Fig. 4: Deterministic Cu⁺ ion transport via α-In₂Se₃ polarization and localized flexoelectric field.

a Schematic illustration of the free-standing 2D ferro-ionic memristor consisting of α-In₂Se₃/CuInP₂S₆ heterostructure. b Topographical line profile of mechanical bending curvature in the axial nanogap array. Reversible conduction threshold modulation through c downward polarization and d upward polarization of the bottom α-In₂Se₃. Conductive filaments were spatially observed within e homogeneous topographical variation with α-In₂Se₃ downward polarization and f inhomogeneous topographical variation with α-In₂Se₃ up polarization, which was correlatively verified with the g cross-sectional line profile and h CAFM current image.