Scanning electron microscope (SEM) images were obtained using a SEM (Zeiss Ultra 40) with an acceleration voltage of 5 kV and an in-lens detector. Surface characterization was performed by atomic force microscopy (AFM, Molecular Imaging, Pico Plus) in tapping mode using SSS-NCHR probes from Nanosensors TM . For the AFM image analysis, the software Gwyddion was used. Low energy ion scattering (LEIS) measurements using an ION-TOF Qtac 100 spectrometer (IONTOF, Germany), were carried out directly on the sputter-coated PTFE electrodes, using a Ne + primary ion beam accelerated at 5 keV. For each sample, 15 spectra were recorded in the energy range 1000 -1500 eV, analyzing two spots of 2.5 × 2.5 mm. Ar + sputtering (500 eV for 25 seconds) was applied in between measurements. Charge compensation was turned on to avoid charging effects. Reference measurements of pure single metal foils were acquired and used for data evaluation. The evaluation was performed using the SurfaceLab 7.x software to fit the sample measurements with the reference measurement data and converted into oxide surface coverage (at.%). The elemental ratios were derived from the respective stoichiometry of the oxides and their relative ratios. X-ray photoelectron spectroscopy (XPS) measurements were performed using a Versa Probe III spectrometer (Physical electronics GMBH) at the ELSA cluster of the Vienna University of Technology. Monochromatic Al Kα (1486.6 eV) was used as the radiation source, with the beam diameter set to 100 µm and the beam voltage to 15 kV. The samples were mounted on a Cu tape and measurements were performed using an E-I neutralization gun to compensate for the charging effect. Survey scans of all samples were recorded at a pass energy of 140 eV and a step size of 0.125 eV. High resolution core level spectra were recorded at a pass energy of 27 eV and a step size of 0.05 eV.