Optical Imaging and Tracking of Single Molecules in Ultrahigh Vacuum

Molecule-surface interaction is key to many physical and chemical processes at interfaces. Here, we show that the dynamics of single molecules on a surface under ultrahigh vacuum can be resolved using fluorescence imaging. By adapting oil-immersion microscopy to a thin vacuum window, we measure the adsorption, translational and rotational diffusion of single perylene molecules on a fused silica surface with high spatial and temporal resolution. Time-dependent measurements of the fluorescence signal allow us to deduce two characteristic decay time scales, which can be explained through a simplified model involving two adsorption states and five energy levels. The system presented in this work combines fluorescence imaging with essential ingredients for surface science and promises a platform for probing molecule-surface interactions in highly defined conditions.