Force-distance curves on lubricant films: An approach to the characterization of the shape of the AFM tip

Abstract

Force-distance curves have been acquired with an atomic force microscope on perfluorpolyether films. It is shown that curves acquired on films of different thickness, at different rates and with different dwell times can be overlapped by rescaling the time or distance axis. When the time or distance axis is rescaled, the force depends only on the surface tension of perfluorpolyether and on geometrical properties of the tip (aperture and perimeter of the tip at a given distance from the apex). Hence, curves acquired with the same tip overlap. By comparing curves acquired at different rates the dynamics of tip-wetting can be investigated. Furthermore, rescaled force-distance curves have been matched with the perimeter of cross sections of the tip, i.e. with the perimeter of the three-phase contact line. Such measurements pave the way for a non-destructive investigation of the tip shape.

Keywords: AFM tip shape; Atomic force microscopy; Force-distance curves; Lubricant films; Surface tension.