Das Schalten und das Auslesen der magnetischen Ausrichtung einzelner winziger magnetischer Informationsspeicher müssen zu wirklich nanoskopischer Dimension entwickelt werden, um mit der Miniaturisierung von modernen, nanoelektronischen Bauteilen Schritt zu halten. Daher sind neue Konzepte, den magnetischen Zustand von Nanostrukturen elektronisch gezielt zu beeinflussen, derzeitig im Mittelpunkt wissenschaftlicher Untersuchungen. Diese Arbeit befasst sich mit dem zuverlässigen Einstellen der Magnetisierung eines rein horizontal kontaktierten, nanoskopischen Magneten, in zwei stabile Zustände. Ein spinpolarisierter Strom wird bei Raumtemperatur in eine Leiterbahn unterhalb des magnetischen Nanopillars injiziert. Spindiffusion durch den Kontakt zwischen der Leiterbahn (Cu) und dem Pillar (CoFe) ruft eine Spin-Akkumulation im Nanopillar hervor, der durch den Spin Transfer Torque-Effekt (STT) vermittelt wird. Bei diesem Prozess verursachen die akkumulierten Elektronenspins ein auftretendes Netto-Moment, das senkrecht auf die Magnetisierungsorientierung des Nanopillars wirkt und so das Schalten ermöglicht. In den STT-induzierten Schaltexperimenten wird der magnetische Zustand des Nanopillars durch eine bildgebendes Messverfahren mittels Rasterröntgentransmissionsmikroskopie (STXM) erfasst. So konnte gezeigt werden, dass sich die Magnetisierung des Pillars auch gegen das Oersted-Feld des Schaltstroms reversibel schalten lässt. / “Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nano electronic components. Therefore, new concepts for controlling the state of nano magnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate reproducible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar by means of Spin Transfer Torque (STT). In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM)” [1]. Therefore it could be demonstrated, to reversibly switch the nanopillar’s magnetic state even against the Oersted field which is induced by the switching current. Furthermore we could show, that magnetization switching is possible by a pure spin current that is diffusively transported beneath the nanopillar.

This thesis presents a new optical imaging technique which measures the structure of objects without the use of lenses. Termed diffraction-contrast imaging (DCI), the method retrieves the object structure from a Fresnel diffraction pattern of the object, using a deconvolution algorithm. DCI is particularly adept at imaging highly transparent objects and this is demonstrated by retrieving the structure of an almost transparent cloud of laser-cooled atoms. Applied to transparent Bose-Einstein condensates, DCI should allow the non-destructive imaging of the condensate while requiring only the minimum possible apparatus of a light source and a detector. (For complete abstract open document)

Le développement de sources cohérentes de rayons X offre de nouvelles possibilités pour visualiser les structures biologiques à différentes échelles en exploitant la réfraction des rayons X. La cohérence des sources synchrotron de troisième génération permettent des implémentations efficaces des techniques de contraste de phase. Une des premières mesures des variations d’intensité dues au contraste de phase a été réalisée en 1995 à l’Installation Européenne de Rayonnement Synchrotron (ESRF). L’imagerie de phase couplée à l’acquisition tomographique permet une imagerie tridimensionnelle avec une sensibilité accrue par rapport à la tomographie standard basée sur absorption. Cette technique est particulièrement adaptée pour les échantillons faiblement absorbante ou bien présentent des faibles différences d’absorption. Le contraste de phase a ainsi une large gamme d’applications, allant de la science des matériaux, à la paléontologie, en passant par la médecine et par la biologie. Plusieurs techniques de contraste de phase aux rayons X ont été proposées au cours des dernières années. Dans la méthode de contraste de phase basée sur le phénomène de propagation l’intensité est mesurée pour différentes distances de propagation obtenues en déplaçant le détecteur. Bien que l’intensité diffractée puisse être acquise et enregistrée, les informations de phase du signal doivent être "récupérées" à partir seulement du module des données mesurées. L’estimation de la phase est donc un problème inverse non linéaire mal posé et une connaissance a priori est nécessaire pour obtenir des solutions stables. Si la plupart de méthodes d’estimation de phase reposent sur une linéarisation du problème inverse, les traitements non linéaires ont été eux très peu étudiés. Le but de ce travail était de proposer et d’évaluer des nouveaux algorithmes, prenant en particulier en compte la non linéarité du problème direct. Dans la première partie de ce travail, nous présentons un schéma de type Landweber non linéaire itératif pour résoudre le problème de la récupération de phase. Cette approche utilise l’expression analytique de la dérivée de Fréchet de la relation phase-intensité et de son adjoint. Nous étudions aussi l’effet des opérateurs de projection sur les propriétés de convergence de la méthode. Dans la