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

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Abstract

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting1,2,3. 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 rectification2. 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 tip4. 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.

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Fig. 1: The working principle of conventional TENGs with a metal–insulator system and the system used in this study.
Fig. 2: IV spectra of MoS2 crystal grains and the equivalent system circuits.
Fig. 3: C-AFM current maps on the single crystal grain in Fig. 1c with varied sample bias V, simulated field distribution and FEM modelling.
Fig. 4: C-AFM current mapping of MoS2 with different contact forces and resultant current characteristics.

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Acknowledgements

This work was supported by the Canada Excellence Research Chair (CERC) program at the University of Alberta, the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT & Future Planning (NRF-2017R1A2B3009610 and NRF-2017R1A4A1015564), the Natural Science Foundation of China (Grant No. 51776126) and the Yunnan Provincial Science and Technology Department School Science and Technology Cooperation Project (grant no. 2014IB007). The authors would like to thank S. Xu, A. He and N. Zhang from Nanofab at the University of Alberta for material characterization, and thank K. Schofield, U. Rengarajan, D. Majak and D. Scott for discussions. The authors would also like to acknowledge support from the Alberta Innovates-Technology Futures (AITF) Graduate Scholarship.

Author information

J.Liu, K.J. and T.T. conceived the C-AFM study. A.G., R.McG. and J. Liu carried out the PLD synthesis of sample. F.K. and J.Liu designed and carried out the macroscale demonstration. Z.L. prepared the exfoliated MoS2 sample and conducted Raman measurements. J.Liu performed FEM simulations. J.Liu, J.Lee and T.T. co-wrote the manuscript. S.K., J.Lee, and Z.H. helped with data analysis. All authors contributed to discussions.

Correspondence to Jun Liu or Thomas Thundat.

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Supplementary Methods, Supplementary Table 1 and Supplementary Figures 1–18.

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