Nitrogen-containing graphene analyzed by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been commonly used to determine the nitrogen-containing functional groups of graphene. However, reported assignments of C1s shifts of nitrogen-containing functional groups are unclear. Most works discuss peak shifts of only N1s spectra and C1s shifts and the full width at half maximum (FWHM) are excluded. Thus, peak shifts and FWHMs of C1s and N1s XPS spectra of graphene with nitrogen-containing functional groups such as pyridinic, phenanthroline-like, sp2C–NH2, sp3C–NH2, pyrrolic, imine, pyridazine-like, pyrazole-like, sp2C–CN, sp3C–CN, and valley quaternary nitrogen (Q–N) on edges and sp3C–NH2, center amine, and center Q–N in the basal plane were simulated using density functional theory calculation. Main peaks of C1s spectra were shifted positively and negatively by the electron-withdrawing and electron-donating functional groups, respectively. FWHMs of the main peaks of C1s spectra were influenced by mainly electron-withdrawing functional groups on edges and most functional groups in the basal plane. Sp2C–NH2 on zigzag edges is suggested as a reference functional group to adjust the N1s spectra because influence of the functional group on the shift of main peak and the FWHM of C1s spectrum was small.