Capillary fluctuations of surface steps: An atomistic simulation study for the model Cu(111) system

Area of Science:

• Surface Science and Materials Science
• Computational Materials Science
• Statistical Mechanics

Background:

• Understanding surface step dynamics is crucial for materials properties.
• Capillary fluctuations provide insights into step stiffness and kinetics.
• Previous studies have utilized thermodynamic integration for step free energies.

Purpose of the Study:

• To investigate capillary fluctuations of surface steps on a model metal.
• To calculate step stiffness and fluctuation lifetimes using molecular dynamics.
• To compare molecular dynamics-derived step stiffness with thermodynamic integration results.

Main Methods:

• Employed molecular dynamics (MD) simulations to model a copper {111} surface.
• Calculated the fluctuation spectrum, including wave number dependence of amplitudes and relaxation times.
• Derived step stiffnesses and analyzed fluctuation lifetimes for different step orientations.

Main Results:

• Step stiffness was found to be isotropic, with values around (37±1) meV/Å.
• Fluctuation lifetimes varied significantly across wave numbers, consistent with step-edge diffusion.
• Statistically significant differences were observed between capillary-fluctuation analysis and thermodynamic integration for step free energies.

Conclusions:

• Molecular dynamics simulations effectively capture capillary fluctuations and step stiffness.
• The findings support step-edge mediated diffusion as the dominant kinetic process.
• Discrepancies between methods highlight the importance of configurational contributions in step free energy theories.