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(a) XPS survey scans for the black knot powder and extracted melanin. The spectra have been vertically offset for clarity. (b,c) High-resolution carbon C 1s spectra for the black knot powder and extracted melanin, respectively. The fit line and the individual bands from curve fitting have been indicated on the graph. (d) Comparison of high-resolution nitrogen N 1s spectra for both black knot powder and extracted melanin samples.
