XP spectroscopy measurements were performed with a spectrometer from SPECS GmbH equipped with a PHOIBOS 150 1D-DLD hemispherical energy analyser. The monochromatized Al K X-ray source (E = 1486.6 eV) was operated at 14 kV and 200 W. For the narrow scans, an analyser pass energy of 20 eV was applied. The medium area mode was used as lens mode. The base pressure during the experiment in the analysis chamber was 5 • 10 -10 mbar. To account for charging effects, all spectra have been referred to C 1s at 284.8 eV. Spectra were further analysed with the program package CasaXPS Version 2.3.5PR1.0 66 .