal oxidation and the Feulvarch’s numerical model. These models describe the evolution of nodular oxidation up to the transition between internal to external oxidation which happens at around 11 wt%Cr.Auger Electron Spectroscopy (AES) measurements on a model Ni-16Cr-9Fe alloy oxidised at 950°C during 10 hours has allowed a detailed analysis in the immediate vicinity of the oxide/alloy interface and resulted in a very low Cr content in first 20 nm of the subsurface layer. This result is in agreement with Wagner’s theory of external oxidation of binary alloys. Higher oxidation times, from 100h to 5000h, have resulted in extensive cavitation and chromium depletion, both quantified respectively by image analysis and EDX. These profiles appear to be strongly correlated (same parabolic constant). Higher oxidation times result in an inflection point on chromium depletion profile and higher Cr interface content, which are due to the increased chromium diffusivity. The overall results are interpreted in the frame of a new analytical model based on the assumption of Kirkendall vacancy injection at the inflection point.

Die Untersuchung von korrelationsinduzierten Effekten, wie beispielsweise der kollektiven magnetischen Ordnung, verlangt einen Einblick in die elektronische Struktur der Festkörper. Hier stehen mit den Ein-Teilchen-Spektroskopien (Photoemission und inverse Photoemission) sowie den Zwei-Teilchen-Spektroskopien (Auger-Elektronen- und Appearance-Potential-Spektroskopien) nützliche experimentelle Werkzeuge zur Verfügung. Eine adäquate Interpretation der experimentell ermittelten Spektren erfordert die Berücksichtigung (i) der elektronischen Korrelationen, (ii) der orbitalen Entartung sowie (iii) der Übergangsmatrixelemente. Der vorliegenden Arbeit liegt ein Multiband-Hubbard-Modell zugrunde, das die Hopping- und Hybridisierungsprozesse der für die 3d-Übergangsmetalle relevanten Orbitale (4s-, 4p- und 3d-Orbitale) und die lokalen Coulomb-Wechselwirkungen der stark lokalisierten 3d-Elektronen beschreibt. Die Hopping- und Hybridisierungsparameter werden Bandstrukturrechnungen (lokale Dichteapproximation der Dichtefunktionaltheorie) entnommen. Als Ein-Teilchen-Basis werden quasiatomare Orbitale verwendet, deren hohe Symmetrie es erlaubt, die vollständige lokale 3d-Coulomb-Matrix mithilfe von lediglich drei Zahlen (effektive Slater-Parameter) zu parametrisieren. Fasst man die effektiven Slater-Parameter zu einer mittleren direkten Wechselwirkungsstärke U und einer mittleren Austauschwechselwirkungsstärke J zusammen, so sind U und J die beiden einzigen Parameter des Modells, die dann an experimentelle Daten (z.B. Spinmoment bei T=0K) angepasst werden können. Für die Berechnung der Ein-Teilchen-Green-Funktion, die die Photoemissionsspektren bestimmt, wird die Störungstheorie zweiter Ordnung um die Hartree-Fock-Lösung verwendet und damit die Magnetisierung als Funktion der Temperatur für Nickel berechnet. Die Kombination der errechneten Green-Funktion mit den Übergangsmatrixelementen der Photoemission gestattet dann einen quantitiven Vergleich mit experimentellen spin- und winkelaufgelösten Daten für endliche Temperaturen und verschiedene Photonenenergien. Die Zwei-Teilchen-Spektren lassen sich als Funktionale der Ein-Teilchen-Green-Funktion auffassen. Durch die Verwendung sogenannter Leiter-Näherungen werden nicht nur die Wechselwirkungen der an den Übergangsprozessen beteiligten Teilchen mit dem Restsystem (Selbstenergieeinschübe) berücksichtigt, sonderen auch die Wechselwirkungen der direkt am Prozess beteiligten Teilchen untereinander (Endzustandskorrelationen). Die Verwendung des Zwei-Stufen-Modells impliziert jedoch, dass die Valenzbandelektronen das Potential des zuvor erzeugten Core-Lochs abschirmen werden, was sich insbesondere auf die Auger-Spektren auswirkt. Am Beispiel der Appearance-Potential-Spektren wird die vielteilchentheoretisch berechnete Green-Funktion mit entsprechenden Übergangsmatrixelementen kombiniert. Die resultierenden Spektren sind für alle betrachteten Temperaturen in sehr guter Übereinstimmung mit gemessenen Spektren. / The investigation of correlation-induced effects, as for example the collective magnetic order, requires an insight into the electronic structure of solids. In this context the one-particle spectroscopies (photoemission and inverse photoemission) as well as the two-particle spectroscopies (Auger electron and appearance potential spectroscopies) represent useful experimental tools. An adequate interpretation of the experimentally determined spectra requires the consideration of (i) electronic correlations, (ii) orbital degeneration as well as (iii) transition-matrix elements. The present work uses a multi-band Hubbard model, which describes the hopping and hybridization processes of the relevant orbitals in the 3d-transition metals (4s, 4p and 3d orbitals) and the local Coulomb interactions of the strongly localized 3d electrons. The hopping and hybridization parameters are taken from band-structure calculations (local density approximation of the density functional theory). As one-particle basis quasi-atomic orbitals are used, whose high symmetry permits it to parameterize the complete local Coulomb-matrix among 3d-electrons by only three numbers (effective Slater parameters). If one combines the effective Slater parameters into an averaged direct interaction strength U and an averaged exchange interaction strength J, then U and J are the only parameters of the model, which can be fitted to experimental data (e.g. spin moment at T=0K). For the calculation of the one-particle Green function, which determines the photoemission spectra, the second order perturbation theory around the Hartree-Fock solution is used. Within this framework the magnetization as function of the temperature is calculated for nickel. The combination of the calculated Green function and the photoemission transition-matrix elements permits a quantitative comparison with spin- and angle-resolved measurements for finite temperatures and different photon energies. The two-particle spectra can be understood as functionals of the one-particle Green function. Due to the usage of so called ladder approximations one is able to account not only for the correlations between the considered particles and the remainder system (self-energy insertations) but also for the correlations among those particles directly involved in the transition (final state correlations). The usage of the two-step model implies, however, that the valence band electrons tend to screen the additional potential of the core hole created before, which in particular affects the Auger spectra. As an example, the appearance potential spectra of nickel are calculated by combining the corresponding Green function with appropriate transition-matrix elements. The resulting spectra are in a very good agreement with measured spectra for all temperatures.