deuxième partie de cette thèse, nous étudions la résolution du problème inverse linéaire avec un algorithme en coordonnées ondelettes basé sur un seuillage itératif. Par la suite, les deux algorithmes sont combinés et comparés avec une autre approche non linéaire basée sur une régularisation parcimonieuse et un algorithme de point fixe. Les performances des algorithmes sont évaluées sur des données simulées pour différents niveaux de bruit. Enfin, les algorithmes ont été adaptés pour traiter des données réelles acquises en tomographie de phase à l’ESRF à Grenoble. / The development of highly coherent X-ray sources offers new possibilities to image biological structures at different scales exploiting the refraction of X-rays. The coherence properties of the third-generation synchrotron radiation sources enables efficient implementations of phase contrast techniques. One of the first measurements of the intensity variations due to phase contrast has been reported in 1995 at the European Synchrotron Radiation Facility (ESRF). Phase imaging coupled to tomography acquisition allows threedimensional imaging with an increased sensitivity compared to absorption CT. This technique is particularly attractive to image samples with low absorption constituents. Phase contrast has many applications, ranging from material science, paleontology, bone research to medicine and biology. Several methods to achieve X-ray phase contrast have been proposed during the last years. In propagation based phase contrast, the measurements are made at different sample-to-detector distances. While the intensity data can be acquired and recorded, the phase information of the signal has to be "retrieved" from the modulus data only. Phase retrieval is thus an illposed nonlinear problem and regularization techniques including a priori knowledge are necessary to obtain stable solutions. Several phase recovery methods have been developed in recent years. These approaches generally formulate the phase retrieval problem as a linear one. Nonlinear treatments have not been much investigated. The main purpose of this work was to propose and evaluate new algorithms, in particularly taking into account the nonlinearity of the direct problem. In the first part of this work, we present a Landweber type nonlinear iterative scheme to solve the propagation based phase retrieval problem. This approach uses the analytic expression of the Fréchet derivative of the phase-intensity relationship and of its adjoint, which are presented in detail. We also study the effect of projection operators on the convergence properties of the method. In the second part of this thesis, we investigate the resolution of the linear inverse problem with an iterative thresholding algorithm in wavelet coordinates. In the following, the two former algorithms are combined and compared with another nonlinear approach based on sparsity regularization and a fixed point algorithm. The performance of theses algorithms are evaluated on simulated data for different noise levels. Finally the algorithms were adapted to process real data sets obtained in phase CT at the ESRF at Grenoble.

Das Schalten und das Auslesen der magnetischen Ausrichtung einzelner winziger magnetischer Informationsspeicher müssen zu wirklich nanoskopischer Dimension entwickelt werden, um mit der Miniaturisierung von modernen, nanoelektronischen Bauteilen Schritt zu halten. Daher sind neue Konzepte, den magnetischen Zustand von Nanostrukturen elektronisch gezielt zu beeinflussen, derzeitig im Mittelpunkt wissenschaftlicher Untersuchungen. Diese Arbeit befasst sich mit dem zuverlässigen Einstellen der Magnetisierung eines rein horizontal kontaktierten, nanoskopischen Magneten, in zwei stabile Zustände. Ein spinpolarisierter Strom wird bei Raumtemperatur in eine Leiterbahn unterhalb des magnetischen Nanopillars injiziert. Spindiffusion durch den Kontakt zwischen der Leiterbahn (Cu) und dem Pillar (CoFe) ruft eine Spin-Akkumulation im Nanopillar hervor, der durch den Spin Transfer Torque-Effekt (STT) vermittelt wird. Bei diesem Prozess verursachen die akkumulierten Elektronenspins ein auftretendes Netto-Moment, das senkrecht auf die Magnetisierungsorientierung des Nanopillars wirkt und so das Schalten ermöglicht. In den STT-induzierten Schaltexperimenten wird der magnetische Zustand des Nanopillars durch eine bildgebendes Messverfahren mittels Rasterröntgentransmissionsmikroskopie (STXM) erfasst. So konnte gezeigt werden, dass sich die Magnetisierung des Pillars auch gegen das Oersted-Feld des Schaltstroms reversibel schalten lässt.:Kurzfassung v Abstract vi Danksagung xi 1 Einleitung 1 2 Grundlagen zu Spintronic 5 2.1 Elektronenspins als Grundlage für den Ferromagnetismus . . . . . . 6 2.2 Magnetowiderstandseffekte . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.1 Anisotroper Magnetowiderstandseffekt (AMR) . . . . . . . . 8 2.2.2 Riesenmagnetowidersandseffekt (GMR) . . . . . . . . . . . . 10 2.2.3 Tunnelmagnetowiderstandeffekt (TMR) . . . . . . . . . . . 13 2.3 Spin–Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3.1 Spinpolarisation . