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 10(6) 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.