Anisotropic Growth of 2D Nonlayered α-Fe2O3 for Artificial Optoelectronic Synapse

Inspired by the human visual system, artificial optoelectronic synaptic devices are capable of performing perception, recognition, and memory tasks in a highly efficient and parallel way. Among the materials explored for constructing these devices, 2D transition metal oxides (TMOs) stand out due to their tunable compositions, exceptional stability, and unique optoelectronic properties. However, challenges such as complex device architectures, compromised material quality, and high energy consumption persist. Herein, the successful growth of 2D nonlayered α-Fe₂O₃ nanoflakes is reported via a molecular sieve-assisted chemical vapor deposition (CVD) method. These nanoflakes, with a minimum thickness of two unit cells, exhibit high crystallinity, n-type charge carrier transport properties, and response to 450 nm laser illumination. Notably, the charge trapping/de-trapping at oxygen vacancies (V_O) and the light-induced ionization of V_O contribute to the distinct electron concentration and current hysteresis during cyclic voltage sweeps in the thin α-Fe₂O₃ nanoflakes. This mechanism results in a significantly prolonged photocurrent decay, enabling the emulation of biological synaptic behaviors such as excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term potentiation (STP), and long-term potentiation (LTP). Combined with the scalability of the CVD process, this work highlights the potential of 2D α-Fe₂O₃ for applications in integrated artificial vision systems.