Tapping-mode AFM - Force measurement capabilities on compliant surfaces

We investigate the feasibility of tapping-mode atomic force microscopy (TM-AFM) as a force measurement tool for compliant surfaces. For quantitative extraction of the tip-sample interactions, numerical modeling of the cantilever dynamics is required using a defined form for the interaction, with the results compared to experiment. Through TM force measurements on silicon, we illustrate that a forced damped harmonic oscillator model sufficiently represents the motion of the cantilever. Particularly for liquid operation, distance-dependent dissipation must be included in the model for accurate quantification of the tip-sample interactions and for successful reproduction of experimental force curves. This dissipation is not due to damping from the bulk viscous medium, but is likely frictional in origin. This investigation shows that TM force measurement in liquid is feasible and could be particularly advantageous for the measurement of intermolecular interactions from soft and easily deformed. molecular layers.