# Band dispersion in the deep 1 s core level of graphene 

S. Lizzit, 1 G. Zampieri, 2 L. Petaccia, 1 R. Larciprete, 3 P. 

Lacovig, 1, 4 E. D. L. Rienks, 5 A. Baraldi, 4, 6, 7 and Ph. Hofmann 5 

$^{1}$Sincrotrone Trieste, S.S. 14 Km. 163.5, 34149 Trieste, Italy 

$^{2}$Centro At´ omico Bariloche and Instituto Balseiro, Comisi´ on Nacional de Energ´ıa At´ omica, 8400-Bariloche, Argentina 

$^{3}$CNR-Institute for Complex Systems, Via Fosso del Cavaliere 100, 00133 Roma, Italy 

$^{4}$Physics Department, University of Trieste, Via Valerio 2, 34127 Trieste, Italy 

$^{5}$Institute for Storage Ring Facilities and Interdisciplinary Nanoscience Center (iNANO), University of Aarhus, 8000 Aarhus C, Denmark 

$^{6}$CENMAT, University of Trieste, Via Valerio 2, 34127 Trieste, Italy 

$^{7}$Laboratorio TASC INFM-CNR, AREA Science Park, S.S. 14 Km 163.5, 34149 Trieste, Italy 

(Dated: February 13, 2018) 

## Abstract 

Chemical bonding in molecules and solids arises from the overlap of valence electron wave func- tions, 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. Here we report the observation of band formation and considerable dispersion (up to 60 meV) in the 1 s core level of the carbon atoms forming graphene, despite the high C 1 s binding energy of ≈ 284 eV. Due to a Young’s double slit-like interference effect, a situation arises in which only the bonding or only the anti-bonding states is observed for a given photoemission geometry. 

