Interatomic Potential in the Nonequilibrium Warm Dense Matter Regime

Area of Science:

• Materials Science
• Condensed Matter Physics
• Laser-Matter Interactions

Background:

• Understanding material behavior under extreme conditions is crucial for developing advanced technologies.
• Polycrystalline materials exhibit unique properties influenced by grain boundaries, especially during rapid heating events.
• Femtosecond laser interactions provide a unique probe for studying nonequilibrium states of matter.

Purpose of the Study:

• To measure lattice disassembly times in femtosecond-laser-heated polycrystalline gold (Au) nanofoils.
• To compare experimental results with molecular dynamics (MD) simulations using an optimized embedded-atom-method (EAM) potential.
• To investigate the transition from single-crystal-like to nanocrystal-like melting behavior as a function of absorbed energy density.

Main Methods:

• Experimental measurement of lattice disassembly times using femtosecond laser heating of Au nanofoils.
• Molecular dynamics simulations employing a highly optimized EAM interatomic potential.
• Analysis of experimental and simulation data to identify melting mechanisms and regimes.

Main Results:

• Experimental and simulation results showed excellent agreement for absorbed energy densities between 0.9–4.3 MJ/kg.
• This agreement indicates homogeneous, single-crystal-like melting behavior in the nonequilibrium warm dense matter regime.
• At energy densities below 0.9 MJ/kg, experimental data aligned with nanocrystal behavior, with melting initiating at grain boundaries.

Conclusions:

• The study validates the use of the optimized EAM potential for simulating nonequilibrium warm dense matter.
• It demonstrates that polycrystalline gold nanofoils can exhibit single-crystal-like melting under specific high-energy laser conditions.
• The findings highlight the critical role of grain boundaries in initiating melting at lower energy densities in nanocrystalline materials.