Grain Boundaries in Graphene on SiC(000$\bar{1}$) Substrate

TL;DR

This study investigates grain boundaries in epitaxial graphene on SiC(000$ar{1}$), revealing buckling transitions, structural motifs, and potential for valleytronic device applications through microscopy and spectroscopy.

Contribution

It identifies the critical misorientation angle for buckling transition and characterizes a highly ordered grain boundary with valley filtering potential.

Findings

Buckling occurs in small-angle grain boundaries with misorientation angles below 19°.

A highly ordered grain boundary at 33° exhibits a chain of pentagons and heptagons.

The observed defect structure can enable all-electric valleytronic devices.

Abstract

Grain boundaries in epitaxial graphene on the SiC(000$\bar{1}$) substrate are studied using scanning tunneling microscopy and spectroscopy. All investigated small-angle grain boundaries show pronounced out-of-plane buckling induced by the strain fields of constituent dislocations. The ensemble of observations allows to determine the critical misorientation angle of buckling transition $\theta_c = 19 \pm~2^\circ$. Periodic structures are found among the flat large-angle grain boundaries. In particular, the observed $\theta = 33\pm2^\circ$ highly ordered grain boundary is assigned to the previously proposed lowest formation energy structural motif composed of a continuous chain of edge-sharing alternating pentagons and heptagons. This periodic grain boundary defect is predicted to exhibit strong valley filtering of charge carriers thus promising the practical realization of all-electric valleytronic devices.