Optical investigation of diffusion of single Ag markers in confined water films

Silver (Ag) clusters with sub-nanometer diameter show as a kind of marker fluorescence emission in the visible range and allow besides optical single-cluster tracking for spectroscopy of single clusters revealing a vibronic coupling of the Ag clusters to the interface. Fluorescence intensity intermittence (blinking) and laser power-dependent photobleaching are observed. The spatial diffusion of monodisperse silver nanoclusters explores ultrathin nanostructured water films on silicon dioxide (SiO2). These heterogeneous diffusion dynamics depend strongly on the thickness of wetting with ultrathin water films and the chemical composition of the SiO2 interface. Thickness-dependent structural changes of the water film have significant influence on diffusion dynamics. We present a numerical model which explains the heterogeneous diffusion across the layers of water with varying viscosity. Our results do not only demonstrate the feasibility to use Ag nano markers to explore nanostructures but also reveal the complexity of nanostructured liquids at solid interfaces.