In spite of their high abundance and importance, aqueous systems are enigmatic on the microscopic scale. In order to obtain information about their geometrical and electronic structure, simple aqueous solutions have been studied experimentally by photo- and Auger electron spectroscopy using the novel liquid micro-jet technique in conjunction with synchrotron radiation. The thesis is thematically divided into three parts. In the first part we utilize the surface sensitivity of photoelectron spectroscopy to probe the distributions of solutes near the water surface. In agreement with recent theoretical predictions we find that large polarizable anions, such as I- and ClO4-, display enhanced surface propensities compared to smaller rigid ions. Surface effects arising from ion-ion interactions at higher electrolyte concentrations and as function of pH are investigated. Studies of linear mono-carboxylic acids and benzoic acid show that the neutral molecular forms of such weak acids are better stabilized at the water surface than their respective conjugate base forms. The second part examines what type of information core-electron spectra can yield about the chemical state and hydration structure of small organic molecules in water. We demonstrate that the method is sensitive to the protonation state of titratable functional groups and that core-level lineshapes are dependent on local water hydration configurations. Using a combination of photoelectron and X-ray absorption spectroscopy we also show that the electronic re-arrangement upon hydrolysis of aldehydes yields characteristic fingerprints in core-level spectra. In the last part of this thesis we study ultrafast charge delocalization dynamics in aqueous solutions using resonant and off-resonant Auger spectroscopy. Intermolecular Coulombic decay (ICD) is found to occur in a number of core-excited solutions where excess energy is transferred between the solvent and the solute. The rate of ultrafast electron delocalization between hydrogen bonded water molecules upon oxygen 1s resonant core-excitation is found to decrease upon solvation of inorganic ions. The presented work is illustrative of how core-level photoelectron spectroscopy can be valuable in the study of fundamental phenomena in aqueous solutions.

