Seeing and feeling nano with intermittent-contact AFM: it’s all in the details
University of Minnesota, US
AFM, polymer, force, mechanical
The proliferation of atomic force microscopy (AFM) for routine characterization of materials attests to its power and simplicity. The exquisite sensitivity of the AFM tip/cantilever to both morphology and nanomechanical properties results in revealing, even beautiful, images obtained with minimal effort. The extension of this sensitivity to the widest range of nanomaterials – including soft, viscous and weakly adhering/cohering nanostructures – has been enabled by intermittent contact methods. Here the tip-sample interaction time is brief, minimizing deleterious shear forces. Subtleties in this brief interaction can produce a variety of results, good and bad. Careful exploration of parameter space can clarify what is being imaged and help to avoid interpretive blunders. Intermittent contact methods fall into two classes, resonant or nonresonant, depending on whether the approach-retract cycling frequency is near, or far below, any cantilever resonance, respectively. Resonant AFM, usually called “tapping mode”, is by far the most commonly employed. Recently, methods have been developed to measure forces at high sampling rates during approach-retract cycles such that high pixel-density images can be constructed in a few minutes, yet detailed distance dependent data also acquired. We focus on complex polymeric systems including blends, block copolymers, complexes with crystalline drugs or surfactants, and semicrystalline films.
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Nanotech 2007 Conference Program Abstract