Regensburg 2004 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 16: POSTER: Computational Physics, Complex Systems

CPP 16.21: Poster

Dienstag, 9. März 2004, 17:00–19:00, B

Single Molecule Adsorption and Desorption on Solid Surfaces — •Jörg Schuster¹, Frank Cichos², and Christian von Borczyskowski¹ — ¹Institut für Physik 121501, TU Chemnitz, 09107 Chemnitz — ²Institut für Physik 123705, TU Chemnitz, 09107 Chemnitz

Adsorption and desorption are key elements in many processes in physical chemistry such as self assembly, self organization, surface chemical reactions or even chromatography. By means of single molecule tracking in wide field fluorescence microscopy we are able to follow directly the absorption and desorption of molecules on a solid surface. Experiments on ultrathin liquid films on solid surfaces show, that the re-adsorption process of single molecules on the surface is directly influenced by the reduced film thickness. While the re-adsorption time for a molecule at a liquid solid boundary is usually expected to follow a power law statistics, we observe an exponential statistics for liquid films of a few nanometer thickness. The exponential statistics is the result of the reflection of dye molecules on the liquid vapor interface. Therefore the mean re-adsorption time gets finite compared to an infinite time in the bulk and shows further an exponential tail. The decay time of the exponential tail is directly related to the film thickness and the diffusion constant perpendicular to the surface. The measurement of the film thickness and the re-adsorption statistics thus allows for the first time the determination of the diffusion constant perpendicular to the surface in a 4 nm film. The experiments show, that this diffusion is slowed down by 4 orders of magnitude compared to the in plane diffusion. Thus diffusion in liquid films close to solid surfaces can be extremely anisotropic.