Secondly, the SiO2 thicknesses after growth of YSZ were calculated for the samples grown in a total pressure of 2*10−2 mbar. In order to perform the calculation, a homogeneous Si-SiO2-YSZ stacking sequence was assumed. After fitting, only the parts of the spectra indicating SiO2 and Si were taken into account by subtracting the silicide, silicate and SiOx contributions, which were especially present in the low pO2 samples. A significant increase in silicon oxide thickness with increasing pO2 was calculated, as shown in Fig. 4b. Although the samples were cooled down in vacuum directly after growth, the oxide thicknesses were much larger compared to the bare substrates annealed at the same pO2. In the case of growth at pO2 = 5*10−3 mbar, where an optimum crystalline quality was observed with XRD, a silicon oxide thickness of 2.6 nm was determined.