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

Abstract

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.

Understanding the intrinsic water wettability of graphite

“…Foremost, the Doniach-Sunjic asymmetry parameter (α) was similar for both ZYA and PG: 0.07 and 0.08, respectively, which is similar to previously reported values for HOPG and natural graphite. 358,[365][366][367] Considering that previous work intentionally irradiated the HOPG surface with ions to induce asymmetry of the C1 peak (284.3 eV), 360 the results of this study conclude that intrinsic defects of high quality samples do not manifest with significant asymmetry; therefore, quantifying intrinsic defects by α is not possible.…”

The effect of downstream plasma treatments on graphene surfaces

“…The delocalization is of great importance for the electronic properties and strongly relates to the electrical conductivity of graphene. The peak has an asymmetry factor = 0.07, smaller than that of graphite which has been reported as 0.15 [38]. Highly disordered graphitic structures, such as pyrolytic carbon, for example have higher asymmetry factors ( =0.19 [38]).…”

“…Slight differential charging is created on disordered sheets (no differential charging on graphite is observed as it is conductive), thus disorder and defects create excitonic states and excitonic screening [38]. The smaller singularity asymmetry factor indicates a graphitic net with higher delocalization of electrons.…”

“…The singularity asymmetry factor could be an indication of thickness (layers) in a clean graphitic net as it increases with increasing number of layers; 0.07 for monolayer, 0.12 for a few layers and 0.14 [38] for graphite. In Figure 4c Raman spectra before and after the annealing are shown.…”

“…1b) has a well pronounced asymmetry on the higher binding energy side typical of polyaromatic carbons [38][39][40][41]. This implies graphitic structure and conducting films as opposed to non-conducting aliphatic or sp 3 based carbon materials which exhibit symmetric spectra [38]. The spectrum has been fitted accordingly with several peaks that describe different chemical carbon functionalities by taking into account the combined instrumental resolution of the XPS system.…”