Tunable Nonlinear Optical Properties and Ultrafast Dynamics in 2D α-In₂Se₃ via Thickness Control

This study focuses on the two-dimensional semiconductor α-In₂Se₃, which exhibits excellent nonlinear optical response and tunable bandgap characteristics. It systematically investigates the evolution of its nonlinear optical properties and ultrafast carrier dynamics with thickness variation. A series of nanosheets with controllable thicknesses were fabricated via mechanical exfoliation. X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy confirmed their high-quality 2H-phase crystal structure. Steady-state spectroscopic analysis revealed that the optical bandgap widens significantly from 1.57 eV to 2.13 eV as the thickness decreases, demonstrating a pronounced quantum confinement effect. Furthermore, micro-I-scan, transient absorption spectroscopy, and pump-probe techniques were employed to systematically study its third-order nonlinear optical response and ultrafast carrier relaxation behavior. The experiments revealed that the nonlinear absorption coefficient of the material exhibits a significant thickness dependence. This work reveals the thickness-tunable nonlinear optical properties and the defect-dominated carrier relaxation mechanism in two-dimensional In₂Se₃. It also provides crucial experimental and theoretical support for designing and developing customizable nonlinear optoelectronic devices based on this material.