On each sample surface, a full set of spectra was aquired from at least two different spots, using a step size of 0.1 eV and a pass energy of 50 eV for the detailed spectra. For intense peaks and/or peaks clearly evidenced by the peak shape, the binding energy uncertainty was set around ± 0.1 eV during curve fitting. In case of weak peaks and no direct justification by the peak shape, the uncertainty was set to ± 0.2 eV. Spectral changes due to X-ray radiation exposure was checked via repeated measurements but was not observed.