Imaging cobalt nanoparticles by amplitude modulation atomic force microscopy: comparison between low and high amplitude solutions.

In many situations of interest amplitude modulation AFM is characterized by the coexistence of two solutions with different physical properties. Here, we compare the performance of those solutions in the imaging of cobalt nanoparticles. We show that imaging with the high amplitude solution implies an irreversible deformation of the nanoparticles while repeated imaging with the low solution does not produce noticeable changes in the nanoparticles. Theoretical simulations show that the maximum tip-surface force in the high amplitude solution is about 14nN while in the low amplitude solution is about -4nN. We attribute the differences in the high and low amplitude images to the differences in the exerted forces on the sample.