Hybridization of graphene and a Ag monolayer supported on Re(0001)

We have investigated the electronic structure of graphene supported on Re(0001) before and after the intercalation of one monolayer of Ag by means of angle-resolved photoemission spectroscopy measurements and density functional theory calculations. The intercalation of Ag reduces the graphene-Re interaction and modifies the electronic band structure of graphene. Although the linear dispersion of the $\pi$ state of graphene in proximity of the Fermi level highlights a rather weak graphene–noble-metal layer interaction, we still observe a significant hybridization between the Ag bands and the $\pi$ state in lower energy regions. These results demonstrate that covering a surface with a noble-metal layer does decouple the electronic states, but still leads to a noticeable change in the electronic structure of graphene.

Figure 1

(a) Photoemission intensity plot along the $\Gamma$$\mathrm{K}$ direction of Re(0001), (b) of graphene/Re (G/Re), and (c) after intercalation of one ML of Ag (G/Ag/Re). Panels (d), (e), and (f) display magnified views of (a), (b), and (c), respectively. (g) Energy distribution curve measured at the $\mathrm{K}$ point of graphene at the G/Ag/Re surface [red dashed curve in (c)] gives evidence of a band gap highlighted by arrows. To increase the signal/noise ratio, the energy distribution curve was obtained by summing curves with momenta $\pm$0.004 Å${}^{-1}$ around the $\mathrm{K}$ point. (h) LEED pattern measured at 55 eV displaying the (0, 0) spot for G/Re (top) and G/Ag/Re (bottom) surfaces.

Figure 2

(a) C 1$s$ photoemission peak measured at normal emission with photon energy of 410 eV for G/Re (black solid curve) and G/Ag/Re (red dotted curve). (b) Re 4$f$ states for clean Re (yellow dashed curve), G/Re (black solid curve), and G/Ag/Re (red dotted curve) collected with photon energy of 650 eV at normal emission. Re 4$f$ spectrum for clean Re has been vertically shifted for the purpose of comparison. (c) First derivative ARPES map of G/Ag/Re along the $\Gamma$$\mathrm{K}$ direction in the energy range 3–10 eV below $E_F$. A–D denote new features in the electronic band structure due to Ag intercalation. The arrows highlight the induced electronic gap in the graphene $\pi$ band. (d) Calculated (vdW-DF) band structure of a monolayer Ag/Re along the $\Gamma$$\mathrm{K}$ direction (dot size indicates the localization in the Ag layer), and (e) $G_0{W}_0$ band structure along the $\Gamma$$\mathrm{K}$ direction for Ag/Re.

Figure 3

Band structure (vdW-DF, model structure) along the $\Gamma$$\mathrm{K}$ direction (a) for graphene on a single ML Ag (G/Ag), (b) for graphene/Ag/Re (G/Ag/Re) in a (1$\times$1) model system, and (c) the unfolded band structure of a large (9$\times$9) model (bulk Re bands not shown). Bands localized in the Ag layer with symmetries $d_{xz}$, $d_{yz}$, $d_{xy}$, and $d_{x^2-y^2}$ are shown in red and with $s$ and $d_{z^2}$ like character in blue. The localization in the respective layer is indicated by the dot size. The $\pi$ band of graphene is displayed in green. Circles identify distinct electronic band gaps of graphene bands.