The role of shear forces in scanning force microscopy: a comparison between the jumping mode and tapping mode

Shear forces are known to be one of the main causes of sample damage in scanning force microscopy. In this work, we compare two related imaging methods: jumping mode and tapping mode. These methods have been used in the imaging of two delicate samples such as DNA on mica and single-wall carbon nanotubes on silicon oxide. The results of these experiments show that while the tapping mode does not produce any visible modification, the jumping mode introduces irreversible sample damage. In the jumping mode case, the damage is explained assuming the presence of lateral force components derived from the normal force. In the tapping mode and under our usual experimental conditions, normal forces are found to be extremely weak, and thus, lateral contributions are negligible. From the experiments, we conclude that the absence of friction forces introduced by the tip scanning is not sufficient to obtain non-intrusive images.