The controllable tuning of nanofriction on atomically thin hexagonal boron nitride with external electric field

Hexagonal boron nitride (h-BN) with good lubricity as well as excellent insulation and hydrophobicity has many potential applications in micro/nano-electromechanical devices. The nanofriction of h-BN on SiO2/Si substrate was studied under an external electric field using atomic force microscopy. The nanofriction increased after applying a bias voltage to the substrate. The increase of nanofriction under the positive bias was relatively greater than under the negative bias. The nanofriction on h-BN can be tuned controllably, dynamically, and reversibly by regulating the direction and magnitude of the external electric field. Electrostatic interaction plays the dominant role in the increase of nanofriction based on the calculation of the electrostatic force and adhesion measurements. Both the inherent potential difference and the ice-like water layer confined between the SiO2/Si substrate and h-BN layers contribute to the asymmetric influence of the electric field. The potential barrier between the tip and h-BN increased with the increase of the external electric field, resulting in a transition of stick-slip behavior from single-slip to multi-slip. The stronger the interaction potential, the greater the energy dissipation required in the friction process. These findings indicate that h-BN may be more suitable as a tunable insulating lubricant in micro/nano-electromechanical devices in charged environments.