Piezoelectricity of single-atomic-layer MoS2 (molybdenum disulphide ) for energy conversion and piezotronics

Piezoelectricity of single-atomic-layer MoS₂ for energy conversion and piezotronics

(more at link)
http://www.nature.com/nature/journal/v514/n7523/full/nature13792.html

    Wenzhuo Wu1, n1 Lei Wang2, n1 Yilei Li3, Fan Zhang4, Long Lin1, Simiao Niu1, Daniel Chenet4, Xian Zhang4, Yufeng Hao4, Tony F. Heinz3, James Hone4, Zhong Lin Wang1, 5,
   Nature
   514,
   470–474
   (23 October 2014)

Published online
   15 October 2014

Two-dimensional semiconducting materials are the focus of much research effort thanks to their unusual and potentially useful physical properties. Wenzhou Wu and colleagues now confirm theoretical expectations that one such material — molybdenum disulphide — exhibits strong piezoelectricity in its single-layered form. Such a coupling of mechanical and electrical properties suggests possible applications in nanoscale electromechanical devices for sensing and energy harvesting.

The piezoelectric characteristics of nanowires, thin films and bulk crystals have been closely studied for potential applications in sensors, transducers, energy conversion and electronics. With their high crystallinity and ability to withstand enormous strain two-dimensional materials are of great interest as high-performance piezoelectric materials. Monolayer MoS₂ is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers. Here we report the first experimental study of the piezoelectric properties of two-dimensional MoS₂ and show that cyclic stretching and releasing of thin MoS₂ flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m−2 and a 5.08% mechanical-to-electrical energy conversion efficiency. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90°. Transport measurements show a strong piezotronic effect in single-layer MoS₂, but not in bilayer and bulk MoS₂. The coupling between piezoelectricity and semiconducting properties in two-dimensional nanomaterials may enable the development of applications in powering nanodevices, adaptive bioprobes and tunable/stretchable electronics/optoelectronics.