Grain boundaries in graphene on SiC(0001̅) substrate

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Epitaxial graphene grown on silicon carbide (SiC) substrates exhibits grain boundaries that influence its electronic properties.
• Understanding the atomic structure and electronic behavior of these grain boundaries is crucial for advanced electronic applications.

Purpose of the Study:

• To investigate the structural characteristics of grain boundaries in epitaxial graphene on SiC(0001̅).
• To determine the critical misorientation angle for buckling transitions at small-angle grain boundaries.
• To identify and characterize periodic structures in large-angle grain boundaries and assess their potential for electronic devices.

Main Methods:

• Scanning tunneling microscopy (STM) for high-resolution surface imaging.
• Scanning tunneling spectroscopy (STS) for probing local electronic properties.
• Analysis of atomic structures and strain fields at grain boundaries.

Main Results:

• Small-angle grain boundaries exhibit significant out-of-plane buckling due to dislocation strain fields.
• A critical misorientation angle for buckling transition was determined to be θc = 19 ± 2°.
• A highly ordered large-angle grain boundary (θ = 33 ± 2°) was identified, consistent with a low-energy structure of alternating pentagons and heptagons.

Conclusions:

• Grain boundary structure in epitaxial graphene on SiC is strongly influenced by misorientation angle and strain.
• The identified periodic grain boundary structure is predicted to possess strong valley filtering capabilities.
• This finding offers a promising pathway for the development of all-electric valleytronic devices.