Characterization of surface defects on MgO thin films by ultraviolet photoelectron and metastable impact electron spectroscopies

Metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy are used in this study to investigate low-defect and defective MgO(100) thin films. Unlike low-defect films, defective films exhibit a new spectroscopic feature located ∼2 eV above the top of valence band. Exposing the defective film to oxygen quenches the emission of electrons from F centers created on the surface and in the subsurface regions. Extended defects, unseen in the MIES spectra of the clean surface, are detectable using NO titration. MIES and thermal programmed desorption indicate that at ∼100 K NO adsorbs dissociatively on defects, forming ${\mathrm{N}}_{\mathrm{2}}\mathrm{O}.$ Only a small fraction of the MgO surface becomes covered with ${\mathrm{N}}_{\mathrm{2}}\mathrm{O}$ at ∼100 K for the low-defect MgO film indicating that ${\mathrm{N}}_{\mathrm{2}}\mathrm{O}$ molecules preferentially adsorb on the extended defects. The saturation coverage of ${\mathrm{N}}_{\mathrm{2}}\mathrm{O}$ increases appreciably for the defective sample.