Theory of Q control in atomic force microscopy

We discuss the performance of an atomic force microscope (AFM) operated in the amplitude modulation mode under a self-excitation signal, known as quality factor control (Q control). By using the point-mass description of the AFM, we provide a complete description of Q control in tapping mode AFM. The theoretical simulations show three major results: (i) the steady-state motion of the system contains contributions from homogeneous and particular components, (ii) the active response of the microcantilever can be increased or decreased depending on the phase shift of the self-excitation with respect to the instantaneous deflexion, and (iii) in general, Q enhancement reduces the maximum force exerted for the tip on the sample surface. (C) 2003 American Institute of Physics.