Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 44: Poster Session II (Semiconductors; Oxides and Insulators: Adsorption, Clean Surfaces, Epitaxy and Growth; Surface Chemical Reactions and Heterogeneous Catalysis; Surface or Interface Magnetism; Solid-Liquid Interfaces; Organic, Polymeric, Biomolecular Films; Particles and Clusters; Methods: Atomic and Electronic Structure; Time-resolved Spectroscopies)

O 44.73: Poster

Mittwoch, 28. März 2007, 17:00–19:30, Poster C

High-resolution in-situ x-ray study of the hydrophobic gap at the water-OTS interface — •Markus Mezger, Harald Reichert, Heiko Schröder, John Okasinski, Sebastian Schöder, and Helmut Dosch — Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, D-70569 Stuttgart

The detailed knowledge of the microscopic structure of water at hydrophobic interfaces is essential for the understanding of key interfacial phenomena in biology, drug design and technology. In order to access such hydrophobic interfaces and extract the microscopic details of the local interfacial structure of water with highest resolution we have applied x-ray reflectivity using high energy x-ray microbeams. The experiments have been carried out with the new HEMD (High Energy Micro Diffraction) setup, which has recently been installed at beamline ID15A (ESRF, Grenoble). We have studied in great detail atomically smooth silicon substrates covered by a native oxide layer which have been functionalized by a densely packed self-assembled monolayer of Octadecy-Trichloro-Silane (OTS). We have obtained high quality scattering data up to q_z = 0.8 Å⁻¹ from which structural information on a sub-nanometer length scale can be extracted. The experimental data provide clear evidence for the existence of a hydrophobic gap on the molecular scale with an integrated density deficit ρ d = 1.1 Å g cm⁻³ at the solid-water interface. In addition, measurements on the influence of gases (Ar, Xe, Kr, N₂, O₂, CO, CO₂), dissolved in the water, have been performed. No effect on the hydrophobic water gap was found. [1] M. Mezger et al., PNAS 103, 18401-18404 (2006).