When recording images with an atomic force microscope using the resonant vibrating cantilever mode, surprising strange results are often achieved. Typical artifacts are strange contours, unexpected height shifts, and sudden changes of the apparent resolution in the acquired images. Such artifacts can be related to the dynamical properties of the cantilever under the influence of the force between the tip and the sample. The damping of the cantilever oscillation can be either due to attractive interaction between the tip and the sample or due to a combination of attractive and repulsive interaction. The oscillating cantilever will be in a specific swing mode according to which type of interaction is dominating, and it is the switching between these modes that is responsible for a range of artifacts observed during image acquisition. This includes the artifact often referred to as "contrast reversal".
Kyhle, A., Sørensen, A. H., Zandbergen, J. B., & Bohr, J. (1998). Contrast artifacts in tapping tip atomic force microscopy. Applied Physics A: Materials Science & Processing, 66(S), S329-S332. https://doi.org/10.1007/s003390051156