Electrochemical Force Spectroscopy

Force spectroscopy, though originally conceived as a tool for calibrating the atomic force microscope, has become an invaluable tool for studying adhesive interactions on the nanometer scale [29 - 31]. In force spectroscopy the deflection of an atomic force microscopy (AFM) tip is measured as a sample is moved into and then out of contact with the tip. The characteristic hysteresis observed as the sample is retracted is due to adhesion between the tip and sample. The point at which the adhesion is broken and the AFM tip pulls off the sample surface is characterized by a sharp discontinuity in the force plot. The magnitude of this discontinuity provides a direct measure of the adhesion force between the tip and the sample with near-piconewton resolution.

We have utilized force spectroscopy in electrolyte solution to perform the first study of the potential-dependent adhesion between two electroactive polymer films immobilized onto electrode surfaces. A schematic of the experimental apparatus is shown in Fig. 6(A). A gold foil and gold-coated AFM tip, modified with a 35 nm-thick film of poly(vinylferrocene) (PVF) [32, 33], were grounded together and kept under potential control in a 0.10 M aqueous KCIO4 solution. Force measurements were performed while holding the potential of the tip and substrate either negative or positive of the PVF oxidation wave (E = +0.05 V vs. polished silver) corresponding to the neutral and oxidized forms of the polymer film respectively.

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