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.2 Spin-Injektion und Spin-Akkumulation . . . . . . . . . . . . 17 2.3.3 Spinpolarisierter elektrischer Transport . . . . . . . . . . . . 20 2.4 Spin Transfer Torque (STT) . . . . . . . . . . . . . . . . . . . . . . 25 2.5 Geometrien für Spintronic–Bauelemente . . . . . . . . . . . . . . . 30 3 Probenkonzept und Fabrikationsmethoden 35 3.1 Probenkonzept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.1.1 Anforderungen an die CIP–STT-Struktur . . . . . . . . . . . 37 3.1.2 Anforderungen an die ferromagnetischer Materialien . . . . . 38 3.2 Techniken der Probenfabrikation . . . . . . . . . . . . . . . . . . . . 40 3.2.1 Elektronenstrahllithografie (EBL) . . . . . . . . . . . . . . . 41 3.2.2 Positiv- und Negtivlack Prozess . . . . . . . . . . . . . . . . 41 3.2.3 Physikalisches Ätzen . . . . . . . . . . . . . . . . . . . . . . 43 3.3 Probenfabrikation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4 Experimentelle Methoden 49 4.1 Transmissionsröntgenmikroskopie . . . . . . . . . . . . . . . . . . . 49 4.1.1 Rastertransmissionsröntgenmikroskopie (STXM) . . . . . . . 51 4.1.2 Kontrastmechanismen . . . . . . . . . . . . . . . . . . . . . 53 4.1.3 Röntgenmagnetischer zirkularer Dichroismus (XMCD) . . . 54 4.2 Magneto-optische Kerr–Effekt Mikroskopie . . . . . . . . . . . . . . 57 4.2.1 Kerr–Mikroskop . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.2.2 Longitudinale Kerr–Geometrie . . . . . . . . . . . . . . . . . 58 5 STT–Experimente und Diskussion 61 5.1 Experimenteller Aufbau . . . . . . . . . . . . . . . . . . . . . . . . 62 5.2 Eigenschaften der magnetischen Bauelemente . . . . . . . . . . . . . 64 5.2.1 MOKE-Mikroskopie . . . . . . . . . . . . . . . . . . . . . . . 65 5.2.2 Mikromagnetische Simulation . . . . . . . . . . . . . . . . . 67 5.2.3 Analytische Berechnung zum Nanopillar . . . . . . . . . . . 70 5.2.4 Röntgentransmissionsmikroskopie . . . . . . . . . . . . . . . 72 5.3 Spin Transfer Torque-Schalten . . . . . . . . . . . . . . . . . . . . 74 5.3.1 STT-Schalten mit unterstützendem Magnetfeld . . . . . . . 74 5.3.2 STT-Schalten ohne unterstützendes Magnetfeld . . . . . . . 79 5.3.3 Betrachtung besonderer experimenteller Aspekte . . . . . . . 81 5.3.4 STT-Schalten ohne direkten Ladungstransport . . . . . . . . 89 5.3.5 Magnetisierungsumkehr durch Oersted-Feld . . . . . . . . . 93 6 Zusammenfassung und Ausblick 97 A STXM-Hysteresemessungen der Polarisatoren und Nanopillar 101 Literaturverzeichnis 105 / “Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nano electronic components. Therefore, new concepts for controlling the state of nano magnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate reproducible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar by means of Spin Transfer Torque (STT). In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM)” [1]. Therefore it could be demonstrated, to reversibly switch the nanopillar’s magnetic state even against the Oersted field which is induced by the switching current. Furthermore we could show, that magnetization switching is possible by a pure spin current that is diffusively transported beneath the nanopillar.:Kurzfassung v Abstract vi Danksagung xi 1 Einleitung 1 2 Grundlagen zu Spintronic 5 2.1 Elektronenspins als Grundlage für den Ferromagnetismus . . . . . . 6 2.2 Magnetowiderstandseffekte . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.1 Anisotroper Magnetowiderstandseffekt (AMR) . . . . . . . . 8 2.2.2 Riesenmagnetowidersandseffekt (GMR) . . . . . . . . . . . . 10 2.2.3 Tunnelmagnetowiderstandeffekt (TMR) . . . . . . . . . . . 13 2.3 Spin–Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3.1 Spinpolarisation . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.2 Spin-Injektion und Spin-Akkumulation . . . . . . . . . . . . 17 2.3.3 Spinpolarisierter elektrischer Transport . . . . . . . . . . . . 20 2.4 Spin Transfer Torque (STT) . . . . . . . . . . . . . . . . . . . . . . 25 2.5 Geometrien für Spintronic–Bauelemente . . . . . . . . . . . . . . . 30 3 Probenkonzept und Fabrikationsmethoden 35 3.1 Probenkonzept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.1.1 Anforderungen an die CIP–STT-Struktur . . . . . . . . . . . 37 3.1.2 Anforderungen an die ferromagnetischer Materialien . . . . . 38 3.2 Techniken der Probenfabrikation . . . . . . . . . . . . . . . . . . . . 40 3.2.1 Elektronenstrahllithografie (EBL) . . . . . . . . . . . . . . . 41 3.2.2 Positiv- und Negtivlack Prozess . . . . . . . . . . . . . . . . 41 3.2.3 Physikalisches Ätzen . . . . . . . . . . . . . . . . . . . . . . 43 3.3 Probenfabrikation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4 Experimentelle Methoden 49 4.1 Transmissionsröntgenmikroskopie . . . . . . . . . . . . . . . . . . . 49 4.1.1 Rastertransmissionsröntgenmikroskopie (STXM) . . . . . . . 51 4.1.2 Kontrastmechanismen . . . . . . . . . . . . . . . . . . . . . 53 4.1.3 Röntgenmagnetischer zirkularer Dichroismus (XMCD) . . . 54 4.2 Magneto-optische Kerr–Effekt Mikroskopie . . . . . . . . . . . . . . 57 4.2.1 Kerr–Mikroskop . