Ab initio study of field emission from graphitic ribbons

Area of Science:

• Materials Science
• Condensed Matter Physics
• Quantum Chemistry

Background:

• Field emission (FE) is a quantum mechanical phenomenon where electrons are emitted from a material under a strong electric field.
• Graphitic nanostructures, such as ribbons and nanotubes, are promising materials for FE applications due to their unique electronic properties.
• Understanding the role of edge states and surface termination is crucial for optimizing FE performance.

Purpose of the Study:

• To investigate the contribution of edge states to field emission in graphitic ribbons using first-principles calculations.
• To analyze the impact of hydrogen termination on the field emission properties of graphitic ribbons.
• To determine the field emission current density from specific graphitic nanostructures.

Main Methods:

• Employed first-principles calculations based on time-dependent density-functional theory (TDDFT).
• Analyzed the electronic structure and localized states at the edges of graphitic ribbons.
• Simulated field emission current under high electric fields.

Main Results:

• Dangling bond states localized at clean ribbon edges are identified as major contributors to FE current.
• Hydrogen termination significantly reduces FE current due to the disappearance of dangling-bond states.
• FE does not occur from the edge state of a H-terminated zigzag ribbon, even when at the Fermi level.
• Calculated maximum FE current of approximately 1 microA for a 1 nm diameter graphitic sheet edge under a high electric field.

Conclusions:

• The electronic states localized at the edges of graphitic ribbons play a critical role in field emission.
• Surface functionalization, such as H termination, can drastically alter FE properties by modifying these edge states.
• These findings provide insights for designing and engineering graphitic nanostructures for efficient field emission devices.