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-Fe ₂O₃ appear with a LEEM-IV fingerprint different from both FeO(111) and the YSZ(001) substrate.