Room-Temperature Epitaxial Growth of Zn-Doped Iron Oxide Films on c-, a-, and r-Cut Sapphire Substrates

The room-temperature growth of zinc-doped iron oxide films (Zn:FeOx) was studied on c-cut, a-cut, and r-cut sapphire substrates using the pulsed-laser deposition method. Rutherford backscattering spectrometry, X-ray diffraction analysis, pole figure measurements, and transmission electron microscopy were used to determine the nature of the oxide phases (wustite and/or spinel) present in the films, their precise texture and in-plane epitaxial relationships between films and substrates. On c-cut sapphire, both wustite and spinel phases were present with a (111) texture. The wustite phase was mainly found at the film-substrate interface, while the spinel was observed in the upper part of the film. On the a-cut and r-cut substrates, the main phase observed was the wustite, with a very small spinel contribution. The (111) and (100) wustite textures were obtained on the a-cut and r-cut substrates, respectively. The in-plane epitaxial relationships between the Zn-doped iron oxide phases and the substrates were deduced from transmission electron spectroscopy observations and pole figure measurements. The possible mechanisms of the room temperature epitaxial growth of the oxide films on r-cut and a-cut sapphire substrates are presented and discussed.