Effect of tip sharpness on the relative contributions of attractive and repulsive forces in the phase imaging of tapping mode atomic force microscopy

Abstract

The way in which the sharpness of a tip affects phase imaging in tapping mode atomic force microscopy was examined by performing experiments on polystyrene and Si surfaces with tips of different sharpness. The dominant tip–sample interaction controlling the cantilever vibration can be made repulsive with a sharp tip, and attractive with a dull tip. When the dominant interaction is either attractive or repulsive, the magnitude of the phase shift (Δφ) increases with decreasing set-point ratio rsp=Asp/A0, and the Δφ-vs.-rsp plots are nearly independent of the drive amplitude, A0. These observations indicate that the cantilever vibration is affected mainly by the amount of time the tip spends in going through the lower turning point of each oscillation and by the forces whose force derivatives change sharply during this period.