Femtosecond laser-induced graphite structural patterning and surface gasification: a molecular dynamics study.

Area of Science:

• Materials Science
• Laser Physics
• Nanotechnology

Background:

• Femtosecond lasers offer superior precision for graphite micro-nano manufacturing compared to nanosecond lasers.
• Existing research primarily focuses on monolayer graphene on substrates, with limited studies on laser-graphite interactions.
• Understanding laser energy absorption and propagation within graphite layers is crucial for advanced manufacturing.

Purpose of the Study:

• To systematically investigate the propagation of femtosecond laser energy within graphite material.
• To analyze the ablation mechanisms and resulting cavity morphology at varying pulse energy densities.
• To characterize the gasification products formed during laser ablation of graphite.

Main Methods:

• Utilized a two-temperature equation model integrated with molecular dynamics (TTM-MD) simulations.
• Simulated femtosecond laser energy propagation in graphite across a range of pulse energy densities (1.6-6.4 J cm⁻²).
• Analyzed ablation cavity morphology and identified vaporization products.

Main Results:

• At 1.6-3.2 J cm⁻², laser absorption in the transverse direction varied with depth, changing ablation cavity morphology from vertebral to hemispherical.
• Above 4.8 J cm⁻², energy spread to a fixed layer caused atomic vaporization, sublimation, and peeling of graphene layers.
• Vaporization products evolved from small carbon clusters to longer chains (C18 and beyond) at higher pulse energies (1.6-6.4 J cm⁻²).

Conclusions:

• Femtosecond laser ablation induces distinct energy propagation and ablation behaviors in graphite at different energy densities.
• The study elucidates the formation of complex carbon chains during high-energy ablation.
• Findings provide valuable insights for precise graphite micro-nano manufacturing and potential applications in carbon film deposition.