Height anomalies in tapping mode atomic force microscopy (AFM) in air
are shown to be caused by adhesion. Depending on the damping of the os
cillation the height of a sticking surface is reduced compared to less
sticking surfaces. It is shown that the height artefacts result from
a modulation of oscillatory movement of the cantilever. Damping and ex
citation of the cantilever by the driver continuously compete. As a co
nsequence a severe modulation of the cantilever oscillation occurs, de
pending on the phase mismatch between the driver and the cantilever. P
hase images of tapping a mode AFM show contrast which correlates with
adhesion. Examples of a partially removed gold layer on mica, a Langmu
ir-Blodgett film and DNA show height artefacts ranging up to 10 nm.