Measuring the short-range force field above a single molecule with atomic resolution

We present a method that enables atomic-resolution measurements of the short-range force field above a single organic admolecule using noncontact atomic force microscopy. We have extended the standard force-mapping technique to be able to measure at close tip–molecule distances, in regions that cannot be accessed by normal constant-height or constant-frequency-shift imaging. Our technique can be used to study the interaction between a well-defined scanning probe tip and an admolecule on the atomic scale and yields atomic resolution of both molecule and substrate. Furthermore, it enables the measurement of constant-frequency-shift topographies of molecules with nonplanar adsorption geometries.