with platinum conductive coating. The typical set of atomic force microscopy (AFM) measurements included observations of the surface topography in the semicontact mode and the contact Volta potential difference (VCPD) between tip and sample measurements using the twopass amplitude-modulated scanning Kelvin probe force microscopy (SKPFM) mode. The sample was grounded in VCPD measurements and the applied voltage for the SKPFM measurements in the second pass was usually 4 V. The lift distance was 100 nm in the second pass to reduce the effect of topography on the measured VCPD. The measurements were conducted in air at ambient conditions at temperatures around 24˚C with a relative humidity of around 30%. The probe stability was controlled by measuring the VCPD on a freshly sputtered gold surface before and after the experiments. Raw AFM topographic images were analyzed in the Gwyddion 2.66 software and subjected to a plane subtraction and line fit in the fast scan direction followed by a second order polynomial fit to remove any influence from the scanner bow. The SKPFM Volta potential difference images in this study are shown as raw data as measured. For AFM measurements, Mg samples were ground up to 4000 grit and then polished to a mirror glance using polishing pastes with the final particle size of 0.25 µm. To remove remnant polishing particles, before AFM The binding energy values were charge-corrected to the carbon C 1s excitation (284.6 eV).