Step free energies at faceted solid-liquid interfaces from equilibrium molecular dynamics simulations

Area of Science:

• Materials Science
• Computational Physics
• Chemical Engineering

Background:

• Calculating step free energies is crucial for understanding crystal growth mechanisms.
• Faceted solid-liquid interfaces present unique challenges for atomistic simulations.

Purpose of the Study:

• To develop and demonstrate a novel method for computing step free energies of faceted solid-liquid interfaces.
• To apply this method to (111) interfaces in elemental silicon using atomistic simulations.

Main Methods:

• Utilized an adiabatic trapping procedure with atomistic simulations.
• Simulated coexisting solid and liquid phases with faceted interfaces of varying island sizes.
• Computed equilibrium temperatures and fitted simulation data using classical nucleation theory.

Main Results:

• The calculated coexistence temperature is significantly influenced by interface geometry.
• Island radius was found to be inversely proportional to superheating.
• The step free energy for silicon was determined to be γ(st) = 0.103 ± 0.005 × 10⁻¹⁰ J/m.

Conclusions:

• The proposed method enables the calculation of step free energies for faceted crystals.
• This approach is applicable to nanowire growth (e.g., vapor-liquid-solid mechanism) and alloy casting.
• The Stillinger-Weber potential for Si favors wurtzite over diamond-cubic structures at low undercoolings.