Structure of PAA coating. (a) FT-IR reflection spectroscopy of chemically synthesized (black) and electrodeposited PAA (red). (b) Labeled chemical structures of AA, PAA, and three crosslinking possibilities in the lower panel. (c) Solid-state 13C-NMR spectra of PAA coating, with Mg:2AA salt added as a reference; marked C1-9 in one-to-one correspondence with labeled carbon in (b). (d) C1s and (e) O2p XPS spectra of PAA coating, showing overall fitting and deconvoluted components.