Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 35: Single molecules I

CPP 35.4: Talk

Wednesday, March 9, 2005, 10:30–10:45, TU C243

Molecular motion in thin liquid films near surface steps — •Arne Schob and Frank Cichos — Photonics and optical materials, Institute of physics, TU Chemnitz, 09107 Chemnitz

Solid surfaces strongly influence structure and dynamics of liquids close to them. These solid-liquid-interactions lead for example to a layering of the liquid near the interface which results in anisotropic diffusion of molecules. This anistropy is difficult to uncover in common ensemble experiments, while single molecule tracking experiments however are able to reveal such effects. While typically single molecule diffusion is recorded viewing normal to the surface, we present for the first time experiments on single molecule diffusion observing along the surface with the help of a surface step. Our experiments on rhodamine doped thin liquid films on a cleaved mica surface reveal an enhanced probability to find single molecules close to the surface step. Further the single molecule diffusion is found to be strongly anisotropic at the step with a diffusion constant being three times larger along the step than perpendicular to it. The anisotropic diffusion is a clear sign that the molecules are trapped in a potential near the surface. From our experimental data we estimate this potential to be deeper than 60 meV.