(a) XPS Si2p spectra of Si substrates after heating to 800 °C at different pO2. Increase of oxide thickness was observed above 1*10−4 mbar. (b) Calculated silicon oxide thicknesses for as received and annealed substrates, and after growth of YSZ. The silicon oxide thicknesses for the samples with YSZ film were calculated from the samples shown in Fig. 1a, i.e. 6 nm YSZ films grown at a total pressure of 2*10−2 mbar with a laser repetition rate of 14 Hz. The black line is a linear fit of the data..