Probing the non-pairwise interactions between CO molecules moving on a Cu(111) surface

Area of Science:

• Surface Science
• Chemical Physics
• Materials Science

Background:

• Understanding molecule-surface interactions is crucial for catalysis and materials design.
• Carbon monoxide (CO) adsorption on metal surfaces, particularly copper, is a fundamental system with significant industrial relevance.

Purpose of the Study:

• To investigate the coverage-dependent dynamics of CO molecules on a Cu(111) surface at an atomic scale.
• To determine the adsorption sites, hopping rates, and energy barriers governing CO motion.
• To correlate experimental observations with theoretical models of surface dynamics.

Main Methods:

• Helium spin-echo spectroscopy was employed to probe CO dynamics with high resolution.
• Langevin molecular dynamics simulations were used to model thermal motion.
• A potential energy surface incorporating top and bridge adsorption sites was developed.

Main Results:

• CO molecules preferentially occupy top sites but also visit intermediate bridge sites.
• The hopping rate of CO increases with increasing coverage, remaining uncorrelated up to 0.10 monolayers.
• An effective diffusion barrier of 98 ± 5 meV was determined from temperature dependence.
• Simulations using an adiabatic barrier of 123 meV accurately represent the experimental data.
• Coverage-dependent rate changes were successfully modeled by altering the adiabatic potential energy surface shape.

Conclusions:

• Helium spin-echo spectroscopy provides detailed information on adsorption sites and energy landscapes.
• The dynamics of CO on Cu(111) are influenced by coverage, affecting hopping rates and potential energy surfaces.
• The study successfully links experimental measurements to atomic-scale motion and energy barriers.