Pushing the temporal resolution in absorption and Zernike phase contrast nanotomography: Enabling fast in situ experiments

Hard X-ray nanotomography enables 3D investigations of a wide range of samples with high resolution (<100 nm) with both synchrotron-based and laboratory-based setups. However, the advantage of synchrotron-based setups is the high flux, enabling time resolution, which cannot be achieved at laboratory sources. Here, the nanotomography setup at the imaging beamline P05 at PETRA III is presented, which offers high time resolution not only in absorption but for the first time also in Zernike phase contrast. Two test samples are used to evaluate the image quality in both contrast modalities based on the quantitative analysis of contrast-to-noise ratio (CNR) and spatial resolution. High-quality scans can be recorded in 15 min and fast scans down to 3 min are also possible without significant loss of image quality. At scan times well below 3 min, the CNR values decrease significantly and classical image-filtering techniques reach their limitation. A machine-learning approach shows promising results, enabling acquisition of a full tomography in only 6 s. Overall, the transmission X-ray microscopy instrument offers high temporal resolution in absorption and Zernike phase contrast, enabling in situ experiments at the beamline

Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser

Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray–matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the L3-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm2. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale

Modeling and manufacturing of multilayer laue lenses for highest resolution X-ray microscopy

Röntgenmikroskopie ist eine vielversprechende Technik, welche die Lücke zwischen optischer und Elektronenmikroskopie schließt. Sie ermöglicht es, Untersuchungen der Struktur und der Zusammensetzung verschiedenartiger Proben mit Auflösungen deutlich unter 100nm vorzunehmen. Je nach Probenbeschaffenheit ist dies zerstörungsfrei und zusammen mit der Ermittlung von Tiefeninformationen möglich. Der Schwerpunkt des hier beschriebenen Promotionsvorhabens ist der Entwicklung und die Berechnung der Eigenschaften von Multischicht Laue Linsen (MLL) für höchstaufgelöste Röntgenmessungen. Bei MLL handelt sich dabei um diffraktive Röntgenoptiken, welche insbesondere für die Nutzung mit harter Röntgenstrahlung mit einer Energie von mehr als 5 keV geeignet sind und in diesem Bereich höhere Effizienzen sowie gegenüber anderen Röntgenoptiken bessere Auflösungen versprechen. Im Rahmen des Promotionsverfahrens wurden insbesondere die Herstellung, Charakterisierung und Berechnung der Eigenschaften von MLL durchgeführt. Hierbei steht als Ziel die Anwendung von MLL als Fokussierungsoptik für Synchrotronstrahlanwendungen im Vordergrund. MLL fokussieren Röntgenstrahlen nach dem Prinzip einer linearen Zonenplatte. Im Unterschied zu elektronenstrahllithografisch hergestellten Zonenplatten wird die Zonenstruktur durch eine Multischicht aus vielen tausend Einzelschichten erzeugt. Aus der so hergestellten Multischicht wird anschließend ein Linsensegment geformt, wobei die Beschichtung hierfür zunächst grob und anschließend fein strukturiert wird, um die gewünschte Geometrie zu erreichen. Diese Schritte können mit Laserschneiden und durch Abtrag mit einem fokussierten Ionenstrahl durchgeführt werden. Da es sich bei einer so hergestellten MLL um ein eindimensional beugendes optisches Element handelt, müssen zwei vergleichbar hergestellte Segmente zu einer zweidimensional fokussierenden Optik kombiniert werden. Die Charakterisierung der Ergebnisse der einzelnen Produktionsschritte ist dabei notwendig, um Herstellungsfehler bzw. vorhandenes Verbesserungspotential zu ermitteln; hierbei wurden insbesondere die Rasterelektronenmikroskopie und Röntgenverfahren wie die Röntgendiffraktometrie eingesetzt. Aufgrund der geplanten Anwendung für die Fokussierung von Röntgenstrahlen an Synchrotronstrahleinrichtungen ist der Einsatz als Optik an entsprechenden Strahlrohren auch als finaler Test einer hergestellten Linse zu verstehen. Entsprechende Experimente wurden an den Röntgenstrahlungsquellen PETRA III und ESRF durchgeführt. Hierbei wurden vor allem die Fokussierungseigenschaften in Bezug auf Form und Intensität des mit den Linsen fokussierten Linsenstrahles untersucht. Experimente zur Vermessung der Beugungseigenschaften wurden auch an der Advanced Photon Source durchgeführt. Um die Eigenschaften der Linsen zu verstehen, wurden die Fokussierungseigenschaften von MLL berechnet. Dies erfolgte unter Nutzung von Algorithmen basierend auf der Coupled Wave Theory und der Beam Propagation Method. Die Berechnung der Eigenschaften erfolgt insbesondere unter den Gesichtspunkten von verschiedenen Materialsystemen, der Einrichtung zur Fokussierung der Linsen und möglichen Herstellungsfehlern. Die wesentlichen Arbeitsschritte der Herstellung erfolgten am Fraunhofer Institut für Werkstoff und Strahltechnik (IWS) in Dresden. Die Herstellung sowie Charakterisierung der Fokussierungseigenschaften der Linsen erfolgte in Zusammenarbeit mit dem Institut für Strukturphysik der Technischen Universität Dresden, der X-ray Nanoscience und X-ray Optics Gruppe des PETRA III, dem Fraunhofer IKTS sowie der AXO Dresden GmbH. Die Charakterisierung der Beugungseigenschaften und Teilen der Berechnungen erfolgten in Zusammenarbeit mit der X-ray Optics Group der Advanced Photon Source. Während der Arbeit an diesem Promotionsvorhaben wurde eine Referenzprobenfreie Methode zur Messung der Verbiegung von MLL entwickelt. Aus dem Strahlprofil der besten hergestellten Linse ergibt sich eine Aflösung von besser als 25 nm; diese weist die höchste bisher mit MLL erreichte Effizienz auf und es konnte der bisher größte Fluss mit MLL erreicht werden

