Mechanisms of formation of phase contrast in tapping mode atomic force microscopy

Phase imaging for hard materials with atomic force microscope in tapping mo de has been analyzed. It was shown by the example of imaging diamond-like c arbon coating that the cantilever probes should have spring constant higher than 100 N/m to obtain reliable data. Experiments showed that the oscillat ing probe can operate in different regimes depending on the cantilever stif fness and set-point amplitude. The regimes are characterized by the interpl ay between the attractive and repulsive interactions between tip and sample . Repulsive condition of intermittent contact oscillation is effective for obtaining structural information of hard materials. The regime correspondin g to the mixed attractive-repulsive tip-sample interaction provides the hig hest phase contrast. However, the operation in this regime produces signifi cant artifacts in height imaging. A complex parameter is suggested to estim ate the effect of contact adhesion in the tip-sample interaction. The param eter takes into account the cantilever characteristics, its oscillation con dition and surface energy of the sample material. It can be used to define the regime of a cantilever oscillation during scanning in tapping mode.