The L10 FePt phase belongs to the most promising hard ferromagnetic materials for high density recording media. The main challenges for thin FePt films are: (i) to lower the process temperature for the transition from the soft magnetic A1 to the hard magnetic L10 phase, (ii) to realize c-axes preferential oriented layers independently from the substrate nature and (iii) to control layer morphology supporting the formation of FePt - L10 self-organized isolated nanoislands towards an increase of the signal-to-noise ratio. In this study, dc magnetron sputtered FePt thin films on amorphous substrates were inve-stigated. The work is focalized on the correlation between structural and magnetic properties with respect to the influence of deposition parameters like growth mode (co-sputtering vs. layer – by - layer) and the variation of the deposition gas (Ar, Xe) or pressure (0.3 - 3 Pa). In low-pressure Ar discharges, high energetic particle impacts support vacancies formation during layer growth lowering the phase transition temperature to (320 +/- 20)°C. By reducing the particle kinetic energy in Xe discharges, highly (001) preferential oriented L10 - FePt films were obtained on a-SiO2 after vacuum annealing. L10 - FePt nano-island formation was supported by the introduction of an Ag matrix, or by random ballistic aggregation and atomic self shadowing realized by FePt depositions at very high pressure (3 Pa). The high coercivity (1.5 T) of granular, magnetic isotropic FePt layers, deposited in Ar discharges, was measured with SQUID magnetometer hysteresis loops. For non-granular films with (001) preferential orientation the coercivity decreased (0.6 T) together with an enhancement of the out-of- plane anisotropy. Nanoislands show a coercive field close to the values obtained for granular layers but exhibit an in-plane easy axis due to shape anisotropy effects. An extensive study with different synchrotron X-ray scattering techniques, mainly performed at the ESRF, BM-20 (ROBL-Beamline), pointed out the importance of in-situ investigations to clearly understand the kinetic mechanism of the A1 to L10 transition and ordering and to control FePt nanoclusters evolution.

Es wird die Entwicklung der Röntgenspektralanalyse und die Entdeckung der Röntgenfluoreszenzanalyse durch Georg von Hevesy und Richard Glocker mit ihren Assistenten in Freiburg i. Br. und in Stuttgart 1928 beschrieben. / The development of the x-ray chemical analysis and the discovery of the x-ray fluorescence analysis by Georg de Hevesy and Richard Glocker with their assistants in Freiburg i. Br. and in Stuttgard 1928 is described.

The recent availability of X-ray Free Electron Lasers (XFELs) has opened a completely new and unexplored regime for the study of light-matter interactions. The extremely bright intensities delivered by XFELs can couple many photons into the target, turning well known interactions such as photoionization and scattering into new, non-linear, complex many-body phenomena. This thesis reports theoretical investigations aiming to improve the understanding of the fundamental processes and dynamics triggered by intense X-ray pulses, with a special focus in finite systems such as molecules and clusters. Sequential multiple photoionization in atomic clusters was investigated, where previous observations were extended for higher charge states where direct photoionization is frustrated. Through a rate equation study and subsequent molecular dynamics simulations, it was found that frustrated ionization is partially responsible for the low-energy peak observed in the electron energy spectrum. The influence of plasma evaporation over the formation of the sequential low-energy peak was also investigated, identifying the effects of the system size and photon energy. Multiple channel ionization was also investigated for the case of fullerenes. This is done through a series of studies, starting from a simplified rate equation scheme, and culminating with full molecular dynamics simulations. From these results, a good insight was obtained over the origin, physical meaning, and relevant parameters that give rise to the complicated features observed in the electronic spectra. The mechanisms responsible of all these features are expected to be present in other systems, making these results quite general. Diffractive imaging of biomolecules was studied in a final step, with a particular focus on the influence of intramolecular charge transfer mechanisms. To this end a conformer of T4 Lysozyme was used, a representative enzyme with well known structure. Charge migration is found to allow for additional processes such as proton ejection, a mechanism which enables an efficient release of energy from the system. This mechanism considerably suppresses structural damage for heavy ions, improving the quality of the measured diffraction patterns.

