Attractive and repulsive tip-sample interaction regimes in tapping-mode atomic force microscopy

Attractive and repulsive tip-sample interaction regimes of a force microsco pe operated with an amplitude modulation feedback were investigated as a fu nction of tip-sample separation, free amplitude, and sample properties. In the attractive regime, a net attractive force dominates the amplitude reduc tion while in the repulsive regime the amplitude reduction is dominated by a net repulsive force. The transition between both regimes may be smooth or steplike, depending on free amplitude and sample properties. A steplike di scontinuity is always a consequence of the existence of two oscillation sta tes for the same conditions. Stiff materials and small free amplitudes give rise to steplike transitions while the use of large free amplitudes produc e smooth transitions. Simulations performed on compliant samples showed cas es where the cantilever dynamics is fully controlled by a net attractive fo rce. Phase-shift measurements provide a practical method to determine the o perating regime. Finally, we discuss the influence of those regimes in data acquisition and image interpretation. [S0163-1829(99)03231-2].