X-ray photoemission of carbon: Lineshape analysis and application to studies of coals

The singularity index α of the asymmetric C(1s) x-ray photoelectron spectrum (XPS) of vitreous carbon is determined to be 0.19±0.01, independent of the interlayer separation of the graphitic layers. This result is interpreted within the framework of the many-electron theory; two mechanisms are suggested: (1) the modulation of the two-dimensional graphite band structures by the random interlayer perturbation, and (2) the excitonic screening. By assigning the value α=0.19 to be characteristic of carbon atoms associated with polynuclear aromatic rings, we show that the fraction of carbon in these rings in coal can be determined by the asymmetry of the C(1s) XPS line.