Height anomalies in tapping mode atomic force microscopy in air caused by adhesion

Height anomalies in tapping mode atomic force microscopy (AFM) in air are shown to be caused by adhesion. Depending on the damping of the oscillation 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 excitation of the cantilever by the driver continuously compete. As a consequence a severe modulation of the cantilever oscillation occurs, depending on the phase mismatch between the driver and the cantilever. Phase images of tapping a mode AFM show contrast which correlates with adhesion. Examples of a partially removed gold layer on mica, a Langmuir-Blodgett film and DNA show height artefacts ranging up to 10 nm.