VersaProbe (ULVAC-PHI) spectrometer with monochromatic Al Kα radiation (h = 1486.6 eV) from an X-ray source operating at 100 µm spot size, 25 W and 15 kV. The high-resolution (HR) XPS spectra were collected with a hemispherical analyzer at the pass energy of 117.4 and the energy step size of 0.1 eV. The X-ray beam was incident at the sample surface at an angle of 45° with respect to the surface normal, and the analyzer axis was located at 45° with respect to the surface. The CasaXPS software (Ver. 2.3.19, Casa Software Ltd., 26 Burford Crescent, Wilmslow, Cheshire, UK) was used to evaluate the XPS data. Deconvolution of all HR XPS spectra were performed using a Shirley background and a