Differences between thermal and laser-induced diffusion.

Area of Science:

• Surface science
• Physical chemistry
• Femtosecond spectroscopy

Background:

• Understanding molecule diffusion on surfaces is crucial for catalysis and materials science.
• Carbon monoxide (CO) diffusion on metal surfaces like copper (Cu) is a fundamental process.
• Investigating long-range interactions during diffusion can reveal novel mechanisms.

Purpose of the Study:

• To investigate the long-range interaction during carbon monoxide (CO) diffusion on a Cu(111) surface.
• To compare the energy dependence of thermal and laser-driven diffusion.
• To elucidate the underlying mechanism for observed diffusion behaviors.

Main Methods:

• Utilizing femtosecond laser excitation combined with a low-temperature scanning tunneling microscope (STM).
• Studying the diffusion of CO molecules on a well-defined Cu(111) surface.
• Performing ab initio calculations to support experimental findings.

Main Results:

• Both thermal and laser-driven CO diffusion exhibit oscillatory energy dependence on the distance to neighboring molecules.
• An unexpected inverted phase relationship was observed between thermal and laser-driven diffusion.
• Laser-driven diffusion is facile at distances where thermal diffusion is hindered, and vice versa.

Conclusions:

• The inverted phase in diffusion is attributed to transient stabilization of the CO negative ion during laser excitation.
• Femtosecond laser excitation provides a unique pathway to control and study surface diffusion dynamics.
• This study offers new insights into molecule-surface interactions and non-thermal diffusion mechanisms.