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The results of a statistical study of hard x-ray solar flares are presented in this dissertation. Two methods of analysis were used, the Diffusion Entropy (DE) method coupled with an analysis of the data distributions and the Rescaled Range (R/S) Method, sometimes referred to as "Hurst's method". Chapter one provides an introduction to hard x-ray flares within the context of the solar environment and a summary of the statistical paradigms solar astronomers currently work under. Chapter two presents the theory behind the DE and R/S methods. Chapter three presents the results of the two analysis methodologies: most notably important evidence of the conflicting results of the R/S and DE methods, evidence of a Levy statistical signature for the underlying dynamics of the hard x-ray flaring process and a possible separate memory signature for the waiting times. In addition, the stationary and nonstationary characteristics of the waiting times and peak intensities, are revealed. Chapter four provides a concise summary and discussion of the results.

The BAT Slew Survey (BATSS) is the first wide-field survey of the hard X-ray sky (15–150 keV) with a slewing coded aperture imaging telescope. Its fine time resolution, high sensitivity and large sky coverage make it particularly well-suited for detections of transient sources with variability timescales in the \(\sim 1 sec–1 hour\) range, such as Gamma-Ray Bursts (GRBs), flaring stars and Blazars. As implemented, BATSS observations are found to be consistently more sensitive than their BAT pointing-mode counterparts, by an average of 20% over the 10 sec–3 ksec exposure range, due to intrinsic systematic differences between them. The survey’s motivation, development and implementation are presented, including a description of the software and hardware infrastructure that made this effort possible. The analysis of BATSS science data concentrates on the results of the 4.8-year BATSS GRB survey, beginning with the discovery of GRB 070326 during its preliminary testing phase. A total of nineteen (19) GRBs were detected exclusively in BATSS slews over this period, making it the largest contribution to the Swift GRB catalog from all ground-based analysis. The timing and spectral properties of prompt emission from BATSS GRBs reveal their consistency with Swift long GRBs (L-GRBs), though with instances of GRBs with unusually soft spectra or X-Ray Flashes (XRFs), GRBs near the faint end of the fluence distribution accessible to Swift-BAT, and a probable short GRB with extended emission, all uncommon traits within the general Swift GRB population. In addition, the BATSS overall detection rate of 0.49 GRBs/day of instrument time is a significant increase (45%) above the BAT pointing detection rate. This result was confirmed by a GRB detection simulation model, which further showed the increased sky coverage of slews to be the dominant effect in enhancing GRB detection probabilities. A review of lessons learned is included, with specific proposals to broaden both the number and range of astrophysical sources found in future enhancements. The BATSS survey results provide solid empirical evidence in support of an all-slewing hard X-ray survey mission, a prospect that may be realized with the launch of the proposed MIRAX-HXI mission in 2017. / Physics

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This thesis describes studies of materials which can be exploited for hydrogen production from water and sunlight. The materials investigated are maghemite (γ-Fe2O3), magnetite (Fe3O4) and especially hematite (α-Fe2O3), which is an iron oxide with most promising properties in this field. Hematite has been deposited using Atomic Layer Deposition (ALD) - a thin-film technique facilitating layer-by-layer growth with excellent thickness control and step coverage. The iron oxides were deposited using bis-cyclopentadienyl iron (Fe(Cp)2) or iron pentacarbonyl (Fe(CO)5) in combination with an O2 precursor. Since it is crucial to have good control of the deposition process, the influence of substrate, process temperature, precursor and carrier gas have been investigated systematically. By careful control of these deposition parameters, three polymorphs of iron oxide could be deposited: hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4). The deposited materials were characterized using X-ray Diffraction, Raman and UV-VIS Spectroscopy, and Scanning Electron Microscopy. Hard X-ray Photoelectron Spectroscopy (HAXPES) was also used, since it is a non-destructive, chemically specific, surface sensitive technique – the surface sensitivity resulting from the short mean escape depth of the photoelectrons. The depth probed can be controlled by varying the excitation energy; higher photoelectron energies increasing the inelastic mean-free-path in the material. HAXPES studies of atomic diffusion from F-doped SnO2 substrates showed increased doping levels of Sn, Si and F in the deposited films. Diffusion from the substrate was detected at annealing temperatures between 550 °C and 800 °C. Films annealed in air exhibited improved photocatalytic behavior; a photocurrent of 0.23 mA/cm2 was observed for those films, while the as-deposited hematite films showed no photo-activity whatsoever. The optical properties of low-dimensional hematite were studied in a series of ultra-thin films (thicknesses in the 2-70 nm range). The absorption maxima were shifted to higher energies for films thinner than 20 nm, revealing a different electronic structure in thin films.

