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 aic 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 Angstrom for OMCTS and 6.5 Angstrom for mesitylene. (C) 1998 American Institute of Physics.