|dc.description.abstract||This thesis has focused on exploring methods of using coherent X-ray scattering at synchrotron sources. New imaging techniques using coherent X-ray scattering have been investigated, and it has been discussed how limitations of already existing techniques can be overcome.
It has been demonstrated how an X-ray beam used for coherent X-ray diffraction imaging can be characterized by scanning a micro sphere in the beam. By moving the microsphere in the beam, and measuring the corresponding shift of the scattering pattern, the local curvature of the wavefront could be measured. The wavefront measured had a radius of curvature at the sample position of 55 cm, which corresponded to the distance between the sample and the last beam defining slits.
A series of experiments have demonstrated the possibilities and limitations of coherent X-ray diffraction imaging (CXDI). It has been shown that for metal-polymer composites beads in the size range of 3 µm the commonly employed reconstruction algorithm which assumes that the scattering pattern is proportional to the absolute square of the Fourier transform of the electron density is not fully applicable. When the phase shift of the X-rays propagating through a material is large, the reconstruction algorithm has to be modified to correctly describe the produced scattering pattern, and retrieve the correct density distribution of the scattering sample. Nevertheless, detailed maps of the surfaces of different coating layers of the imaged sample could be retrieved, showing surface roughness and imperfections. It has also been demonstrated how the core in a metal coated polymer sphere was affected by X-ray imaging. 3D imaging reviled how a bubble of low density polymer developed in the core of the sphere as the bead was exposed to X-rays. The 3D analysis was supplemented with X-ray photo correlation spectroscopy(XPCS) analysis, were it was seen that the shape of the correlation functions could be used to predict the radiation damage in the particle.
Ptychography has been used to image objects in complex sample environments and samples with low contrast between the material components. A 10 µm metal-polymer composite bead was compressed stepwise, and between each step a full 3D tomogram was acquired. The images revealed that preexisting defects in the metal coating affected how the bead fractured. The densification in the polymer core was also extracted, and found to be similar to the densification predicted by numerical methods. Ptychography has also been used to image polymer blends of poly(3-hexylthiophene) (P3HT) and phenyl-C61-buturic acid methyl ester (PCBM) used in organic solar cells. It was found that ptychography is well suited to image sample systems with low inherent contrast, and that one could follow thermal annealing processes ex situ. It was observed that increasing the thermal annealing time made the domains of electron donor and electron acceptor material grow in size. The diffusion constant of PCBM molecules in the P3HT phase was also extracted from the images and found to match previously reported values.
A final experiment showed how small-angle X-ray scattering can be combined with tomographic techniques to retrieve the spatially varying orientation distribution of embedded microparticles in a macroscopic sample. Small-angle X-ray scattering patterns were recorded for multiple sample positions with respect to the incoming X-ray beam, and for multiple rotations of the sample with respect to an axis normal to the optical axis. A method for retrieving the spatially varying orientation distribution from all the measured scattering patterns was deduced and implemented in a computer script. The method implemented provided qualitatively similar results as finding the orientation distribution by destructive methods. By comparing the method used in this thesis with other techniques recently developed for combining SAXS and tomography, the method implemented in this thesis was faster both when it came to acquiring the SAXS patterns and also when it came to reconstructing the orientation distribution from the scattering pattern, however, the acquired resolution from the method implemented in this thesis was lower.||nb_NO