Identification of Ni2 C electronic states in graphene-Ni(111) growth through resonant and dichroic angle-resolved photoemission at the C K -edge

The graphene-Ni(111) (GrNi) growth via chemical vapor deposition has been explored by resonant, angle-resolved, and dichroic photoemission spectroscopy (soft x-ray Res-ARPES) in order to identify the possible contributions to the electronic structure deriving from different phases that can coexist in this complex system. We provide evidences of electronic states so far unexplored at the Γ point of GrNi, appearing at the C K-edge resonance. These states show both circular dichroism (CD) and k dependence, suggesting a long-range orbital ordering, as well as a coherent matching with the underlying lattice. Through a comparison of core-level photoemission, valence band resonances, and constant initial-state spectroscopy, we demonstrate that these states are actually induced by a low residual component of nickel carbide (Ni2C). These results also show that caution must be exercised while interpreting x-ray magnetic circular dichroism collected on C K-edge with Auger partial yield method, due to the presence of CD in photoelectron spectra unrelated to magnetic effects.