Tomographic Surface X-ray Diffraction

The atomic structure of catalytic surfaces and its relation to function is important for the understanding and development of industrial catalysts. However, many surface sensitive methods are limited to low-pressure environments, creating a gap between experimental results and reality, and it is not certain that the findings can be applied to the real system. Surface X-ray diffraction is a method that is not limited to low pressures but is, on the other hand, limited to single crystals. This limitation is due to the long beam footprint caused by the grazing incidence angle needed to achieve surface sensitivity. In this thesis, we present the development of tomographic surface X-ray diffraction, an approach that enables surface X-ray diffraction measurements of polycrystalline surfaces. The tomographic surface X-ray diffraction approach can be divided into two steps: grain mapping using grazing incidence X-ray diffraction and sorting of surface X-ray diffraction signal from a polycrystalline sample.The grain mapping, introduced in Paper I, uses Bragg reflections to determine grain orientation, and generate spatial maps of the grains across the sample surface. The result is maps comparable to maps from electron backscatter diffraction and the approach can distinguish grains as small as the beam width.The signal-sorting step utilizes the grain map to assign surface diffraction signals to individual grains. At a given angle, the same signal should be present at all translations with the beam over a single grain and not be present outside the grain boundaries. By comparing the spatial occurrence of each signal with the grain map, single crystal diffraction patterns can be extracted from the measurements of the polycrystalline sample. This can then be applied to industry-relevant systems to study many surface orientations simultaneously.