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| Home > Publications database > Implementation of Phase Contrast Methods at the P05 Nanotomography Endstation at PETRA III: Enabling in situ experiments |
| Dissertation / PhD Thesis | PUBDB-2021-04377 |
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2021
Abstract: 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.
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