Giant Bandgap Engineering in Two-Dimensional Ferroelectric alpha-In2Se3

Bandgap engineering is an efficient strategy for controlling the physicalproperties of semiconductor materials. Forflexible two-dimensional (2D) materials, strainprovides a nondestructive and adjustable method for bandgap adjustment. Here, we proposethat, in 2D materials with out-of-plane ferroelectricity, the antibonding nature of the valenceband maximum and conduction band minimum and polarized charge distribution induced byferroelectricity give rise to giant changes of the bandgap under curvature strainfield. Thishypothesis was proven by scanning tunneling microscopy/spectroscopy measurements onmonolayer alpha-In2Se3that revealed that the bandgap of alpha-In2Se3increases significantly due tobending. Both experiments and theoretical calculations indicated that the bandgap increasesmonotonically with the degree of bending of the alpha-In2Se3layer. Our work suggests thatbending is an effective method for tuning the gaps of 2D ferroelectric materials, providing anew platform for bandgap engineering under the combination of ferroelectricity and strainfield