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.2.2 Longitudinale Kerr–Geometrie . . . . . . . . . . . . . . . . . 58 5 STT–Experimente und Diskussion 61 5.1 Experimenteller Aufbau . . . . . . . . . . . . . . . . . . . . . . . . 62 5.2 Eigenschaften der magnetischen Bauelemente . . . . . . . . . . . . . 64 5.2.1 MOKE-Mikroskopie . . . . . . . . . . . . . . . . . . . . . . . 65 5.2.2 Mikromagnetische Simulation . . . . . . . . . . . . . . . . . 67 5.2.3 Analytische Berechnung zum Nanopillar . . . . . . . . . . . 70 5.2.4 Röntgentransmissionsmikroskopie . . . . . . . . . . . . . . . 72 5.3 Spin Transfer Torque-Schalten . . . . . . . . . . . . . . . . . . . . 74 5.3.1 STT-Schalten mit unterstützendem Magnetfeld . . . . . . . 74 5.3.2 STT-Schalten ohne unterstützendes Magnetfeld . . . . . . . 79 5.3.3 Betrachtung besonderer experimenteller Aspekte . . . . . . . 81 5.3.4 STT-Schalten ohne direkten Ladungstransport . . . . . . . . 89 5.3.5 Magnetisierungsumkehr durch Oersted-Feld . . . . . . . . . 93 6 Zusammenfassung und Ausblick 97 A STXM-Hysteresemessungen der Polarisatoren und Nanopillar 101 Literaturverzeichnis 105

<p>Probing the subsurface for evidence related to the degradation of porous mediums and the evolution of damage mechanisms has been a long-standing challenge in geophysics. As such imaging and predicting fracture network development has remained a difficult area for subsurface science for decades despite the seminal and significant works put forward by many researchers. While this has provide great understanding about the behaviours and properties of natural porous media, there is still much that needs to be explored particularly in regard to the mineralogical composition and chemistry of clay-rich rocks. Despite the fact that argillaceous rocks which consist of different types of clays and varied mineral composition are ubiquitous in nature and are often the target of several technologies (e.g. geotechnical engineering, nuclear waste storage and disposal,hydrocarbon exploration and extraction, carbon capture and sequestration, etc.), many studies focus primarily on the bulk properties or the percentage of components in the matrix. For these reason and due to the problems that can be encountered with natural rocks that contain a swelling clay component whether randomly distirbuted or localized in consolidated globs in zones of the matrix, the influence of clay chemistry in relation to fracture development which is not well characterized, especially during desaturation is investigated with analogue rock samples which were systematically fabricated for this purpose.</p> <p><br></p> <p>The research performed in this dissertation investigated, the applicability of  the fabrication protocol for developing synthetic rocks with desirable rock like features and behavior, the impact and relationship between the rock properties, the microstructural composition, water loss, and the macroscopic behavior of the analogue rocks, focusing on the structure and chemistry of the constituent clay materials. Synthetic rocks were fashioned with the necessary geometries, properties, and material compositions. On the macroscopic scale the fracture and drying behavior of the synthetic rocks were examined with 3D X-ray microscopy and further evaluated through the utility of acoustic emission monitoring, water loss monitoring, and unconfined compressive testing. On the finer scale (nano-microscale), the chemical and mechanical properties, and behavior of select clays was explored by exploiting several methods of material characterization which also included cation exchange experiments coupled with inductively coupled plasma – optical emission spectrometry (ICP-OES). </p> <p><br></p> <p>For the finer scale, experiments verified that calcined kaolinite clay had a different mineral structure and negligible to non-existence shrinkage abilities. In contrast, the montmorillonite clays possessed higher and similar moisture contents but, owing to the different principal cations these clays interacted a bit differently in the highly akaline environment, experienced varying degrees of shrinkage, and had observedly minor structural dissimilarities. For the relatively larger scale, the emergence of damage, extent of the damage network, and the patterns of the crack network mainly depended on the microstructural composition of the analogue rocks, particularly it's clay chemistry and/ or distribution. The location of damage depended on the emplacement and percentage of swelling clay in the matrix, and numerical investigations with peridynamics revealed that the observed damage was a consequence of the action of the swelling and non-swelling components of the matrix. Furthermore, if the microstructure consisted of no clay or calcined kaolinite the AE activity was solely attributed to interfacial processes that occurred during fluid front movement. If the microstructure consisted of a particular montmorillonite, the cracks propagated in the direction of the drying front. Conversely, for montmorillonite clay predominated by a different principal cation, the crack network developed and propagated differently during water