Controllable Synthesis of Two-Dimensional Ferroelectric α-In₂Se₃ via Low-Temperature Chemical Vapor Deposition

Two-dimensional ferroelectric α-In₂Se₃ possess many fascinating physical properties. However, chemical-vapor-deposited ferroelectric α-In₂Se₃ typically requires high temperatures (> 650 °C). In this work, a KCl/LiCl/NH4Cl ternary catalyst was introduced to synthesize α-In₂Se₃ at 400-460 °C, giving rise to a 200 °C reduction in growth temperature compared with traditional chemical vapor deposition (CVD) method for ferroelectric α-In₂Se₃. The surface morphology of the as-prepared materials was controlled by temperature and gas flow rate. As the growth temperature increased from 400 to 460 °C, the synthesized α-In₂Se₃ was changed from discrete hexagonal flakes to a continuous and uniform thin film, which was confirmed by the scanning electron microscope. Raman spectroscopy showed the characteristic peaks of In₂Se₃ located at 103, 180, and 195 cm⁻¹, respectively, indicating that the CVD-grown In₂Se₃ was α-phase. Furthermore, energy dispersive spectrometer and X-ray photoelectron spectroscopy indicated that the elemental composition was close to the ideal stoichiometric ratio, confirming the successful synthesis of the α-In₂Se₃. Then, the as-prepared α-In₂Se₃ was transferred onto Si/SiO₂ substrate for device fabrication. Atomic force microscope showed that the film was uniform with the thickness of approximately 63 nm. The fabricated two-terminal memristors exhibited analog resistive switching behaviors. And such memristors were used to achieve synaptic functions of long-term potentiation/long-term depression. For artificial neural network simulations based on the synaptic memristors, the recognition accuracy for hand-written digit image exceeded 90%. This work provides a feasible way to low-temperature growth 2D ferroelectric α-In₂Se₃ for applications in synaptic devices and neuromorphic computing.