Abstract
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.