Les travaux de thèse présentés dans ce manuscrit portent sur l’étude d’électrodes de silicium, matériau prometteur pour remplacer le graphite en tant que matériau actif d’électrode négative pour accumulateur Li-ion. Les mécanismes de (dé)lithiation du silicium sont d’abord étudiés, par Spectroscopie des Electrons Auger (AES). En utilisant cette technique de caractérisation de surface, qui permet d’analyser les particules individuellement dans leur environnement d’électrode, nos résultats montrent que la première lithiation du silicium s’effectue selon un mécanisme biphasé cr-Si / a-Li3,1Si tandis que les processus de (dé)lithiation suivants apparaissent complètement différents et sont du type solution solide. Ces mécanismes d’insertion / désinsertion du lithium conduisent à des variations volumiques importantes des particules de matériau actif lors du cyclage, à l’origine d’une détérioration rapide des performances électrochimiques. En combinant plusieurs techniques de caractérisation, les mécanismes de dégradation d’une électrode de silicium sont étudiés au cours du vieillissement. En utilisant en particulier la spectroscopie d’impédance électrochimique et des analyses par porosimétrie mercure, une véritable dynamique de la porosité de l’électrode est mise en évidence lors du cyclage. Un modèle de dégradation, mettant en cause principalement l’instabilité de la Solid Electrolyte Interphase (SEI) à la surface des particules de silicium, est proposé. Pour tenter de stabiliser cette couche de passivation et ainsi améliorer les performances électrochimiques des électrodes de silicium, l’influence de deux paramètres est étudiée : l’électrolyte et le « domaine de lithiation » du silicium, ce dernier paramètre étant associé à l’évolution de la composition du matériau actif lors du cyclage. A l’issue de ces travaux, des performances prometteuses sont obtenues pour des accumulateurs Li-ion comprenant une électrode de silicium. / The work presented here focuses on electrodes made of silicon, a promising material to replace graphite as an anode active material for Li-ion Batteries (LIBs). The first part of the manuscript is dedicated to the study of silicon (de)lithiation mechanisms by Auger Electron Spectroscopy (AES). By using this technique of surface characterization, which allows investigating individual particles in their electrode environment, our results show that the first silicon lithiation occurs through a two-phase region mechanism cr-Si / a-Li3,1Si, whereas the following (de)lithiation steps are solid solution type process. Upon (de)alloying with lithium, silicon particles undergo huge volume variations leading to a quick capacity fading. By combining several techniques of characterization, the failure mechanisms of a silicon electrode are studied during aging. In particular, by using electrochemical impedance spectroscopy and mercury porosimetry analyses, an impressive dynamic upon cycling of the electrode porosity is shown. A model, which mainly attributes the capacity fading to the Solid Electrolyte Interphase instability at the silicon particles surface, is proposed. To try to stabilize this passivation layer and thus improve silicon electrodes electrochemical performances, the influence of two parameters is studied: the electrolyte and the “lithiation domain” of silicon; the latter is associated with the evolution of the active material composition upon cycling. Finally, by using these last results, promising performances are obtained for silicon electrode containing LIBs.

<p>In this thesis we have performed core-electron spectroscopy studies of gas phase molecular systems starting with smaller diatomic, continuing with triatomic and extending our research to more complex polyatomic ones. We can subdivide the results presented here into two categories: the first one focusing on electronic fine structure and effect of the chemical bonds on molecular core-levels and the other one dealing with nuclear dynamics induced by creation of a core hole. In our research we have mostly used synchrotron radiation based techniques such as X-ray Photoelectron (XPS), X-ray Absorption (XAS), normal and Resonant Auger (AES and RAS, respectively) and Energy-Selected Auger Electron PhotoIon COincidence (ES-AEPICO) spectroscopies.</p><p>We have demonstrated that resonant Auger spectroscopy can be used to aid interpretation of the features observed in XAS for Rydberg structures in the case of Cl₂ and C1s⁻¹π*¹ states of allene molecules. The combined use of high-resolution spectroscopy with <i>ab initio</i> calculations can help the interpretation of strongly overlapped spectral features and disentangle their complex profiles. This approach enabled us to determine the differences in the lifetimes for core-hole 2p sublevels of Cl₂ which are caused by the presence of the chemical bond. We have shown that contribution in terms of the Mulliken population of valence molecular orbitals is a determining factor for resonant enhancement of different final states and fragmentation patterns reached after resonant Auger decays in N₂O.</p><p>We have also performed a systematic study of the dependence of the C1s resonant Auger kinetic energies on the presence of different substituents in CH₃X compounds. For the first time we have studied possible isomerization reaction induced by core excitation of acetylacetone. We could observe a new spectral feature in the resonant Auger decay spectra which we interpreted as a signature of core-excitation-induced keto-enol tautomerism.</p>

<p>Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (<i>i.e.</i> nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques.</p><p>The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures.</p><p>Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well.</p><p>Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger <i>vis-à-vis</i> Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups.</p><p>Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.</p>

Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (i.e. nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques. The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures. Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well. Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger vis-à-vis Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups. Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.