Site-specific laser modification of MgO nanoclusters: Towards atomic-scale surface structuring

Direct neutral metal emission from MgO nanostructures is induced using laser light tuned to excite specific surface sites at energies well below the excitation threshold of the bulk material. We find that near UV excitation of MgO nanocrystalline films and nanocube samples desorbs neutral Mg atoms with hyperthermal kinetic energies in the range of 0.1-0.4 eV. Our ab initio calculations suggest that metal atom emission is induced predominantly by electron trapping at surface three-coordinated Mg sites followed by electronic excitation at these sites. The proposed general mechanism can be used to control atomic-scale modification of insulating surfaces.