loss. Additionally, on the laboratory core scale, properties and behavior similar to natural rocks were confirmed and the rock strength, porosity, AE activity, and velocities were primarily affected by the microstructural composition of the analogue rocks. </p> <p><br></p> <p>An added challenge for investigating and monitoring evolving systems and processes, whether on the laboratory or field scale, is the problem of extracting useful information from the physical data that can be used to identify signatures of developing processes, and changes in the properties or the behavior of a system. Here, data driven machine learning modeling and clustering techniques were undertaken to build a mechanistic understanding of the AE activity generated during drying. The intent is for this work to add to the fundamental research aimed at developing methods that will robustly detect and extract signatures related to evolutionary processes or features in the AE signals, and group them according to some degree of similarity. Such research will support reliable interpretations of the physical data for predictions of the behavior of systems, development of engineering controls, and improvement of the understanding of intrinsic dynamics related to complex processes particularly those that occur in clay-rich systems.</p> <p><br></p> <p>Combined chemical and mechanical investigations have great potential for unraveling practical challenges in subsurface science, especially regarding damage processes in clay-rich rock systems, and identifying and interpreting the presence of discontinuities from geophysical data. The present findings are useful for establishing a link between the constituent clay and observed damage, and improving our understanding of the development of damage in clay-bearing systems. These results provide insight on the influence of swelling clay and the chemistry of such clays on the generation of cracks and crack networks in rock like materials which can be useful for the characterization of damage in both laboratory and the field. The work presented here can also be a basis for further experiments that aim to uncover methods and protocols that will help with the indirect characterization of evolutionary processes, damage mechanisms, and damage in clay rich porous media. Additionally support for the use of analogue rocks in experimental rock physics, architected with specific material compositions, pore structures, crack systems, or clay fractions, is provided here. </p>

Hard x rays come along with a variety of extraordinary properties which make them an excellent probe for investigation in science, technology and medicine. Their large attenuation length in matter opens up the possibility to use hard x-rays for non-destructive investigation of the inner structure of specimens. Medical radiography is one important example of exploiting this feature. Since their discovery by W. C. Röntgen in 1895, a large variety of x-ray analytical techniques have been developed and successfully applied, such as x-ray crystallography, reflectometry, fluorescence spectroscopy, x-ray absorption spectroscopy, small angle x-ray scattering, and many more. Each of those methods reveals information about certain physical properties, but usually, these properties are an average over the complete sample region illuminated by the x rays. In order to obtain the spatial distribution of those properties in inhomogeneous samples, scanning microscopy techniques have to be applied, screening the sample with a small x-ray beam. The spatial resolution is limited by the finite size of the beam. The availability of highly brilliant x-ray sources at third generation synchrotron radiation facilities together with the development of enhanced focusing x-ray optics made it possible to generate increasingly small high intense x-ray beams, pushing the spatial resolution down to the sub-100 nm range. During this thesis the prototype of a hard x-ray scanning microscope utilizing microstructured nanofocusing lenses was designed, built, and successfully tested. The nanofocusing x-ray lenses were developed by our research group of the Institute of Structural Physics at the Technische Universität Dresden. The prototype instrument was installed at the ESRF beamline ID 13. A wide range of experiments like fluorescence element mapping, fluorescence tomography, x-ray nano-diffraction, coherent x-ray diffraction imaging, and x-ray ptychography were performed as part of this thesis. The hard x-ray scanning microscope provides a stable x-ray beam with a full width at half maximum size of 50-100 nm near the focal plane. The nanoprobe was also used for characterization of nanofocusing lenses, crucial to further improve them. Based on the experiences with the prototype, an advanced version of a hard x-ray scanning microscope is under development and will be installed at the PETRA III beamline P06 dedicated as a user instrument for scanning microscopy. This document is organized as follows. A short introduction motivating the necessity for building a hard x-ray scanning microscope is followed by a brief review of the