Grain Boundary Loops in Graphene

TL;DR

This paper introduces a new class of topological defects in graphene called grain boundary loops, which influence material properties and are observed as flower patterns in STM studies, with implications for graphene growth and defect control.

Contribution

It presents a novel type of topological defect in graphene, characterized by grain boundary loops that can conserve atoms or accommodate vacancies, explaining their formation and stability.

Findings

Flower defect has the lowest energy per dislocation core in graphene.

Grain boundary loops can form via coalescence of mobile dislocations.

Observed as flower patterns in STM studies of epitaxial graphene.

Abstract

Topological defects can affect the physical properties of graphene in unexpected ways. Harnessing their influence may lead to enhanced control of both material strength and electrical properties. Here we present a new class of topological defects in graphene composed of a rotating sequence of dislocations that close on themselves, forming grain boundary loops that either conserve the number of atoms in the hexagonal lattice or accommodate vacancy/interstitial reconstruction, while leaving no unsatisfied bonds. One grain boundary loop is observed as a "flower" pattern in scanning tunneling microscopy (STM) studies of epitaxial graphene grown on SiC(0001). We show that the flower defect has the lowest energy per dislocation core of any known topological defect in graphene, providing a natural explanation for its growth via the coalescence of mobile dislocations.