Electronic decoupling of an epitaxial graphene monolayer by gold intercalation

The application of graphene in electronic devices requires large-scale epitaxial growth. The presence of the substrate, however, usually reduces the charge-carrier mobility considerably. We show that it is possible to decouple the partially $s{p}^3$-hybridized first graphitic layer formed on the Si-terminated face of silicon carbide from the substrate by gold intercalation, leading to a completely $s{p}^2$-hybridized graphene layer with improved electronic properties.

Figure 1

(Color online) Comparison of ARPES data for conventional graphene on SiC and graphene intercalated with Au: panel (a) shows the band structure measured in the direction perpendicular to the $\overline{\Gamma \text{K}}$ direction near the $\overline{\text{K}}$ point of the surface Brillouin zone of the zero layer, the conventional graphene monolayer, the p-doped graphene monolayer intercalated with gold, and the n-doped graphene monolayer intercalated with gold together with the corresponding Fermi surfaces in panel (b). The Fermi surfaces are plotted on a logarithmic color scale to enhance weak features. The Fermi surfaces for the cML and the ${\text{nML}}_{\text{Au}}$ were measured with a step size of $0.25°$ along the $\overline{\Gamma \text{K}}$ direction. As the linewidth for the ${\text{pML}}_{\text{Au}}$ is narrower than for the cML and the ${\text{nML}}_{\text{Au}}$ we had to reduce the stepsize to $0.1°$ to allow for reasonable accuracy. $k_x$ is perpendicular to the $\overline{\Gamma \text{K}}$ direction, $k_y$ is along the $\overline{\Gamma \text{K}}$ direction. The Fermi surface for the p-doped graphene monolayer shows a weak contribution of the n-doped phase due to an inhomogeneous Au coverage on the sample.

Figure 2

LEED images taken at 126 eV for the cML, the ZL, the ${\text{pML}}_{\text{Au}}$, and the ${\text{nML}}_{\text{Au}}$. The relative intensity between graphene spot and satellite spots is a measure for the strength of the substrate influence on the graphene layer.

Figure 3

(Color online) Linewidth analysis, $\text{Au}4f$ core-level spectra and schematic: panel (a) shows the FWHM of momentum distribution curves obtained from Fig. 1a for the conventional graphene monolayer (red), the p-doped graphene monolayer intercalated with Au (blue), and the n-doped graphene monolayer intercalated with Au (green). A constant background was subtracted from the data so that the plotted linewidth is determined by electron-phonon, electron-plasmon, and electron-electron scattering alone. Panel (b) shows the $\text{Au}4f$ core-level spectra recorded with an incident photon energy of 150 eV for the p-doped monolayer (blue) and the n-doped monolayer (green). The core-level spectra indicate the presence of Au-Si bonds (black lines) for both the p- and the n-doped monolayers which is consistent with the schematic (not to scale) shown in panel (c).

Figure 4

(Color online) Panel (a) shows topographic STM images for the conventional graphene monolayer (left) and the p-doped graphene monolayer intercalated with Au (right). The lower panel shows a zoom in into the regions marked by a yellow square. The red diamond indicates the graphene unit cell. The images for the conventional monolayer and p-doped monolayer were recorded at a tunneling current of 0.2 nA and a bias of $-0.5\text{V}$ and $-0.4\text{V}$, respectively. Panel (b) shows a large-scale AFM image for the p-doped graphene monolayer intercalated with Au together with a lineprofile extracted along the dashed line in the image. The AFM data clearly reveals the presence of Au clusters (green) on top of the graphene layer.

Figure 5

(Color online) Comparison of the Raman scattering results for the conventional (red) and the p-doped (blue) graphene monolayers.