Field ion microscopy characterized tips in noncontact atomic force microscopy: Quantification of long-range force interactions

Abstract

Direct comparison of tip-sample forces obtained by dynamic force spectroscopy experiments with theoretical simulations is extremely difficult, since the precise tip shape and chemical identity of the apex atoms of the force sensing tip remain unknown in most experiments. Here, we present force curves measured with a tungsten tip on a Ag(111) surface obtained in a low-temperature atomic force microscope using tips that were analyzed by field ion microscopy down to atomic levels. The resulting van der Waals and electrostatic forces were found to be in quantitative agreement with analytical models, if the tip shape parameters from the field ion microscopy analysis were used. Furthermore, our analysis shows an additional long-range force interaction at tip-sample distances above 1.3 nm. We suggest that this unexpected force is related to patch charges arising from the inhomogeneous work function distribution on the surface of highly faceted sharp tips.