Figure 3. Determining the electrostatic field above a close-packed PTCDA layer.

(a,b) experimental high-resolution AFM images of a self-assembled monolayer of PTCDA deposited on Ag(111) obtained with two different Xe tips. (c) simulated AFM image using an effective charge Q=0.0e and the effective lateral stiffness k=0.16 Nm⁻¹. (d) same as c but with Q=+0.3e and k=0.20 Nm⁻¹. (e,f) the experimental images superimposed with a deformation grid defined by comparing the corresponding sharp features between the two images in a and b. (g) electrostatic potential calculated from the deformation field (grey arrows). (h) calculated Hartree potential from DFT simulations 3.0 Å above the molecular layer.