Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS₂ multilayers

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting ^1-3 . A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification ² . Here, we show that continuous direct-current (d.c.) with a maximum density of 10⁶ A m^-2 can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS₂). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (10⁵-10⁶ V m^-2) at the conductive nanoscale tip ⁴ . We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.