The techniques of small-angle x-ray scattering (SAXS) and grazing-incidence small-angle x-ray scattering (GISAXS) have successfully been used for many years in the analysis of nanostructures in non-crystalline samples, e.g., polymers, metallic alloys, ceramics, and glasses. In many specimens, however, the nanostructure is not distributed homogeneously, but instead varies as a function of position in the sample. Conventional SAXS or GISAXS measurements on such heterogeneous samples merely yield an averaged scattering pattern of all the different structures present along the x-ray beam path. In this thesis, scanning tomography is combined with SAXS and GISAXS, revealing the individual local scattering cross section at each position on a virtual section through the sample. The technique thereby offers unique analytical possibilities in heterogeneous specimens. A brief review of the physics of x rays and x-ray scattering is given, before the methods of tomographic SAXS and GISAXS are introduced. Experimental requirements and limitations of both methods are discussed, including aspects of sampling, local rotational invariance and x-ray beam coherence. Experiments performed at the beamline BW4 at HASYLAB at DESY, Hamburg, Germany are described, illustrating the capabilities of the method. Finally, an outlook on possible future developments in tomographic small-angle x-ray scattering is given. / Die Methoden der Röntgenkleinwinkelstreuung (SAXS) und Röntgenkleinwinkelstreuung unter streifendem Einfall (GISAXS) werden seit vielen Jahren erfolgreich eingesetzt zur Analyse von Nanostrukturen in nicht-kristallinen Proben, z.B. Polymeren, metallischen Legierungen, Keramiken und Gläsern. In vielen Proben ist die Nanostruktur allerdings nicht homogen verteilt, sondern variiert als Funktion des Ortes in der Probe. Konventionelle SAXS- oder GISAXS-Messungen an solch heterogenen Proben liefern lediglich ein über alle unterschiedlichen Strukturen entlang des Röntgenstrahls gemitteltes Streubild. In dieser Arbeit wird Rastertomographie mit SAXS und GISAXS kombiniert und so der lokale Streuquerschnitt an jedem Ort auf einem virtuellen Schnitt durch die Probe gewonnen. Diese Technik bietet so einzigartige Analysemöglichkeiten von heterogenen Proben. Es wird zunächst ein kurzer Überblick über die Physik der Röntgenstrahlung und Röntgenstreuung gegeben, bevor die Methoden der SAXS- und GISAXS-Tomographie eingeführt werden. Die experimentellen Anforderungen und Grenzen beider Methoden werden besprochen, wobei Aspekte der Abtastung, der lokalen Rotationsinvarianz und der Kohärenz im Röntgenstrahl eine Rolle spielen. Experimente, die an der Messstrecke BW4 am HASYLAB bei DESY, Hamburg, durchgeführt wurden, werden beschrieben, um die Möglichkeiten der Methode zu illustrieren. Schließlich wird ein Ausblick auf mögliche zukünftige Entwicklungen der Kleinwinkelstreutomographie gegeben.

Durch erstmalige Anwendung des η-Umlaufverfahrens auf mechanisch ermüdete Ni-Polykristalle konnten – aufgrund konstanter Meßbedingungen und konstanter Eindringtiefe der Röntgenstrahlung – genauere Eigenspannungsmessungen durchgeführt werden als bisher. Ein speziell entwickeltes Auswertungsverfahren, das auf die Eigenspannungsanalyse von η-Umlaufmessungen abgestimmt ist, wird als „sin2η-Methode“ detailliert vorgestellt. Die experimentellen Resultate unterstreichen die Vorteile, die sich – besonders im Falle sehr geringer Eigenspannungen und wenn auch der dehnungsfreie Ausgangszustand (d0 -Wert) gemessen werden konnte – aus der Nutzung dieser Methode ergeben. Mit Hilfe des magnetischen Barkhausen-Rauschens durchgeführte Vergleichsuntersuchungen stehen im Einklang mit den röntgenographischen Messungen. / When applying the η-rotation-method to mechanically fatigued Ni polycrystals the first time, stress measurements with higher accuracy could be realized due to the constant penetration depth of the X-rays and because of constant measuring conditions. A specifically developed procedure, tuned to analyze residual stresses from η-rotation measurements, will be presented in detail as „sin2η-method“. The experimental results emphasize the benefits of using this method – especially in the case of very low residual stresses and if the initial strain-free state (d0 -value) was obtained from reference measurements. Comparative investigations by means of the magnetic Barkhausen noise agree with the X-ray measurements.

Fortschrittliche ingenieurtechnische Anwendungen stellen hohe Ansprüche an neuartige Materialien sowohl hinsichtlich e.g. mechanischer Eigenschaften wie Festigkeit und Duktilität als auch hinsichtlich einer möglichst vielfältigen Einsetzbarkeit (Maßschneiderung etc.). Zudem sind Ressourcenschonung und nachhaltige Produktion bei gleichzeitig hoher Performance zu realisieren. Entsprechend existiert grundlagenseitig Forschungsbedarf zu innovativen Materialien (e.g. Kompositwerkstoffe) und ihren Prozessierungen. In der vorliegenden Dissertation werden submikro-/nanokristalline mehrphasige Gradientenmaterialien zum Einen mittels experimenteller Methoden wie der zweidimensionalen Röntgenmikrobeugung (in geeigneter Weiterentwicklung) sowie zum Anderen mittels analytischer und numerischer Modellrechnungen bezüglich spezieller Eigenschaften und deren Korrelation zum Herstellungsprozess (starke plastische Verformung durch akkumuliertes Rundkneten) untersucht. Insbesondere werden lokale Verteilungen kristallografischer Textur sowie mechanischer (Eigen-)Spannungen analysiert und in Hinblick auf materialrelevante Eigenschaften (e.g. mechanisch, mikrostrukturell) interpretiert und korreliert. Derartige Beziehungen sind hinsichtlich perspektivischer Applikationen, e.g. im Bereich hochfester Leichtbaulösungen, von technischer Relevanz.