Correlation of C1s chemical state intensities with the O1s intensity in the XPS analysis of anodically oxidized glass-like carbon samples

An XPS study of anodic oxidized glass-like carbon (GC) was conducted in order to investigate the inconsistency between O1s/C1s and oxygen concentration (Ocal.) calculated from the curve fitting results of the C1s spectrum. Consideration of the asymmetric peak shape of the C1s spectrum is normally done in order to obtain precise curve fitting results. However, it was found that the 2nd-carbon peak should also be taken into consideration in the curve fitting process in addition to the effect of asymmetric peak shape of carbon to obtain a consistent value of O1s/C1s. The 2nd graphitic peak is normally located +0.7–+0.8 eV away from the original C1s spectrum. The ratio of the 2nd graphitic peak area in the C1s spectrum increased as the electrical charge increased. However, the peak shapes of C1s spectra of anodic oxidized GC after heat treatment at 1500 °C in argon atmosphere were almost the same as the C1s of untreated GC. Although the origin of the 2nd graphitic peak is not well understood, it may be related to the amount of oxygen on the GC surface.