Fig. 6. XPS spectra: (a) general XPS spectra of sample 5 (a) and sample 6 (b); (b) C 1s spectra of sample 5 (c) and sample 6 (d); (c) high-resolution C 1s spectrum of sample 5; (d) high-resolution C 1s spectrum of sample 6; (e) high-resolution Cu 2p spectrum of sample 6; and (f) high-resolution O 1 s spectrum of sample 6.