In this dissertation, we used a combination of synchrotron-based x-ray spectroscopic techniques such as angle-resolved photoelectron spectroscopy (ARPES), soft x-ray ARPES, hard x-ray photoelectron spectroscopy (HAXPES), and soft x-ray absorption spectroscopy (XAS) to investigate momentum-resolved and angle-integrated electronic structure of advanced three- and two-dimensional materials and interfaces. The results from the experiments were compared to several types of state-of-the-art first-principles theoretical calculations. In the first part of this dissertation we investigated the effects of spin excitons on the surface states of samarium hexaboride (SmB6), which has gained a lot of interest since it was proposed to be a candidate topological Kondo insulator. Here, we utilized high-resolution (overall resolution of approximately 3 meV) angle-resolved and angle-integrated valence-band photoemission measurements at cryogenic temperatures (1.2 K and 20 K) to show evidence for a V-shap / Physics

No / The effect of a self-induced electric field is investigated analytically and numerically on differential and mean electron spectra produced by beam electrons during their precipitation into a flaring atmosphere as well as on the emitted hard X-ray (HXR) photon spectra. The induced electric field is found to be a constant in upper atmospheric layers and to fall sharply in the deeper atmosphere from some "turning point" occurring either in the corona (for intense and softer beams) or in the chromosphere (for weaker and harder beams). The stronger and softer the beam, the higher the electric field before the turning point and the steeper its decrease after it. Analytical solutions are presented for the electric fields, which are constant or decreasing with depth, and the characteristic "electric" stopping depths are compared with the "collisional" ones. A constant electric field is found to decelerate precipitating electrons and to significantly reduce their number in the upper atmospheric depth, resulting in their differential spectra flattening at lower energies (<100 keV). While a decreasing electric field slows down the electron deceleration, allowing them to precipitate into deeper atmospheric layers than for a constant electric field, the joint effect of electric and collisional energy losses increases the energy losses by lower energy electrons compared to pure collisions and results in maxima at energies of 40-80 keV in the differential electron spectra. This, in turn, leads to the maxima in the mean source electron spectra and to the "double power law" HXR photon spectra (with flattening at lower energies) similar to those reported from the RHESSI observations. The more intense and soft the beams are, the stronger is the lower energy flattening and the higher is the "break" energy where the flattening occurs.

Bipolar electrochemistry is an interesting concept for high throughput screening techniques due to the ability to induce gradients in a range of materials and their properties, such as composition, particle size, or dopant levels, among many others. One of the key advantages of the method is the ability to test, create or modify materials without the need for a direct electrical connection. In this thesis, the viability of this method has been explored for a range of possible applications, such as metal recycling, nanoparticle modification and corrosion analysis. In the initial part of the work a process to electrodeposit gradients in metal composition was evaluated, with a view to applying the technique to the extraction and recycling of metals from fly ash. Compositional gradients in the metals under study could be readily obtained from controlled reference solutions, although the spatial resolution of the metals was not sufficient to perform separation. Only copper could be easily deposited from the fly ash solution. Bipolar electrodeposition was also successfully used to modify the particle size across substrates decorated with gold nanoparticles. The approach was demonstrated both for surfaces possessing either a uniform particle density or a gradient in particle density. In the latter case samples with simultaneous, orthogonal gradients in both particle size and density were obtained. A combination of the bipolar approach with rapid image analysis was also evaluated as a method for corrosion screening, using quantitative analysis of gradients in pitting corrosion damage on stainless steels in HCl as a model system. The factors affecting gradient formation and the initiation of corrosion were thoroughly investigated by the use of a scanning droplet cell (SDC) technique and hard x-ray photoelectron spectroscopy (HAXPES). The ability to screen arrays of different materials for corrosion properties was also investigated, and demonstrated for stainless steel and Ti-Al alloys with pre-formed compositional gradients. The technique shows much promise for further studies and for high throughput corrosion screening applications.

