Real-time observations of ultra-thin iron oxide film growth on oxygen-deficient YSZ(001)

We use low energy electron microscopy (LEEM) and low energy electron diffraction (LEED) to characterize the initial stages of iron oxide film growth on oxygen-deficient YSZ(001). The films are grown by Fe deposition in a background of 10− 6 to 10− 5 Torr O2. The first layer grows as FeO(111) with four non-equivalent domains arising from two rotational orientations and two stacking sequences. Uniform spreading of 2-D islands is observed by initiating growth at ~ 1000 °C and raising the temperature to 1110-1145 °C during Fe deposition. The growth is anisotropic with the fast growth direction depending strongly on both the rotational and stacking domain structure, most likely the result of preferred O2 dissociation at specific island edge configurations. The FeO(111) film has a distinct LEEM-IV spectrum with three well-defined maxima and is easily distinguished from the YSZ(001) substrate. The coarsening of small islands (< 10 nm diameter) at temperatures above 1160 °C rotates the film orientation by 15° with respect to the substrate and reduces the coverage by about one half suggesting a dewetting process. After completion of the first layer, islands with a surface lattice constant corresponding to Fe3O4/γ-Fe2O3 appear with a LEEM-IV fingerprint different from both FeO(111) and the YSZ(001) substrate.