Atomic-oxygen-assisted MBE growth of Fe3O4 (1 1 1) on α-Al2O3 (0 0 0 1)

The growth of Fe3O4 on α-Al2O3 (0 0 0 1) by atomic-oxygen-assisted molecular beam epitaxy has been studied by real time reflection high energy electron diffraction, low energy electron diffraction and X-ray photoelectron spectroscopy. The in-plane lattice parameter has been followed in situ during growth. For thickness below 1.5 nm, an iron oxide consisting on an expanded oxygen sub-lattice with an incomplete occupation of the Fe sites, is formed. This phase seems to be specific for a given thickness and independent of the growth conditions. For thickness above 1.5 nm, the long-range order of the Fe cations develops simultaneously with a decrease of the oxygen sub-lattice expansion. From this stage, Fe3O4 (1 1 1) is stabilised.