Probing electron transfer dynamics at MgO surfaces by Mg-atom desorption.

Area of Science:

• Surface science
• Materials science
• Physical chemistry

Background:

• High surface area magnesium oxide (MgO) films are technologically relevant.
• Ultraviolet (UV) excitation is a known method for inducing desorption from surfaces.
• Understanding desorption dynamics is crucial for controlling surface reactions and material properties.

Purpose of the Study:

• To investigate the mechanisms of neutral Mg-atom desorption from MgO films induced by femtosecond UV pulses.
• To elucidate the role of electronic and dynamical processes in hyperthermal desorption.
• To compare femtosecond and nanosecond excitation dynamics.

Main Methods:

• High surface area MgO films were prepared.
• Femtosecond UV pulses (4.7 eV) were used for excitation.
• Time-resolved measurements, including two-pulse correlation, were employed to study desorption dynamics.

Main Results:

• Neutral Mg atoms were desorbed with hyperthermal kinetic energies (0.1-0.4 eV).
• Desorption energy and power dependence were similar to nanosecond excitation.
• Femtosecond two-pulse correlation revealed distinct dynamical paths with sub-150 fs and picosecond time scales.

Conclusions:

• Femtosecond UV excitation induces Mg-atom desorption via multiple dynamical pathways.
• A fast mechanism involves simultaneous two-electron transitions to a 3-coordinated Mg(2+) site.
• Slower mechanisms are linked to electron trapping dynamics at surface sites.