Revealing Strong Flexoelectricity and Optoelectronic Coupling in 2D Ferroelectric CuInP<sub>2</sub>S<sub>6</sub> Via Large Strain Gradient
Xiaokeng Wu, Lu Qi, Muhammad Ahsan Iqbal, Sichao Dai, Xiaoliang Weng, Kewen Wu, Chenxu Kang, Zelong Li, Duo Zhao, Wei Tang, Fuwei Zhuge, Tianyou Zhai, Shuangchen Ruan, Y. J. Zeng
Abstract
The interplay between flexoelectric and optoelectronic characteristics provides a paradigm for studying emerging phenomena in various 2D materials. However, an effective way to induce a large and tunable strain gradient in 2D devices remains to be exploited. Herein, we propose a strategy to induce large flexoelectric effect in 2D ferroelectric CuInP 2 S 6 by constructing a 1D-2D mixed-dimensional heterostructure. The strong flexoelectric effect is induced by enormous strain gradient up to 4.2 × 10 6 m –1 resulting from the underlying ZnO nanowires, which is further confirmed by the asymmetric coercive field and the red-shift in the absorption edge. The induced flexoelectric polarization efficiently boosts the self-powered photodetection performance. In addition, the improved photoresponse has a good correlation with the induced strain gradient, showing a consistent size-dependent flexoelectric effect. The mechanism of flexoelectric and optoelectronic coupling is proposed based on the Landau–Ginzburg-Devonshire double-well model, supported by density functional theory (DFT) calculations. This work provides a brand-new method to induce a strong flexoelectric effect in 2D materials, which is not restricted to crystal symmetry and thus offers unprecedented opportunities for state-of-the-art 2D devices.