Fig. 2. Characterization of the in situ formed NaF-rich interphase on the surface of Na metal. (a) High-resolution XPS spectra of Na 1s, F 1s, and C 1s, (b) atomic percentages and (c) relative elemental intensities at different depths, (d) optical photograph, SEM image, and elemental maps (Na and F), (e) retracted force–distance curve, and (f) AFM topography image with a 3D view.
