Mysteries about the origin of friction have remained for centuries. Especially, how friction is tuned by an electric field is still unclear. Present tuning mechanisms mainly focus on the atomic configurations and electrostatic force, yet the role of interfacial electronic properties is not fully understood. Here, we investigate a unique friction tuning effect induced by an electric current in a conductive atomic force microscopy experiment and uncover two main tuning mechanisms of friction by the fluctuation of electronic properties during sliding: (1) electric-field-induced electron density redistribution and (2) current-induced electron transfer. We put forward an electronic level friction model unraveling the relationship between the friction tuning and the electronic property fluctuation (EPF) under electric field/current, which is applicable to tribosystems ranging from conductors to semiconductors and insulators, including two-dimensional material interfaces. This model provides theoretical guidance for tribosystem design and friction control, proposing a new perspective in understanding the origin of friction.
Keywords: ab initio calculations; conductive atomic force microscopy; electronic level model; friction tuning; two-dimensional materials.