Dynamical properties of the Q-controlled atomic force microscope

In intermittent contact mode atomic force microscopy (AFM), the quality factor (Q) of the oscillating probe is believed to account for the imaging speed and sensitivity. Q control is a method to artificially modify the quality factor of the probe. Here, we present a comprehensive study of the dynamics of the Q-controlled AFM. By comparing the analytical solutions of the force equations, we prove that the Q-controlled and non-Q-controlled systems are equivalent in the absence of surface forces. We also determine the conditions for the numerical simulation. In order to study the mechanism of contrast enhancement, we simulate the normal AFM operation including the surface forces. We found that there is a maximal probe sensitivity which cannot be exceeded even with Q control. Consistently, Q control enhances sensitivity only when imaging soft samples. Finally, we show that the phase signal of the Q-controlled system is more sensitive to the changes of the sample properties than in case of non-Q-controlled AFMs.