Intermittent contact: tapping or hammering?

The tip of an atomic force microscope in intermittent contact with a sample surface was numerically simulated. The model for the tip-sample system was that of the simple harmonic oscillator for the cantilever, Maugis continuum mechanics when the tip was in contact with the sample, and either the van der Waals or capillary force if the tip was out of contact with the sample. Of particular interest were (i) the instantaneous pressures beneath the tip, (ii) the contributions from the tip-sample interaction to the damping of the cantilever, and (iii) the role of capillary forces in determining the cantilever response. We found an estimate for the pressure underneath the tip, that there are multiple sources for cantilever damping, and that the behavior due to the capillary force is complex.