Properties of clean surface of BaTiO ₃ single crystals in UHV and virtual absence of nonferroelectric surface layer

Multiple scanning probe microscopy (potential, piezoelectric-response and topological imaging) of 180° domains of atomically clean surface of BaTiO ₃ single crystals is performed in ultrahigh vacuum (UHV). The 180° domains identified by the microscopy exhibit the potential difference across the domain boundaries that is far lower than the conventional Kittel model prediction. This result is inexplicable by nonferroelectric passive surface layer or closure domain. Instead, the surface conduction indicates that an intrinsic electric screening exists and spontaneous polarization reaches almost the top surface.