Small scale rotational disorder observed in epitaxial graphene on SiC(0001)

TL;DR

This study reveals that small-scale rotational disorder in epitaxial graphene on SiC(0001) causes anisotropy in ARPES spectral width, enhancing understanding of graphene's electronic structure and explaining similar ARPES variations.

Contribution

The paper identifies small rotational disorder as the cause of spectral anisotropy in epitaxial graphene on SiC(0001), providing new insights into its electronic properties.

Findings

Rotational disorder of about ±0.15° causes spectral anisotropy.

Comparison with a semi-empirical model confirms the disorder's impact.

Mechanism explains variations in ARPES data for graphene on SiC.

Abstract

Interest in the use of graphene in electronic devices has motivated an explosion in the study of this remarkable material. The simple, linear Dirac cone band structure offers a unique possibility to investigate its finer details by angle-resolved photoelectron spectroscopy (ARPES). Indeed, ARPES has been performed on graphene grown on metal substrates but electronic applications require an insulating substrate. Epitaxial graphene grown by the thermal decomposition of silicon carbide (SiC) is an ideal candidate for this due to the large scale, uniform graphene layers produced. The experimental spectral function of epitaxial graphene on SiC has been extensively studied. However, until now the cause of an anisotropy in the spectral width of the Fermi surface has not been determined. In the current work we show, by comparison of the spectral function to a semi-empirical model, that the anisotropy is due to small scale rotational disorder ($\sim\pm$ 0.15$^{\circ}$) of graphene domains in graphene grown on SiC(0001) samples. In addition to the direct benefit in the understanding of graphene's electronic structure this work suggests a mechanism to explain similar variations in related ARPES data.