Effect of microscopic nonconservative process on noncontact atomic force microscopy

Effects of the tip-induced nonconservative processes of the tip or surface atom on the cantilever dynamics of noncontact atomic force microscopy (nc-AFM) are theoretically analyzed based on the time-averaging perturbation theory. The typical order of the magnitude of the Q value due to such nonconservative processes is estimated to be on the order of 10(4), which is comparable to the intrinsic dissipation of the cantilever free oscillation. The additional frequency shift due to the hysteresis loop of the force curve is estimated to be on the order of 10 Hz. This part of the frequency shift sets in like a step function when the tip turning point approaches the surface within a certain threshold height. This feature explains the experimental observation of the discontinuous frequency shift at chemical reactive sites.