Correct height measurements by Kelvin probe force microscopy: Poly(3-dodecylthiophene) on highly oriented pyrolytic graphite

For correct height measurements by noncontact atomic force microscopy a precise knowledge of the interacting tip-surface forces is required. Preceding studies have shown the necessity to compensate the electrostatic forces between tip and surface with Kelvin probe force microscopy to obtain realistic topographic height values for samples out of multiple components. In the present study we demonstrate, however, that a simple Kelvin compensation can be insufficient using the example of poly(3-dodecylthiophene) on highly oriented pyrolytic graphite (HOPG). The measured polymer height on HOPG can be strongly falsified due to the uncompensated long-range (LR) van der Waals (vdW) forces. We conclude that in order to minimize the perturbing influence of these LR-vdW forces on the height measurement, imaging should be performed in the regime where the fast-decaying short-range forces are dominant.