Structure determination of MnO₂ films grown on single crystal α-Al₂O₃ substrates

Abstract

Manganese oxide films have been grown by atomic layer deposition and investigated using electron diffraction and high-resolution electron microscopy (HREM). The films were deposited on the (001) surface of monocrystalline α-Al₂O₃. The films were found to consist of an ordered version of the hexagonal ε-MnO₂ (Akhtenskite) type. Using X-ray diffraction, the cell parameters were determined to be a = 2.75(2) Å and c = 4.302(5) Å. The films are epitaxial with a specific orientation relative to the Al₂O₃ substrate. The [210] and [001] axes of ε-MnO₂ are parallel to the [110] and [001] axes of α-Al₂O₃, respectively. Evidence of cation ordering was found by parallel beam electron diffraction. The ordered domains are needle shaped with widths of 2–10 nm. The unit cell of the ordered structure was found to be orthorhombic with cell dimensions a = 2.75, b = 4.76, c = 4.302 Å and space group Pmnn (No. 58).

Acknowledgement

We thank the Norwegian Research Council for financial support through project FIN (Films, Interfaces and Nanomaterials).