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Observation of piezoelectricity in free-standing monolayer MoS2

Abstract

Piezoelectricity allows precise and robust conversion between electricity and mechanical force, and arises from the broken inversion symmetry in the atomic structure1,2,3. Reducing the dimensionality of bulk materials has been suggested to enhance piezoelectricity4. However, when the thickness of a material approaches a single molecular layer, the large surface energy can cause piezoelectric structures to be thermodynamically unstable5. Transition-metal dichalcogenides can retain their atomic structures down to the single-layer limit without lattice reconstruction, even under ambient conditions6. Recent calculations have predicted the existence of piezoelectricity in these two-dimensional crystals due to their broken inversion symmetry7. Here, we report experimental evidence of piezoelectricity in a free-standing single layer of molybdenum disulphide (MoS2) and a measured piezoelectric coefficient of e11 = 2.9 × 10–10 C m−1. The measurement of the intrinsic piezoelectricity in such free-standing crystals is free from substrate effects such as doping and parasitic charges. We observed a finite and zero piezoelectric response in MoS2 in odd and even number of layers, respectively, in sharp contrast to bulk piezoelectric materials. This oscillation is due to the breaking and recovery of the inversion symmetry of the two-dimensional crystal. Through the angular dependence of electromechanical coupling, we determined the two-dimensional crystal orientation. The piezoelectricity discovered in this single molecular membrane promises new applications in low-power logic switches for computing and ultrasensitive biological sensors scaled down to a single atomic unit cell8,9.

Figure 1: Probing the piezoelectric property of free-standing monolayer MoS2.
Figure 2: Design and characterization of the piezoelectric monolayer MoS2 device.
Figure 3: Measuring the piezoelectric coefficient through nano-indentation and electromechanical actuation.
Figure 4: Angular dependence of the piezoelectric response in monolayer MoS2.

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Acknowledgements

This work was supported by the US Department of Energy, Basic Energy Sciences Energy Frontier Research Center (DoE-LMI-EFRC) under award DOE DE-AC02-05CH11231.

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X.Z., X.Y., H.Z. and Z.J.W. conceived the project. H.Z., M.L. and Y.Y. developed the sample design and fabricated the samples. H.Z. and Y.W. performed the measurements. H.Z., S.X. and Z.J.W. carried out the mechanical analysis. J.X., H.Z. and Z.Y. performed the optical measurements. H.Z. and Z.Y. conducted electrical analysis. All authors contributed to writing the manuscript.

Corresponding author

Correspondence to Xiang Zhang.

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The authors declare no competing financial interests.

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Zhu, H., Wang, Y., Xiao, J. et al. Observation of piezoelectricity in free-standing monolayer MoS2. Nature Nanotech 10, 151–155 (2015). https://doi.org/10.1038/nnano.2014.309

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