Harmonic responses of a cantilever interacting with elastomers in tapping mode atomic force microscopy

Frequency-sweep tapping-mode atomic force microscopy experiments were carri ed out on four elastomers, cis-1,4-butadiene rubber, styrene-co-butadiene r ubber, natural rubber and polydimethylsiloxane to examine how well a cantil ever tapping on compliant samples is described by the harmonic approximatio n. The amplitude curves and the phase shifts calculated for these elastomer s using the harmonic approximation are in excellent agreement with the expe rimental values even when the tip-sample interaction is strong. When the ov erall tip-sample interaction is repulsive, the phase shift varies linearly with the reduced tip-sample energy dissipation because both quantities incr ease with increasing the tip-sample contact time. The phase shift is affect ed not only by the reduced tip-sample energy dissipation via the effective quality factor but also by the frequency shift. (C) 2000 Published by Elsev ier Science B.V. All rights reserved.