Modeling and Simulation of Tapping-mode Atomic Force Microscopy in Liquid

Application of atomic force microscopy (AFM) in liquid is necessary for imaging and manipulation of biological specimens. In this paper, we have simulated a tapping-mode AFM tilted cantilever in liquid environment near a surface by well defining the contact forces and extracting frequency response and amplitude versus separation diagrams. Contact forces have some differences in liquid in comparison to air or vacuum in magnitude or formulation. Hydrodynamic forces are also applied on the cantilever due to the motion in liquid. For modeling we have used a continuous beam model with its first mode and forward-time simulation method for simulation of its hybrid dynamics. Then we have extracted frequency response and amplitude versus diagrams in liquid. The results show good agreement with experiments. The resonance frequency in liquid is so smaller in comparison to air due to additional mass and additional damping. The results show that the effect of separation on free vibration amplitude and resonance frequency is considerable.