The high energy X-ray reflectivity technique has been applied to study the interfacial structure of protein adsorbates and protein adsorption kinetics in situ. For this purpose, the adsorption of lysozyme at the hydrophilic silica-water interface has been chosen as a model system. The structure of adsorbed lysozyme layers was probed for various aqueous solution conditions. The effect of solution pH and lysozyme concentration on the interfacial structure was measured. Monolayer formation was observed for all cases except for the highest concentration. The adsorbed protein layers consist of adsorbed lysozyme molecules with side-on or end-on orientation. By means of time-dependent X-ray reflectivity scans, the time-evolution of adsorbed proteins was monitored as well. The results of this study demonstrate the capabilities of in situ X-ray reflectivity experiments on protein adsorbates. The great advantages of this method are the broad wave vector range available and the high time resolution.

An X-ray reflectivity set-up to study buried interfaces at beamline BL9 of the electron storage ring DELTA is presented. The structure of solid-gas and solid-liquid interfaces can be investigated using X-rays with incident energies of about 27 keV. A detailed description of the set-up is given and its performance is demonstrated by a discussion of selected applications, i.e. protein adsorption at the solid-liquid interface and gas adsorption at the solid-gas interface at elevated pressures.

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X-ray reflectivity measurements from multilayer films contain information not only about the layer thickness and interface roughness but also about correlations of the interface roughness parallel and perpendicular to the interface. Due to the finite size of the receiving detector slit, it collects both purely specular and diffusely scattered radiation. Separation of the diffuse contribution to the spectra of specular reflectivity is an important task of processing the experimental data. For this purpose we suggest and implement a measurement method for specularly scattered scans integrated over several solid angles determined by the size of detector slits. Since in all cases the specular reflectivities coincide, this approach allows a separation of the diffuse and pure specular contributions. This separation is, in turn, required for obtaining information about the in-and out-of-plane structural correlation lengths. The method was used to analyze the experimental data of two multilayer systems with different interface properties: MgO/ ͓V͑1.212 nm͒ / Fe͑0.715 nm͔͒ 25 / V͑24.24 nm͒ / Pd͑5-8 nm͒ and SiO 2 / Si/ ͓CoFeB͑2.55 nm͒ / MgO͑1.8 nm͔͒ 15 .

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