Nanoscale Friction Characteristics of a Contact Junction with a Field-Induced Water Meniscus

The effect of the field-induced water meniscus on the friction level and oscillation was studied using an atomic force microscopy tip sliding on a highly ordered pyrolytic graphite (HOPG) surface. The results showed that the friction characteristics were significantly affected by the bias voltage, humidity, and sliding velocity. The friction level increased when the bias voltage increased beyond a threshold value (V _th). The stick–slip-type friction oscillation was observed at low velocity and periodicity, and intensity of the friction oscillation was diminished at high velocity. The velocity dependence of the friction oscillation indicated that the mechanical properties of the field-induced water meniscus were comparable to the solid state due to field-induced ordering of water molecules in the meniscus. The static friction and amplitude of the friction oscillation during scanning were inversely proportional to the scan velocity, suggesting that the hydrophobic HOPG surface turned hydrophilic due to the electrical field at the meniscus and demonstrating the possibility of manipulating the friction using an electrical bias, which can be useful for functionalizing nanoscale devices.