Dresden 2003 – wissenschaftliches Programm

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SYSE: Simulation and experiment

SYSE 2: Poster (gemeinsam mit SYCN und CPP)

SYSE 2.27: Poster

Dienstag, 25. März 2003, 19:00–21:00, ZEU/250

Single Molecule Diffusion in the Confining Gap of a Surface Forces Apparatus — •Frank Cichos — Institut für Physik 122501, TU Chemnitz, 09107 Chemnitz

A surface forces apparatus confines a liquid between two atomically flat surfaces to a thickness of a few nanometers. Thus the influence of the surface on the structure and dynamics of the liquid film is drastically increased and effects like phase transitions or molecular layering are observed. Further the apparatus can be utilized to study the friction properties of such ultrathin liquid films as a function of film thickness. To allow detailed molecular insight into the dynamics in these liquid films we apply for the first time single molecule techniques to this type of experiments. This technique can resolve spatial heterogeneities in these films by measuring distributions of observables such as diffusion constants. We present the experimental details about a wide field fluorescence microscope coupled to a surface forces apparatus. With this tool we are able to image the Brownian motion of single molecules in the confined film. We can extract trajectories from image sequences, which deliver diffusion coefficient distributions and are thus a measure for the viscosity in the films. This is compared to data obtained on free surfaces, where we find a drastic decrease of the molecular diffusion together with a temporal trapping of molecules on adsorption sites.