Modeling and Manufacturing of Multilayer Laue Lenses for Highest Resolution X-ray Microscopy

X-ray microscopy is a technique bridging the gap between optical and electron microscopy. It permits investigations of the structure and composition of various samples with resolutions well below 100 nm. Depending on the sample this is also possible nondestructively and together with the measurement of depth information.The focus of this doctoral project is the development and property calculations of multilayer Laue lenses (MLLs) for highest resolution X-ray measurements. MLLs are diffractive X-ray optics, which are suited for the use with hard X-ray photon energies of more than 5 keV, in particular. MLLs promise high efficiencies as well superior resolutions in this energy range.MLLs focus X-rays according to the principle of a linear zone plate. Unlike these -generally electron-beam lithography produced- zone plates, the zone structure is formed by many thousands individually deposited thin layers. From this multilayer structure a lens segment is formed. For this purpose the multilayer is structured in order to achieve the desired geometry, which is the actual MLL. These structuring steps can be performed with a wafer saw, laser cutting and focused ion beam milling.One MLL is a one-dimensional diffractive optical element; therefore two similar segments have to be combined for two-dimensional focusing. Knowledge of the results of the individual production steps is required to locate manufacturing faults or existing potential for improvements. For the evaluation of the results scanning electron microscopy and X-ray methods, such as X-ray diffraction, have been used in particular.The intended main use of MLLs is the focusing in synchrotron radiation facilities; therefore measurements at beamlines can also be understood as a final performance test of the manufactured lenses. Focusing experiments were conducted at the synchrotron radiation sources PETRA III (Germany) and ESRF (France). The focusing properties were evaluated in terms of shape and intensity of the beam. Further experiments for measuring diffraction properties were carried out at the Advanced Photon Source (United States).In order to understand the characteristics of the MLLs, properties of perfect and imperfect MLLs were calculated. This was done with the use of algorithms based mainly on the Beam Propagation Method and the Coupled Wave Theory. The calculation of the properties was made with emphasis on various material systems, the alignment of the lenses and possible manufacturing defects.During the work on this thesis a method of measuring the bending of MLLs without a reference sample has been developed. The focal profile of the best manufactured MLLs shows a resolution below 25 nm with the largest efficiency and flux in focus yet achieved using MLLs

