Probing molecular ordering at a liquid-solid interface with a magnetically oscillated atomic force microscope

We have demonstrated the ability of an atomic force microscope operated in the magnetic a/c mode to determine the layered structure of liquids at interfaces with high accuracy and reproducibility. Oscillations in surface stiffness were found for octamethylcyclotetrasiloxane (OMCTS) and mesitylene close to a graphite surface and the period of oscillation allowed us to determine the molecular packing to sub-Angstrom precision. The Young’s modulus, measured at the peak stiffness of each layer, decreased exponentially with distance from the interface with a decay length of 8.8 Å for OMCTS and 6.5 Å for mesitylene.