title: Piezoelectricity of single-atomic-layer MoS2 for energy conversion and piezotronics.
abstract: 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.
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, USA.
authors.forename: Wenzhuo
authors.initials: W
authors.lastname: Wu
authors.affiliation: Department of Electrical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Physics, Columbia University, New York, New York 10027, USA.
authors.forename: Yilei
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, USA.
authors.forename: Long
authors.initials: L
authors.lastname: Lin
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, USA.
authors.forename: Simiao
authors.initials: S
authors.lastname: Niu
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Chenet
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Xian
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Hao
authors.affiliation: Department of Physics, Columbia University, New York, New York 10027, USA.
authors.forename: Tony F
authors.initials: TF
authors.lastname: Heinz
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.affiliation: 1] School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, USA [2] Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, 100083 Beijing, China.
authors.forename: Zhong Lin
authors.initials: ZL
authors.lastname: Wang