Surface electronic properties and site-specific laser desorption processes of highly structured nanoporous MgO thin films

The surface electronic properties of metal oxides critically depend on low-coordinated sites, such as kinks, corners and steps. In order to characterize such surface sites, we prepare defect enriched surfaces by growing thin MgO films and measure X-ray photoelectron spectra of films and vacuum-cleaved MgO single crystals. In the case of thin films, we observe O 1s spectra with a significant shoulder feature at 2.3 eV higher binding energy (HBE) than the corresponding peak at 530.0 eV representing regular bulk lattice oxygen. We evaluate this feature in terms of non-stoichiometric oxygen and formation of an oxygen-rich layer at the topmost surface of the MgO columns. Under excitation with 266-nm-laser pulses, known to be resonant with low-coordinated surface anions, we observe preferential depletion of defective oxygen-states (HBE signal) and temporary restoration of ideal surface stoichiometry. The results from XPS studies are in line with 266 nm laser stimulated desorption experiments of Mg- and O-atoms. Both results indicate new surface specific excitation regimes, which might eventually allow site-specific manipulation of surface morphology.