The favourable large misorientation angle grain boundaries in graphene

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Grain boundaries (GBs) are linear defects in polycrystalline materials like graphene.
• Understanding GB structure and stability is crucial for controlling material properties.

Purpose of the Study:

• To systematically investigate the structure and stability of graphene GBs.
• To analyze the influence of misorientation angle (Φ) and GB orientation (Θ) on GB formation energy.

Main Methods:

• Theoretical study of graphene grain boundaries.
• Analysis of GB structure and stability as a function of misorientation and orientation angles.
• Investigating the role of pentagon-heptagon pairs (5|7s) in GB stability.

Main Results:

• GB formation energy shows a local minimum at a misorientation angle (Φ) of approximately 30°, despite maximum disorder from 5|7 pairs.
• An M-shaped energy curve is observed, attributed to strain cancellation from "head-to-tail" 5|7 pair formation.
• GB formation energy is relatively insensitive to GB orientation (Θ), with twin boundaries being slightly more stable.

Conclusions:

• The study explains previously observed experimental phenomena, including multimodal GB distributions and the prevalence of ~30° misorientation angles.
• Theoretical insights provide a framework for understanding and potentially engineering graphene grain boundaries.