Supramolecular structures and dynamics of organic adsorbate layers at the solid-liquid interface

We report on atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) studies of the dynamic structure of adsorbate layers at the interface between highly oriented pyrolytic graphite and solutions of a fluorophore with two alkyl chains in phenyloctane. Layers grown above the saturation concentration showed a stable but highly corrugated surface. Below saturation an adsorbate film with a thickness of several molecular layers formed in equilibrium with the solution. The outer layers exhibit a dynamic supramolecular structure consisting of stripes with a spacing of 7 ± 1 nm. The cross-correlation analysis of several sequences of images revealed a characteristic reorganization time for the pattern of tens of seconds. By scanning at elevated forces (> 5 nN) the outer layers could be removed, thus revealing the structure of the first adsorbate layer, namely a stable stripe pattern. STM images of this first layer confirmed this stripe pattern and revealed details of the molecular arrangement at atomic resolution.