Multidirection Piezoelectricity in Mono- and Multilayered Hexagonal α-In2Se3

Fei Xue, Junwei Zhang, Weijin Hu, Wei Ting Hsu, Ali Han, Siu Fung Leung, Jing Kai Huang, Yi Wan, Shuhai Liu, Junli Zhang, Jr Hau He, Wen Hao Chang, Zhong Lin Wang, Xixiang Zhang*, Lain Jong Li

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

218 Scopus citations


Piezoelectric materials have been widely used for sensors, actuators, electronics, and energy conversion. Two-dimensional (2D) ultrathin semiconductors, such as monolayer h-BN and MoS2 with their atom-level geometry, are currently emerging as new and attractive members of the piezoelectric family. However, their piezoelectric polarization is commonly limited to the in-plane direction of odd-number ultrathin layers, largely restricting their application in integrated nanoelectromechanical systems. Recently, theoretical calculations have predicted the existence of out-of-plane and in-plane piezoelectricity in monolayer α-In2Se3. Here, we experimentally report the coexistence of out-of-plane and in-plane piezoelectricity in monolayer to bulk α-In2Se3, attributed to their noncentrosymmetry originating from the hexagonal stacking. Specifically, the corresponding d33 piezoelectric coefficient of α-In2Se3 increases from 0.34 pm/V (monolayer) to 5.6 pm/V (bulk) without any odd-even effect. In addition, we also demonstrate a type of α-In2Se3-based flexible piezoelectric nanogenerator as an energy-harvesting cell and electronic skin. The out-of-plane and in-plane piezoelectricity in α-In2Se3 flakes offers an opportunity to enable both directional and nondirectional piezoelectric devices to be applicable for self-powered systems and adaptive and strain-tunable electronics/optoelectronics.

Original languageEnglish
Pages (from-to)4976-4983
Number of pages8
JournalACS Nano
Issue number5
StatePublished - 22 May 2018


  • monolayer and bulk
  • multidirection
  • nanogenerator and electronic skin
  • piezoelectricity
  • van der Waals crystal


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