Point defects in turbostratic stacked bilayer graphene

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Graphene's unique properties are sensitive to lattice defects.
• Topological defects in few-layered graphene are understudied.
• Point defects, specifically monovacancies and divacancies, are fundamental lattice imperfections.

Purpose of the Study:

• To characterize monovacancy and divacancy defects in twisted bilayer graphene.
• To investigate the stability and migration behavior of these point defects.
• To understand the influence of defects on few-layered graphene.

Main Methods:

• Aberration-corrected transmission electron microscopy (AC-TEM) at 80 kV for defect imaging.
• Fast Fourier Transform (FFT) with a negative mask to separate graphene layers.
• Density Functional Theory (DFT) calculations for defect energetics.
• Tight-binding molecular dynamics simulations for defect dynamics.

Main Results:

• Monovacancy and divacancy defects in twisted bilayer graphene were successfully characterized.
• A novel FFT masking technique enabled layer-specific defect analysis.
• DFT calculations revealed distinct stability and migration energy barriers for monovacancy and divacancy.
• Monovacancy migration in bilayer graphene requires a higher energy barrier.

Conclusions:

• Point defects significantly influence few-layered graphene's properties.
• AC-TEM combined with FFT masking is effective for studying defects in twisted bilayer graphene.
• Computational methods provide crucial insights into defect behavior and energetics in graphene lattices.