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CPP: Chemische Physik und Polymerphysik

CPP 11: Dünne Filme, Monolagen und Oberfl
ächen

CPP 11.6: Vortrag

Mittwoch, 13. März 2002, 15:10–15:30, H38

Single Molecules Probing the Diffusion in Ultrathin Liquid Films — •Jörg Schuster, Frank Cichos, and Christian von Borczyskowski — Institut für Physik 122501, TU Chemnitz, D-09107 Chemnitz

We present measurements on the diffusion of single dye molecules in ultrathin liquid films prepared on a quartz or oxidized silicon wafer surface. By imaging single molecule motion onto a CCD camera we are able to record single molecule trajectories with a time resolution down to 10 ms. We analyze these trajectories by two different methods - the commonly used analysis of the mean square displacement (MSD) and a method which measures the single molecule spot size in each trajectory image.

We find that the diffusion in these liquid films is restricted to almost discrete diffusion constant values which are related to the layering structure of the liquid. The diffusion is slow close to the surface and the diffusion constant linearly increases with the distance from the surface. We observe that the motion of single molecules is confined to single 2-dimensional liquid layers on a timescale of several 10 to 100 ms. This suggests that the liquid behaves liquid-like parallel to the surface and almost rubbery perpendicular to it. With the help of a new analysis technique we are for the first time able to follow changes in the diffusion constant over a single molecule trajectory and can thus directly visualize the exchange between different molecular layers.