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

Abstract

Attractive and repulsive tip-sample interaction regimes of a force microscope operated with an amplitude modulation feedback were investigated as a function of tip-sample separation, free amplitude, and sample properties. In the attractive regime, a net attractive force dominates the amplitude reduction 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 discontinuity is always a consequence of the existence of two oscillation states for the same conditions. Stiff materials and small free amplitudes give rise to steplike transitions while the use of large free amplitudes produce smooth transitions. Simulations performed on compliant samples showed cases where the cantilever dynamics is fully controlled by a net attractive force. Phase-shift measurements provide a practical method to determine the operating regime. Finally, we discuss the influence of those regimes in data acquisition and image interpretation. ͓S0163-1829͑99͒03231-2͔

A nanomechanical interface to rapid single-molecule interactions

“…This approach is based on a framework used by Stark et al 34 for the analysis of higher harmonic vibrations. In a previous work 35 , we have tested tip-sample force waveforms generated from the torsional vibrations by comparing the measured forces with the previously developed theories 36,37 Sample preparation. A stock solution of streptavidin (Sigma Aldrich) in 1 mg ml − 1 PBS was diluted with 100 mM NaCl to a final streptavidin concentration of 0.8 µg ml − 1 .…”

Phase imaging and the lever-sample tilt angle in dynamic atomic force microscopy

“…This corresponds to the case where the tip-sample interaction is dominated by attractive forces. 10 Preliminary measurements indicate that a corresponding trend is also seen for phase shifts below 90°, i.e., for repulsive tip-sample interactions. This makes sense because the increase in lateral damping with tilt broadens the phase resonance curve (see inset in Fig.…”

“…20 Our model is capable of simulating steady-state imaging conditions in either the repulsive or attractive regimes, consistent with the results of García and San Paulo. 10 Our experiments were carried out in the attractive regime, and consistent with this, our model exhibits repulsive interactions only transiently at the outset of each simulation.…”

“…6 García and San Paulo have emphasized that there are two stable regimes of dynamic AFM, one involving purely attractive forces and one that also involves repulsive forces. 10 Cleveland et al have shown that the phase shift is related to the power dissipated in the tip-sample interaction provided the tip motion is nearly sinusoidal. 11 In all of these models, tip-sample interactions are considered as purely outof-plane phenomena (i.e., with forces and displacements along the surface normal).…”

Enhanced sensitivity and contrast with bimodal atomic force microscopy with small and ultra-small amplitudes in ambient conditions

“…2(a) coincides with the standard attractive regime (AR) of operation or attractive A 1 branch. 30 These are the only two regions available for imaging when employing sufficiently small values of A 0 since the other region, i.e., the one with a negative slope in A 1 , is not suitable for AM operation. The normalized force F ts ¼ F ts /|F AD | (dashed lines) is also plotted in Fig.…”