|Title:||X-ray intensity correlation spectroscopy from fluid surfaces|
|Other Titles:||theory and experiment|
|Abstract:||X-ray intensity correlation spectroscopy (XICS) is a coherent X-ray scattering technique, which enables the investigation of dynamic properties of matter by analyzing the temporal correlations among intensities scattered by the studied material. This novel technique has been intensively applied in the last decade in order to examine the temporal and lateral correlation properties of fluid surfaces. Although, intensity correlation experiments are qualitatively well understood, present theoretical interpretations fail to explain XICS data from some well known fluid surfaces, such as water and glycerol. We believe that the discrepancies, between the theoretical predictions for the intensity correlation function and the experimental results, are due to some idealized assumptions with regard to the coherence of the X-ray beam, as well as the instrumental resolution. This thesis is mainly concerned with the derivation of the intensity correlation function for surface sensitive X-ray intensity correlation experiments including the effects of partial coherence and instrumental resolution. In order to derive the intensity correlation function the theoretical approach is based in this work on the statistical properties of the fluid surface and the scattered electric field. A scalar wave equation for the electric X-ray field is derived to determine the field expressions from time fluctuating and inhomogeneous media. The therefrom obtained field formulas are used to derive systematically field correlation functions and intensity correlation functions. The accuracy of the field expressions and the deduced correlation functions are restricted to the first Born approximation. Within this accuracy, we have provided intensity correlation functions that are applicable to charge scattering from fluid surfaces under the conditions of arbitrary spatial coherence and instrumental resolution. In addition, far and near field scattering conditions, i.e. Fraunhofer and Fresnel conditions, are rigorously incorporated in the theoretical intensity correlation functions. The experimental part in thesis is dedicated to the analysis of XICS measurements from hexane and water surfaces. The data analysis is based in parts on the intensity correlation function which is derived in the theoretical part of this work. We have convincingly illustrated that the conventionally used intensity correlation function is generally not suitable to analyze XICS experiments. In contrast to the conventionally used intensity correlation formula, we have obtained very good agreement between our theoretical intensity correlation function and the experimental results from hexane. This work may therefore be of general interest to scientists who make use of XICS or other scattering techniques using partially coherent X-ray beams.|
Coherent x-ray scattering
|Appears in Collections:||Experimentelle Physik I|
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