Switchable Friction across Insulator–Metal Transition in VO₂

Significant friction turnover across the insulator to metal phase transition of VO₂ microcrystals as measured by friction force microscopy (FFM) and nanoscratch experiments is reported. Insulator to metal transition in chemical vapor deposition-grown VO₂ platelet is confirmed by in situ Raman investigations and electrical resistance measurements that show more than four orders of magnitude change in electrical resistance across transition temperature. The coefficient of friction (COF) for the high-temperature metallic phase, that is about two times higher than that of room-temperature insulating phase, is demonstrated. To avoid temperature effects on friction, the friction of coexisting insulating and metallic phases at a constant temperature of ≈69 °C is measured. Additionally, the results also show that this twofold increase in COF is fully reversible when the phase transition is triggered by a heating–cooling cycle and can potentially be used as tuneable friction-based gripping systems.