Tuning Electronic\nFriction in Structural Superlubric\nSchottky Junctions

Friction\nat sliding interfaces, even in the atomistically\nsmooth\nlimit, can proceed through many energy dissipation channels, such\nas phononic and electronic excitation. These processes are often entangled\nand difficult to distinguish, eliminate, and control, especially in\nthe presence of wear. Structural superlubricity (SSL) is a wear-free\nstate with ultralow friction that closes most of the dissipation channels,\nexcept for electronic friction, which raises a critical concern of\nhow to effectively eliminate and control such a channel. In this work,\nwe construct a Schottky junction between a microscale graphite flake\nand a doped silicon substrate in the SSL state to address the issue\nand achieve wide-range (by 6×), continuous, and reversible electronic\nfriction tuning by changing the bias voltage. No wear or oxidation\nat the sliding interfaces was observed, and the ultralow friction\ncoefficient indicated that electronic friction dominated the friction\ntuning. The mechanism of electronic friction is elucidated by perturbative\nfinite element analysis, which shows that migration of the space-charge\nregion leads to drift and diffusion of charge carriers at Schottky\njunctions, resulting in energy dissipation.