Interpretation of Contrast in Tapping Mode AFM and Shear Force Microscopy. A Study of Nafion

Abstract

The origin of phase contrast in tapping-mode atomic force microscopy has been investigated using two complementary scanning probe microscopy techniques, atomic force microscopy and shear force microscopy, which can be classified as a transverse dynamic force microscopy. The sample chosen for this study was Nafion, and specifically the membrane in different hydration states by virtue of its cation form. Differences in probe-sample adhesion throughout a sample, caused by an inhomogeneous distribution of surface water, were an important phase-contrast mechanism. A new variant in three-dimensional force imaging, phase-volume imaging has been a useful tool in the interpretation of phase contrast. With the use of transverse dynamic force microscopy, approach curves were obtained while the frequency spectrum around resonance was measured. This enabled the damping of the probe oscillation amplitude and the shift in its resonant frequency to be decoupled. Knowing the true oscillation amplitude of the probe, it was also possible to determine quantitatively the elastic and dissipative parts of the probe-sample interaction. Distinct regimes were found at different probe-sample separations.

Probing particle structure in waterborne pressure-sensitive adhesives with atomic force microscopy

“…Unlike what is seen in our results, the contrast in both height and phase images has been found elsewhere [33,44,49] [42], is avoided. Likewise, the attractive regime at very low A sp is avoided.…”

“…Changes in φ reflect variations in the energy dissipation, E D , of the cantilever as its tip moves laterally across a surface. φ is related mathematically to ED as [42,43]: [43]. When the tip interacts with a highly viscous region on a surface, or a viscoelastic region in which the viscous component is high, more energy will be dissipated, and therefore E D and φ will be greater.…”

Torsional Resonance Mode Imaging for High-Speed Atomic Force Microscopy

“…Antognozzi et al reported a sudden drop in lateral oscillation amplitude of a cylindrical cantilever in Transverse Dynamics AFM, which they concluded was due to compressed water layers between the tip and sample exhibiting solid-like properties [22]. James et al observed similar force curve shape contrast between hydrophilic and hydrophobic samples under different humidity conditions [23]. Also, we observed hysteresis between the approaching and retracting portions of the force curves, most likely due to capillary forces.…”

Theories of scanning probe microscopes at the atomic scale

“…For biological applications, e.g., research on DNA and single cells, as well as for electrochemical purposes, the SPM is operating under liquid conditions (see, for example, Driscoll et al, 1990;Ohnesorge and Binnig, 1993;Gü ntherodt et al, 1995;Engel and Mü ller, 2000;Aoki et al, 2001;James et al, 2001;Jandt, 2001;Philippsen et al, 2002). From an experimental point of view these conditions substantially limit the obtainable information and spatial resolution at a given surface structure.…”