Deformation of polystyrene nanoparticles under different AFM tapping loads

Deformation induced by contact force from the tip is the major measurement uncertainty using atomic force microscope (AFM) for the apex height of nanoparticles. Additionally, the contact force by the AFM tip is difficult and not reliable in traditional tapping and contact modes. In this work, the contact forces applied by the AFM were varied using a peak-force tapping method, which is unique technique to perform force-controlled scanning, to characterize the deformation of nanoparticles. The obtained measurement results were compared with a theoretical model developed for predicting the deformation between PS nanoparticles and tip/substrate. It was found that the deformation occurred at low force as 0.5 nN for polystyrene nanoparticles on mica substrate. The deformation was fully plastic. In addition, the deformation has a linear relationship with contact force, which is consistent with contact mechanics model.