fundamentals of hard x-ray physics with an emphasis on free-space propagation and interaction with matter. After a discussion of the requirements on the x-ray source for the nanoprobe, the main features of synchrotron radiation from an undulator source are shown. The properties of the nanobeam generated by refractive x-ray lenses are treated as well as a two-stage focusing scheme for tailoring size, flux and the lateral coherence properties of the x-ray focus. The design and realization of the microscope setup is addressed, and a selection of experiments performed with the prototype version is presented, before this thesis is finished with a conclusion and an outlook on prospective plans for an improved microscope setup to be installed at PETRA III.:1 Introduction ............................................... 1 2 Basic Properties of Hard X Rays ............................ 3 2.1 Free Propagation of X Rays ............................... 3 2.1.1 The Helmholtz Equation ................................. 4 2.1.2 Integral Theorem of Helmholtz and Kirchhoff ............ 6 2.1.3 Fresnel-Kirchhoff's Diffraction Formula ................ 8 2.1.4 Fresnel-Kirchhoff Propagation .......................... 11 2.2 Interaction of X Rays with Matter ........................ 13 2.2.1 Complex Index of Refraction ............................ 13 2.2.2 Attenuation ............................................ 15 2.2.3 Refraction ............................................. 18 3 The X-Ray Source ........................................... 21 3.1 Requirements ............................................. 21 3.1.1 Energy and Energy Bandwidth ............................ 21 3.1.2 Source Size and Divergence ............................. 23 3.1.3 Brilliance ............................................. 23 3.2 Synchrotron Radiation .................................... 24 3.3 Layout of a Synchrotron Radiation Facility ............... 27 3.4 Liénard-Wiechert Fields .................................. 29 3.5 Dipole Magnets ........................................... 31 3.6 Insertion Devices ........................................ 36 3.6.1 Multipole Wigglers ..................................... 36 3.6.2 Undulators ............................................. 37 4 X-Ray Optics ............................................... 39 4.1 Refractive X-Ray Lenses .................................. 40 4.2 Compound Parabolic Refractive Lenses (CRLs) .............. 41 4.3 Nanofocusing Lenses (NFLs) ............................... 43 4.4 Adiabatically Focusing Lenses (AFLs) ..................... 45 4.5 Focal Distance ........................................... 46 4.6 Transverse Focus Size .................................... 50 4.7 Beam Caustic ............................................. 52 4.8 Depth of Focus ........................................... 53 4.9 Beam Divergence .......................................... 53 4.10 Chromaticity ............................................ 54 4.11 Transmission and Cross Section .......................... 55 4.12 Transverse Coherence .................................... 56 4.12.1 Mutual Intensity Function ............................. 57 4.12.2 Free Propagation of Mutual Intensity .................. 57 4.12.3 Mutual Intensity In The Focal Plane ................... 58 4.12.4 Diffraction Limited Focus ............................. 59 4.13 Coherent Flux ........................................... 60 4.14 Two-Stage Focusing ...................................... 64 4.14.1 The Prefocusing Parameter ............................. 65 4.14.2 Required Refractive Power ............................. 67 4.14.3 Flux Considerations ................................... 70 4.14.4 Astigmatic Prefocusing ................................ 75 5 Nanoprobe Setup ............................................ 77 5.1 X-Ray Optics ............................................. 78 5.1.1 Nanofocusing Lenses .................................... 79 5.1.2 Entry Slits ............................................ 82 5.1.3 Pinhole ................................................ 82 5.1.4 Additional Shielding ................................... 83 5.1.5 Vacuum and Helium Tubes ................................ 83 5.2 Sample Stages ............................................ 84 5.2.1 High Resolution Scanner ................................ 84 5.2.2 High Precision Rotational Stage ........................ 85 5.2.3 Coarse Linear Stages ................................... 85 5.2.4 Goniometer Head ........................................ 85 5.3 Detectors ................................................ 86 5.3.1 High Resolution X-Ray Camera ........................... 86 5.3.2 Diffraction Cameras .................................... 89 5.3.3 Energy Dispersive Detectors ............................ 91 5.3.4 Photodiodes ............................................ 93 5.4 Control Software ......................................... 94 6 Experiments ................................................ 97 6.1 Lens Alignment ........................................... 97 6.2 Focus Characterization ................................... 