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

Frequency-sweep tapping-mode atomic force microscopy experiments were carried out on four elastomers, cis-1,4-butadiene rubber, styrene-co-butadiene rubber, natural rubber and polydimethylsiloxane to examine how well a cantilever tapping on compliant samples is described by the harmonic approximation. The amplitude curves and the phase shifts calculated for these elastomers using the harmonic approximation are in excellent agreement with the experimental values even when the tip-sample interaction is strong. When the overall tip-sample interaction is repulsive, the phase shift varies linearly with the reduced tip-sample energy dissipation because both quantities increase with increasing the tip-sample contact time. The phase shift is affected not only by the reduced tip-sample energy dissipation via the effective quality factor but also by the frequency shift. (C) 2000 Published by Elsevier Science B.V. All rights reserved.