Effect of K doping on the quasifreestanding graphene formed on Au/Ni(111): Density-functional calculations

We investigated the atomic and electronic structure of the K-adsorbed graphene/Au/Ni(111) surface by using density-functional calculations. The role of the K adsorbates is verified as a simple donor: the adsorption of K induces a rigid shift of the graphene $\pi$ bands with preserving the quasifreestanding Dirac-cone shape. The $\pi$ character of the Dirac-cone bands, however, undergoes some weakening due to the hybridization with Ni $d$ bands, especially in the energy range of 0.5–0.8 eV (0.1–0.3 eV) below the Fermi level for the majority (minority) spin band structure. This weakening of the $\pi$ character could possibly account for the reduced photoemission intensity of the Dirac cone, which was experimentally reported as a band gap of 0.6 eV.

Figure 1

Atomic structure of the K-adsorbed graphene/Au/Ni(111) surface at 0.25 ML. Dashed lines represent the used ($4\times 4$) supercell.

Figure 2

Atomic structures of the K-adsorbed graphene/Au/Ni(111) surface at high coverages.

Figure 3

Band structures of the K-doped graphene/Au/Ni(111) surfaces: (a) clean, (b) 0.25 ML, and (c) 1 ML. In (a), the ($4\times 4$) surface Brillouin zone is shown, and the bands of freestanding graphene are given by solid lines as a reference. Dark (red) filled circles, gray (yellow) filled circles, open circles, and open squares represent C-, Au-, Ni-, and K-derived states, respectively, and their size is proportional to the amount of charge localized in the corresponding atoms.