Information hidden behind a single peak in the C 1s spectrum of graphene on Ir(111)

The energy resolution that can be achieved in x-ray photoelectron spectroscopy experiments allows to disentangle the contribution arising from the presence of a large variety of surface atoms in non-equivalent configurations which manifests itself not only with the appearance of different spectral components, but also as unusual lineshape. In the present work, we show that the fit of the C 1s core level spectrum of graphene grown on Ir(111) realized using 200 peaks based on ab initio calculations, accounting for the non-equivalent C atoms in the (10 x 10) moire ' cell, does not improve the fit quality with respect to the use of a single component. On the contrary, the quantitative fit quality can be drastically increased by introducing a dependency of the Lorentzian width on the distance between C and Ir first-layer atoms. This result is associated to the different electronic properties, and in particular to the different density of states of the sigma and pi bands, of C atoms sitting on TOP (hills) or FCC (valleys) regions of graphene which affect the lifetimes of the core-holes generated during the photoemission process.

Automated summary

In this study, it was found that fitting the C 1s core level spectrum of graphene grown on Ir(111) using 200 peaks based on ab initio calculations, considering non-equivalent C atoms, does not improve fit quality. On the contrary, introducing a dependency of the Lorentzian width on the distance between C and Ir first-layer atoms can significantly enhance the quantitative fit quality, indicating the different electronic properties and density of states of C atoms in different regions of graphene.