Studying the microscopic nature of diffusion with helium-3 spin-echo

Area of Science:

• Surface Science
• Atomic and Molecular Physics
• Materials Science

Background:

• Studying atomic motion at surfaces is crucial for understanding chemical reactions and material properties.
• Existing techniques often lack the required energy and time resolution to probe fast surface dynamics.

Purpose of the Study:

• To introduce the Helium-3 spin-echo (3HeSE) technique for surface dynamics.
• To demonstrate 3HeSE's capability in revealing adsorbate motion and interactions.
• To challenge existing models of surface processes using 3HeSE data.

Main Methods:

• Utilizing Helium-3 nuclear spin as an internal timer for precise energy change measurements.
• Employing quasi-elastic scattering measurements to study adsorbate dynamics.
• Using Langevin equation simulations for quantitative analysis and illustration of generic behavior.

Main Results:

• 3HeSE provides ultra-high energy resolution for surface dynamical phenomena.
• The technique successfully observed adsorbate hopping and interactions.
• Absence of expected correlations questioned conventional pairwise force models for surface processes.

Conclusions:

• 3HeSE is a powerful tool for probing nanometer length and picosecond-nanosecond timescales of surface processes.
• The technique offers unique insights into adsorbate motion, including interactions and deviations from expected behavior.
• 3HeSE data can challenge and refine theoretical models of surface dynamics.