Band dispersion in the deep 1s core level of graphene

Chemical bonding in molecules and solids arises from the overlap of valence electron wave functions, forming extended molecular orbitals and dispersing Bloch states, respectively. Core electrons with high binding energies, on the other hand, are localized to their respective atoms and their wave functions do not overlap significantly.
High energy resolution core level photoelectron spectroscopy data measured at the SuperESCA beamline coupled to tight-binding and all electron ab initio calculations highlight band formation with considerable dispersion (up to 60 meV) in the carbon 1s core level of graphene, a single-layer net of carbon atoms. Due to a Young’s double slit-like

interference effect, a situation arises in which only the bonding or only the anti-bonding state is observed for a given photoemission geometry.