99 6.2.1 Knife-Edge Scans ....................................... 100 6.2.2 Far-Field Measurements ................................. 102 6.2.3 X-Ray Ptychography ..................................... 103 6.3 Fluorescence Spectroscopy ................................ 105 6.3.1 Fluorescence Element Mapping ........................... 107 6.3.2 Fluorescence Tomography ................................ 110 6.4 Diffraction Experiments .................................. 111 6.4.1 Microdiffraction on Phase Change Media ................. 112 6.4.2 Microdiffraction on Stranski-Krastanow Islands ......... 113 6.4.3 Coherent X-Ray Diffraction Imaging of Gold Particles ... 115 6.4.4 X-Ray Ptychography of a Nano-Structured Microchip ...... 117 7 Conclusion and Outlook ..................................... 121 Bibliography ................................................. 125 List of Figures .............................................. 139 List of Publications ......................................... 141 Danksagung ................................................... 145 Curriculum Vitae ............................................. 149 Erklärung .................................................... 151 / Aufgrund ihrer hervorragenden Eigenschaften kommt harte Röntgenstrahlung in vielfältiger Weise in der Wissenschaft, Industrie und Medizin zum Einsatz. Vor allem die Fähigkeit, makroskopische Gegenstände zu durchdringen, eröffnet die Möglichkeit, im Innern ausgedehnter Objekte verborgene Strukturen zum Vorschein zu bringen, ohne den Gegenstand zerstören zu müssen. Eine Vielzahl röntgenanalytischer Verfahren wie zum Beispiel Kristallographie, Reflektometrie, Fluoreszenzspektroskopie, Absorptionsspektroskopie oder Kleinwinkelstreuung sind entwickelt und erfolgreich angewendet worden. Jede dieser Methoden liefert gewisse strukturelle, chemische oder physikalische Eigenschaften der Probe zutage, allerdings gemittelt über den von der Röntgenstrahlung beleuchteten Bereich. Um eine ortsaufgelöste Verteilung der durch die Röntgenanalyse gewonnenen Information zu erhalten, bedarf es eines sogenannten Mikrostrahls, durch den die Probe lokal abgetastet werden kann. Die dadurch erreichbare räumliche Auflösung ist durch die Größe des Mikrostrahls begrenzt. Aufgrund der Verfügbarkeit hinreichend brillanter Röntgenquellen in Form von Undulatoren an Synchrotronstrahlungseinrichtungen und des Vorhandenseins verbesserter Röntgenoptiken ist es in den vergangen Jahren gelungen, immer kleinere intensive Röntgenfokusse zu erzeugen und somit das räumliche Auflösungsvermögen der Röntgenrastermikroskope auf unter 100 nm zu verbessern. Gegenstand dieser Arbeit ist der Prototyp eines Rastersondenmikroskops für harte Röntgenstrahlung unter Verwendung refraktiver nanofokussierender Röntgenlinsen, die von unserer Arbeitsgruppe am Institut für Strukturphysik entwickelt und hergestellt werden. Das Rastersondenmikroskop wurde im Rahmen dieser Promotion in Dresden konzipiert und gebaut sowie am Strahlrohr ID 13 des ESRF installiert und erfolgreich getestet. Das Gerät stellt einen hochintensiven Röntgenfokus der Größe 50-100 nm zur Verfügung, mit dem im Verlaufe dieser Doktorarbeit zahlreiche Experimente wie Fluoreszenztomographie, Röntgennanobeugung, Abbildung mittels kohärenter Röntgenbeugung sowie Röntgenptychographie erfolgreich durchgeführt wurden. Das Rastermikroskop dient unter anderem auch dem Charakterisieren der nanofokussierenden Linsen, wobei die dadurch gewonnenen Erkenntnisse in die Herstellung verbesserten Linsen einfließen. Diese Arbeit ist wie folgt strukturiert. Ein kurzes einleitendes Kapitel dient als Motivation für den Bau eines Rastersondenmikroskops für harte Röntgenstrahlung. Es folgt eine Einführung in die Grundlagen der Röntgenphysik mit Hauptaugenmerk auf die Ausbreitung von Röntgenstrahlung im Raum und die Wechselwirkungsmechanismen von Röntgenstrahlung mit Materie. Anschließend werden die Anforderungen an die Röntgenquelle besprochen und die Vorzüge eines Undulators herausgestellt. Wichtige Eigenschaften eines mittels refraktiver Röntgenlinsen erzeugten Röntgenfokus werden behandelt, und das Konzept einer Vorfokussierung zur gezielten Anpassung der transversalen Kohärenzeigenschaften an die Erfordernisse des Experiments wird besprochen. Das Design und die technische Realisierung des Rastermikroskops werden ebenso dargestellt wie eine Auswahl erfolgreicher Experimente, die am Gerät vollzogen wurden. Die Arbeit endet mit einem Ausblick, der mögliche Weiterentwicklungen in Aussicht stellt, unter anderem den Aufbau eines verbesserten Rastermikroskops am PETRA III-Strahlrohr P06.:1 Introduction ............................................... 1 2 Basic Properties of Hard X Rays ............................ 3 2.1 Free Propagation of X Rays ............................... 3 2.1.1 The Helmholtz Equation ................................. 4 2.1.2 Integral Theorem of Helmholtz and Kirchhoff ............ 6 2.1.3 Fresnel-Kirchhoff's Diffraction Formula ................ 8 2.1.4 Fresnel-Kirchhoff Propagation .......................... 