Atomic-Scale Visualization of Reversible Phase Transformation in 2D Ferroelectric In₂Se₃

Phase transformation in emerging two dimensional (2D) materials is crucial for understanding and controlling the interplay between structure and electronic properties. In 2D In₂Se₃ synthesized via CVD, we observe that In₂Se₃ layers with thickness ranging from single layer to ~20 layers stabilize at the β phase with a superstructure at room temperature. At around 180 K the β phase converts to a more stable β′ phase that is distinct from previously reported phases in 2D In₂Se₃¹.The kinetics of the reversible thermally driven β-to-β′ phase transformation is investigated by temperature dependent TEM and Raman spectroscopy, corroborated with the expected minimum-energy pathways obtained from our first-principles calculations. DFT calculations further reveal in-plane ferroelectricity in the β′ phase. We will also discuss domain boundaries between β′ phase domains with different orientations. The domain boundary structures are visualized by atomically resolved STM imaging and the localized boundary states are revealed by STS.

1. Zhang, F.; Wang, Z.; Dong, J. Y.; Nie, A. M.; Xiang, J. Y.; Zhu, W. G.; Liu, Z. Y.; Tao, C. G., Atomic-Scale Observation of Reversible Thermally Driven Phase Transformation in 2D In₂Se₃. ACS Nano 2019, 13, 8004-8011.