Anisotropic Charge Diffusion in Polar-Layered Oxides for Ultralong Charge Retention.

Persistent surface charge retention in dielectric oxides is critical for a wide range of electronic and energy applications, including charge-trapping memory devices, triboelectric generators, and supercapacitors. Since charge retention is intrinsically governed by charge diffusion, understanding and controlling the underlying diffusion mechanisms in charge-storing materials remain significant challenges. Here, ultralong charge retention in epitaxially grown LaAlO3 (LAO) thin films is reported, enabled by anisotropic charge diffusion. The surface accumulation of oxygen vacancies, driven by the internal polar field, effectively suppresses out-of-plane electron hopping, allowing ≈90.9% of the initially injected charges to remain on the LAO surface after 180 h, with stable retention persisting for weeks or longer. Time-resolved Kelvin probe force microscopy and finite-difference simulations consistently reveal that this retention enhancement arises from diffusion anisotropy induced by surface-localized defect states in LAO, rather than by isotropic ionic migration. These results provide an effective strategy for designing high-performance charge storage materials based on polar-layered oxides, paving the way for durable surface charge-based electronic and energy devices.