Tuning the interaction forces in tapping mode atomic force microscopy

The driving frequency is a key parameter to determine the tip-sample interaction forces in tapping mode atomic force microscopy (AFM). By adjusting the driving frequency slightly above the resonance frequency stable imaging with net attractive forces can be achieved almost independently from the quality factor of the cantilever. A reduction of the driving frequency below the resonance leads to a repulsive imaging regime with minimized repulsive forces. Numerical simulations as well as experiments show the influence on the interaction forces between tip and sample. Appropriate adjustment of the excitation frequency in dynamic AFM allows one to adjust the interaction forces over the entire range from net attractive to net repulsive.