PNNL

Abstract

Neutral magnesium atom desorption is induced using infrared and visible femtosecond laser pulses at energies well below the excitation threshold of the bulk material. We find that infrared femtosecond laser excitation of MgO nanocrystalline samples desorbs neutral Mg-atoms with hyperthermal kinetic energies ranging from 0.1 to 0.6 eV, while visible femtosecond excitation desorbs neutral Mg-atoms with thermal kinetic energies ranging from 0.01 to 0.1 eV. The hyperthermal kinetic energy distribution is similar to the distribution observed previously under nanosecond laser excitation in the ultraviolet. The hyperthermal kinetic energy distribution supports the contention that emission is induced predominantly by electron trapping at Mg corner surface sites. The results demonstrate that femtosecond photon pulses can serve as a powerful tool for probing desorption dynamics at surfaces.