“…54 These vibrational modes also represent amorphous carbon in graphitic-like domains, typical of eumelanin materials. 18,48,55 We further confirm the SMel structure via XPS. The atomic composition of the film surface was estimated as 74.3 at% for C 1s, 18.0 at% for O 1s, 6.0 at% for N 1s, and 1.6 at% for S 2p (with C/O, C/N, O/N, and S/N atomic ratios of 4.1, 12.3, 3.0, and 0.3, respectively).…”