Electronic structure of epitaxial graphene layers on SiC: effect of the substrate

TL;DR

This study uses DFT calculations to analyze how the substrate affects the electronic structure of epitaxial graphene layers on SiC, revealing that only layers beyond the first recover graphene-like properties and are influenced by charge transfer.

Contribution

It demonstrates that the first graphene layer on SiC is electronically perturbed by the substrate, but subsequent layers regain graphitic properties, with charge transfer affecting doping and gap opening.

Findings

First layer strongly bonded and perturbed by substrate

Second and third layers recover graphene electronic structure

Charge transfer causes doping and gap opening at Dirac point

Abstract

Recent transport measurements on thin graphite films grown on SiC show large coherence lengths and anomalous integer quantum Hall effects expected for isolated graphene sheets. This is the case eventhough the layer-substrate epitaxy of these films implies a strong interface bond that should induce perturbations in the graphene electronic structure. Our DFT calculations confirm this strong substrate-graphite bond in the first adsorbed carbon layer that prevents any graphitic electronic properties for this layer. However, the graphitic nature of the film is recovered by the second and third absorbed layers. This effect is seen in both the (0001)and $(000\bar{1})$ 4H SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. It causes the graphene to be doped and gives rise to a gap opening at the Dirac point after 3 carbon layers are deposited in agreement with recent ARPES experiments (T.Ohta et al, Science {\bf 313} (2006) 951).