11 2.2 Interaction of X Rays with Matter ........................ 13 2.2.1 Complex Index of Refraction ............................ 13 2.2.2 Attenuation ............................................ 15 2.2.3 Refraction ............................................. 18 3 The X-Ray Source ........................................... 21 3.1 Requirements ............................................. 21 3.1.1 Energy and Energy Bandwidth ............................ 21 3.1.2 Source Size and Divergence ............................. 23 3.1.3 Brilliance ............................................. 23 3.2 Synchrotron Radiation .................................... 24 3.3 Layout of a Synchrotron Radiation Facility ............... 27 3.4 Liénard-Wiechert Fields .................................. 29 3.5 Dipole Magnets ........................................... 31 3.6 Insertion Devices ........................................ 36 3.6.1 Multipole Wigglers ..................................... 36 3.6.2 Undulators ............................................. 37 4 X-Ray Optics ............................................... 39 4.1 Refractive X-Ray Lenses .................................. 40 4.2 Compound Parabolic Refractive Lenses (CRLs) .............. 41 4.3 Nanofocusing Lenses (NFLs) ............................... 43 4.4 Adiabatically Focusing Lenses (AFLs) ..................... 45 4.5 Focal Distance ........................................... 46 4.6 Transverse Focus Size .................................... 50 4.7 Beam Caustic ............................................. 52 4.8 Depth of Focus ........................................... 53 4.9 Beam Divergence .......................................... 53 4.10 Chromaticity ............................................ 54 4.11 Transmission and Cross Section .......................... 55 4.12 Transverse Coherence .................................... 56 4.12.1 Mutual Intensity Function ............................. 57 4.12.2 Free Propagation of Mutual Intensity .................. 57 4.12.3 Mutual Intensity In The Focal Plane ................... 58 4.12.4 Diffraction Limited Focus ............................. 59 4.13 Coherent Flux ........................................... 60 4.14 Two-Stage Focusing ...................................... 64 4.14.1 The Prefocusing Parameter ............................. 65 4.14.2 Required Refractive Power ............................. 67 4.14.3 Flux Considerations ................................... 70 4.14.4 Astigmatic Prefocusing ................................ 75 5 Nanoprobe Setup ............................................ 77 5.1 X-Ray Optics ............................................. 78 5.1.1 Nanofocusing Lenses .................................... 79 5.1.2 Entry Slits ............................................ 82 5.1.3 Pinhole ................................................ 82 5.1.4 Additional Shielding ................................... 83 5.1.5 Vacuum and Helium Tubes ................................ 83 5.2 Sample Stages ............................................ 84 5.2.1 High Resolution Scanner ................................ 84 5.2.2 High Precision Rotational Stage ........................ 85 5.2.3 Coarse Linear Stages ................................... 85 5.2.4 Goniometer Head ........................................ 85 5.3 Detectors ................................................ 86 5.3.1 High Resolution X-Ray Camera ........................... 86 5.3.2 Diffraction Cameras .................................... 89 5.3.3 Energy Dispersive Detectors ............................ 91 5.3.4 Photodiodes ............................................ 93 5.4 Control Software ......................................... 94 6 Experiments ................................................ 97 6.1 Lens Alignment ........................................... 97 6.2 Focus Characterization ................................... 99 6.2.1 Knife-Edge Scans ....................................... 100 6.2.2 Far-Field Measurements ................................. 102 6.2.3 X-Ray Ptychography ..................................... 103 6.3 Fluorescence Spectroscopy ................................ 105 6.3.1 Fluorescence Element Mapping ........................... 107 6.3.2 Fluorescence Tomography ................................ 110 6.4 Diffraction Experiments .................................. 111 6.4.1 Microdiffraction on Phase Change Media ................. 112 6.4.2 Microdiffraction on Stranski-Krastanow Islands ......... 113 6.4.3 Coherent X-Ray Diffraction Imaging of Gold Particles ... 115 6.4.4 X-Ray Ptychography of a Nano-Structured Microchip ...... 117 7 Conclusion and Outlook ..................................... 121 Bibliography ................................................. 125 List of Figures .............................................. 139 List of Publications ......................................... 141 Danksagung ................................................... 145 Curriculum Vitae ............................................. 149 Erklärung .................................................... 151