Single molecule observations of desorption-mediated diffusion at the solid-liquid interface.

By directly observing molecular trajectories on a chemically heterogeneous surface, we have identified two distinct modes of diffusion involving (1) displacements within isolated surface islands (crawling mode), and (2) displacements where a molecule desorbs from an island, diffuses through the adjacent liquid phase, and readsorbs on another island (flying mode). The diffusion coefficients corresponding to these two modes differ by an order of magnitude, and both modes are also observed on chemically homogeneous surfaces. Comparison with previous results suggested that desorption-mediated diffusion is the primary transport mechanism in self-assembled monolayer formation.