Chemical characterization of the samples and the state of the surface was obtained with X-Ray Photoemission Spectroscopy (XPS). Core level spectra were measured using a monochromatized Al Kα (1486.6 eV) line with a hemispherical analyzer at NTNU XPS facilities and a Mg Kα (1253.6 eV) non-monochromatized light and a Specs Phoibos 150 hemispherical analyzer at UAM. Measurements were performed at room temperature and with chamber pressures below 10 -9 mbar. The calibration of the binding energy was done using C 1s and Au 4f reference peaks. A Shirley background and asymmetric singlet pseudo-Voigt functions was used to fit the line shape of core levels. The fit was optimized using a Levenberg-Marquardt algorithm and a normalized  2 reliability factor.