Atomic and electronic structure of monolayer graphene on 6H-SiC(000-1)(3 x 3) : a scanning tunneling microscopy study

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to analyze the atomic and electronic structures of monolayer graphene on a reconstructed SiC surface, revealing moiré patterns and substrate passivation effects.

Contribution

It provides detailed insight into the atomic arrangements and electronic properties of graphene on SiC(3x3), highlighting the impact of substrate reconstruction on graphene's electronic structure.

Findings

Moiré patterns are observed due to rotational disorder.

Substrate surface has a 1.5 eV wide bandgap that persists below graphene.

Moiré patterns do not affect the low-energy electronic structure of graphene.

Abstract

We present an investigation of the atomic and electronic structure of graphene monolayer islands on the 6H-SiC(000-1)(3x3) (SiC(3x3)) surface reconstruction using scanning tunneling microscopy (STM) and spectroscopy (STS). The orientation of the graphene lattice changes from one island to the other. In the STM images, this rotational disorder gives rise to various superlattices with periods in the nm range. We show that those superlattices are moir\'e patterns (MPs) and we correlate their apparent height with the stacking at the graphene/SiC(3x3) interface. The contrast of the MP in STM images corresponds to a small topographic modulation of the graphene layer. From STS measurements we find that the substrate surface presents a 1,5 eV wide bandgap encompassing the Fermi level. This substrate surface bandgap subsists below the graphene plane. The tunneling spectra are spatially homogeneous on the islands within the substrate surface gap, which shows that the MPs do not impact the low energy electronic structure of graphene. We conclude that the SiC(3 x 3) reconstruction efficiently passivates the substrate surface and that the properties of the graphene layer which grows on top of it should be similar to those of the ideal material.