Hard X‐ray full‐field nanoimaging using a direct photon‐counting detector

Full‐field X‐ray nanoimaging is a widely used tool in a broad range of scientific areas. In particular, for low‐absorbing biological or medical samples, phase contrast methods have to be considered. Three well established phase contrast methods at the nanoscale are transmission X‐ray microscopy with Zernike phase contrast, near‐field holography and near‐field ptychography. The high spatial resolution, however, often comes with the drawback of a lower signal‐to‐noise ratio and significantly longer scan times, compared with microimaging. In order to tackle these challenges a single‐photon‐counting detector has been implemented at the nanoimaging endstation of the beamline P05 at PETRA III (DESY, Hamburg) operated by Helmholtz‐Zentrum Hereon. Thanks to the long sample‐to‐detector distance available, spatial resolutions of below 100 nm were reached in all three presented nanoimaging techniques. This work shows that a single‐photon‐counting detector in combination with a long sample‐to‐detector distance allows one to increase the time resolution for in situ nanoimaging, while keeping a high signal‐to‐noise level.A direct photon‐counting detector was used for different nanoimaging phase contrast techniques, increasing the temporal resolution

Point focusing with flat and wedged crossed multilayer Laue lenses

Point focusing measurements using pairs of directly bonded crossed multilayer Laue lenses (MLLs) are reported. Several flat and wedged MLLs have been fabricated out of a single deposition and assembled to realise point focusing devices. The wedged lenses have been manufactured by adding a stress layer onto flat lenses. Subsequent bending of the structure changes the relative orientation of the layer interfaces towards the stress-wedged geometry. The characterization at ESRF beamline ID13 at a photon energy of 10.5 keV demonstrated a nearly diffraction-limited focusing to a clean spot of 43 nm × 44 nm without significant side lobes with two wedged crossed MLLs using an illuminated aperture of approximately 17 µm × 17 µm to eliminate aberrations originating from layer placement errors in the full 52.7 µm × 52.7 µm aperture. These MLLs have an average individual diffraction efficiency of 44.5%. Scanning transmission X-ray microscopy measurements with convenient working distances were performed to demonstrate that the lenses are suitable for user experiments. Also discussed are the diffraction and focusing properties of crossed flat lenses made from the same deposition, which have been used as a reference. Here a focal spot size of 28 nm × 33 nm was achieved and significant side lobes were noticed at an illuminated aperture of approximately 23 µm × 23 µm

Ptychography with multilayer Laue lenses

Two different multilayer Laue lens designs were made with total deposition thicknesses of 48 mu m and 53 mu m, and focal lengths of 20.0 mm and 12.5 mm at 20.0 keV, respectively. From these two multilayer systems, several lenses were manufactured for one-and two-dimensional focusing. The latter is realised with a directly bonded assembly of two crossed lenses, that reduces the distance between the lenses in the beam direction to 30 mm and eliminates the necessity of producing different multilayer systems. Characterization of lens fabrication was performed using a laboratory X-ray microscope. Focusing properties have been investigated using ptychography

A dedicated illumination for full-field X-ray microscopy with multilayer Laue lenses

We present a concept of a dedicated illumination to perform full-field X-ray microscopy with multilayer Laue lenses at laboratory X-ray sources. The basic idea is the application of a focusing X-ray multilayer mirror as condenser optics to provide a quasi-monochromatic and solid illumination, and consequently optimal conditions for the operation of the multilayer Laue lenses. First experimental results demonstrate the proof of this concept

Full-field X-ray microscopy with crossed partial multilayer Laue lenses

We demonstrate full-field X-ray microscopy using crossed multilayer Laue lenses (MLL). Two partial MLLs are prepared out of a 48 μm high multilayer stack consisting of 2451 alternating zones of WSi2 and Si. They are assembled perpendicularly in series to obtain two-dimensional imaging. Experiments are done in a laboratory X-ray microscope using Cu-Kα radiation (E = 8.05 keV, focal length f = 8.0 mm). Sub-100 nm resolution is demonstrated without mixed-order imaging at an appropriate position of the image plane. Although existing deviations from design parameters still cause aberrations, MLLs are a promising approach to realize hard X-ray microscopy at high efficiencies with resolutions down to the sub-10 nm range in future