Electron states of mono- and bilayer graphene on SiC probed by STM

TL;DR

This study uses STM to analyze the atomic-scale electronic states of mono- and bilayer graphene on SiC, revealing that the graphene's metallic states are largely unaffected by the substrate interface.

Contribution

It provides direct atomic-scale evidence that the electronic states of graphene layers on SiC are minimally perturbed by the underlying interface, confirming previous photoemission results.

Findings

Mono- and bilayer graphene identified on SiC surface.

Quantum interferences indicate $\pi$-like states near Fermi level.

Graphene's metallic states are nearly unperturbed by the interface.

Abstract

We present a scanning tunneling microscopy (STM) study of a gently-graphitized 6H-SiC(0001) surface in ultra high vacuum. From an analysis of atomic scale images, we identify two different kinds of terraces, which we unambiguously attribute to mono- and bilayer graphene capping a C-rich interface. At low temperature, both terraces show $(\sqrt{3}\times \sqrt{3})$ quantum interferences generated by static impurities. Such interferences are a fingerprint of $\pi$-like states close to the Fermi level. We conclude that the metallic states of the first graphene layer are almost unperturbed by the underlying interface, in agreement with recent photoemission experiments (A. Bostwick et al., Nature Physics 3, 36 (2007))