Herein, we provide a complete description of the intercalation of oxygen at the strongly interacting graphene on Ni(111), highlighting the role of rotated graphene domains in triggering the intercalation. High-resolution core-level photoelectron spectroscopy provided a full characterization of the interface at each stage of the intercalation, revealing the formation of an oxide layer between graphene and the metal substrate. Angle-resolved photoemission spectroscopy measurements showed that the oxide decouples efficiently graphene from the substrate, restoring the Dirac cone and providing a slight n-doping. Photoelectron diffraction experiments revealed that graphene domains not aligned with the Ni substrate are the first to be intercalated with oxygen and are preferential regions under which the oxygen is retained during the deintercalation.

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The electronic structure of ZrSe2 was studied by high resolution angular resolved photoemission spectroscopy (ARPES) and by density functional theory (DFT). ARPES with distinct horizontal (P) and vertical (S)-polarized synchrotron radiation was performed on the sample kept at room temperature and 20 K to unravel the electronic structure especially at the Fermi energy (EF). The DFT calculations including spin-orbit coupling using the modified Becke-Johnson potential reveal the presence of three occupied valence bands at the Γ(A)-point and show that the minimum indirect bandgap is between the Γ- and L-points of the Brillouin zone (BZ) similar to the experimental results. While the DFT calculations give only a single conduction band at the L and M-points of the BZ, the ARPES data (20 K) show two bands with opposite dispersion at EF. The observation of two bands close to EF was already reported in the charge density wave phase of TiSe2. The underlying mechanism of our observations is possibly a folding of the valence band states of ZrSe2 from the Γ(A) to M(L)-point accompanied by an energy shift due to internal dipolar momenta. Furthermore, at the A-point, the experimental dispersion of the lower occupied valence band and the size of its energy separation to the middle occupied band are not in line with the DFT calculations. Possible reasons of such discrepancies are discussed.

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