Fig. 4.

Δf(z) spectroscopy. a, c Δf(z) curves taken over the central benzene ring of 3 (yellow) and IF (purple) adsorbed on a Cu(111) and c 2 ML NaCl. The z scale is offset by z*(3) for the respective surface to show 3 at z = 0 as reference. b, d z* maps of IF adsorbed on b Cu(111) and d 2 ML NaCl. At z = −1.6 Å on Cu(111) and z = −0.7 Å on 2 ML NaCl (black regions), the approach was aborted to avoid tip instabilities, and z^* was not reached above the bare surfaces. Scale bars, 500 pm