Multiple Mechanical Gradients are Responsible for the Strong Adhesion of Spider Attachment Hair

Wandering spiders climb vertically and walk upside-down on rough and smooth surfaces using a nanostructured attachment system on their feet. The spiders are assumed to adhere by intermolecular van der Waals forces between the adhesive structures and the substrate. The adhesive elements are arranged highly ordered on the hierarchically structured attachment hair (setae). While walking, it has been suggested that the spiders apply a shear force on their legs to increase friction. However, the detailed mechanical behavior of the hair's structures during attachment and detachment remains unknown. Here, gradients of the mechanical properties of the attachment hair on different length scales that have evolved to support attachment, stabilize adhesion in contact, and withstand high stress at detachment, examined by in situ experiments, are shown. Shearing helps to self-align the adhesive elements with the substrate. The study is anticipated to contribute to the development of optimized artificial dry adhesives

Single-exposure X-ray phase imaging microscopy with a grating interferometer

The advent of hard X-ray free-electron lasers enables nanoscopic X-ray imaging with sub-picosecond temporal resolution. X-ray grating interferometry offers a phase-sensitive full-field imaging technique where the phase retrieval can be carried out from a single exposure alone. Thus, the method is attractive for imaging applications at X-ray free-electron lasers where intrinsic pulse-to-pulse fluctuations pose a major challenge. In this work, the single-exposure phase imaging capabilities of grating interferometry are characterized by an implementation at the I13-1 beamline of Diamond Light Source (Oxfordshire, UK). For comparison purposes, propagation-based phase contrast imaging was also performed at the same instrument. The characterization is carried out in terms of the quantitativeness and the contrast-to-noise ratio of the phase reconstructions as well as via the achievable spatial resolution. By using a statistical image reconstruction scheme, previous limitations of grating interferometry regarding the spatial resolution can be mitigated as well as the experimental applicability of the technique

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

Flexible plenoptic X-ray microscopy

X-ray computed tomography (CT) is an invaluable technique for generating three-dimensional (3D) images of inert or living specimens. X-ray CT is used in many scientific, industrial, and societal fields. Compared to conventional 2D X-ray imaging, CT requires longer acquisition times because up to several thousand projections are required for reconstructing a single high-resolution 3D volume. Plenoptic imaging—an emerging technology in visible light field photography—highlights the potential of capturing quasi-3D information with a single exposure. Here, we show the first demonstration of a flexible plenoptic microscope operating with hard X-rays; it is used to computationally reconstruct images at different depths along the optical axis. The experimental results are consistent with the expected axial refocusing, precision, and spatial resolution. Thus, this proof-of-concept experiment opens the horizons to quasi-3D X-ray imaging, without sample rotation, with spatial resolution of a few hundred nanometres

Implementierung von Phasenkontrastmethoden an der P05 Nanotomographie an PETRA III: Zur Ermöglichung von in situ Experimenten

