Interpretation of contrast in tapping mode AFM and shear force microscopy.A study of nafion

The origin of phase contrast in tapping-mode atomic force microscopy has be en investigated using two complementary scanning probe microscopy technique s, atomic force microscopy and shear force microscopy, which can be classif ied as a transverse dynamic force microscopy. The sample chosen for this st udy was Nafion, and specifically the membrane in different hydration states by virtue of its cation form. Differences in probe-sample adhesion through out a sample, caused by an inhomogeneous distribution of surface water, wer e an important phase-contrast mechanism. A new variant in three-dimensional force imaging, phase-volume imaging has been a useful tool in the interpre tation of phase contrast. With the use of transverse dynamic force microsco py, approach curves were obtained while the frequency spectrum around reson ance was measured. This enabled the damping of the probe oscillation amplit ude and the shift in its resonant frequency to be decoupled. Knowing the tr ue oscillation amplitude of the probe, it was also possible to determine qu antitatively the elastic and dissipative parts of the probe-sample interact ion. Distinct regimes were found at different probe-sample separations.