Unusually stable ferroelectric 180° a-a nanostripe and nanoneedle domains in thin films prepared from a bulk single crystal of BaTiO3 with FIB: TEM observations and phase-field simulations

Unusually stable ferroelectric 180deg a-a nanostripe domain structure in a thin (les100 nm) film prepared from a bulk single crystal of BaTiO₃ with focused-ion beam (FIB) was observed by transmission electron microscopy (TEM). The domain consists of alternate sequences of narrow and wide anti-parallel domains. High-magnification images of a stable 180deg nanoneedle domain, with a sharp tip penetrating into the nanostripe domains, were also obtained. Two-dimensional phase-field simulations based on TDGL equations suggest that such a domain structure is stabilized by an in-plane anisotropic stress and an anisotropic mechanical boundary condition of the thin film prepared with FIB.