Iron oxide thin films grown on (00l) sapphire substrate by pulsed-laser deposition

Abstract

Magnetite (Fe3O4) and wustite (FeO) are well-known oxides for their promising magnetic properties. However, growing stable FeOx thin films with controlled iron oxidation states could be of interest for further applications. In this work, we highlight the formation of different FeOx-based thin films grown by pulsed-laser deposition (PLD) from Fe or α-Fe2O3 targets onto sapphire substrates. Based on X-ray diffraction and Rutherford backscattering spectroscopy analyses, we report on films with various O/Fe ratios obtained by controlling both the substrate temperature and the oxygen pressure in the 10−5 – 10 Pa range during the PLD growth. Thus, the different crystalline phases of the Fe-O system can be grown: metallic iron, α-Fe2O3, Fe3O4, and the thermodynamically metastable phase FeO. On one hand, we demonstrate that at low pressures (< 10−4 Pa) metal-oxide composite thin films with both metallic Fe and Fe3O4 phase are epitaxially grown on the sapphire substrates even at room temperature. On the other hand, we highlight that using a α-Fe2O3 target, films composed with a mixture of wustite and spinel phases have been obtained at room temperature. The precise growth conditions leading to the formation of FeO-based films or metal-oxide composite films are discussed.