Hard X-ray full-field nanotomography is an ideal technique to study the inner structure of materials non-destructively at high spatial resolution, covering research areas such as material science, biology and medical research. In particular, in situ experiments are of high importance to study dynamics and processes in materials. High X-ray energies have the advantage to reduce the dose at the sample and in the case of a transmission X-ray microscope (TXM), to increase the focal depth. One disadvantage of higher photon energies however is the low absorption contrast for many materials, not only for biological or biomedical specimen. One approach to enhance the contrast is given by phase contrast methods. The main aim of this thesis is the implementation of full-field phase contrast methods at the nanotomography endstation of the imaging beamline P05 at the PETRA III storage ring. In this context, the temporal resolution is an important point in order to further reduce the dose as well as enable in situ nanotomography experiments. These two points are tackled by combining the unique geometry of the presented beamline with optimized experimental parameters and the development of new tomographic techniques, as well as integrating additional post-processing steps using machine learning algorithms. One approach to improve the contrast in a TXM is realized by implementing Zernike phase contrast (ZPC). In addition, a new denoising approach based on machine learning was developed, eliminating noise from nanotomographic data, in particular when using fast scanning modes. Utilizing these methods at high temporal resolutions is key to perform the first in situ nanotomography experiments at P05: A spider attachment hair is attached to a surface under force control and scanned at different states of attachment. An interesting aspect is here also the orientation distribution of single attachment elements, which is linked to previously recorded diffraction data. Another phase contrast approach utilizing the high coherence of 3rd generation sources, is near-field holotomography (NFH) based on propagation phase contrast. In the framework of this thesis the worldwide first hard X-ray holotomography setup using Fresnel zone plates has been developed and realized at the P05 imaging beamline. In contrast to ZPC, it offers a scalable field of view and magnification, the quantitative analysis of the phase signal and sufficient space for extended sample environments. The developed and implemented phase contrast methods at the P05 nanotomography station will enable the analysis of materials with high resolution in 3D at high temporal resolutions. Altogether this will open doors to in situ experiments and offer great opportunities to study dynamical processes.Nanotomographie mit harter Röntgenstrahlung ist eine ideale Methode, um zerstörungsfrei die innere Struktur von Materialien zu untersuchen. Diese Methode kann in vielen verschiedenen Forschungsbereichen eingesetzt werden, beispielsweise in den Materialwissenschaften, der Biologie oder der medizinischen Forschung. Von besonderem Interesse sind zudem in situ Experimente, in denen dynamische Prozesse in Materialien beobachtet werden können. Dabei hat harte Röntgenstrahlung den Vorteil einer geringen Strahlenbelastung der Proben. Besonders bei biologischen Proben ist der Kontrast in der klassischen Tomographie jedoch häufig nicht ausreichend. Eine Möglichkeit, den Kontrast zu verstärken, bietet die Verwendung von Phasenkontrastmethoden. Das Ziel der vorliegenden Arbeit ist daher die Implementierung von Phasenkontrastverfahren am Nanotomographie Aufbau der Imaging Beamline P05 am PETRA III Speicherring am DESY. Gleichzeitig wird die Zeitauflösung drastisch erhöht, wodurch sowohl die Strahlendosis reduziert wird, als auch in situ Experimente ermöglicht werden. Unter Berücksichtigung der Besonderheiten der Beamline P05 werden sowohl Verbesserungen und technische Weiterentwicklungen des experimentellen Aufbaus vorgenommen als auch eine Verbesserung der Datenqualität durch nachträgliche Bearbeitung unter Zuhilfenahme von maschinellem Lernen erreicht. Eine Phasenkontrastmethode, welche sich einfach in ein bestehendes Röntgenmikroskop integrieren lässt, wird durch den Zernike-Phasenkontrast realisiert. Zudem wird eine auf maschinellem Lernen basierende Filtermethode entwickelt, die es ermöglicht, Rauschen in den Tomographiedaten zu minimieren. Diese Methoden werden benötigt, um die ersten in situ Experimente an der P05 Nanotomographie durchzuführen: Hierbei wird ein Spinnenhafthaar bei gleichzeitiger Kraftmessung an eine Oberfläche angehaftet und in verschiedenen Stadien tomographiert. Dabei ist die Orientierungsverteilung einzelner Haftelemente von besonderem Interesse und wird mit zuvor aufgenommenen Diffraktionsmessungen verglichen. Eine weitere Phasenkontrastmethode, die die Kohärenzeigenschaften von PETRA III ausschöpft, ist die Nahfeld-Holotomographie, welche auf propagationsbasiertem Phasenkontrast aufbaut. Im Zusammenhang dieser Arbeit entsteht dabei der erste Holotomographieaufbau im harten Röntgenbereich, welcher eine Fresnel-Zonenplatte zum Fokussieren verwendet. Der Aufbau verwendet einen divergenten Strahl und ermöglicht eine skalierbare Vergrößerung. Im Gegensatz zum Zernike-Phasenkontrast ist diese Methode quantitativ und ermöglicht die Implementierung größerer in situ Umgebungen. Die Entwicklung und Implementierung von Phasenkontrastmethoden an der Nanotomographie an P05 ermöglicht die Analyse von wenig absorbierenden Materialen in 3D mit hoher Zeitauflösung. Insbesondere durch die schnelle Tomographie mit Auflösungen unter 100 nm werden Experimente ermöglicht, in denen dynamische Prozesse in situ untersucht werden können

