Revealing the atomic structure of the buffer layer between SiC(0001) and epitaxial graphene

TL;DR

This study uses scanning tunneling microscopy to elucidate the atomic structure of the buffer layer between SiC(0001) and epitaxial graphene, revealing its graphene-like atomic arrangement and how hydrogen intercalation decouples it.

Contribution

The paper provides direct atomic-resolution imaging of the buffer layer and demonstrates how hydrogen intercalation transforms it into quasi-free-standing graphene.

Findings

Buffer layer has a graphene-like atomic arrangement.

Hydrogen intercalation removes periodic corrugation.

QFMLG shows no detectable defect sites.

Abstract

On the SiC(0001) surface (the silicon face of SiC), epitaxial graphene is obtained by sublimation of Si from the substrate. The graphene film is separated from the bulk by a carbon-rich interface layer (hereafter called the buffer layer) which in part covalently binds to the substrate. Its structural and electronic properties are currently under debate. In the present work we report scanning tunneling microscopy (STM) studies of the buffer layer and of quasi-free-standing monolayer graphene (QFMLG) that is obtained by decoupling the buffer layer from the SiC(0001) substrate by means of hydrogen intercalation. Atomic resolution STM images of the buffer layer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no detectable defect sites.