We present an exploratory study of the tribological properties between an AFM probe and a Au (111) surface under an aqueous environment while subjected to applied surface potentials.  Using a 3-electrode setup, the electrical potential and interfacial electric field on the Au(111) working electrode is controlled.  Lateral force microscopy is used to measure the friction forces between the AFM probe and the Au surface.  Normal forces are also measured as the AFM probe approaches the surface to gain insight into the interfacial properties.  When a cathodic potential is applied on the Au surface, the friction is found to rise sharply at a critical potential and level off at a relatively high value.  However, when an anodic potential is applied, the friction forces are low, even lower compared to the open circuit potential case.  These changes in friction, by a factor of approximately 35, as a function of the applied potential are found to be reversible over multiple cycles. We attribute the origin of the high friction at cathodic potentials to the formation of a highly confined ordered ice-like water layer at the Au/electrolyte interface which results in effective hydrogen bonding with the AFM probe. At anodic potentials, the ice-like water layer is disrupted resulting in the water molecules acting as boundary lubricants and providing low friction.  Such friction experiments can provide valuable insight into formation of ice-like water at charged surfaces under various conditions and can potentially impact a variety of technologies relying on molecular level friction such as MEMs.

Anomalous potential dependent friction on Au (111) measured by AFM

255th National Meeting (2018)

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