Implementation of Phase Contrast Methods at the P05 Nanotomography Endstation at PETRA III: Enabling in situ experiments

Hard X-ray full-field nanotomography is an ideal technique to study the inner structureof materials non-destructively at high spatial resolution, covering research areas suchas material science, biology and medical research. In particular, in situ experiments areof high importance to study dynamics and processes in materials. High X-ray energieshave the advantage to reduce the dose at the sample and in the case of a transmissionX-ray microscope (TXM), to increase the focal depth. One disadvantage of higherphoton energies however is the low absorption contrast for many materials, not onlyfor biological or biomedical specimen. One approach to enhance the contrast is givenby phase contrast methods.The main aim of this thesis is the implementation of full-field phase contrast methods atthe nanotomography endstation of the imaging beamline P05 at the PETRA III storagering. In this context, the temporal resolution is an important point in order to furtherreduce the dose as well as enable in situ nanotomography experiments. These two pointsare tackled by combining the unique geometry of the presented beamline with optimizedexperimental parameters and the development of new tomographic techniques, as wellas integrating additional post-processing steps using machine learning algorithms.One approach to improve the contrast in a TXM is realized by implementing Zernikephase contrast (ZPC). In addition, a new denoising approach based on machine learningwas developed, eliminating noise from nanotomographic data, in particular when usingfast scanning modes. Utilizing these methods at high temporal resolutions is key toperform the first in situ nanotomography experiments at P05: A spider attachmenthair is attached to a surface under force control and scanned at different states ofattachment. An interesting aspect is here also the orientation distribution of singleattachment elements, which is linked to previously recorded diffraction data.Another phase contrast approach utilizing the high coherence of 3rd generation sources,is near-field holotomography (NFH) based on propagation phase contrast. In the frame-work of this thesis the worldwide first hard X-ray holotomography setup using Fresnelzone plates has been developed and realized at the P05 imaging beamline. In contrastto ZPC, it offers a scalable field of view and magnification, the quantitative analysis ofthe phase signal and sufficient space for extended sample environments.The developed and implemented phase contrast methods at the P05 nanotomographystation will enable the analysis of materials with high resolution in 3D at high temporalresolutions. Altogether this will open doors to in situ experiments and offer greatopportunities to study dynamical processes

Phase retrieval framework for direct reconstruction of the projected refractive index applied to ptychography and holography

The interaction of an object with a coherent probe often encodes its properties in a complex-valued function, which is then detected in an intensity-only measurement. Phase retrieval methods commonly infer this complex-valued function from the intensity. However, the decoding of the object from the complex-valued function often involves some ambiguity in the phase, e.g., when the phase shift in the object exceeds 2. Here, we present a phase retrieval framework to directly recover the amplitude and phase of the object. This refractive framework is straightforward to integrate into existing algorithms. As examples, we introduce refractive algorithms for ptychography and near-field holography and demonstrate this method using measured data

Hard X-ray nano-holotomography with a Fresnel zone plate

X-ray phase contrast nanotomography enables imaging of a wide range of samples with high spatial resolution in 3D. Near-field holography, as one of the major phase contrast techniques, is often implemented using X-ray optics such as Kirkpatrick-Baez mirrors, waveguides and compound refractive lenses. However, these optics are often tailor-made for a specific beamline and challenging to implement and align. Here, we present a near-field holography setup based on Fresnel zone plates which is fast and easy to align and provides a smooth illumination and flat field. The imaging quality of different types of Fresnel zone plates is compared in terms of the flat-field quality, the achievable resolution and exposure efficiency i.e. the photons arriving at the detector. Overall, this setup is capable of imaging different types of samples at high spatial resolution of below 100 nm in 3D with access to the quantitative phase information

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