The corresponding RHEED patterns revealed similar information. Rings were observed after growth of 5 nm in 1*10−5 mbar O2, indicating the presence of polycrystalline phases (see Fig. 2c). The presence of polycrystalline phases was consistent with the presence of the (111) orientation measured with XRD. Other orientations were hardly visible in the XRD spectra due to the low relative intensities of these peaks. Typically, streaks, indicating a flat surface, appeared when the FWHM of the XRD (002) rocking curve was below 1° (see Fig. 2e), while spots, indicating a rougher surface, appeared above this value (Fig. 2d,f). In all cases, the sharpness of the RHEED spots or streaks increased after growth of the 100 film YSZ film (see Fig. 2g–j), indicating improved surface crystallinity. Even in the case rings were observed after growth of the 5 nm film, a well-defined pattern evolved gradually during growth of the 100 nm film (see Fig. 2g).