PHASE-CONTRAST IN TAPPING-MODE SCANNING FORCE MICROSCOPY

The tapping-mode operation of a scanning force microscope represents a n intermediate situation between contact and noncontact regimes. Its r apid development and expansion are due to lateral force minimization a nd its ability to give phase-contrast images of heterogeneous surfaces . Here, we calculate the phase shift between the cantilever excitation and its response as a function of the sample mechanical properties, t ip-sample separation, and adhesion forces. We show that the phase shif t that gives rise to phase-contrast images is associated with tip-samp le interactions that involve energy dissipation such as adhesion energ y hysteresis and viscoelasticity. Experimental phase-shift measurement s performed on mica surfaces support the conclusions of the model.