Christian Schlepuetz Seminar

The past couple of years have marked the centennial anniversary of x-ray crystallography - a field of research that has seen a tremendous growth ever since its birth. Rather than going out of fashion eventually, it has helped to push the boundaries of our understanding of matter and materials steadily further. New x-ray techniques are continuously added to our set of available research tools, while established methods of crystallograpy are reaching new frontiers by taking advantage of the latest instrumentation developments.
The exploration of reciprocal space has taken a leap in terms of speed, accuracy, reliability, and the obtainable level of detail with the advent of modern single-photon-counting x-ray area detectors featuring high frame rates and zero readout noise. Each detector image represents a 2-dimensional slice through reciprocal space, and a single diffractometer scan extends this to a stack of slices probing a 3-dimensional volume. This allows for the rapid characterization of large volumes of reciprocal space, revealing all of the structural phases and their orientations present in a sample. The method is particularly powerful if not all the constituent phases and the corresponding locations of their diffraction signals are known, and aids in the discovery of unexpected phenomena or crystal structures.
In this talk, Christian gave a basic tutorial on how to navigate in reciprocal space and showed how to use a Pilatus 100K pixel detector to collect large volume data sets, which could then be processed to yield 3-dimensional reciprocal space maps (RSMs), high-quality powder diffraction data, or simultaneous measurements of pole figures for a whole range of 2-theta values. The capabilities of this approach were then highlighted using several topical research examples: The detailed investigation of the domain structure of multiferroic bismuth ferrite (BiFeO3) thin films and its phase transitions with temperature and film thickness was only possible due to the rapid collection of many RSMs, including those around the half-order film Bragg Peaks, which contain sensitive information about the oxygen octahedra rotation patterns in this material. Iron oxide (Fe2O3), as another example, is an attractive material for the photoelectrochemical (PEC) oxidation of water, particularly when it is heteroepitaxially grown on the facets of indium tin oxide (ITO) nanowires to form a core-shell structure with a large catalytic surface area, long optical absoption paths, and short charge transfer pathways. Simultaneous pole figure measurements of the ITO and Fe2O3 diffraction signals help to reveal the epitaxial relationship at the interface between the ITO nanowire facets and the Fe2O3 layer and provide information which can ultimately be used to guide the design and optimization of future PEC devices.