Effects of elastic and inelastic interactions on phase contrast images in tapping-mode scanning force microscopy

The dependence of phase contrast in tapping-mode scanning force microscopy on elastic and inelastic interactions is studied. The cantilever-tip ensemble is simulated as a driven, damped harmonic oscillator. It is found that for tip-sample elastic interactions, phase contrast is independent of the sample's elastic properties, However. phase contrast associated with elastic modulus variations are observed if viscous damping or adhesion energy hysteresis is considered during tip-sample contact. The phase shift versus tip-sample equilibrium separation tvas measured for a compliant material (polypropylene) and for a stiff sample (mica), The agreement obtained between theory and experiment supports the conclusions derived from the model, These results emphasize the relevance of energy dissipating processes at the nanometer scale to explain phase contrast imaging in tapping-mode force microscopy. (C) 1997 American Institute of Physics.