Epitaxial BaTiO3 thin films grown in unit-cell layer-by-layer mode by laser molecular beam epitaxy

Two-dimensional (2-D) layer-by-layer epitaxial growth of BaTiO3 (001) film on the atomically flat SrTiO3 (100) substrate was investigated in an atomic scale by in situ analyses of reflection high energy electron diffraction (RHEED) and coaxial impact collision ion scattering spectroscopy (CAICISS) as well as ex situ atomic force microscopy (AFM). Under the optimized growth condition in laser molecular beam epitaxy (laser MBE), we could observe the intensity oscillations at the specular beam spot in RHEED pattern during the deposition. One period of the intensity oscillations corresponded to the growth of a 0.4 nm thick film, which indicates that the growth unit layer in the 2-D growth mode is one molecular layer of [BaO/TiO2]. Through the AFM observation of the surface morphology of the films, the growth of which was halted at a RHEED intensity maximum or minimum, we clarified that the RHEED intensity oscillations was caused by the 2-D nucleation and growth of one molecular layer. From in situ CAICISS measurements, it was found that the terminating plane of BaTiO3 (001) films (80 nm thick) grown by the present conditions was the BaO atomic plane.