(580a) Effect of Applied Potential on Friction between an AFM Probe and a Au(111) Surface

We present an exploratory study of the tribological properties between an AFM probe and a Au(111) surface in an aqueous environment while subjected to applied surface potentials. Using a three-electrode setup, the electrical potential and interfacial electric field on a Au(111) working electrode are controlled. Lateral force microscopy is used to measure the friction forces between the AFM probe and the Au surface. When a positive potential is applied to the Au surface, the friction is found to rise sharply at a critical potential and level off at a relatively high value. However, when a negative 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 positive potentials to the formation of a viscous interfacial water layer at the Au/electrolyte interface that results in effective hydrogen bonding with the AFM probe. At negative potentials, the interfacial water layer is disrupted, resulting in the water molecules acting as boundary lubricants and providing low friction.