Ferroelectric 180° a-a nanostripe and nanoneedle domains in thin BaTiO3 films prepared with focused-ion beam

Ferroelectric 180° a-a nanostripe domain structure was observed by transmission electron microscopy in a thin (≤100 nm) film prepared from a bulk single crystal of BaTiO₃ with focused-ion beam (FIB). The domain consists of alternate sequences of narrow and wide anti-parallel domains. High-magnification images of a stable 180° nanoneedle domain, with a sharp tip penetrating into the nanostripe domains, were also obtained. Two-dimensional phase-field simulations based on time-dependent Ginzburg-Landau (TDGL) equations suggest a possibility that such a domain structure is created and stabilized by an in-plane anisotropic stress and an anisotropic mechanical boundary condition of the thin film prepared with FIB.