Anisotropic Ion Migration and Electronic Conduction in van der Waals Ferroelectric CuInP₂S₆

Van der Waals (vdW) thio- and seleno-phosphates have recently gained considerable attention for the use as “active” dielectrics in two-dimensional/quasi-two-dimensional electronic devices. Bulk ionic conductivity these materials has been identified a key factor control of their properties. However, direct evidence specific ion species’ migration at nanoscale, particularly under electric fields, its impact on material properties elusive. Here, we report phase-selective anisotropic Cu-ion-hopping mechanism copper indium thiophosphate (CuInP2S6) through detailed scanning probe microscopy measurements. A two-step Cu-hopping path including first intralayer hopping (in-plane) second interlayer (out-of-plane) crossing vdW gap is unveiled. Evidence electrically controlled Cu further verified by nanoscale energy-dispersive X-ray spectroscopy (EDS) mapping. These findings offer new insight into manipulation layered ferroelectric/dielectric emergent device design.