Le travail de thèse "Modification of the electronic structure of catalytic active metal centres upon adsorption of molecules : a XAS and XES study" porte sur l'étude de la structure électronique des métaux de transition utilisés dans les catalyseurs par les techniques spectroscopiques d'absorption et d'émission de rayons durs (rayonnement synchrotron). Il s'agit, en particulier, d'utiliser les avancées dans les techniques spectroscopiques des rayons X pour l'étude des matériaux nanostructurés en conditions in situ. Le premier chapitre de la thèse, "X-Ray Spectroscopy: an Overview", présente brièvement les techniques spectroscopiques disponibles sur la ligne de lumière ID26 de l'Installation Européenne de Rayonnement Synchrotron (en anglais European Synchrotron Radiation Facility (ESRF), Grenoble), où toutes les mesures présentées dans ce travail ont été effectuées. Dans le deuxième chapitre, "Study of the Electronic structure of the Ti-sites in TS-1 using X-ray spectroscopy", est décrite la caractérisation électronique des centres de Ti en TS-1, qui est un important catalyseur, employé dans de nombreuses usines à travers le monde. Nous montrons que la combinaison des techniques spectroscopiques d'absorption et d'émission des rayons avec des calculs de mécanique quantique permet d'obtenir des informations importantes sur la structure électronique des centres de Ti dans des conditions in situ. Le troisième chapitre, “Identification of the Ti-Ligands in a Silica Supported Ziegler-Natta Catalyst by X-Ray Emission Spectroscopy", présente l'étude d'un catalyseur (une variante du catalyseur Ziegler-Natta), qui affiche un degré élevé/important de désordre chimique. L'utilisation de la théorie fonctionnelle de la densité des états (DFT) pour l'interprétation des données expérimentales a permis de développer des modèles possibles pour l'environnement d'un ligand Ti. Le quatrième chapitre, "Observing the dd-Excitations in CPO-27-Ni using Resonant Inelastic X-ray Scattering", conclut la partie principale de la thèse. Il présente un exemple d'utilisation de la diffusion inélastique des rayons X (RIXS) en chimie pour la détermination des excitations du champ cristallin des ions Ni dans l'oxyde de nickel et d'une cage organique autour d'un Ni métallique (CPO-27-Ni). Le chapitre explique brièvement les différentes approches théoriques qui peuvent être utilisées pour l'interprétation des caractéristiques spectrales. De plus, l'adsorption de molécules sonde, comme le CO sur les centres de Ni en CPO-27-Ni, est discutée sur la base des données expérimentales RIXS. Le dernier chapitre synthétise les résultats obtenus et indique des perspectives futures. Enfin, dans les annexes sont reportés les dispositifs expérimentaux développés dans le cadre du travail de thèse pour des mesures résolues en temps, ainsi que le curriculum vitae et les publications du candidat. / The purpose of this research project was to apply advanced X-ray based spectroscopic techniques for investigating the electronic structure of transition metals within catalysts and molecular sieves under in-situ conditions. Thus, the first chapter of the thesis, "X-Ray Spectroscopy: an Overview " briefly presents the spectroscopic techniques available at ID26, beamline of the European Synchrotron Radiation Facility (Grenoble) where all the measurements reported in this work have been obtained. In the second chapter, "Study of the Electronic structure of the Ti-sites in TS-1 using hard X-ray spectroscopy", it is reported the electronic characterization of the Ti centres in titanium silicalite-1 (TS-1), that is a relevant catalyst employed in industrial plants worldwide. The chapter shows that the combination of X-ray absorption and X-ray emission spectroscopy with quantum mechanical calculations is effective to obtain important insights on the electronic structure of the Ti-centres under in-situ conditions. The third chapter entitled “Identification of the Ti-Ligands in Silica Supported Ziegler-Natta Catalyst by X- Ray Emission Spectroscopy" presents the study of a variant of the Ziegler-Natta catalyst. The chapter discusses the interpretation of the valence emission lines within the theoretical framework provided by the density functional theory (DFT) and proposes possible models for the Ti-ligand-environment. The fourth chapter, entitled "Observing the dd-Excitations in CPO-27-Ni using Resonant Inelastic X-ray Scattering", concludes the main part of the thesis. It presents the application of resonant inelastic X-ray scattering (RIXS) for obtaining the crystal field excitations of the Ni ions within nickel oxide and within a Ni- metal-organic-framework (CPO-27-Ni). The chapter briefly describes the different theoretical approaches that can be used for the interpretation of the spectral features and discusses the adsorption of probe molecules like H2O, CO and H2S on the Ni centres of CPO-27-Ni. The last chapter (Chapter five) drawn a series of conclusions concerning the performed investigations and indicates possible future research directions. In Appendix A entitled "Pump and Probe Time Resolved Experiments at ID26" it is reported the description of the experimental setup co-developed and co-realized by the candidate for time resolved experiments. The appendix also accounts for the scientific outcome of the performed pump and probe measurements. The curriculum vitae and the publications list of the candidate are respectively reported in Appendix B and C.

