Anisotropic diffusion of single molecules in thin liquid films.

Single molecule wide field imaging is applied to study the diffusion in ultrathin liquid films on solid surfaces. The results show a broad distribution of diffusion coefficients. This is tentatively ascribed to an anisotropy of the diffusion coefficient perpendicular to the surface and a slow exchange of molecules between regions of different diffusion coefficients. We have evidence, that these changes as well as the slow motion perpendicular to the surface are related to the molecular layering of the liquid close to the surface.