I am not expert on KPFM, but possibly 'cause with Pt/Ir tips , one can reach ~1 nm resolution: "Enevoldsen et al. observed a 20 meV potential variation between the row and trough of a TiO2(110) surface, as seen in Fig. 18 [16]. AM mode KPFM with a 70 kHz Pt/Ir coated cantilever was used to achieve atomic resolution. The row spacing on the TiO2 (110) was measured as ∼1 nm."

http://kummelgroup.ucsd.edu/pubs/paper/110.pdf

1) Melitz et al 2011; Kelvin probe force microscopy and its application; Surface Science Reports 66 (2011) 1–27.

2) G.H. Enevoldsen, T. Glatzel, M.C. Christensen, J.V. Lauritsen, F. Besenbacher, Phys. Rev. Lett. 100 (2008) 236104.

Good luck!