Impact of electrostatic forces in contact-mode scanning force microscopy

In this contribution we address the question to what extent surface charges affect contact-mode scanning force microscopy measurements. We therefore designed samples where we could generate localized electric-field distributions near the surface as and when required. We performed a series of experiments where we varied the load of the tip, the stiffness of the cantilever and the hardness of the sample surface. It turned out that only for soft cantilevers could an electrostatic interaction between tip and surface charges be detected, irrespective of the surface properties, i.e., basically regardless its hardness. We explain these results through a model based on the alteration of the tip-sample potential by the additional electric field between charged tip and surface charges.