How Atomic Steps Modify Diffusion and Inter-adsorbate Forces: Empirical Evidence from Hopping Dynamics in Na/Cu(115)

Area of Science:

• Surface science
• Condensed matter physics
• Atomic-scale dynamics

Background:

• Understanding atomic motion on surfaces is crucial for catalysis and materials science.
• Vicinal surfaces with well-defined steps offer model systems to study step-edge effects.

Purpose of the Study:

• To investigate the atomic-scale motion of sodium (Na) atoms on a vicinal copper (Cu)(115) surface.
• To determine the influence of atomic steps on Na adsorption, diffusion rates, and interatomic interactions.
• To explore the collective behavior and correlations of Na atoms.

Main Methods:

• Helium spin echo spectroscopy was employed to track atomic motion over pico- to nanosecond timescales.
• Molecular dynamics simulations were utilized to support experimental observations and interpret atomic interactions.

Main Results:

• Na atoms exhibit highly anisotropic one-dimensional (1D) hopping motion predominantly parallel to the step edges.
• The spatial and temporal correlations between Na atoms demonstrate anisotropic behavior.
• Atomic steps were found to effectively screen lateral interactions between Na atoms on different terraces.

Conclusions:

• Atomic steps on Cu(115) surfaces significantly direct and influence the diffusion dynamics of adsorbed Na atoms.
• The observed anisotropic collective motion highlights the role of step edges in mediating interatomic interactions.
• Surface steps act as efficient barriers or screens for lateral interactions between adatoms on adjacent terraces.