Out-of-Plane Piezoelectricity and Ferroelectricity in Layered α‑In2Se3 Nanoflakes

• Published in: Nano letters 2017-09, Vol.17 (9), p.5508-5513
• Main Authors: Zhou, Yu, Wu, Di, Zhu, Yihan, Cho, Yujin, He, Qing, Yang, Xiao, Herrera, Kevin, Chu, Zhaodong, Han, Yu, Downer, Michael C, Peng, Hailin, Lai, Keji
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.7b02198

Piezoelectric and ferroelectric properties in the two-dimensional (2D) limit are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we report the first experimental evidence of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered α-In2Se3 nanoflakes. The noncentrosymmetric R3m symmetry of the α-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Domains with opposite polarizations are visualized by piezo-response force microscopy. Single-point poling experiments suggest that the polarization is potentially switchable for α-In2Se3 nanoflakes with thicknesses down to ∼10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar α-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in electronic and photonic applications.