How electronic charge is distributed over a molecule determines to a large extent its chemical properties. Here, we demonstrate how the electrostatic force field, originating from the inhomogeneous charge distribution in a molecule, can be measured with submolecular resolution. We exploit the fact that distortions typically observed in high-resolution atomic force microscopy images are for a significant part caused by the electrostatic force acting between charges of the tip and the molecule of interest. By finding a geometrical transformation between two high-resolution AFM images acquired with two different tips, the electrostatic force field or potential over individual molecules and self-assemblies thereof can be reconstructed with submolecular resolution.
Description
Determining the electrostatic field above an individual
molecule. (a) High-pass filtered constant-height AFM images of a TOAT
molecule on Cu(111) acquired with a Xe tip. Crosses indicate characteristic
vertices. (b) Same as a but measured with a CO tip. (c) electrostatic force
field calculated from DFT. (d) experimentally determined electrostatic force
field obtained after subtraction of the van der Waals component from the
deformation field obtained from the images shown in a and b. (e) calculated
Hartree potential; (f) electrostatic potential calculated from the
experimental deformation field shown in (d).
