Electrochemically Exfoliated Amorphous TaIrTe₄ Nanosheets for Bidirectional Optical Neuromorphic Devices

Amorphous van der Waals (vdW) materials introduce atomic disorder into layered systems, providing an additional degree of freedom for tailoring optoelectronic responses and photoinduced carrier dynamics beyond the crystalline regime. Yet, atomically thin amorphous van der Waals nanosheets with reproducible device-level properties remain largely unexplored. Here, we report an electrochemical exfoliation strategy that directly converts single-crystal TaIrTe₄ into amorphous nanosheets with average lateral dimensions exceeding 50 µm, thickness down to 2 nm, and high ambient stability. Structural amorphization induces a metallic-to-semiconducting transition accompanied by bandgap opening and the formation of distributed trap states, as supported by density functional theory. Field-effect transistors fabricated from these nanosheets exhibit ambipolar transport with on/off ratios above 103 and mobilities of ∼1.5 cm² V^-1 s^-1, enabling sensitive electrical readout. Upon optical stimulation, the devices generate self-powered, persistent photocurrents. Wavelength-selective excitation between 405 nm and 638 nm produces reversible conductance potentiation and depression, realizing fully optical and bidirectional synaptic plasticity with ultralow energy consumption (< 5.65 pJ per pulse). Neuromorphic network simulations incorporating the experimentally extracted dynamics achieve 92.1% on the MNIST dataset. These results demonstrate a scalable platform for producing amorphous vdW nanosheets and show that crystalline-to-amorphous conversion enables light-programmable signal processing and energy-efficient intelligent hardware.