Ce travail de thèse est focalisé sur la détermination, de manière non-destructive, d'interfaces profondément enterrées dans des empilements multi-couches utilisés dans les conditions de technologie réelles au travers d'une méthode innovante basée sur la photoémission avec utilisation de rayons-x de haute énergie (HAXPES) et l'analyse du fond continu inélastique. Au cours de cette thèse, une procédure numérique a été développée pour quantifier la correspondance entre la mesure du fond continu faite par HAXPES et la simulation du fond continu représentative d'une distribution en profondeur donnée. Cette méthode permet de trouver la distribution en profondeur d'un élément grâce à une procédure semi automatisée. Dans un premier temps cette méthode a été testée en étudiant une couche ultra fine de lanthane enterrée à une profondeur >50 nm dans un dispositif de grille métallique high-k. L'influence des paramètres utilisés lors de l'analyse y est étudiée et révèle l'importance principale d'un paramètre en particulier, la section efficace de diffusion inélastique. La combinaison de mesures HAXPES avec l'analyse du fond continu inélastique utilisant cette nouvelle méthode permet d'augmenter la profondeur de sonde jusqu'à un niveau sans précédent. Ainsi l'échantillon peut être sondé jusqu'à 65 nm sous la surface avec une haute sensibilité à une couche nanométrique. Dans un second temps, la méthode précédemment validée d'analyse de fond continu inélastique est combinée avec une étude haute résolution des niveaux de cœur dans un échantillon servant de source dans un transistor à haute mobilité. Les deux analyses sont complémentaires puisqu'elles permettent d'obtenir la distribution en profondeur des éléments ainsi que leur environnement chimique. Le résultat donne une description complète des diffusions élémentaires dans l'échantillon suivant les différentes conditions de recuit. / This thesis tackles the challenge of probing in a non-destructive way deeply buried interfaces in multilayer stacks used in technologically-relevant devices with an innovative photoemission method based on Hard X-ray PhotoElectron Spectroscopy (HAXPES) and inelastic background analysis. In this thesis, a numerical procedure has been implemented to quantify the matching between a HAXPES measured inelastic background and a simulated inelastic background that is representative of a given depth distribution of the chemical elements. The method allows retrieving depth distributions at large depths via a semi-automated procedure. First, this method has been tested by studying an ultra-thin layer of lanthanum buried at depth >50 nm in a high-k metal gate sample. The influence of the parameters involved in the analysis is studied unraveling the primary importance of the inelastic scattering cross section. The combination of HAXPES with inelastic background analysis using this novel method maximizes the probing depth to an unprecedented level, allowing to probe the sample up to 65 nm below the surface with a high sensitivity to a nm-thick layer. Second, the previously-checked inelastic background analysis is combined with that of high resolution core-level spectra in the case of the source part of a high electron mobility transistor. The two analyses are complementary as they allow retrieving the elemental depth distribution and the chemical state, respectively. The result gives a complete picture of the elemental intermixing within the sample when it is annealed at various temperatures. / Denne afhandling omhandler problemet med at probe dybt begravede grænseflader i multilags stacks, som bruges i teknologisk relevante devices, med en innovativ fotoemissions metode, der er baseret på Hard X-ray PhotoElectron Spectroscopy (HAXPES) og analyse af den uelastiske baggrund. I afhandlingen er en numerisk procedure blevet implementeret til at kvantificere forskellen mellem en HAXPES målt uelastisk baggrund og en modelleret baggrund, som svarer til en given dybdefordeling af atomerne. Metoden muliggør, med en halv-automatisk procedure, at bestemme dybdefordelingen i store dybder. Metoden er først blevet testet ved at studere et ultra-tyndt lag af lanthan, som er begravet i en dybde > 50 nm i en high-k-metal-gate prøve. Indflydelsen af parametrene der ingår i analysen er blevet studeret for at opklare den primære betydning af det anvendte uelastiske spredningstværsnit. Kombinationen af HAXPES med analyse af den uelastiske baggrund og brug af den nye numeriske metode giver en hidtil uset probe-dybde, som giver mulighed for at probe den atomare sammens ætning i op til 65 nm dybde under overfladen og med høj følsomhed af et kun nm tykt lag. Dernæst er den uelastiske baggrundsanalyse blevet kombineret med højopløst core-level spektroskopi for at studere de aktive dele i en høj-elektronmobilitets transistor. De to analyser er komplementære, idet de henholdsvis bestemmer den atomare fordeling og atomernes kemiske bindingstilstand. Resultatet giver et fuldstændigt billede af atomernes omfordeling i prøven når denne opvarmes til forskellige temperaturer.