2016 年 58 巻 2 号 p. 96-102
Despite extensive studies on crystal structure of thin film BiFeO3 (BFO) thin film, it remains debated primarily due to its structural complexity as well as stress effect from underlying substrates. We have examined comprehensive crystal structure analysis for BFO thin layer (30 nm) grown on SrTiO3 (STO) substrate using cross-sectional transmission electron microscopy technique along three different zone axes. Nano-beam electron diffraction (NBED) patterns combined with structure factor (SF) calculations and high-resolution transmission electron microscopy images unambiguously reveal that BFO thin layer grows with rhombohedral structure that is identical to its bulk form. No evidence of monoclinic and/or tetragonal distortion is found. The rhombohedral BFO thin layer is found to grow onto STO by maintaining an epitaxial relationship in a manner that can minimize lattice mismatch at BFO/STO interface. Our current work clearly demonstrates that multiple-zone axes NBED combined with SF calculation is highly effective for precise crystal structure analysis of thin film BFO.