Coherent X-ray scattering from soft-matter surfaces

Abstract

The main focus of the thesis is the special application of X-ray photon correlation spectroscopy (XPCS) to the study of surface dynamics. Since XPCS is still a very new technique, not all effects and measurement artifacts are commonly taken into account during data analysis. The finite coherence of the radiation and other effects yield a limited experimental resolution, which modifies the results significantly, i.e. the measured dynamic structure factor of the sample is broadened and shifted. XPCS resolution effects are studied experimentally and the implementation of a simplified convolution formalism is tested, which makes it possible to take resolution effects into consideration in a practical way. A possible slight dependence of the experimental resolution (i.e. the coherence of the X-rays) on the sample material has been observed during the XPCS experiments. To get more information on this effect, Young's double-slit experiment is combined with a surface-sensitive scattering setup to analyse the coherence properties of the specularly scattered radiation. The results indicate a sample-dependent decrease in the coherence of the scattered radiation. Furthermore, measurements on thin adsorbed alkane films on silicon substrates are discussed. The results indicate that the sample is static on the observed length scales, resulting in static speckle patterns during the measurements.