Tunable Band Structures of Polycrystalline Graphene by External and Mismatch Strains

TL;DR

This study uses density functional theory to explore how external and mismatch strains can modify the band structure of polycrystalline graphene, revealing that certain asymmetrical grain boundaries can open and tune a band gap.

Contribution

It demonstrates that specific asymmetrical grain boundaries in polycrystalline graphene can have their band gaps effectively tuned by external strains, a novel insight for electronic applications.

Findings

Symmetrical GBs maintain zero band gap under strain.

Asymmetrical GBs can open a band gap up to 0.19 eV.

Mismatch strain has minimal impact on the band gap.

Abstract

Lacking a band gap largely limits the application of graphene in electronic devices. Previous study shows that grain boundaries (GBs) in polycrystalline graphene can dramatically alter the electrical properties of graphene. Here, we investigate the band structure of polycrystalline graphene tuned by externally imposed strains and intrinsic mismatch strains at the GB by density functional theory (DFT) calculations. We found that graphene with symmetrical GBs typically has zero band gap even with large uniaxial and biaxial strain. However, some particular asymmetrical GBs can open a band gap in graphene and their band structures can be substantially tuned by external strains. A maximum band gap about 0.19 eV was observed in matched-armchair GB (5, 5) | (3, 7) with a misorientation of {\theta}=13o when the applied uniaxial strain increases to 9%. Although mismatch strain is inevitable in asymmetrical GBs, it has a small influence on the band gap of polycrystalline graphene.